INFECTIOUS DISEASE EPIDEMIOLOGY Maj Fawad

1. INFECTIOUS DISEASEEPIDEMIOLOGYMajFawad

2. Topics to be covered in this lecture • Definitions • Dynamics of Infectious Disease Transmission • Control of Infection

3. Terms 1. Disease • Manifest / Overt • Inapparent / Asymptomatic/ • Subclinical / Covert • Latent • Colonization Communicabledisease / Contagious disease 3. Contamination 4. Pollution

4. Parasite Virus Infection Bacteria Fungi

5. Infection The entry and development or multiplication of an infection agent in body of man or animal is called infection. The infectious agent can be virus, bacteria, fungi, parasite etc.

6. 1. Disease (infection) 1.1.Manifest Synonymouswith disease. 1.2 .Inapparent, asymptomatic or sub- clinical infection Where infectious agent fails to produce signs and symptoms but infectious agent survives and multiplies in the body of man or animal and is capable of being transmitted to another susceptible individual or animal. . This results from the infectious agent when it produces signs and symptoms.

7. 1.3 .Latent When infection is present in the body but does not Produce any sign and symptoms and at the same time cannot be transmitted to a susceptible host during the period of latency i.e. Herpes simplex, Syphilis.

8. Latent period: This period is the interval of subclinical infection during which the previously active infectious agent becomes dormant in the host. Example: Subsequent to the appearance of genital lesions induced by a herpes simplex type II infection, patients often experience period of remission, after which reactivation of the virus elicits the reappearance of lesions. This interval of remission is referred to as the latent period of the virus.

9. 1.4Colonization In the case of Commensal or low grade pathogen, the multiplication may cause little or no harm to the host and may best be described as colonization.

10. 2. Communicable disease / Contagious Disease: An illness due to a specific infectious agent or its toxic products. This arises through transmission of that agent or its products from an infected person, animal, or inanimate reservoir to a susceptible host, either directly or indirectly through an intermediate plant or animal host, vector, or the inanimate environment.

11. Spread of Communicable disease Direct Indirect Reservoir (Man, animal, Inanimate) Susceptible Host (Man, animal) Airborne Vehicle Vector Inanimate Direct:______ Indirect:……… Intermediate host

12. Mode of transmission Direct: 1. Close physical contact e.g. sexually transmitted disease (AIDS) ,skin to skin contact (leprosy): 2. Droplet infections 3. Contact with the soil 4. Vertical transmission

13. Indirect : • Vehicle-borne :These infection are transmitted through the agency of water, food, ice, blood, serum, plasma, and other biological products e.g. tissues and organs. • Vector –borne : These infection are transmitted by an arthropod or a living invertebrate carrier such as snails or Cyclops.

14. Indirect (contd.) 3. Air –borne: (Droplet Nuclei & Dust ) 4. Fomite – borne: fomites refer to inanimate objects such as handkerchiefs, bed linen, towels, books, spoons, forks, etc., which have been soiled with infective material. Freshly soiled fomites are likely to spread the agents of infection.

15. 3. Contamination: This refers to the presence of organic material or micro – organisms on the body surfaces, articles or inanimate object.

16. 4. Pollution:Pollution refers to the presence of both inorganic and organic matter such as offensive material like trade effluvia or industrial pollutants.

17. Reservoirs of infection Living Non living Animals soil Birds substances Human beings Arthropods patients carriers

18. Reservoir Any person, animal, arthropod, plant, soil or substance (or combination of these) in which an infectious agent normally lives and multiplies, on which it depends primarily for a prolonged survival and where it reproduces itself in such a manner that it can be transmitted to a susceptible host.

19. Human reservoirs Patients Carriers

20. Carrier A person or animal that harbours a specific infectious agent in the absence of discernable clinical disease and serves as a potential source of infection.

21. Classification of carriers Based on the stage of disease Based on the portal of exit of infection Based on the duration

22. Based on the stage of disease • a. Incubatory carriers e.g. Hepatitis • b. Convalescent carrier e.g. typhoid • c. Healthy carrier e.g. Typhoid

23. a. Incubatory CarrierIt is that type of the carrier which transmits micro-organism during incubation period of the disease. b. Healthy Carrier. An individual with an infection that is in- apparent throughout its course but can transmit infection to others, is commonly known as a healthy carrier.

24. c. Convalescent carrier This carrier transmits micro-organisms during the period of convalescence or recovery.

25. 2. Based on the portal of exit of infection 3. Based on the duration Nasal e.g. Streptococcal Oral e.g. Meningococcal Urinary tract e.g. Typhoid Intestinal e.g. Cholera Genital e.g. HIV • Temporary (duration<12 months) carrier • Chronic (duration> 12 months) carrier

26. Types of host Susceptible Host Immunity Resistance

27. Host A person or another living animal including birds and arthropods that affords subsistence and lodgment to an infectious agent under natural conditions. Types of Host Definitive Host. Hosts in which parasite attains maturity or passes its sexual stage, are primary or definitive hosts.

28. Intermediate Host: • Hosts in which the parasite is in larval or • asexual stage, are secondary or intermediate Hosts. • Propagative Host: • A transport or propagative host, is the one in which, the organism remains but does not undergo development. • 4. Obligate Host: • This term refers to the only host of infections such as man in measles

29. Mutualism Beneficial Parasitism Harmful Host parasite relationship (Symbiosis) Commensalisms Neither beneficial Nor harmful

30. Mutualism: It is a type of symbiosis in which there is reciprocal benefit to both the host and parasite. Commensalisms: It is a relationship where the host gives the food and shelter to the parasite. It can either move to the mutualism or parasitism. It is neither good nor bad. Parasitism: It is of unilateral benefit to the parasite only and harmful for the host.

31. Phases in infections • Infective period • Communicability period • Incubation period • External Incubation period • Prodromal Period • Convalescence period • Generation time • Serial interval

32. The period during which an infectious agent may be transferred directly or indirectly from an infected person to another person, from an infected person to an animal, including arthropods. Communicable period/Infective period:

33. The time interval between initial contact with an infectious agent and the appearance of first symptom of the disease in question, or in a vector, if The first time transmission is possible (Extrinsic incubation period). Incubation Period Example: After exposure to the measles virus and before the onset of symptoms, a child is considered to be highly contagious due to continued attendance at school and social encounters with other children.

34. Importance of Incubation Period: • Quarantine regulations • Tracing the source of infection • Determining the type of epidemic • For immunization, active as well as passive • Predicting prognosis

35. Prodromal period: It is the interval between the onset of symptoms & appearance of characteristic clinical manifestations, for example as in measles, the interval between the onset of symptoms such as fever and coryza and appearance of rash.

36. Convalescent PeriodThis is the period of recovery when the clinical symptoms have subsided.Generation timeThe interval of time between receipt of infection by a host and maximum communicability / infectivity of that host. Serial IntervalThe gap in time between the onset of primary case and the secondary case is called the serial interval.

37. Disease spread Source Contact Suspect Reservoir Fomites

38. Source: The person, animal, object or substance from which an infectious agent passes to a host. Contact: A person or animal that has been in an association with an infected person or animal or a contaminated environment and might provide an opportunity to acquire the infective agent.

39. Suspect: A person whose medical history and symptoms suggest that he or she may have or be developing some communicable disease. Fomites: It refers to inanimate object such as handkerchiefs, bed lines towels, books, spoons, forks, etc. Which have been soiled with infective material. Freshly soiled fomites are likely to spread the agents of infection.

40. Infections Nosocomial Opportunistic Cross- infection Exotic Infestation Zoonosis • Epizootic Enzootic

41. Nosocomial infection: An infection occurring in a patient in a hospital or other health-care facility and in whom it was not present or incubating at the time of admission or residual of an infection during the period of previous admission. It includes infection (unrelated to the primary condition) acquired in the hospital but appearing either before or after discharge and also such infection among the staff of the facility. Various types of the nosocomial infections may be. 1.Exogenous: Which are acquired from contaminated hospital environment air, water, food, equipment, infected staff, infectious patients, etc.) 2.Endogenous: Which are acquired from patient’s normal flora……

42. Nosocomial infection: Hospital stay After Discharge Before admission 2 3 1 Case#1 Not nosocomial infection Case #2 &3 Nosocomial infection Infection symptoms

43. Cross infection: This is the infection acquired by an admitted patient from the other patients during the period of hospitalization. Infestation: For persons or animal, the lodgment, development and reproduction of arthropods on the surface of the body or in the clothing. Infested articles or premises are those which harbor or give shelter to animal forms, especially arthropods and rodents.

44. Zoonosis: It is an infection or infectious disease transmissible under natural conditions from vertebrate animal to man. It may be: 1.Enzootic: It is identical to endemic in man. 2.Epizootic: It is identical to epidemic. Outbreaks that affect large number of animals are referred to as epizootic.

45. Iatrogenic: It is an adverse consequence of a preventive, diagnostic or therapeutic regimen or procedure. . Exotic: It is an infection that is not usually present in the given country but introduced from abroad. Opportunistic: An infection caused by the micro-organism which are not normally pathogenic but can assume pathogenecity, when the immune status is compromised.

46. Pandemic Epidemic 1 2 Distribution. 3 4 Endemic Sporadic

47. 1.Pandemic: Global occurrence of a disease. Pandemics are widespread epidemics that achieve large geographic proportions. Example :during the influenza pandemic of the 19th century, millions of people across the continents were affected. Today, AIDS is considered to be the most alarming pandemic of the century.

48. 2.Endemic: The constant presence of a disease or infectious agent within a given geographic area, may also refer to the usual prevalence of a given disease within such area. 3.Sporadic : it refers to the scattered presence of the disease in the given population (a case here and a case there). This indicates that the number of the susceptible is less than the number of resistant in the population

49. 4.Epidemic : • This is occurrence, in a community or region, of cases of an illness (an outbreak) clearly in excess of expected occurrence. This indicates that the number of susceptible is more than the resistant in the community. • Epidemic are classified as follows: • Common source epidemics • Point source epidemics • Propagative (progressive) Epidemics • .

50. Disease control • Surveillance • Eradication • Control • Quarantine • Segregation • Isolation • Disinfections • sterilization