1. INFECTIOUS DISEASE EPIDEMIOLOGY Maj Fawad

2. OBJECTIVES OF THE LECTURE To Enable the student to: Acquire knowledge of various definitions used to describe infectious diseases. Acquire knowledge of various definitions used to describe infectious diseases. Acquire understanding of the origin & mode of transmission of communicable diseases. Acquire understanding of the origin & mode of transmission of communicable diseases. Acquire understanding of logical sequence of link in the control chain. Acquire understanding of logical sequence of link in the control chain. Possess ability to apply the knowledge of communicable diseases in developing preventive & control strategies. Possess ability to apply the knowledge of communicable diseases in developing preventive & control strategies.

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

4. 1. Disease Manifest / Overt Inapparent / Asymptomatic/ Subclinical / Covert Latent Colonization 3. Contamination 4. Pollution 2. Communicable disease / Contagious disease Terms

5. Infection Bacteria Virus Fungi Parasite

6. 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.

7. 1.Disease (infection) This results from the infectious agent when it produces signs and symptoms. 1.1.Manifest Synonymous with 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..

8. 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.

9. Latent period : 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.

10. 1.4 Colonization 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.

11. 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.

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

13. Mode of transmission Direct: 1.Close physical contact e.g. sexually transmitted disease (AIDS),skin to skin contact (leprosy): 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

14. Indirect : 1. 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. 2. Vector –borne : These infection are transmitted by an arthropod or a living invertebrate carrier such as snails or Cyclops.

15. 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.

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

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

18. Reservoirs of infection patientscarriers Living Non living Arthropods Birds Animals Human beings beings soil substances

19. 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.

20. Human reservoirs Patients Carriers

21. 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. Carrier

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

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

24. a. Incubatory Carrier It 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.

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

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

27. Host Types of host ImmunityResistance Susceptible

28. Host A person or another living animal including birds and arthropods that affords subsistence and lodgment to an infectious agent under natural conditions. A. Types of Host 1. Definitive Host. Hosts in which parasite attains maturity or passes its sexual stage, are primary or definitive hosts.

29. 2.Intermediate Host: Hosts in which the parasite is in larval or asexual stage, are secondary or intermediate Hosts. 3.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

30. B. Immunity: It is the resistance usually associated with the presence of antibodies or cells having a specific action on the microorganism concerned with a particular infectious disease or on its toxin. C. Resistance: The sum total of natural body mechanisms which interpose barriers to the progress of invasion or multiplication of infectious agent or the damage by their toxic products. Virus Fungi Bacteria

31. D. Susceptible: A person or animal presumably not possessing sufficient resistance and immunity against pathogenic agents to prevent contracting infections or diseases if or when exposed to the agents.

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

33. 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.

34. Spectrum of an infectious Disease The sequence of events beginning with the exposure of a susceptible individual to an pathogenic agent and ending with a patient’s recovery or death is illustrated in the following diagrams.

35. Period of pre-pathogenesis AGENT HOST ENVIRONMENTAL FACTORS DURING THIS PERIOD AGENT AND HOST COME TOGETHER FOR PRODUCING A DISEASE. Primary prevention

36. Exposure to an infectious Agent Recovery, Latency or Death Incubation period Symptoms Recovery Latency Or Death Recurrence Of Symptoms Signs Prodromal period Disability Clinical period Period of pathogenesis Sub clinical period Secondary preventionTertiary prevention

37. Preventions This aims at avoiding the emergence of those factors which are known risk factors of diseases. e.g. Curbing (initiation control) the habit of cigarette smoking. 1.Primordial Prevention

38. Primary Prevention Primary prevention is a reduction in the incidence of disease through immunization, sanitation, education, or other means of eliminating pathogenic contamination in the human environment. This is applied in the period of pre-pathogenesis and includes measures on general health improvement and specific measures for prevention of health problem.

39. Secondary Prevention This is applied in the period of pathogenesis and aims at early detection of the disease followed by its treatment. Example: Pap smears for the early detection of cervical cancer and surgical intervention if necessary.

40. Tertiary Prevention This is applied in the period of pathogenesis and extends in the period of recovery. It aims at reducing impairments/disabilities and helping patients to utilize the residual capacities maximally. Example: Shortly after the occurrence of hemiplegia secondary to stroke, bed care and physiotherapy are employed to prevent the development of decubitus ulcers and flexion contractures.

41. Types of Disability Impairment: Any loss or abnormality of psychological, physiological or anatomical structure or function. Disability: Any restriction or lack (resulting from an impairment) of ability to perform an activity in the manner or with in the range considered normal for a human being; Handicap: A disadvantage for a given individuals, resulting from an impairment or a disability, that limits or prevents the fulfillment of a role that is normal (depending on age, sex, and social and cultural factors) for that individual. A disadvantage for a given individuals, resulting from an impairment or a disability, that limits or prevents the fulfillment of a role that is normal (depending on age, sex, and social and cultural factors) for that individual.

42. A classification of Agent, Host, and Environmental Factors that determine the occurrence of diseases in human populations. 1. Agents of Disease (etiological Factors) 2. Host factors (Influence Exposure, Susceptibility, Or response to agents) 3. Environmental Factors (Influence Existence of the agent)

43. Agents of Disease (etiological Factors) Nutritive Element Infectious agents Physical agents Chemical agents 12 3 4 Mechanical agents 5

44. Human behavior Host Factors (Influence Exposure, Susceptibility, response to agents Genetic Age Sex Ethnic group Physiologic state Prior immunologic experience Intercurrent or Preexisting disease

45. Environmental factors (influence existence of the agent) Physical environment Socioeconomic environment Biologic environment

46. Assessment#1 Marks=20 Time=5min Q 1. All the following activities meet the criteria for primary prevention except? 1. Tetanus vaccination for teenagers. 2. Measles/mumps/rubella (MMR) vaccination for first time pregnant mothers. 3. Fluoridation of water. 4. Pap smear screening. 5. Sex education.

47. Q 2. All the following are reservoirs of infection except? 1. 1. Dog 2. 2. Soil 3. 3. Man 4. 4. Birds 5. 5. Glass of water

48. Q 3. All the following are indirect modes of spread of infection except? 1. 1. Blood transfusion 2. 2. Mosquito bite 3. 3. Tissue Grafts 4. 4. Inhalation of dust 5. 5. Contact with infected soil

49. Q 4. Define ? 1. 1. Pollution 2. 2. Reservoir 3. 3. Fomite

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

55. Communicable period/Infective period: 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.

56. Incubation Period The time interval between initial contact with an The time interval between initial contact with an infectious agent and the appearance of first infectious agent and the appearance of first symptom of the disease in question, or in a vector, symptom of the disease in question, or in a vector, if The first time transmission is possible if The first time transmission is possible (Extrinsic incubation period). (Extrinsic 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.

57. Importance of Incubation Period: 1.Quarantine regulations 2.Tracing the source of infection 3.Determining the type of epidemic 4.For immunization, active as well as passive 5.Predicting prognosis

58. 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.

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

60. Disease spread Source Contact Suspect Reservoir Fomites

61. 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.

62. 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.

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

64. 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……

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

66. 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 shelter to animal forms, especially arthropods and rodents.

67. 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. large number of animals are referred to as epizootic.

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

69. Distribution. Pandemic Endemic 12 3 4 Epidemic Sporadic

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

71. 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. 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

72. 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: 1.Common source epidemics 2.Point source epidemics 3.Propagative (progressive) Epidemics.

73. 1.Common Source Epidemic In common source epidemics, all susceptible individuals are exposed to a specific infectious pathogen or noxious agent (chemicals, pollution, heat, etc) originating from a usual, conventional or customary source that is common exposure. Mode of transmission: 1. Indirect (vehicle borne) 1.1 Food 1.2 Water 1.3 Air 1.4 Fomites 2. No direct transmission

74. AB Exposure 0 Time Number of Cases A-Minimum Incubation Period A+B-Usual Incubation Period Common Source Epidemic curve

75. Common Source Epidemic Curve Fewest number of cases become apparent after a minimum incubation period and that the largest number peaks at the end of the usual incubation period. Unimodal shape.. Although common source epidemics may involve only one incubation period of an organism, repeated or prolonged population exposure to the common source often involves infection by a pathogen over the course of more than one incubation period, producing a wide peak or apex in the common source curve.

76. Point source Epidemic In a point source epidemic, all susceptible individuals are exposed to a specific pathogen at one point in time. Point source epidemics are essentially a subcategory of the common source epidemic in which common exposure to the offending pathogen or agent is both brief and simultaneous.

77. A Exposure 0 Time Number of Cases A- Incubation Period Point Source Epidemic

78. 1. All the cases are in one incubation period of the infectious agent. 2. Apex is much sharper. 3. Rapid decline as compared to common source. 4. No secondary transmission is seen. Point Source Epidemic

79. Propagative (progressive) Epidemic In propagative (progressive, serial transmission) epidemics, the pathogen is transmitted from person to person In propagative (progressive, serial transmission) epidemics, the pathogen is transmitted from person to person. Mode of transmission: Direct: 1.genital 2.anal 3.oral 4.skin Contact 5.Droplets(fungi, bacterial spores) Indirect: In which the pathogen is either vectorborne (arthropods) or airborne (dried droplet residues and dust)

80. Number of Cases Secondary Cases 0 Time Propagative (progressive) Epidemic curve

81. 1. Curve for a propagative epidemic shows an initial rise in the number of cases that is less explosive than in a point source epidemic. 2. Successive generations of secondary infection produce a polymodal distribution conforming to several generations of incubation period. Propagative (progressive) Epidemic curve

82. Shortly after a dormitory barbeque at wah medical college, students came back to their rooms and most of them (62 out of 74 students) experienced acute vomiting and diarrhea. This epidemic may be classified as Shortly after a dormitory barbeque at wah medical college, students came back to their rooms and most of them (62 out of 74 students) experienced acute vomiting and diarrhea. This epidemic may be classified as Exercise 1.Point source 2.propagative 3.Common source 4.Serial 5.direct

83. Ten days after a measles outbreak in Wah Cantt, several elementary school children became symptomatic. Subsequently, additional cases were found among friends and families of the infected students. This epidemic may be classified as Ten days after a measles outbreak in Wah Cantt, several elementary school children became symptomatic. Subsequently, additional cases were found among friends and families of the infected students. This epidemic may be classified as Exercise 1.Point source 2.propagative 3.Common source 4.indirect 5.Vectorborne

84. Exercise After returning home from a family planning clinical, Dr. Saeed noticed a slight itching between his fingers. Within 2 days his wife had similar itching, as did his son one day later. This epidemic (scabies) may be classified as After returning home from a family planning clinical, Dr. Saeed noticed a slight itching between his fingers. Within 2 days his wife had similar itching, as did his son one day later. This epidemic (scabies) may be classified as 1.Point source 2.Indirect transmission 3.Common source 4.Serial transmission 5.Vehicleborne transmission

85. How to investigate an epidemic 1. Make sure whether there is an Epidemic 2. Confirmation or the diagnosis 3. Count the Number of cases 4. Environmental Assessment 5. Describing the epidemic in terms of time, place and person 6. Find out who is at risk of having the health problem 7. Formulate a hypothesis explaining the epidemic 8. Conduct a more detailed systematic study 9. Control of the epidemic 10. Preparing the written report

86. Disease control 1. Surveillance 2. Eradication 3. Control 4. Quarantine 5. Segregation 6. Isolation 7. Disinfections 8. sterilization

87. Surveillance: Surveillance of disease is the continuous scrutiny of all aspects of occurrence and spread of disease / other condition of ill health that are pertinent to effective control. Isolation: As applied to patients, it represents separation for the period of communicability to prevent or limit the direct or indirect transmission of the infectious agent from those infected to those who are susceptible or who may spread the disease to others.

88. Segregation: This refers to the separation of a healthy person from an infected person. Quarantine: Restriction of the activities of well person or animals who have been exposed to a case of communicable disease during its period of communicability (i.e. contacts) for maximum incubation period to prevent disease transmission during the incubation period, if the infection should occur.

89. Eradication: It means ending the transmission of the disease and elimination of reservoirs of infection, in a campaign limited in time and carried out to such a degree of perfection that when it comes to an end, there is no resumption of transmission. Control : It means to reduce the prevalence of the disease to such a low level that it no longer remains a big public health problem.

90. Disinfection: It refers to the destruction of the pathogenic micro- organisms. Sterilization: It refers to the destruction of pathogenic as well as non-pathogenic microorganisms and it includes destruction of spores also.

91. a. Chain of infection Infectious agent Infectious agent Reservoir / source of infection Reservoir / source of infection Exit of infectious agent Exit of infectious agent Transmission (mode) of infection Transmission (mode) of infection Entry into a new host Entry into a new host Host susceptibility Host susceptibility Summary of disease transmission and control

92. Infectious Agent: An organism (viruses, rickettsia, bacteria, fungus, protozoa or helminthes) that is capable of producing infection or infectious disease.

93. Exit of infectious agent Avenues of escape are : 1. Respiratory tract-droplet nuclei (continuous emission) 2. Intestinal tract-discharge of faeces (discontinuous emission) 3. Urinary tract. 4. Open wounds (escape from the lesions on to clothes) 5. Mechanical escape (biting or sucking insects e.g. malaria spread by mosquitoes) 6. Contact (close physical contact)

94. Transfer of infection to new host: Direct transmission (person to person) Direct transmission (person to person) Indirect transmission (requires a vehicle) Indirect transmission (requires a vehicle) Classification of vehicle: Animate refers to as vectors e.g. housefly, flea. Mosquito. Animate refers to as vectors e.g. housefly, flea. Mosquito. Inanimate-water, milk, food, air soil and fomites (e.g. clothes, door knobs, moneyetc.), blood transfusion. Inanimate-water, milk, food, air soil and fomites (e.g. clothes, door knobs, moneyetc.), blood transfusion.

95. Entry into new susceptible host Portals of entry are : Respiratory tract- contaminated food or drink. Respiratory tract- contaminated food or drink. Gastro-intestinal tract- contaminated food or drink. Gastro-intestinal tract- contaminated food or drink. Direct infection of membranes e.g. diphtheria, venereal diseases. Direct infection of membranes e.g. diphtheria, venereal diseases. Percutaneous infection passage through skin via bite, for rabies and malaria, direct penetration by infectious agent e.g. schistosomiasis, hookworm. Percutaneous infection passage through skin via bite, for rabies and malaria, direct penetration by infectious agent e.g. schistosomiasis, hookworm.

96. A person or animal presumably not possessing sufficient resistance against a particular pathogenic agent to prevent contracting infection or disease if or when exposed to the agent. Host susceptibility:

97. b. Chain of control 1.Notification 2.Early diagnosis 3.Isolation 4.Destruction of infecting agent 5.Investigation of an attack of illness 6.Immunization 7.Health education

98. Chain of control Notification: It means the immediate intimation of the occurrence of every case of infectious disease to the healthy officers. Early diagnosis: The first step in the control of a communicable disease is its rapid identification for.. a) The treatment of patients b) For epidemiological investigations c) To study the time, place and person distribution.

99. Isolation: Separation for the period of communicability of infected person or animals from others in such places and in such conditions as to prevent or limit the direct or indirect transmission of infectious agent from those infected to those who are susceptible or who may spread the agent to others. Destruction of the infecting agent (disinfection) Destruction of pathogenic microorganism is called disinfection.

100. Investigation of an attack of an illness Broadly the investigation covers the identification of the source of infection and of the factors influencing its spread in the community. Immunization: Increasing the resistance of the susceptible host. Health education: Health education is the process by which individuals and groups of people learn to behave in a manner conducive to the promotion, maintenance or restoration of health