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Part III: Infectious Disease Epidemiology

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Title: 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
65
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71
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

82
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

88
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

92
Question 25.
  • Answer
  • (e) All of the above

93
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

94
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

97
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

99
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.

100
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

101
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.

104
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

106
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

109
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

110
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.

111
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)

114
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
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