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The definitions used in the epidemiology of infectious diseases. Learning Objectives. At the end of this lecture you (will) be able to: Explain common definitions and basic concepts used in epidemiology. Apply these definitions in different situations.

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The definitions used in the epidemiology of infectious diseases


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    1. The definitions used in the epidemiology of infectious diseases Dr.Ozlem Tanriover

    2. Learning Objectives At the end of this lecture you (will) be able to: Explain common definitions and basic concepts used in epidemiology. Apply these definitions in different situations. Identify the epidemiological approach to study health problems Describe natural history and spectrum of infectious diseases and their implications for public health. Dr.Ozlem Tanriover

    3. Definitions Epidemiology is the study of • distribution and • determinants of • health-related events in specified populations and • the application of this study to prevent and control of health problems. Dr.Ozlem Tanriover

    4. Distribution • Person………. • Place………….. • Time…………… • Describe disease frequency • Incidence Rate…… • Prevalence Rate…… Dr.Ozlem Tanriover

    5. The Epidemiologic Triad Disease Determinants HOST AGENT ENVIRONMENT Dr.Ozlem Tanriover

    6. The epidemiological approach: An Epidemiologist’ approach to study health-related events involves answering five questions: • What? • Who? • Where? • When? • Why? Dr.Ozlem Tanriover

    7. Infection: • It is the entry, development and multiplication of an infectious agent in the body of man or animal. • Outcome of infection varies. Infectious disease: • A clinically manifest disease of man or animal resulting from infection. In-apparent infection: • The infection does not become manifest at any stage. Dr.Ozlem Tanriover

    8. Communicable Disease • An illness due to a specific infectious agent or its toxic products that arises through transmission of that agent from reservoir to susceptible host. • Communicable Disease (typhoid, influenza,.. • Non- Communicable Disease (DM, cancer,.. Dr.Ozlem Tanriover

    9. Contamination: The presence of living infectious agents on the exterior surface of the body or on the clothes or articles of the person or on any inanimate object in the environment including water and food. Contagious diseases A disease that is capable of being transmitted from one person to another by contact or close proximity. e.g. scabies, trachoma and leprosy. Dr.Ozlem Tanriover

    10. Endemic The constant presence of a disease or infectious agent within a given geographic area or population group; It may also refer to the usual prevalence of a given disease within such area or group. • Epidemic The occurrence of more cases of a disease than expected in a given area or among a specific group of people over a particular period of time. Dr.Ozlem Tanriover

    11. Pandemic An epidemic occurring over a very wide area (several countries or continents) at the same time and usually affecting a large proportion of the population. e.g. Influenza,cholera • Outbreak A more or less localized epidemic affecting large number of a group, in the community e.g. outbreak of food poisoning Dr.Ozlem Tanriover

    12. Sporadic Cases occur irregularly, haphazardly from time to time and generally infrequently. Cases are few and separated widely in space and time showing no connection to each other. Dr.Ozlem Tanriover

    13. Nosocomial infection (Hospital acquired infection): • It is an infection occurring in a patient while in a hospital or other health care facility • It should not be present or incubating at the time of admission. Dr.Ozlem Tanriover

    14. Elimination of disease Disease incidence is reduced to a minimal level at which the disease is no longer considered a public health problem, while infection may still occur Example: The aim of elimination of Neonatal tetanus is reduction of its incidence to less than one case/1000 live births. Dr.Ozlem Tanriover

    15. Eradication: • It means worldwide disappearance of a disease (permanent reduction to zero level) with complete destruction of the agent. • The organism can be present only in laboratories and no need for interventions. • e.g. smallpox eradication from the world since 1979. Dr.Ozlem Tanriover

    16. Natural history • Naturalhistoryof disease refers to the progress of a disease process in an individual over time, in the absence of intervention. • The natural history of a disease describes the course of the disease in an individual starting from the moment of exposure to the causal agents till one of the possible outcomes occurs. Dr.Ozlem Tanriover

    17. Dr.Ozlem Tanriover

    18. Spectrum of disease • The idea that an exposure can lead to varying signs, symptoms and severity of the same disease in the population is the spectrum of disease. • Why do we have varying degrees of severity? Prognosis? • The outcome will depend on the interactions of host, agent and environmental factors. Dr.Ozlem Tanriover

    19. The Epidemiologic Triad Disease Determinants HOST AGENT ENVIRONMENT Dr.Ozlem Tanriover

    20. Agent factors refer to an infectious microorganism—virus, bacterium, parasite, or other microbes. • They are necessary but not always sufficient alone to cause disease. • Host factors are intrinsic factors that influence an individual’s exposure, susceptibility, or response to a causative agent.( age, nutrition, race,… • Environmental factors are extrinsic factors which affect the agent and the opportunity for exposure. Dr.Ozlem Tanriover

    21. 1 Diseased, diagnosed & controlled 2 Diagnosed, uncontrolled 3 Undiagnosed or wrongly diagnosed disease 4 Risk factors for disease 5 Free of risk factors Diagnosed disease Undiagnosed or wrongly diagnosed disease The pyramid and iceberg of disease Dr.Ozlem Tanriover

    22. Iceberg phenomenon • Cases of illness correctly diagnosed by clinicians in the community often represent only the “tip of the iceberg.” • Many additional cases may be too early to diagnose or may remain asymptomatic. • Examples: Tuberculosis, meningitis, polio, hepatitis A, AIDS. • The risk is that persons with in-apparent or undiagnosed infections may be able to transmit infection to others. Dr.Ozlem Tanriover

    23. 1 Diseased, diagnosed & controlled 2 Diagnosed, uncontrolled 3 Undiagnosed or wrongly diagnosed disease 4 Risk factors for disease 5 Free of risk factors Diagnosed disease Undiagnosed or wrongly diagnosed disease The pyramid and iceberg of disease Dr.Ozlem Tanriover

    24. Applications of the concepts of natural history and spectrum of disease • Persons with in-apparent or undiagnosed infections can transmit infections to others. • Control measures must be directed toward all infections capable of being transmitted to others; • both clinically apparent cases and • those with in-apparent or undiagnosed infections. Dr.Ozlem Tanriover

    25. INFECTION PREVENTION AT HEALTH CARE FACILITIES

    26. PURPOSE OF INFECTION PREVENTION: • * to minimize infections due to microorganisms causing serious wound infections,abscesses, PID, gangrene and tetanus etc. • to prevent transmission of serious life-threatening diseases such as Hep.B and AIDS • to prevent the spread of infections at health care facilities can be possible only if we can break the inf. chain somewhere

    27. Infection Transmission at Health Care Facilities • 1.Transmission from patient to health worker: preventable accidents (puncture wounds), splash of body fluids into the eye or on to broken skin (scratch, ache, dermatitis)

    28. Infection Prevention • 2.Transmissionfromhealthworkertopatient: • touchingthepatientwithdirtyhands, sneezing, coughingduringcleaningthewound. • 3.Transmissionfrompatienttopatient : • occursthroughuse of contaminatedequipment, instruments, environment, surfaces, air in theoperationroom.

    29. Health care workers should know these and teach these! • 3.Transmissionfrompatienttopatient: • occursthroughuse of contaminatedequipment, instruments, environment, surfaces, air in theoperationroom.

    30. PROTECTIVE BARRIERSat health care facilities • Placing a physical, mechanical or chemical barrier between inf.agent and an individual will break the inf. chain: • -handwashing • -wearing gloves, either for surgery or to protect clinic staff when handling contaminated waste materials and instruments • - using antiseptic solutions for cleaning wounds or preparing the skin prior to surgery, decontaminating, cleaning, sterilizing or high –level disinfecting solutions. • -wearing face-masks, eye glasses, gowns, caps etc.

    31. ASEPSIS • Is a general termusedtodescribethecombination of effortsmadetoprevententry of microorganismsintoanyarea of the body wheretheyarelikelytocauseinfection (Livingandnonlivingobjects)

    32. ANTISEPSIS • Prevention of infection by killing or inhibiting the growth of microorganisms using a chemical agent (antiseptic) on living surfaces • Iodophors, 70% alcohol

    33. DECONTAMINATION • The process that makes nonliving objects safer to be handled by staff before cleaning • Soak in 0.5 % chlorine solution for ten minutes • 1 (household bleach) + 9 (water) = prevents from Hep B and AIDS

    34. HIGH LEVEL DISINFECTION • The process that eliminates all microorganisms except for some bacterial endospores Boiling for 10 minutes or Soak in 0.5 % chlorine solution for 20 minutes

    35. STERILIZATION • The process that eliminates all microorganisms • Heat sterilization (autoclaving or dry heating) • Chemical sterilization (glutaraldehide or formaldehide)

    36. Processes for reuse of contaminated instruments

    37. CORRECT

    38. WRONG

    39. MEDICAL waste disposal

    40. * allow persons to accidentally step and injure • * are a fire hazard • * produce bad odors • attract insects

    41. NONCONTAMINATED WASTE: * poses no infectious risk to persons who handle them CONTAMINATED WASTE: * may carry microorganisms which are potentially infectious to any body who contact or handle the waste and to the community if not disposed properly * blood,pus,urine,stool and other body fluids as well as items which contact them such as used dressings

    42. * wastes from operating rooms and laboratories should be considered contaminated * items which are capable of inflicting injury (e.g. used needles, scalpel blades) and are capable of spreading blood-borne diseases such as hepatitis-B and AIDS * Proper handling of waste items minimizes the spread of infection to clinic personnel and to the local community

    43. * Where available noncontaminated wastes should be transported to disposal sites in covered containers (blue bags or green bags) * Contaminated wastes in red bags with the amblem of clinical waste in noncorrosive washable covered containers * Persons handling wastes should wear heavy gloves,wastes should be buried or incinerated(burnt)

    44. Reusable glass wastes should be first decontaminated in chlorine solution then transported in black bags • * Inside the health facility, the waste bags should be transported in rust proof small cars, to transitory storage containers ,rooms,small buildings etc.

    45. * Waste must not wait in these transitory storage containers longer than 48 hours * Transitory storage containers have two departments (one for red bags, the other for the blue,green and black bags)

    46. INCINERATION (BURNING): * Provides high temperatures which destroy the item as well as microorganisms ;therefore it is the best method for disposal of contaminated wastes * Incineration also reduces the bulk size of wastes to be buried and ensures that the items are not reused dangerously

    47. IF INCINERATION IS NOT POSSIBLE , ALL CONTAMINATED WASTES MUST BE BURIED TO PREVENT SCATTERING OF THE WASTES

    48. Mortalityandmorbidityindicesused in theepidemiology of infectiousdiseases

    49. Population • Group of people with a common characteristic like age, race, sex