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Part III: Infectious Disease Epidemiology. Epidemics & Their Control. Epidemiological Triad for Infectious Disease. Agent. Environment. Host. Notifiable Diseases.

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Notifiable diseases l.jpg
Notifiable Diseases

Acute Flaccid ParalysisAIDSAmoebiasisAnthraxBotulismBrucellosisCampylobacteriosisChancroidChickenpoxChlamydia, GenitalCholera Creutzfeldt-Jakob Disease Cryptosporidiosis Cyclosporiasis DiphtheriaGiardiasisGonorrheaGonococcal Ophthalmia Neonatorum Group B Streptococcal Disease of the Newborn Hantavirus Pulmonary SyndromeHepatitis AHepatitis BHepatitis CHepatitis Non-A, Non-B Human Immonodeficiency Virus Influenza,Laboratory-ConfirmedInvasive Haemophilus influenzae type b Disease Invasive Group A Streptococcal Disease Invasive Meningococcal DiseaseInvasive Pneumococcal DiseaseLegionellosisLeprosyListeriosis (all types)MalariaMeaslesMeningitis, PneumococcalMeningitis, Other BacterialMeningitis, ViralMumpsParatyphoidPertussisPlague* Poliomyelitis RabiesRubellaRubella, CongenitalSalmonellosisShigellosisSmallpox Syphilis, All Syphilis, CongenitalSyphilis, Early LatentSyphilis, Early Symptomatic (Primary and Secondary)Syphilis, OtherTetanusTuberculosisTularemia TrichinosisTyphoidVerotoxigenic E. coli1990 -Viral Hemorrhagic Fevers (Crimean Congo, Ebola, Lassa, Margurg) West Nile Virus Asymptomatic Infection West Nile Virus Fever West Nile Virus Neurological Syndromes West Nile Virus Unclassified/ Unspecified Yellow Fever


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Emerging communicable disease

  • Cryptosporidium parvum 1976

  • Ebola virus 1976

  • Legionella 1977

  • Campylobacter jejuni 1977

  • E. Coli 0157:H7 1982

  • HIV 1983

  • Hepatitis C 1989

  • nv CJD 1996

  • Avian influenza ( Type A H5N1) 1997

  • WNV 1999

  • SARS 2003

  • ……… Pandemic influenza???



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Environment

Agent

Reservoir

Contact (Host)

Chain of Infection


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Clinical Spectrum

Severe

Moderate

Mild

subclinical

Iceberg of infectious disease

Symptomatic disease

Asymptomatic disease


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Course of Disease

Incubation period

Illness

Latent Period

Infectious

Infected


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Immunity

  • Active

    • infection

    • immunization

  • Passive

    • immunoglobulin

    • intrauterine

  • Herd Immunity


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Portals of Entry for Infection

  • Respiratory tract

  • Genitourinary tract

  • Gastrointestinal tract

  • Skin / Mucous membrane

  • Transplacental

  • Parenteral( percutaneaous , via blood)


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Direct

Direct contact (bite,soil,touch)

Droplet spread

Vertical transmission (through placenta)

Indirect

Airborne (droplet nuclei , dust particles)

Vehicle borne (food, water)

Vector borne ( mosquito)

Mechanical ( flies)

Modes of Transmission


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Opportunities for interrupting transmission

Quarantine

Vehicle control

Treatment

Physical protection

Infection control

Improve general environment

Chemoprophylaxis

Immunization

Isolation

Herd immunity


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Opportunities for interrupting transmission

  • Reservoir

    • Infection control measures,treatment,isolation

  • Susceptible contact

    • chemoprophylaxis, immunization (active and /or passive),quarantine , physical protection

  • Route of transmission

    • food preparation , water purification, vector control

  • Agent

    • Infection control measures, treatment



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Epidemics

  • Epidemics are temporary increases in the incidence of disease in populations

    • E.g. Infectious Disease- SARS, West Nile Virus

    • E.g. Non-infectious Disease- Asthma deaths in the 1960s associated with increased use of pressurized aerosol broncholdilators

  • Increases in incidence are usually significantly above the level expected from past experience in the same population


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Epidemics and Outbreaks

The occurrence of cases of an illness clearly in excess of expectancy

Examples of recent epidemics:

  • HIV / AIDS- Retrovirus;

  • Ebola- African filovirus via monkey; causes viral hemorrhagic fevers (VHF); often fatal;

  • Hanta virus (US)- Bunyavirus via rodents; causes severe infections of the lungs and kidneys;

  • Lyme disease (US)- Borrellia burgdorferi bacteria via tick bite; symptoms include: fatigue, fever, stiff muscles/joints, meningitis, arrhythmias, arthritis.


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Definitions

  • Primary or index case- the first case (or group of cases) arising from the introduction of an agent in to a community

  • Secondary case- people who acquire infection from the primary case(s)

  • Incubation period- the time interval between infection of an individual and the onset of symptoms

  • Generation time- the time interval between the onset of primary and secondary cases

  • Derived infection- this is an infection arising by direction transmission from an infected contact


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Types of Epidemic

  • There are two main types of epidemic: common source and propagated

  • Point or Common Source Epidemics-result from the exposure of a group of people to the same source of infection or noxious substance. Continuous exposure or intermittent exposure of the population to the causal agent produces a more extended and irregular epidemic curve.

    • E.g. outbreak of Salmonella typhimurium food poisoning amongst delegates ate a medical conference

    • E.g. outbreak of respiratory disease due to adulterated cooking oil in Spain


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Propagated (Person-Person) Epidemics

  • Propagated epidemics are due to the transmission of infectious agent from one person to another. The epidemic curve usually shows a gradual rise and decline, often with further waves as each successive generation of cases infects a new generation.

    • E.g. An outbreak of measles occurred in a primary school. After two index cases , there were two epidemic waves at approximately 10-14 days intervals. The outbreak was modified by those vaccinated. The attack rate among those unvaccinated was 86%.


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Investigation of an Outbreak

  • Stages In Investigation

    • Descriptive enquiries into the facts of the outbreak

    • Investigative reservoirs and vehicles of infection

    • Analysis of the data collected

    • Formulation of a causal hypothesis

    • Testing its validity in the control of the outbreak


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Descriptive enquiries

  • Verify the diagnosis by clinical and laboratory investigations

  • Verify the existence of the epidemic by comparison with previous incidence of the disease in the same population

  • Compile a list of all cases

  • Investigate patients and others who might be involved in the case (i.e. age, sex, occupation, address etc.)

  • Ensure all clinical and laboratory investigations required to confirm the identity of the infection in patients were carried out


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Investigate reservoirs and vehicle of infection

  • Human- an epidemic may originate from an individual who a minor clinical episode or is a carrier of disease

  • Animal- enquire about the contacts patients may have had with sick animals or animal products

  • Environment- investigate sources of foods consumed by individuals and the circumstances of their production, storage, preservation and preparation. Arrange for laboratory examination of food, water supplies and other environmental sources and typing of any organisms that are isolated


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Analysis of the data collected

  • Plot of the epidemic curve- this may give some clue to the mode of spread and probable time of initial exposure

  • Plot the cases on a map- this will detect clustering and the distribution of cases

  • Analyze the incidence rates in different groups- for example by age, sex or occupation. Attack rates must be calculated among both exposed and non-exposed

  • Look for a quantitative relationship- this may exist between the degree of exposure (or dose) and attack rate


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Formulation of a causal hypothesis

  • Factors for hypothesis:

    • The properties of the agent, it’s reservoirs, favored vehicles and the nature of illness

    • The probable source and route of transmission

    • Time and duration of exposure of the patients to the agent in relation to the onset of their illness

    • Attack rates of the different sub-groups of the population at risk


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Testing validity in the control of the outbreak

  • Seek support for the causal hypothesis by further investigation of cases, if necessary, to confirm the proposed explanation of their illness

  • Implement appropriate control measures on the assumption that the hypothesis is correct and monitor their success in reducing the incidence of further cases


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Epidemic Curves

  • # cases by time of onset

  • Shape of the curve gives you clues:

  • Agent known: use incubation period to look back at exposure

  • Agent unknown (but common event likely): postulate agent by determining the incubation period

  • Draw the curve relative to specific sites/groups



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Salmonellosis in passengers on a flight from London to the US by time of onset, March 13-14, 1984

Supper

4 a.m.

Index case

|

|

Hours since exposure


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Epidemic Curve: US by time of onset, March 13-14, 1984Propagated or Person-Person

Tertiary

Cases

Secondary

Cases

Index

Case

Days since exposure


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VHF Deaths, Bandudo Province, Zaire US by time of onset, March 13-14, 1984March - April 1995


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Epidemic Curve: Continuous Source Outbreak US by time of onset, March 13-14, 1984


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Occurrence/Cessation of an Outbreak US by time of onset, March 13-14, 1984

  • There are numerous conditions that might change and precipitate an outbreak, although all lead to an increase in the number of exposed and susceptible persons required for an outbreak. Some include:

    • The new appearance of or sudden increase in an infectious agent or toxic material

    • The arrival of susceptible to an environment which has an endemic pathogen

    • The introduction of an effective route of transmission from source to susceptible (e.g. climatic change and malaria)


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Question 1. US by time of onset, March 13-14, 1984

The quarantine or surveillance period

prescribed for a specific infectious disease is based upon:

(a) Incubation period of the disease

(b) Epidemic cycle of the disease

(c) Period of infectivity of the disease

(d) Normal maximum duration of acute symptoms

(e) Proportion of susceptibles in the contact population


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Question 1. US by time of onset, March 13-14, 1984

Answer

(a) Incubation period of the disease


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Question 2. US by time of onset, March 13-14, 1984

The isolation period prescribed for a specific infectious disease is based upon:

(a) Incubation period of the disease

(b) Epidemic cycle of the disease

(c) Period of infectivity of the disease

(d) Normal maximum duration of acute symptoms

(e) Proportion of susceptibles in contact population


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Question 2. US by time of onset, March 13-14, 1984

Answer

(c) Period of infectivity of the disease


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Question 3. US by time of onset, March 13-14, 1984

When is the isolation of infectious disease cases most useful as a method of preventing new cases?

  • During the period before the onset of clinical disease

  • When the ratio of unapparent to apparent cases is high

  • During period of greatest communicability occurs after onset of the disease

  • Isolating cases of infectious disease is never a useful method of preventing new cases

  • Isolating cases of infectious disease is always a useful method of preventing new cases


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Question 3. US by time of onset, March 13-14, 1984

Answer

(C) During period of greatest communicability occurs after onset of the disease


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Question 4. US by time of onset, March 13-14, 1984

An outbreak of measles occurred in an elementary school with an enrolment of 300 pupils. During October and November, 72 pupils in the school were absent with measles.

(a) Compute the attack rate for October and November

The 72 pupils with measles had a total of 100 brothers and sisters living at home. Of the siblings, 20 subsequently developed measles during October through December.

(b) Compute the secondary attack rate among the siblings.


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Question 4. US by time of onset, March 13-14, 1984

Answer

  • 24%

  • 20%


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Question 5. US by time of onset, March 13-14, 1984

With one exception, all the following diseases are notifiable in Saskatchewan. The one exception is:

(a) HIV infection

(b) Gonorrhea

(c) Non‑gonococcal urethritis

(d) Chancroid

(e) Chlamydia


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Question 5. US by time of onset, March 13-14, 1984

Answer

(c) Non‑gonococcal urethritis


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Question 6. US by time of onset, March 13-14, 1984

In Canada, which of the following methods of transmission apply BEST to each of the four diseases mentioned below?

(a) Person‑to‑person

(b) Foodborne

(c) Airborne

(d) Waterborne

(e) Bloodborne

____ salmonellosis

____ hepatitis A

____ psittacosis

____ hepatitis B


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Question 6. US by time of onset, March 13-14, 1984

Answer

B salmonellosis

A hepatitis A

C psittacosis

E hepatitis B


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Question 7. US by time of onset, March 13-14, 1984

The Culex tarsalis mosquito is the vector in:

(a) Malaria

(b) Typhus

(c) Western equine encephalitis

(d) Yellow fever


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Question 7. US by time of onset, March 13-14, 1984

Answer

(c) Western equine encephalitis


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Question 8. US by time of onset, March 13-14, 1984

The A.I.D.S. (Acquired Immune Deficiency Syndrome) is due to a HIV infection. The mode of transmission for HIV infection is similar to:

(a) Hepatitis A

(b) Tuberculosis

(c) Typhoid

(d) Hepatitis B

(e) None of these


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Question 8. US by time of onset, March 13-14, 1984

Answer

(d) Hepatitis B


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Question 9. US by time of onset, March 13-14, 1984

Notification of infectious disease is the duty of:

(a) The attending physician

(b) A teacher or principal

(c) A nurse providing professional services

(d) The manager of a medical laboratory

(e) All of the above


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Question 9. US by time of onset, March 13-14, 1984

(a) The attending physician


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Question 10. US by time of onset, March 13-14, 1984

With one exception, all of the following are notifiable communicable disease under Saskatchewan public health legislation. The one exception is:

(a) Food poisoning

(b) Diphtheria

(c) Measles

(d) HIV infection

(e) Pneumococcal pneumonia


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Question 10. US by time of onset, March 13-14, 1984

Answer

(e) Pneumococcal pneumonia


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Question 11. US by time of onset, March 13-14, 1984

Communicable disease control in a population may be brought about by:

(a) Reduction in size of disease reservoir

(b) Increasing host resistance

(c) Limiting transmission of disease

(d) Chemoprophylaxis

(e) All of the above


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Question 11. US by time of onset, March 13-14, 1984

Answer

(e) All of the above


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Question 12. US by time of onset, March 13-14, 1984

A reduction in the size of the disease reservoir is basic to prevention of disease. Such a principle has been successfully applied to the control of:

(a) Hepatitis B

(b) Gonorrhea

(c) Syphilis

(d) Salmonellosis

(e) None of the above


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Question 12. US by time of onset, March 13-14, 1984

Answer

(e) None of the above


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Question 13. US by time of onset, March 13-14, 1984

The most important cause of the decline in United States tuberculosis mortality rate from 194 per 100,000 in 1900 to 23 per 100,000 in 1950 was:

(a) Immunization

(b) Chemotherapy

(c) Environmental sanitation

(d) Aging of the population

(e) Improvement in general social conditions


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Question 13. US by time of onset, March 13-14, 1984

Answer

(e) Improvement in general social conditions


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Question 14. US by time of onset, March 13-14, 1984

Immunization, testing of herds and destruction of infected animals has been applied to the control of brucellosis. It is an example of infection control by:

(a) Interrupting the transmission of organisms

(b) Reducing host susceptibility

(c) Reducing the size of the reservoir

(d) All of these

(e) None of these


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Question 14. US by time of onset, March 13-14, 1984

Answer

(c) Reducing the size of the reservoir


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Question 15. US by time of onset, March 13-14, 1984

A child has been bitten by a dog. Which of the following factors would you take into account in deciding what action to take?

(a) If the bite were on the head or neck

(b) The child provoked the animal (e.g. poke with a stick)

(c) The child knew the animal and its normal residence

(d) The dog has shown abnormal behaviour over the last 24 hours

(e) All of the above


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Question 15. US by time of onset, March 13-14, 1984

Answer

(e) All of the above


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Immunization US by time of onset, March 13-14, 1984


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Immunization of Travellers US by time of onset, March 13-14, 1984

  • Required Immunizations

    • Yellow fever

    • Meningococcal disease

    • Cholera

  • Recommended Immunizations

    • Hepatitis A

    • Typhoid

    • Meningococcal disease

    • Japanese encephalitis

    • Cholera

    • Influenza

    • BCG


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Vaccines Recommended for All Health Care Workers US by time of onset, March 13-14, 1984

  • Diphtheria and tetanus toxoid

  • Measles vaccine

  • Polio vaccine

  • Rubella vaccine

  • Hepatitis B vaccine

  • Influenza vaccine


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Question 16. US by time of onset, March 13-14, 1984

A child of 4 months of age has had its second dose of DPaT (Adsorbed) Vaccine. Mother reports that three hours after receiving the immunization, the child screamed for about 12 hours. She was unable to console him. For the third immunization in the series, you would use:

(a) DPaT Adsorbed

(b) Diphtheria only

(c) Tetanus only

(d) Pertussis only

(e) DT (Adsorbed)


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Question 16. US by time of onset, March 13-14, 1984

Answer

(a) DPaT Adsorbed


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Question 17. US by time of onset, March 13-14, 1984

Which of the following is not a contraindication to the use of live vaccine?

(a) Pregnancy

(b) Immunosuppression (drug induced)

(c) Immunocompromised host (disease induced)

(d) History of allergy to house dust


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Question 17. US by time of onset, March 13-14, 1984

Answer

(d) History of allergy to house dust


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Question 18. US by time of onset, March 13-14, 1984

Canadian provinces have introduced the adsorbed vaccine for many of their childhood immunizations. One of the main advantages of the adsorbed vaccine DPT are:

(a) It can be given subcutaneously

(b) It has a longer lasting effect than the plain vaccine

(c) It can be taken intranasally

(d) They are 100% effective

(e) They cause fewer side effects


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Question 18. US by time of onset, March 13-14, 1984

Answer

(e) They cause fewer side effects


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Question 19. US by time of onset, March 13-14, 1984

A 27 year old woman presents with a minor wound caused while gardening. She has had no immunization since completing a full course of childhood immunizations. You would administer:

  • (a) DPaT vaccine

  • (b) Tetanus and diphtheria toxoid (Td)

  • (c) Tetanus toxoid alone

  • (d) Tetanus immune globulin

  • (e) None of the above


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Question 19. US by time of onset, March 13-14, 1984

Answer

(b) Tetanus and diphtheria toxoid (Td)


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Question 20. US by time of onset, March 13-14, 1984

Mortality rates in Canada for diphtheria have declined from 20/100,000 in 1921 to 0.02 in 1970. The most important cause for this was:

(a) Immunization

(b) Chemotherapy

(c) Environmental sanitation

(d) Aging of the population

(e) Improved standard of living


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Question 20. US by time of onset, March 13-14, 1984

Answer

(a) Immunization


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Question 21. US by time of onset, March 13-14, 1984

Case fatality from diphtheria is as great now as 50 years ago. But there are fewer deaths from diphtheria in Canada because:

(a) Antitoxin is more easily available

(b) The organism is sensitive to penicillin

(c) Fewer cases of diphtheria occur now

(d) There is better reporting of cases

(e) Early diagnosis of diphtheria occurs currently


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Question 21. US by time of onset, March 13-14, 1984

Answer

(c) Fewer cases of diphtheria occur now


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Question 22. US by time of onset, March 13-14, 1984

The rubella vaccine currently used in Canada is a live vaccine which produces a good antibody response. Contra‑indications to its use are:

(a) Pregnancy

(b) Infants whose mothers are pregnant

(c) Male interns working in obstetrics

(d) All of the above

(e) None of the above


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Question 22. US by time of onset, March 13-14, 1984

Answer

(a) Pregnancy


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Question 23. US by time of onset, March 13-14, 1984

Which of the following diseases has a non-human reservoir?

(a) Typhoid

(b) Shigellosis

(c) Smallpox

(d) Salmonellosis

(e) None of the above


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Question 23. US by time of onset, March 13-14, 1984

Answer

(d) Salmonellosis


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Question 24. US by time of onset, March 13-14, 1984

In a national vaccine trial, the incidence rate of poliomyelitis was 16/100,000 for vaccinated children and 57 for children who received the placebo. The effectiveness was, therefore:

(a) 45%

(b) 70%

(c) 72%

(d) 79%

(e) 87%


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Question 24. US by time of onset, March 13-14, 1984

Answer

(c) 72%


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Question 25. US by time of onset, March 13-14, 1984

Following a bite from a skunk in an area where rabies is endemic, the physician should:

(a) Ensure immediate washing and flushing of the wound, preferably with soap or detergent

(b) Administer rabies immune globulin immediately

(c) Administer rabies human diploid cell vaccine immediately

(d) Report the case to public health

(e) All of the above


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Question 25. US by time of onset, March 13-14, 1984

Answer

(e) All of the above


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Question 26. US by time of onset, March 13-14, 1984

Chronic carriers may be important in infectious disease epidemics. Which of the following diseases can produce a chronic carrier state?

(a) Smallpox

(b) Hepatitis B

(c) Hepatitis A

(d) Pertussis

(e) None of the above


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Question 26. US by time of onset, March 13-14, 1984

Answer

(b) Hepatitis B


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Specific Diseases of Public Health Importance US by time of onset, March 13-14, 1984


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TB US by time of onset, March 13-14, 1984

  • What is TB?

    • Tuberculosis (TB) is caused by a bacterium called Mycobacterium tuberculosis. TB usually attacks the lungs, but can also affect other parts of the body such as the lymph nodes.

    • Airborne transmission


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TB US by time of onset, March 13-14, 1984

  • What are the symptoms of TB disease?

    • a bad cough that lasts longer than 2 weeks

    • pain in the chest

    • coughing up blood or sputum (phlegm)

    • weakness or feeling very tired

    • weight loss

    • no appetite

    • chills

    • fever

    • night sweats.


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TB US by time of onset, March 13-14, 1984

  • Treatment

    • Isoniazid (INH)

    • Pyrazinamide (PZA)

    • Rifampin

    • Ethambutol


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TB US by time of onset, March 13-14, 1984

  • What is BCG?

    • BCG (Bacille Calmette-Guérin) is a live vaccine that was developed by two French scientists Calmette and Guérin in the 1920s. It helps protect babies and young children against the most severe forms of TB disease.

    • Today, only some First Nations children on reserves receive BCG routinely.


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Measles US by time of onset, March 13-14, 1984

  • Disease profile

    • Measles is a highly contagious and acute infectious disease caused by a virus of the genus Morbillivirus in the family Paramyxoviridae. It is one of the best known and deadliest of all childhood rash and febrile illnesses. In severe cases, complications such as pneumonia, diarrhoea, middle ear infection and encephalitis (a dangerous infection of the brain causing inflammation) may occur. Measles mainly affects young children, but can strike older children and adults as well.

    • Transmission- airborne droplets


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Measles US by time of onset, March 13-14, 1984

  • In Canada

    • Measles is no longer endemic in Canada . Between 2000 and 2002, the number of reported Canadian cases dropped from 199 to 6, the lowest number of cases ever reported in Canada . In 2004, only 7 cases were reported. The majority of cases were international importations or the result of limited spread following imported cases . Clusters or small outbreaks, ranging from 2 to 155 cases, have occurred among un-immunized Canadians who oppose immunization on religious or philosophic grounds.


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Measles US by time of onset, March 13-14, 1984

  • Treatment

    • There is no specific treatment for measles. Bed rest is recommended

  • Vaccine

    • Measles vaccine contains live attenuated measles virus. It is available alone or in combination with live rubella vaccine (MR) or with mumps and rubella vaccines (MMR).


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Typhoid US by time of onset, March 13-14, 1984

  • Typhoid fever is caused bySalmonella typhi, which differs from most other Salmonella species in that it infects only humans and frequently causes severe systemic illness. The organism is generally transmitted via food contaminated with the feces or urine of people with the disease or those who are S. typhi carriers. The fatality rate is approximately 16% for untreated cases and 1% for those given appropriate antibiotic therapy. Between 2% and 5% of typhoid cases become chronic carriers, sometimes shedding bacteria in stool for years. The risk of severe illness is increased in people with depressed immunity (e.g., due to HIV) or decreased gastric acid levels.


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Typhoid US by time of onset, March 13-14, 1984

  • What are the signs and symptoms of typhoid fever?

    • Persons with typhoid fever usually have a sustained fever as high as 103° to 104° F (39° to 40° C). They may also feel weak, or have stomach pains, headache, or loss of appetite. In some cases, patients have a rash of flat, rose-colored spots. The only way to know for sure if an illness is typhoid fever is to have samples of stool or blood tested for the presence of S. Typhi .


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Typhoid US by time of onset, March 13-14, 1984

  • Vaccines

    • Two typhoid vaccines are currently available for use: an oral live, attenuated vaccine (Vivotif Berna vaccine, manufactured from the Ty21a strain of S. Typhi by the Swiss Serum and Vaccine Institute) and a Vi capsular polysaccharide vaccine (ViCPS) (Typhim Vi, manufactured by Aventis Pasteur) for intramuscular use


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Typhoid US by time of onset, March 13-14, 1984

  • Specific antimicrobial therapy shortens the clinical course of typhoid fever and reduces the risk of death. Persons who are potentially exposed to S. Typhi and who develop symptoms of typhoid fever should seek appropriate medical care. Antimicrobial therapy should be guided by local data on antimicrobial sensitivity.


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HAV US by time of onset, March 13-14, 1984

  • Cause

    • Hepatitis A virus (HAV)

    • Non-enveloped virus of the Picornoviridae family

    • One serotype identified

    • Identified in 1972

    • HAV is an enteric viral infection, generally transmitted through a fecal-oral route.


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HAV US by time of onset, March 13-14, 1984

  • Clinical Characteristics

    • Incubation Period From 15-50 days, average 28-30 days

    • Acute Illness Can cause a renewed illness up to one year after initial infection. This can happen in about 15% of patients.

    • Chronic Infection People usually do not remain infected for life. The body will most often fight off the virus naturally.

    • Global Incidence1.5 million cases each year.

    • Global Prevalence15-100% in various parts of the world


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HAV US by time of onset, March 13-14, 1984

  • Signs and Symptoms

    • Jaundice (yellowing of the skin and eyes), other general symptoms such as uneasiness, loss of appetite, pain in the stomach area, dark urine and fatigue.

    • Most people mild to serious Hep A recover naturally


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HAV US by time of onset, March 13-14, 1984

  • Modes of Transmission

    • Exposure to water or food products contaminated with HAV (feces containing the virus)

    • Transmission through household or sexual contact is seen as a very rare event, particularly in heterosexual relationships

    • Transmission through blood does not happen often.


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HAV US by time of onset, March 13-14, 1984

  • Prevention

    • A vaccine to protect against HAV is available. A combination vaccine for Hep A and B is also available.

  • Treatment

    • There is no effective treatment to date. People generally recover from symptoms in 4 to 6 weeks.


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HAV US by time of onset, March 13-14, 1984

  • Canadian Data on the trends of HAV

    • The incidence of Hep A was approximately 2.9 cases for every 100,000 persons in 1999 (Health Canada, Notifiable Diseases Online)


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HBV US by time of onset, March 13-14, 1984

  • Cause

    • Hepatitis B Virus (HBV)

    • DNA virus from the Hepadnaviridae family of viruses. Some features in common with retroviruses.

    • Hepatitis B surface antigen (HbsAg) discovered in 1965

    • HbsAg also called Australian Antigen

    • Four serotypes and seven genotypes of human hepatitis B (Hep B)


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HBV US by time of onset, March 13-14, 1984

  • Clinical Characteristics

    • Incubation Period From 2 to 6 months

    • Infectivity About 100 times more infective than HIV

    • Acute Illness About 90% of adults clear the virus from their system after serious infection.

    • Chronic Infection About 350 million people worldwide have long-term infection (>=5%).15 to 40% advance to liver damage and liver disease.

    • Death from Chronic Liver Disease, Disease from liver damage, and Cancer of the Liver 15-25% risk, >1 million people per year worldwide


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HBV US by time of onset, March 13-14, 1984

  • Signs and Symptoms

    • Jaundice (yellowing of the skin and eyes), other general symptoms such as tiredness, loss of appetite, joint pain, pain in the stomach area, and feelings of sickness.

    • Symptoms may not appear in all cases, and at least 30% of seriously infected people may not show symptoms


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HBV US by time of onset, March 13-14, 1984

  • Modes of Transmission

    • Most infections can happen when body fluids including blood, blood products of an infected person enters the body of a person who is not protected against the virus. HBV has also been found in semen.

    • Infection routes include sexual contact with an infected person and exposure to needlesticks and other 'sharps' which have been contaminated with HBV (this includes people who inject drugs).

    • Can also be passed from mother to newborn infant at the time of birth (vertical transmission).


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HBV US by time of onset, March 13-14, 1984

  • Prevention

    • Vaccine options are available to protect against HBV.

    • Most provinces in Canada have school-based immunization programs, and it is recommended that all children aged 0-15 ask about vaccination against HBV

  • Treatment

    • Two standard treatments for Hep B: interferon and lamivudine. Interferon is used for short periods of time. If this treatment is effective, the body will then suppress the virus on its own. Lamivudine may be used in a similar manner, or may be used to achieve long-term viral suppression. Newer treatments such as adefovir are effective in lamivudine-resistant infections.


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HBV US by time of onset, March 13-14, 1984

  • Canadian Data on the trends of HBV

    • The incidence of Hep B was approximately 4.2 cases for every 100,000 persons in 1999 (Health Canada, Notifiable Diseases Online)

    • The prevalence is estimated to be 0.7-0.9%, and the distribution of cases varies by ethnic origin, job and risk group.


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HCV US by time of onset, March 13-14, 1984

  • Cause

    • Hepatitis C virus (HCV)

    • Identified in 1989

    • Responsible for 90% of non-A, non-B hepatitis cases following blood transfusion prior to 1989

    • HCV is a viral infection carried in the blood

    • There are six genotypes and more than 100 subtypes of HCV identified.


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HCV US by time of onset, March 13-14, 1984

  • Clinical Characteristics

    • Incubation Period Average 6-7 weeks

    • Acute Illness Mild acute illness is seen in less than 25 % of infected people

    • Chronic Infection70-80% of people progress to chronic infection.

    • Death from Chronic Liver Disease, Disease from liver damage, and Cancer of the Liver1-5% of infected people per year.


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HCV US by time of onset, March 13-14, 1984

  • Signs and Symptoms

    • Jaundice (yellowing of the skin and eyes) can occur in 20-30% of those infected. Other general symptoms such as uneasiness, loss of appetite, pain in the stomach area, dark urine and fatigue can be seen in 10-20% of those infected.

    • About 70-80% of people show no signs or symptoms of infection.

    • About 20-30% or individuals who are infected with acute Hep C will recover without treatment.


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HCV US by time of onset, March 13-14, 1984

  • Modes of Transmission

    • Exposure to blood or blood products infected with HCV

    • An infected mother can pass the infection to her newborn child (vertical transmission).

    • Sexual transmission is a rare event, but can happen in the presence of blood.

    • Household transmission through sharing of razors, toothbrushes and combs is possible


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HCV US by time of onset, March 13-14, 1984

  • Treatment

    • Treatment of people with new Hep C infections with long acting interferon and ribavirin can get rid of the virus in up to 60% of people within 24 to 48 weeks.


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HCV US by time of onset, March 13-14, 1984

  • Canadian Data on the trends of HCV

    • Incidence is currently between 10-20 cases per 100,000 /year in Canada

    • Prevalence was estimated at 250,000 or 0.8% of the Canadian population in 2002


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Syphilis US by time of onset, March 13-14, 1984

  • Cause/symptoms

    • Syphilis is a systemic disease caused by T. pallidum. Patients who have syphilis may seek treatment for signs or symptoms of primary infection (i.e., ulcer or chancre at the infection site), secondary infection (i.e., manifestations that include but are not limited to skin rash, mucocutaneous lesions, and lymphadenopathy), or tertiary infection (e.g., cardiac, ophthalmic, auditory abnormalities, and gummatous lesions).


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Syphilis- US by time of onset, March 13-14, 1984Diagnosis

  • A presumptive diagnosis is possible with the use of two types of serologic tests for syphilis: a) nontreponemal tests (e.g., Venereal Disease Research Laboratory [VDRL] and Rapid Plasma Reagin [RPR]) and b) treponemal tests (e.g., fluorescent treponemal antibody absorbed [FTA-ABS] and T. pallidum particle agglutination [TP-PA]). The use of only one type of serologic test is insufficient for diagnosis, because false-positive nontreponemal test results may occur secondary to various medical conditions.


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Syphilis US by time of onset, March 13-14, 1984

  • Treatment

    • Penicillin G, administered parenterally, is the preferred drug for treatment of all stages of syphilis. The preparation(s) used (i.e., benzathine, aqueous procaine, or aqueous crystalline), the dosage, and the length of treatment depend on the stage and clinical manifestations of disease.


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Question 27. US by time of onset, March 13-14, 1984

People over 65 years of age have a higher incidence of tuberculosis than do young adults because:

(a) Their diets are poorer

(b) They live under more crowded conditions

(c) They were exposed to more tuberculosis infection in childhood

(d) Their disease is more often reported

(e) None of the above


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Question 27. US by time of onset, March 13-14, 1984

Answer

(c) They were exposed to more tuberculosis infection in childhood


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Question 28. US by time of onset, March 13-14, 1984

The number and percent distribution of tuberculosis deaths by age for white males in the U.S.,1955 is as follows:

  • % OF ALL DEATHS

  • AGE DEATHS IN EACH AGE GROUP

  • under 1 21 0.2

  • 1‑ 4 32 0.1

  • 5‑14 14 0.2

  • 15‑24 92 1.0

  • 25‑34 470 5.2

  • 35‑44 993 11.1

  • 45‑54 1858 20.7

  • 55‑64 2246 25.1

  • 65‑74 2152 24.0

  • 75‑84 913 10.2

  • 85+ 1671.9

  • 8958 100%


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Question 28. US by time of onset, March 13-14, 1984

The inference that tuberculosis mortality rates in extreme old age are lower than they are in persons who are not so old is:

(a) Correct

(b) Incorrect because of failure to distinguish between incidence and prevalence

(c) Incorrect because a percentage distribution is used when a rate is required to support the inference

(d) Incorrect because of failure to recognize a possible cohort phenomenon

(e) Incorrect because there is no control or comparison group


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Question 28. US by time of onset, March 13-14, 1984

Answer

(c) Incorrect because a percentage distribution is used when a rate is required to support the inference


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Question 29. US by time of onset, March 13-14, 1984

Typhoid fever is characterized by the following:

(a) Domestic animals are reservoirs of S. Typhi

(b) Less than 1% of typhoid fever patients will still discharge typhoid bacilli three months after the onset of their disease

(c) Cholecystectomies are recommended for typhoid patients who are still carrying the typhoid bacillus three months after onset of the illness

(d) Typhoid vaccine is not an important means of controlling typhoid fever in developed countries


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Question 29. US by time of onset, March 13-14, 1984

Answer

(d) Typhoid vaccine is not an important means of controlling typhoid fever in developed countries


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Question 30. US by time of onset, March 13-14, 1984

The screening test for HIV infection used by the Red Cross Blood Transfusion Services tests for:

(a) HIV antigen

(b) HIV antibody

(c) T Helper T Suppressor ratio

(d) A combination of the above


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Question 30. US by time of onset, March 13-14, 1984

Answer

(b) HIV antibody


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Question 31. US by time of onset, March 13-14, 1984

What is the estimated risk of a child born to an HIV positive mother becoming HIV positive?

(a) Nil

(b) 100%

(c) 20 - 25%

(d) 80 - 90%


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Question 31. US by time of onset, March 13-14, 1984

Answer

(c) 20 - 25%


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Question 32. US by time of onset, March 13-14, 1984

B.C.G. vaccination is an example of immunization using:

(a) A live virus vaccine

(b) A killed vaccine

(c) A live attenuated bacillus

(d) A killed bacterial culture using a bacterial product


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Question 32. US by time of onset, March 13-14, 1984

Answer

(c) A live attenuated bacillus


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Question 33. US by time of onset, March 13-14, 1984

Pediculosis pubis is an infestation by the crab louse. It is commonly found in all but one of the following areas:

(a) Pubic hair

(b) Perianal hairs

(c) Scalp

(d) Eyelashes

(e) Axillae


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Question 33. US by time of onset, March 13-14, 1984

Answer

(c) Scalp


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Question 34. US by time of onset, March 13-14, 1984

Which of the following disease epidemics can be controlled by immunization of the population?

(a) Typhoid

(b) Polio

(c) Cholera

(d) Cryptosporidiosis

(e) None of the above


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Question 34. US by time of onset, March 13-14, 1984

Answer

(b) Polio


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Question 35. US by time of onset, March 13-14, 1984

In a point source epidemic all cases will present:

(a) Within the infectious period of the source

(b) Within the range of minimum and maximum incubation periods of the disease

(c) Within the minimum incubation period of the disease

(d) Within the maximum incubation period of the disease

(e) At one point in time


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Question 35. US by time of onset, March 13-14, 1984

Answer

(b) Within the range of minimum and maximum incubation periods of the disease


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Question 36. US by time of onset, March 13-14, 1984

Which of the following statements are not true about the West Nile virus?

(a) The West Nile virus can be transmitted by culex mosquitos.

(b) Human transmission of West Nile virus is possible

(c) The main reservoir for West Nile virus is horses

(d) 80% of people infected with West Nile virus are asymptomatic

(e) Crows play an important part in the surveillence of West Nile virus


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Question 36. US by time of onset, March 13-14, 1984

Answer

(c) The main reservoir for West Nile virus is horses


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Question 37. US by time of onset, March 13-14, 1984

It has been reported that approximately 13% of refugees from south east Asia have a positive test for Hepatitis B surface antigen (HBsAg). However, other groups in our community are recognized as having rates equal to or greater than those of the south east Asian refugee. Such groups would be:

(a) Physicians

(b) Injection drug users

(c) Microbiologists

(d) Physiotherapists

(e) Laboratory technicians ‑ chemical pathology


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Question 37. US by time of onset, March 13-14, 1984

Answer

(b) Injection drug users


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Question 38. US by time of onset, March 13-14, 1984

The control of epidemics by isolation of cases is of little value if the disease produces a large number of sub-clinical infections. Examples of such a diseases would be:

(a) Tuberculosis

(b) Infectious Hepatitis A

(c) Polio

(d) Cholera

(e) All of the above


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Question 38. US by time of onset, March 13-14, 1984

Answer

(e) All of the above


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Question 39. US by time of onset, March 13-14, 1984

The following represents the epidemic curve for 24 cases of Hepatitis A.

It is an example of:

(a) Person to person spread

(b) Possible point source epidemic

(c) A recurrent food borne outbreak

(d) None of the above


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Question 39. US by time of onset, March 13-14, 1984

Answer

(b) Possible point source epidemic


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Question 40. US by time of onset, March 13-14, 1984

Examine the graph of an epidemic curve. The cases in this epidemic all have gastrointestinal complaints. Which of the following is the most likely cause of the epidemic?

(a) Staphylococcal food poisoning

(b) Salmonella

(c) Influenza‑like virus

(d) A spill of a toxic chemical into the area's water supply

(e) Pollution of the air by a toxic chemical from a nearby paint factory


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Question 40. US by time of onset, March 13-14, 1984

Answer

(b) Salmonella


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Question 41. US by time of onset, March 13-14, 1984

In 1967 WHO started a program of smallpox eradication. This was successful because:

(a) Sub‑clinical cases occur commonly

(b) Humans constituted the only reservoir

(c) Vaccine effectiveness is not easily measured

(d) 100% vaccination has been possible in the developing countries


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Question 41. US by time of onset, March 13-14, 1984

Answer

(b) Humans constituted the only reservoir


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Question 42. US by time of onset, March 13-14, 1984

Which of the following factors contributed to the global eradication of smallpox?

(a) There were no sub-clinical cases

(b) Immunization was highly effective

(c) Isolation of clinical cases was effective in preventing transmission

(d) Action was organized at an international level

(e) All of the above


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Question 42. US by time of onset, March 13-14, 1984

Answer

(e) All of the above


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Question 43. US by time of onset, March 13-14, 1984

An adult patient of yours is going to Central Africa. What immunization(s) should be considered?

(a) Gonorrhea

(b) Malaria

(c) Yellow fever

(d) West Nile virus

(e) All of the above


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Question 43. US by time of onset, March 13-14, 1984

Answer

(c) Yellow fever


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Question 44. US by time of onset, March 13-14, 1984

For adult travellers from Canada to malarious areas, which of the following would not be considered for prophylactic use?

(a) Mefloquine

(b) Chloroquine

(c) Malarone

(d) Doxycycline

(e) All of the above


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Question 44. US by time of onset, March 13-14, 1984

Answer

(e) All of the above


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Question 45. US by time of onset, March 13-14, 1984

A certificate for yellow fever is required by one of your patients who is travelling to South America. After primary vaccination the certificate will be valid after:

(a) 3 days

(b) 6 days

(c) 10 days

(d) 14 days


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Question 45. US by time of onset, March 13-14, 1984

Answer

(c) 10 days


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Question 46. US by time of onset, March 13-14, 1984

Maximum time from intercourse with a person infected with syphilis to the development of a primary chancre is:

(a) Three weeks

(b) Three months

(c) Six months

(d) One year

(e) None of the above


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Question 46. US by time of onset, March 13-14, 1984

Answer

(b) Three months


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Question 47. US by time of onset, March 13-14, 1984

Chlamydia trachomatis infection has been associated in females with:

(a) Chronic pelvic pain

(b) Infertility

(c) Pelvic inflammatory disease

(d) Ectopic pregnancy

(e) All of the above


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Question 47. US by time of onset, March 13-14, 1984

Answer

(e) All of the above


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Food Poisoning US by time of onset, March 13-14, 1984


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Food Poisoning- US by time of onset, March 13-14, 1984causes

  • Staph aureus

  • E. coli enteritis

  • Salmonella

  • Shigella

  • Campylobacter

  • Cholera

  • Botulism

  • Mushroom poisoning

  • Listeria

  • Bacillus cereus

  • Fish poisoning

  • Yersinia


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Food Poinsoning US by time of onset, March 13-14, 1984

  • Lab studies

    • Gram staining and Loeffler methylene blue staining of the stool for WBCs help to differentiate invasive disease from noninvasive disease.

    • Perform microscopic examination of the stool for ova and parasites.

    • Bacterial culture for enteric pathogens such as Salmonella, Shigella, and Campylobacter organisms becomes mandatory if a stool sample shows positive results for WBCs or blood or if patients have fever or symptoms persisting for longer than 3-4 days.

    • Perform blood culture if the patient is notably febrile.

    • CBC count with differential, serum electrolyte assessment, and BUN and creatinine levels help to assess the inflammatory response and the degree of dehydration.

    • Assay for C difficile to help rule out antibiotic-associated diarrhea in patients receiving antibiotics or those with a history of recent antibiotic use.


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Food Poisoning US by time of onset, March 13-14, 1984

  • Imaging Studies

    • Flat and upright abdominal radiographs should be obtained if the patient experiences bloating, severe pain, or obstructive symptoms or if perforation is suggested.

  • Other Tests:

    • Consider sigmoidoscopy in patients with bloody diarrhea. It can be useful in diagnosing inflammatory bowel disease, antibiotic-associated diarrhea, shigellosis, and amebic dysentery.


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Food Poisoning US by time of onset, March 13-14, 1984

  • Treatment

    • Oral rehydration solution (ORS)

    • Intravenous Solutions

    • Absorbents (eg, Kaopectate, aluminum hydroxide)

    • Antisecretory agents such as bismuth subsalicylate (Pepto-Bismol)

    • Antiperistaltics (opiate derivatives)

    • Diphenoxylate with atropine (Lomotil)

    • Loperamide (Imodium)


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Question 48. US by time of onset, March 13-14, 1984

Bacillus cereus is a recognized agent of food poisoning. The food most likely to be contaminated with this agent is:

(a) Hamburger meat

(b) Shellfish

(c) Rice

(d) Potato Salad

(e) Chicken

(f) Home-made canned vegetables


Question 48177 l.jpg
Question 48. US by time of onset, March 13-14, 1984

Answer

(c) Rice


Questions 49 54 l.jpg
Questions 49-54. US by time of onset, March 13-14, 1984

Match each of the following with the food listed.

49. B. cereus

50. E. coli (0l57)

51. Demoic Acid

52. Staphylococcus

53. Salmonella

54. Clostridium botulinum

(a) Hamburger meat

(b) Shellfish

(c) Rice

(d) Potato Salad

(e) Chicken

(f) Home-made canned vegetables


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Questions 49-54. US by time of onset, March 13-14, 1984

Answers

49- c

50- a

51- b

52- d

53- e

54- f


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Question 55. US by time of onset, March 13-14, 1984

Within 30 minutes of eating a bouillabaisse containing tuna, mackerel and shellfish, the subject became flushed, developed urticaria and abdominal cramps. The most likely cause was:

(a) Scrombotoxin (histamine)

(b) Staphylococcal toxin

(c) Clostridrium perfringens

(d) Salmonella

(e) Botulinum toxin

(f) Shigella

(g) Campylobacter


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Question 55. US by time of onset, March 13-14, 1984

Answer

(a) Scrombotoxin (histamine)


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Question 56. US by time of onset, March 13-14, 1984

66. One method of pasteurisation is to hold the product at 71.6oC for 15 seconds. This treatment can be relied on to:

(a) Kill spoilage organisms only

(b) Kill most pathogenic bacteria

(c) Sterilize the product


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Question 56. US by time of onset, March 13-14, 1984

Answer

(b) Kill most pathogenic bacteria


Question 57 l.jpg
Question 57. US by time of onset, March 13-14, 1984

Which of the following statements about scabies are true? (Check any number)

(a) Now an uncommon condition

(b) Always associated with poor personal hygiene

(c) Characterized by relentless itching, more intense by day.

(d) Distribution of rash characteristically between fingers, around wrists, and in flexures and buttocks.

(e) Spread by personal contact

(f) Persons who are re-infected develop symptoms within 1-4 days


Question 57185 l.jpg
Question 57. US by time of onset, March 13-14, 1984

Answer

True- d, e, f


Questions 58 67 l.jpg
Questions 58-67. US by time of onset, March 13-14, 1984

An outbreak of illness from West Nile virus infection took place in the northeastern United States between July and October, 2001.

For each of the numbered situation below, select the most appropriate term from the following lettered options. Each option can used once, more than once or not at all.


Slide187 l.jpg

  • Epidemic US by time of onset, March 13-14, 1984

  • Sentinel case

  • Incidence rate

  • Risk

  • False- positive

  • False- negative

  • Risk factor

  • Prognostic factor

  • Natural history

  • Case fatality

  • Median survival

  • Randomized controlled clinical trial

  • Cohort study

  • Case-control study


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Question 58. US by time of onset, March 13-14, 1984

Persons with fever/headache were ten times more likely than others to have serum evidence of WNV. Fever/ headache is best described as


Question 58189 l.jpg
Question 58. US by time of onset, March 13-14, 1984

G. Risk factor


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Question 59. US by time of onset, March 13-14, 1984

Among Staten Island residents 2.5 per 100,000 persons developed severe WNV neurologic disease during this time period. This measure best described as


Question 59191 l.jpg
Question 59. US by time of onset, March 13-14, 1984

C. Incidence rate


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Question 60. US by time of onset, March 13-14, 1984

WNV has occurred for the first time in the United States the preceding year. This unusual pattern of occurrence is best described as


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Question 60. US by time of onset, March 13-14, 1984

A. Epidemic


Question 61 l.jpg
Question 61. US by time of onset, March 13-14, 1984

A person who has the symptoms consistent with severe WNV neurologic disease, but does not have definitive serologic evidence of infection


Question 61195 l.jpg
Question 61. US by time of onset, March 13-14, 1984

E. False-positive


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Question 62. US by time of onset, March 13-14, 1984

Two of 21 patients with severe WNV neurologic disease died. This best described by


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Question 62. US by time of onset, March 13-14, 1984

J. Case fatality


Question 63 l.jpg
Question 63. US by time of onset, March 13-14, 1984

The first person with severe WNV neurologic disease died. This is best described by


Question 63199 l.jpg
Question 63. US by time of onset, March 13-14, 1984

B. Sentinel case


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Question 64. US by time of onset, March 13-14, 1984

Clinical outcome of severe WNV nerologic disease was substantially worse for elderly patients. Advanced age is best described as


Question 64201 l.jpg
Question 64. US by time of onset, March 13-14, 1984

H. Prognostic factor


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Question 65. US by time of onset, March 13-14, 1984

A study of antiviral agents is conducted for the treatment of severe WNV neurologic disease in which treatment assignments to individual patients are made by chance


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Question 65. US by time of onset, March 13-14, 1984

L. RCT


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Question 66. US by time of onset, March 13-14, 1984

A study is conducted comparing prior use of mosquito repellent by persons with and without severe WNV neurologic disease. This best described as


Question 66205 l.jpg
Question 66. US by time of onset, March 13-14, 1984

N. Case-control study


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Question 67. US by time of onset, March 13-14, 1984

A study is conducted in which the rates of subsequent WNV infection are compared in communities with and without mosquito abatement programs. This best described as


Question 67207 l.jpg
Question 67. US by time of onset, March 13-14, 1984

M. Cohort study


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