Part III: Infectious Disease Epidemiology

1
Part III Infectious Disease Epidemiology
2
Epidemics Their Control
3
Epidemiological Triad for Infectious Disease
Agent
Environment
Host
4
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 

5
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???

6
Basics of Disease Transmission
7
Chain of Infection
8
Iceberg of infectious disease
Symptomatic disease
Asymptomatic disease
9
Course of Disease
Incubation period
Illness
Latent Period
Infectious
Infected
10
Immunity

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

11
Portals of Entry for Infection

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

12
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)

13
Opportunities for interrupting transmission
Quarantine
Vehicle control
Treatment
Physical protection
Infection control
Improve general environment
Chemoprophylaxis
Immunization
Isolation
Herd immunity
14
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

15
Investigation of disease outbreaks
16
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

17
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.

18
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

19
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

20
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.

21
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

22
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

23
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

24
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

25
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

26
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

27
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

28
Epidemic Curves Point Source
29
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
30
Epidemic Curve Propagated or Person-Person
Tertiary Cases
Secondary Cases
Index Case
Days since exposure
31
VHF Deaths, Bandudo Province, ZaireMarch - April
1995
32
Epidemic Curve Continuous Source Outbreak
33
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)

34
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

35
Question 1.

• Answer
• (a) Incubation period of the disease

36
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

37
Question 2.

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

38
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

39
Question 3.

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

40
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.

41
Question 4.

• Answer
• 24
• 20

42
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

43
Question 5.

• Answer
• (c) Non-gonococcal urethritis

44
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

45
Question 6.

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

46
Question 7.

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

47
Question 7.

• Answer
• (c) Western equine encephalitis

48
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

49
Question 8.

• Answer
• (d) Hepatitis B

50
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

51
Question 9.

• (a) The attending physician

52
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

53
Question 10.

• Answer
• (e) Pneumococcal pneumonia

54
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

55
Question 11.

• Answer
• (e) All of the above

56
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

57
Question 12.

• Answer
• (e) None of the above

58
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

59
Question 13.

• Answer
• (e) Improvement in general social
  conditions

60
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

61
Question 14.

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

62
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

63
Question 15.

• Answer
• (e) All of the above

64
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

72
Vaccines Recommended for All Health Care Workers

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

73
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)

74
Question 16.

• Answer
• (a) DPaT Adsorbed

75
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

76
Question 17.

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

77
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

78
Question 18.

• Answer
• (e) They cause fewer side effects

79
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

80
Question 19.

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

81
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

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Question 20.

• Answer
• (a) Immunization

83
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

84
Question 21.

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

85
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

86
Question 22.

• Answer
• (a) Pregnancy

87
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

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Question 23.

• Answer
• (d) Salmonellosis

89
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

90
Question 24.

• Answer
• (c) 72

91
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

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Question 25.

• Answer
• (e) All of the above

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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

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Question 26.

• Answer
• (b) Hepatitis B

95
Specific Diseases of Public Health Importance
96
TB

• What is TB?
• Tuberculosis (TB) is caused by a bacterium called
  Mycobacterium tuberculosis. TB usually attacks
  the lungs, but can also affect other parts of the
  body such as the lymph nodes.
• Airborne transmission

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TB

• What are the symptoms of TB disease?
• a bad cough that lasts longer than 2 weeks
• pain in the chest
• coughing up blood or sputum (phlegm)
• weakness or feeling very tired
• weight loss
• no appetite
• chills
• fever
• night sweats.

98
TB

• Treatment
• Isoniazid (INH)
• Pyrazinamide (PZA)
• Rifampin
• Ethambutol

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TB

• What is BCG?
• BCG (Bacille Calmette-Guérin) is a live vaccine
  that was developed by two French scientists
  Calmette and Guérin in the 1920s. It helps
  protect babies and young children against the
  most severe forms of TB disease.
• Today, only some First Nations children on
  reserves receive BCG routinely.

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Measles

• Disease profile
• Measles is a highly contagious and acute
  infectious disease caused by a virus of the genus
  Morbillivirus in the family Paramyxoviridae. It
  is one of the best known and deadliest of all
  childhood rash and febrile illnesses. In severe
  cases, complications such as pneumonia,
  diarrhoea, middle ear infection and encephalitis
  (a dangerous infection of the brain causing
  inflammation) may occur. Measles mainly affects
  young children, but can strike older children and
  adults as well.
• Transmission- airborne droplets

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Measles

• In Canada
• Measles is no longer endemic in Canada . Between
  2000 and 2002, the number of reported Canadian
  cases dropped from 199 to 6, the lowest number of
  cases ever reported in Canada . In 2004, only 7
  cases were reported. The majority of cases were
  international importations or the result of
  limited spread following imported cases .
  Clusters or small outbreaks, ranging from 2 to
  155 cases, have occurred among un-immunized
  Canadians who oppose immunization on religious or
  philosophic grounds.

102
Measles

• Treatment
• There is no specific treatment for measles.
  Bed rest is recommended
• Vaccine
• Measles vaccine contains live attenuated measles
  virus. It is available alone or in combination
  with live rubella vaccine (MR) or with mumps and
  rubella vaccines (MMR).

103
Typhoid

• Typhoid fever is caused by Salmonella typhi,
  which differs from most other Salmonella species
  in that it infects only humans and frequently
  causes severe systemic illness. The organism is
  generally transmitted via food contaminated with
  the feces or urine of people with the disease or
  those who are S. typhi carriers. The fatality
  rate is approximately 16 for untreated cases and
  1 for those given appropriate antibiotic
  therapy. Between 2 and 5 of typhoid cases
  become chronic carriers, sometimes shedding
  bacteria in stool for years. The risk of severe
  illness is increased in people with depressed
  immunity (e.g., due to HIV) or decreased gastric
  acid levels.

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Typhoid

• What are the signs and symptoms of typhoid fever?
  
• Persons with typhoid fever usually have a
  sustained fever as high as 103 to 104 F (39 to
  40 C). They may also feel weak, or have stomach
  pains, headache, or loss of appetite. In some
  cases, patients have a rash of flat, rose-colored
  spots. The only way to know for sure if an
  illness is typhoid fever is to have samples of
  stool or blood tested for the presence of S.
  Typhi .

105
Typhoid

• Vaccines
• Two typhoid vaccines are currently available for
  use an oral live, attenuated vaccine (Vivotif
  Berna vaccine, manufactured from the Ty21a strain
  of S. Typhi by the Swiss Serum and Vaccine
  Institute) and a Vi capsular polysaccharide
  vaccine (ViCPS) (Typhim Vi, manufactured by
  Aventis Pasteur) for intramuscular use

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Typhoid

• Specific antimicrobial therapy shortens the
  clinical course of typhoid fever and reduces the
  risk of death. Persons who are potentially
  exposed to S. Typhi and who develop symptoms of
  typhoid fever should seek appropriate medical
  care. Antimicrobial therapy should be guided by
  local data on antimicrobial sensitivity.

107
HAV

• Cause
• Hepatitis A virus (HAV)
• Non-enveloped virus of the Picornoviridae family
• One serotype identified
• Identified in 1972
• HAV is an enteric viral infection, generally
  transmitted through a fecal-oral route.

108
HAV

• Clinical Characteristics
• Incubation Period From 15-50 days, average 28-30
  days
• Acute Illness Can cause a renewed illness up to
  one year after initial infection. This can happen
  in about 15 of patients.
• Chronic Infection People usually do not remain
  infected for life. The body will most often fight
  off the virus naturally.
• Global Incidence1.5 million cases each year.
• Global Prevalence15-100 in various parts of the
  world

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HAV

• Signs and Symptoms
• Jaundice (yellowing of the skin and eyes), other
  general symptoms such as uneasiness, loss of
  appetite, pain in the stomach area, dark urine
  and fatigue.
• Most people mild to serious Hep A recover
  naturally

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HAV

• Modes of Transmission
• Exposure to water or food products contaminated
  with HAV (feces containing the virus)
• Transmission through household or sexual contact
  is seen as a very rare event, particularly in
  heterosexual relationships
• Transmission through blood does not happen often.
  

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HAV

• Prevention
• A vaccine to protect against HAV is available. A
  combination vaccine for Hep A and B is also
  available.
• Treatment
• There is no effective treatment to date. People
  generally recover from symptoms in 4 to 6 weeks.

112
HAV

• Canadian Data on the trends of HAV
• The incidence of Hep A was approximately 2.9
  cases for every 100,000 persons in 1999 (Health
  Canada, Notifiable Diseases Online)

113
HBV

• Cause
• Hepatitis B Virus (HBV)
• DNA virus from the Hepadnaviridae family of
  viruses. Some features in common with
  retroviruses.
• Hepatitis B surface antigen (HbsAg) discovered in
  1965
• HbsAg also called Australian Antigen
• Four serotypes and seven genotypes of human
  hepatitis B (Hep B)

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HBV

• Clinical Characteristics
• Incubation Period From 2 to 6 months
• Infectivity About 100 times more infective than
  HIV
• Acute Illness About 90 of adults clear the virus
  from their system after serious infection.
• Chronic Infection About 350 million people
  worldwide have long-term infection (gt5).15 to
  40 advance to liver damage and liver disease.
• Death from Chronic Liver Disease, Disease from
  liver damage, and Cancer of the Liver 15-25
  risk, gt1 million people per year worldwide

115
HBV

• Signs and Symptoms
• Jaundice (yellowing of the skin and eyes), other
  general symptoms such as tiredness, loss of
  appetite, joint pain, pain in the stomach area,
  and feelings of sickness.
• Symptoms may not appear in all cases, and at
  least 30 of seriously infected people may not
  show symptoms

116
HBV

• Modes of Transmission
• Most infections can happen when body fluids
  including blood, blood products of an infected
  person enters the body of a person who is not
  protected against the virus. HBV has also been
  found in semen.
• Infection routes include sexual contact with an
  infected person and exposure to needlesticks and
  other 'sharps' which have been contaminated with
  HBV (this includes people who inject drugs).
• Can also be passed from mother to newborn infant
  at the time of birth (vertical transmission).

117
HBV

• Prevention
• Vaccine options are available to protect against
  HBV.
• Most provinces in Canada have school-based
  immunization programs, and it is recommended that
  all children aged 0-15 ask about vaccination
  against HBV
• Treatment
• Two standard treatments for Hep B interferon and
  lamivudine. Interferon is used for short periods
  of time. If this treatment is effective, the body
  will then suppress the virus on its own.
  Lamivudine may be used in a similar manner, or
  may be used to achieve long-term viral
  suppression. Newer treatments such as adefovir
  are effective in lamivudine-resistant infections.

118
HBV

• Canadian Data on the trends of HBV
• The incidence of Hep B was approximately 4.2
  cases for every 100,000 persons in 1999 (Health
  Canada, Notifiable Diseases Online)
• The prevalence is estimated to be 0.7-0.9, and
  the distribution of cases varies by ethnic
  origin, job and risk group.

119
HCV

• Cause
• Hepatitis C virus (HCV)
• Identified in 1989
• Responsible for 90 of non-A, non-B hepatitis
  cases following blood transfusion prior to 1989
• HCV is a viral infection carried in the blood
• There are six genotypes and more than 100
  subtypes of HCV identified.

120
HCV

• Clinical Characteristics
• Incubation Period Average 6-7 weeks
• Acute Illness Mild acute illness is seen in less
  than 25 of infected people
• Chronic Infection70-80 of people progress to
  chronic infection.
• Death from Chronic Liver Disease, Disease from
  liver damage, and Cancer of the Liver1-5 of
  infected people per year.

121
HCV

• Signs and Symptoms
• Jaundice (yellowing of the skin and eyes) can
  occur in 20-30 of those infected. Other general
  symptoms such as uneasiness, loss of appetite,
  pain in the stomach area, dark urine and fatigue
  can be seen in 10-20 of those infected.
• About 70-80 of people show no signs or symptoms
  of infection.
• About 20-30 or individuals who are infected with
  acute Hep C will recover without treatment.

122
HCV

• Modes of Transmission
• Exposure to blood or blood products infected with
  HCV
• An infected mother can pass the infection to her
  newborn child (vertical transmission).
• Sexual transmission is a rare event, but can
  happen in the presence of blood.
• Household transmission through sharing of razors,
  toothbrushes and combs is possible

123
HCV

• Treatment
• Treatment of people with new Hep C infections
  with long acting interferon and ribavirin can get
  rid of the virus in up to 60 of people within 24
  to 48 weeks.

124
HCV

• Canadian Data on the trends of HCV
• Incidence is currently between 10-20 cases per
  100,000 /year in Canada
• Prevalence was estimated at 250,000 or 0.8 of
  the Canadian population in 2002

125
Syphilis

• Cause/symptoms
• Syphilis is a systemic disease caused by T.
  pallidum. Patients who have syphilis may seek
  treatment for signs or symptoms of primary
  infection (i.e., ulcer or chancre at the
  infection site), secondary infection (i.e.,
  manifestations that include but are not limited
  to skin rash, mucocutaneous lesions, and
  lymphadenopathy), or tertiary infection (e.g.,
  cardiac, ophthalmic, auditory abnormalities, and
  gummatous lesions).

126
Syphilis- Diagnosis

• A presumptive diagnosis is possible with the use
  of two types of serologic tests for syphilis a)
  nontreponemal tests (e.g., Venereal Disease
  Research Laboratory VDRL and Rapid Plasma
  Reagin RPR) and b) treponemal tests (e.g.,
  fluorescent treponemal antibody absorbed
  FTA-ABS and T. pallidum particle agglutination
  TP-PA). The use of only one type of serologic
  test is insufficient for diagnosis, because
  false-positive nontreponemal test results may
  occur secondary to various medical conditions.

127
Syphilis

• Treatment
• Penicillin G, administered parenterally, is the
  preferred drug for treatment of all stages of
  syphilis. The preparation(s) used (i.e.,
  benzathine, aqueous procaine, or aqueous
  crystalline), the dosage, and the length of
  treatment depend on the stage and clinical
  manifestations of disease.

128
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

129
Question 27.

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

130
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

131
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

132
Question 28.

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

133
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

134
Question 29.

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

135
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

136
Question 30.

• Answer
• (b) HIV antibody

137
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

138
Question 31.

• Answer
• (c) 20 - 25

139
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

140
Question 32.

• Answer
• (c) A live attenuated bacillus

141
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

142
Question 33.

• Answer
• (c) Scalp

143
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

144
Question 34.

• Answer
• (b) Polio

145
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

146
Question 35.

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

147
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

148
Question 36.

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

149
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

150
Question 37.

• Answer
• (b) Injection drug users

151
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

152
Question 38.

• Answer
• (e) All of the above

153
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

154
Question 39.

• Answer
• (b) Possible point source epidemic

155
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

156
Question 40.

• Answer
• (b) Salmonella

157
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

158
Question 41.

• Answer
• (b) Humans constituted the only reservoir

159
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

160
Question 42.

• Answer
• (e) All of the above

161
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

162
Question 43.

• Answer
• (c) Yellow fever

163
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

164
Question 44.

• Answer
• (e) All of the above

165
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

166
Question 45.

• Answer
• (c) 10 days

167
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

168
Question 46.

• Answer
• (b) Three months

169
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

170
Question 47.

• Answer
• (e) All of the above

171
Food Poisoning
172
Food Poisoning- causes

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

173
Food Poinsoning

• Lab studies
• Gram staining and Loeffler methylene blue
  staining of the stool for WBCs help to
  differentiate invasive disease from noninvasive
  disease.
• Perform microscopic examination of the stool for
  ova and parasites.
• Bacterial culture for enteric pathogens such as
  Salmonella, Shigella, and Campylobacter organisms
  becomes mandatory if a stool sample shows
  positive results for WBCs or blood or if patients
  have fever or symptoms persisting for longer than
  3-4 days.
• Perform blood culture if the patient is notably
  febrile.
• CBC count with differential, serum electrolyte
  assessment, and BUN and creatinine levels help to
  assess the inflammatory response and the degree
  of dehydration.
• Assay for C difficile to help rule out
  antibiotic-associated diarrhea in patients
  receiving antibiotics or those with a history of
  recent antibiotic use.

174
Food Poisoning

• Imaging Studies
• Flat and upright abdominal radiographs should be
  obtained if the patient experiences bloating,
  severe pain, or obstructive symptoms or if
  perforation is suggested.
• Other Tests
• Consider sigmoidoscopy in patients with bloody
  diarrhea. It can be useful in diagnosing
  inflammatory bowel disease, antibiotic-associated
  diarrhea, shigellosis, and amebic dysentery.

175
Food Poisoning

• Treatment
• Oral rehydration solution (ORS)
• Intravenous Solutions
• Absorbents (eg, Kaopectate, aluminum hydroxide)
• Antisecretory agents such as bismuth
  subsalicylate (Pepto-Bismol)
• Antiperistaltics (opiate derivatives)
• Diphenoxylate with atropine (Lomotil)
• Loperamide (Imodium)

176
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

177
Question 48.

• Answer
• (c) Rice

178
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
179
Questions 49-54.

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

180
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

181
Question 55.

• Answer
• (a) Scrombotoxin (histamine)

182
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

183
Question 56.

• Answer
• (b) Kill most pathogenic bacteria

184
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

185
Question 57.

• Answer
• True- d, e, f

186
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.

187

• 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

188
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

189
Question 58.

• G. Risk factor

190
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

191
Question 59.

• C. Incidence rate

192
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

193
Question 60.

• A. Epidemic

194
Question 61.

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

195
Question 61.

• E. False-positive

196
Question 62.

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

197
Question 62.

• J. Case fatality

198
Question 63.

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

199
Question 63.

• B. Sentinel case

200
Question 64.

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

201
Question 64.

• H. Prognostic factor

202
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

203
Question 65.

• L. RCT

204
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

205
Question 66.

• N. Case-control study

206
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

207
Question 67.

• M. Cohort study