Part III: Infectious Disease Epidemiology

1
Part III Infectious Disease Epidemiology
2
Epidemiological Triad for Infectious Disease
Agent
Environment
Host
3
Notifiable Diseases

• Acute Flaccid Paralysis AIDS Amoebiasis Anthrax
  BotulismBrucellosis Campylobacteriosis Chancroid
  Chickenpox Chlamydia, Genital Cholera
  Creutzfeldt-Jakob Disease Cryptosporidiosis
  Cyclosporiasis Diphtheria Giardiasis Gonorrhea
  Gonococcal Ophthalmia Neonatorum Group B
  Streptococcal Disease of the Newborn Hantavirus
  Pulmonary Syndrome Hepatitis A Hepatitis B
  Hepatitis C Hepatitis Non-A, Non-B Human
  Immonodeficiency Virus Influenza,Laboratory-Confir
  med Invasive Haemophilus influenzae type b
  Disease Invasive Group A Streptococcal Disease
  Invasive Meningococcal Disease Invasive
  Pneumococcal Disease Legionellosis Leprosy
  Listeriosis (all types) Malaria Measles
  Meningitis, Pneumococcal Meningitis, Other
  Bacterial Meningitis, Viral Mumps Paratyphoid
  Pertussis Plague Poliomyelitis Rabies Rubella
  Rubella, Congenital Salmonellosis Shigellosis
  Smallpox Syphilis, All Syphilis, Congenital
  Syphilis, Early Latent Syphilis, Early
  Symptomatic (Primary and Secondary) Syphilis,
  Other Tetanus Tuberculosis Tularemia Trichinosis
  Typhoid Verotoxigenic 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 

4
Emerging communicable disease

• Cryptosporidium parvum 1976
• Ebola virus 1976
• Legionella 1977
• Campylobacter jejuni 1977
• E. Coli 0157H7 1982
• HIV 1983
• Hepatitis C 1989
• nv CJD 1996
• Avian influenza ( Type A H5N1) 1997
• WNV 1999
• SARS 2003
• Pandemic influenza???

5
Basics of Disease Transmission
6
Chain of Infection
7
Iceberg of infectious disease
Symptomatic disease
Asymptomatic disease
8
Course of Disease
Incubation period
Illness
Latent Period
Infectious
Infected
9
Immunity

• Active
• infection
• immunization
• Passive
• immunoglobulin
• intrauterine
• Herd Immunity

10
Portals of Entry for Infection

• Respiratory tract
• Genitourinary tract
• Gastrointestinal tract
• Skin / Mucous membrane
• Transplacental
• Parenteral( percutaneaous , via blood)

11
Modes of Transmission

• Indirect
• Airborne (droplet nuclei , dust particles)
• Vehicle borne (food, water)
• Vector borne ( mosquito)
• Mechanical ( flies)

• Direct
• Direct contact (bite,soil,touch)
• Droplet spread
• Vertical transmission (through placenta)

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Opportunities for interrupting transmission
Quarantine
Vehicle control
Treatment
Physical protection
Infection control
Improve general environment
Chemoprophylaxis
Immunization
Isolation
Herd immunity
13
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

14
Investigation of disease outbreaks
15
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

16
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.

17
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

18
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

19
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

22
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

23
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

24
Formulation of a causal hypothesis

• Factors for hypothesis
• The properties of the agent, its 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

25
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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Epidemic Curves Point Source
28
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
29
Epidemic Curve Propagated or Person-Person
Tertiary Cases
Secondary Cases
Index Case
Days since exposure
30
VHF Deaths, Bandudo Province, ZaireMarch - April
1995
31
Epidemic Curve Continuous Source Outbreak
32
Occurrence/Cessation of an Outbreak

• 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.

• 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.

• Answer
• (a) Incubation period of the disease

35
Question 2.

• 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

36
Question 2.

• Answer
• (c) Period of infectivity of the disease

37
Question 3.

• 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

38
Question 3.

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

39
Question 4.

• 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.

40
Question 4.

• Answer
• 24
• 20

41
Question 5.

• 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

42
Question 5.

• Answer
• (c) Non-gonococcal urethritis

43
Question 6.

• 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

44
Question 6.

• Answer
• B salmonellosis
• A hepatitis A
• C psittacosis
• E hepatitis B

45
Question 7.

• The Culex tarsalis mosquito is the vector in
• (a) Malaria
• (b) Typhus
• (c) Western equine encephalitis
• (d) Yellow fever

46
Question 7.

• Answer
• (c) Western equine encephalitis

47
Question 8.

• 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

48
Question 8.

• Answer
• (d) Hepatitis B

49
Question 9.

• 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

50
Question 9.

• (a) The attending physician

51
Question 10.

• 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

52
Question 10.

• Answer
• (e) Pneumococcal pneumonia

53
Question 11.

• 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

54
Question 11.

• Answer
• (e) All of the above

55
Question 12.

• 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

56
Question 12.

• Answer
• (e) None of the above

57
Question 13.

• 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

58
Question 13.

• Answer
• (e) Improvement in general social
  conditions

59
Question 14.

• 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

60
Question 14.

• Answer
• (c) Reducing the size of the reservoir

61
Question 15.

• 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

62
Question 15.

• Answer
• (e) All of the above

63
Immunization
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Immunization of Travellers

• Required Immunizations
• Yellow fever
• Meningococcal disease
• Cholera
• Recommended Immunizations
• Hepatitis A
• Typhoid
• Meningococcal disease
• Japanese encephalitis
• Cholera
• Influenza
• BCG

71
Vaccines Recommended for All Health Care Workers

• Diphtheria and tetanus toxoid
• Measles vaccine
• Polio vaccine
• Rubella vaccine
• Hepatitis B vaccine
• Influenza vaccine

72
Question 16.

• 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)

73
Question 16.

• Answer
• (a) DPaT Adsorbed

74
Question 17.

• 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

75
Question 17.

• Answer
• (d) History of allergy to house dust

76
Question 18.

• 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

77
Question 18.

• Answer
• (e) They cause fewer side effects

78
Question 19.

• 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

79
Question 19.

• Answer
• (b) Tetanus and diphtheria toxoid (Td)

80
Question 20.

• 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

81
Question 20.

• Answer
• (a) Immunization

82
Question 21.

• 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

83
Question 21.

• Answer
• (c) Fewer cases of diphtheria occur now

84
Question 22.

• 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

85
Question 22.

• Answer
• (a) Pregnancy

86
Question 23.

• Which of the following diseases has a non-human
  reservoir?
• (a) Typhoid
• (b) Shigellosis
• (c) Smallpox
• (d) Salmonellosis
• (e) None of the above

87
Question 23.

• Answer
• (d) Salmonellosis

88
Question 24.

• 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

89
Question 24.

• Answer
• (c) 72

90
Question 25.

• 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

91
Question 25.

• Answer
• (e) All of the above

92
Question 26.

• 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

93
Question 26.

• Answer
• (b) Hepatitis B

94
Question 27.

• 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

95
Question 27.

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

96
Question 28.

• 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
• 85 167
  1.9
• 8958
  100

97
Question 28.

• 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

98
Question 28.

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

99
Question 29.

• 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

100
Question 29.

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

101
Question 30.

• 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

102
Question 30.

• Answer
• (b) HIV antibody

103
Question 31.

• 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

104
Question 31.

• Answer
• (c) 20 - 25

105
Question 32.

• 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

106
Question 32.

• Answer
• (c) A live attenuated bacillus

107
Question 33.

• 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

108
Question 33.

• Answer
• (c) Scalp

109
Question 34.

• 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

110
Question 34.

• Answer
• (b) Polio

111
Question 35.

• 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

112
Question 35.

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

113
Question 36.

• 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

114
Question 36.

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

115
Question 37.

• 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

116
Question 37.

• Answer
• (b) Injection drug users

117
Question 38.

• 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

118
Question 38.

• Answer
• (e) All of the above

119
Question 39.

• 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

120
Question 39.

• Answer
• (b) Possible point source epidemic

121
Question 40.

• 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

122
Question 40.

• Answer
• (b) Salmonella

123
Question 41.

• 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

124
Question 41.

• Answer
• (b) Humans constituted the only reservoir

125
Question 42.

• 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

126
Question 42.

• Answer
• (e) All of the above

127
Question 43.

• 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

128
Question 43.

• Answer
• (c) Yellow fever

129
Question 44.

• 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

130
Question 44.

• Answer
• (e) All of the above

131
Question 45.

• 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

132
Question 45.

• Answer
• (c) 10 days

133
Question 46.

• 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

134
Question 46.

• Answer
• (b) Three months

135
Question 47.

• 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

136
Question 47.

• Answer
• (e) All of the above

137
Food Poisoning
138
Food Poisoning- causes

• Staph aureus
• E. coli enteritis
• Salmonella
• Shigella
• Campylobacter
• Cholera
• Botulism
• Mushroom poisoning
• Listeria
• Bacillus cereus
• Fish poisoning
• Yersinia

139
Question 48.

• 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

140
Question 48.

• Answer
• (c) Rice

141
Questions 49-54.

• 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
142
Questions 49-54.

• Answers
• 49- c
• 50- a
• 51- b
• 52- d
• 53- e
• 54- f

143
Question 55.

• 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

144
Question 55.

• Answer
• (a) Scrombotoxin (histamine)

145
Question 56.

• 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

146
Question 56.

• Answer
• (b) Kill most pathogenic bacteria

147
Question 57.

• 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

148
Question 57.

• Answer
• True- d, e, f

149
Questions 58-67.

• 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.

150

• Epidemic
• 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

151
Question 58.

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

152

• Epidemic
• 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

153
Question 58.

• G. Risk factor

154
Question 59.

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

155

• Epidemic
• 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

156
Question 59.

• C. Incidence rate

157
Question 60.

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

158

• Epidemic
• 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

159
Question 60.

• A. Epidemic

160
Question 61.

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

161

• Epidemic
• 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

162
Question 61.

• E. False-positive

163
Question 62.

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

164

• Epidemic
• 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

165
Question 62.

• J. Case fatality

166
Question 63.

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

167

• Epidemic
• 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

168
Question 63.

• B. Sentinel case

169
Question 64.

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

170

• Epidemic
• 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

171
Question 64.

• H. Prognostic factor

172
Question 65.

• 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

173

• Epidemic
• 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

174
Question 65.

• L. RCT

175
Question 66.

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

176

• Epidemic
• 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

177
Question 66.

• N. Case-control study

178
Question 67.

• 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

179

• Epidemic
• 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

180
Question 67.

• M. Cohort study