Back to Basics, 2013 POPULATION HEALTH: Infectious Diseases and Outbreak Investigation

1. Back to Basics, 2013POPULATION HEALTH:Infectious Diseases and Outbreak Investigation N. Birkett, MD Epidemiology & Community Medicine Other resources available on Individual & Population Health web site

2. 78-5 Outbreak Management (1) • Physicians are crucial participants in the control of outbreaks of disease. • They must be able to • diagnose cases, • recognize outbreaks, • report these to public health authorities and • work with authorities to limit the spread of the outbreak. • A common example includes physicians working in nursing homes and being asked to assist in the control of an outbreak of influenza or diarrhoea.

3. 78-5 Outbreak Management (2) Key Objectives • Know the defining characteristics of an outbreak and how to recognize one when it occurs. • Demonstrate essential skills involved in controlling an outbreak and its impact on the public, in collaboration with public health authorities as appropriate.

4. 78-5 Outbreak Management (3) Enabling Objectives • Define an outbreak in terms of an excessive number of cases beyond that usually expected. • Describe and understand the main steps in outbreak management and prevention. • Demonstrate skills in effective outbreak management including infection control when the outbreak is due to an infectious agent. • Describe the different types of infection control practices and justify which type is most appropriately implemented for different outbreak conditions. • Demonstrate effective communication skills with patients and the community as a whole. • Describe appropriate approaches to prevent or reduce the risk of the outbreak recurring.

5. Infectious Disease Summary • Terminology • Nature of diseases • Outbreaks/epidemics • Identification • Methods of control

7. Infections: Sources and agents (1) • Foodborne • Botulism • Clostridium perfringens • Hepatitis A • Norovirus • Salmonellosis • Shigellosis • Staphylococcal disease • Trichinosis • Person-to-person spread • Aseptic meningitis • Hepatitis B and C • Respiratory Infections (e.g., influenza) • Herpes simplex • Streptococcal disease • Tuberculosis • Leprosy • Water & Foodborne • Amebiasis • Cholera • Giardiasis • Legionellosis • E coli

8. Infections: Sources and agents (2) • Vaccine preventable • Chickenpox • Diphtheria, pertussis, tetanus • Hepatitis A and B • HPV • Influenza • Measles, mumps, rubella • Meningococcal • Pneumococcal • Poliomyelitis • Arthropod Borne • Encephalitis (West Nile) • Lyme Disease • Malaria • Plague • Rocky Mountain Spotted Fever • Zoonotic • Psittacosis • Q fever • Rabies • Hantavirus • West Nile • Prions • Kuru • vCJD • Sexually Transmitted • HIV/AIDS • Gonorrhea • Syphilis • Chlamydia trachomatis • Fungal • Candidiasis • Coccidioidomycosis • Histoplasmosis

9. Terminology (1) • Infectivity • The ability of an agent to invade and multiply in a host (an infection). • Dose of organism required to establish infection in 50% of animals. • Pathogenicity • The ability of an agent to produce clinically apparent illness. • Pathogen • Infectious and non-infectious substances capable of producing tissue damage or initiating a process which can lead to a disease.

10. Terminology (2) • Virulence • The proportion of clinical cases which produce severe disease and/or permanent sequelae. • Immunogenicity • The ability of an agent to produce specific immunity against the agent • Can be produced in general body or within specific sites such as the GI tract. • Determines the ability of an agent to re-infect the same host • e.g., measles vs. gonorrhea

11. Terminology (3) • Reservoir • Living organisms or inanimate matter in which infectious agent normally lives and multiplies • Fomites (Vehicle) • Inanimate objects contaminated with infectious agent (not the reservoir). • E.g. toys in a daycare centre. • Vector • An animate source of an infectious agent. • The vector may be infected with the organism (e.g. mosquitoes and malaria) or just be a mechanical carrier (e.g. flies). • Usually insects or small mammals such as rodents.

12. Terminology (4) • Zoonoses • Diseases transmitted to humans from animals (e.g. anthrax) • Carrier • An infected person without apparent clinical disease who remains infectious (e.g. Typhoid Mary) • Index Case • The first case to be diagnosed in an outbreak • Sometimes defined as the first case noticed in the outbreak • Contacts • People who have possibly been infected due to relevant contact with an infectious case

13. Terminology (5) • Attack Rate • The probability that people will get ill from the disease. Usually applied in an outbreak situation.

14. Terminology (6) • Secondary Attack Rate • Probability of infection in a closed group who are at risk but excluding the index case(s). Formula is:

15. Terminology (7) • Case Fatality Rate (CFR) • The probability of death in people with an infection.

19. Pathogenic Mechanisms (1) • Direct Tissue Invasion (Group A Strep) • Production of Toxins (Diphtheria) • Allergic Host Reaction • Resistant/latent infection (carriers) • Enhancement of host susceptibility to drugs (e.g. Reye’s syndrome and ASA). • Immune Suppression

20. Reservoirs (examples of transmission patterns) • Human Human Human • Animal Animal Animal Human Animal Vector Vector Human

21. Mechanisms of Spread (1) • Touch (many URI’s, scabies) • Bite (rabies) • Kiss (mononucleosis) • Sexual contact (Chlamydia) • Droplet, over 5μ, spread 1-2 meters (resp. virus) • Soil (tetanus) • Transplacental (hepatitis B) Indirect transmission Direct transmission • Vehicle borne (inanimate) • fomites (e.g. toys) • Food • IV fluid • organism may or may not multiply • E. coli in hamburger • Vector borne (animate) • mechanical (e.g. soiled feet of insect) • biological (e.g. malaria)

22. Mechanisms of Spread (2) Airborne transmission • Droplet nuclei • tuberculosis • measles • varicella • smallpox • ? Influenza • Dust • anthrax

23. Epidemics (1) • Epidemic • now often called an ‘outbreak’, especially if localized • the occurrence (in a community or region) of a disease/condition/behaviour clearly in excess of normal expectancy • Pandemic • an epidemic covering a very wide area and affecting a large proportion of the population (SIM web link) • Controversial definition • Consider H1N1 outbreak • Endemic • the occurrence of a disease/condition at a relatively constant level in a given setting, usually with on-going transmission

24. Epidemics (2) • Conditions increasing likelihood of an epidemic • Agent conditions • Introduction of a new pathogen • Increased amount of a pathogen • Change in the virulence of a pathogen. • Population conditions • An adequate number of exposed and susceptible persons. • An effective means of transmission between the source of the pathogen and the susceptible person.

25. Epidemics (3) • Incubation period and possible causal agents

26. Epidemics (4) • Types of epidemics • Common source • Point source • Ongoing exposure • Need not be geographically localized • Propagated/progressive • Mixed • Epidemic curve • Spot maps • Note that epidemics can arise from behaviour as well as from traditional infectious sources.

27. Epidemic Curves: point source (1)

28. Epidemic Curves: propagated (2) 10 days

29. Distribution of cases by onset of symptoms: point source type Maximum incubation period Average incubation period Minimum incubation period Exposure

30. Exposurebegins & continues

32. Factors Influencing Spread of Disease in a Population (1) • Period of infectivity in relationship to symptoms • Includes consideration of carrier states • Herd immunity • Type of spread • Direct • Indirect • Airborne • Transmission mechanics • Consider sexual vs. droplet spread

33. Herd Immunity Develop disease Immune

34. Epidemic Control (1) • Twin goals: • Minimize the impact to the affected community • Understand the cause and mode of transmission • Goals can conflict: • Need to take action in absence of full information • Need to collect full information base • Effective and clear communication with general public is essential • Designate one spokesperson • Regular press briefings • Lessons from the SARS outbreak

35. Outbreak control measures (1) Isolation • separation of infectious persons or animals from others during the period of communicability • usually isolate for at least two incubation periods. Quarantine • restrictions on the activities of well people who (may) have been exposed to a communicable disease during its period of communicability. • active surveillance is an alternative • Quarantine for the longest usual incubation period • Often at least two incubation periods. • More controversial than isolation since it affects people who are not currently ill (and may never get ill). • we expect some who are quarantined to get sick

36. Outbreak control measures (2) Immunization • passive or active • Passive can be more useful for acute outbreak control Chemoprophylaxis • Treat people with disease • Preventive use of antibiotics for people exposed • tuberculosis • meningococcal infection Harm Reduction (for long term outbreaks) • Focus on prevent adverse effects from harmful exposures • Needle exchange • Safe Injection sites

37. Outbreak control measures (3) Reduce host susceptibility • Immunization (active and passive) • nutrition • improve living conditions and other social determinants of health Interrupt transmission of the agent • quarantine/isolation • case treatment • contract tracing • inspections • environmental clean-up • animal population control • rabies vaccination of wild animals • insect spraying • monitor for animal infections

38. Outbreak control measures (4) Inactivate agent • water purification; chlorination Personal hygiene measures • hand hygiene (#1 strategy) • cough etiquette • protective clothing (masks, gowns) • avoid at risk situations Family/community measures • preventing sexual abuse of children leads to reduction in STIs • Needle exchange and related programmes.

39. Surveillance (1) The continuing scrutiny of all aspects of occurrence and spread of disease that are pertinent to effective control • Reportablediseases. • legal obligation to report designated diseases to local public health department • list includes • AIDS • food poisoning • encephalitis • STIs • influenza • Lassa fever • SARS • plus many more

40. Surveillance (2) The continuing scrutiny of all aspects of occurrence and spread of disease that are pertinent to effective control • Reportable diseases. • Sentinel practices • Animal/water surveys • Environmental monitoring • Mortality (vital statistics) • Provincial laboratory tests • Epidemic investigations • Disease registries • CIHI and related data.