Infectious Disease Epidemiology - PowerPoint PPT Presentation

1 / 47
About This Presentation
Title:

Infectious Disease Epidemiology

Description:

Gonorrhea. Gonorrhea. Chlamydia. Chlamydia. TEXAS. USA ... Chlamydia, gonorrhea. Skin, genital membranes. Direct contact, sexual contact. Lesions, exudate ... – PowerPoint PPT presentation

Number of Views:3162
Avg rating:3.0/5.0
Slides: 48
Provided by: SPH9
Category:

less

Transcript and Presenter's Notes

Title: Infectious Disease Epidemiology


1
Infectious Disease Epidemiology
  • Casey E. Barton, M.S.
  • July 26, 2001

2
REMINDERS!!!!!!!!!!
  • TODAY by 5pm
  • Submit all outstanding homeworks and redos
  • July 31st
  • Teaching-Learning Exam
  • Course Evaluations
  • Tutorial after class
  • August 2nd
  • FINAL EXAM
  • Last day of class!!!!!!!

3
Top 10 Reported Infectious Diseases 1999
4
Epidemiologic Triangle
HOST
AGENT
ENVIRONMENT
5
AGENTS
  • An Agent MUST be present for an infectious
    disease to develop
  • Epidemiologists describe
  • Frequency of disease
  • Mechanisms of transmission
  • The causal agent

6
AGENTS
  • Bacteria
  • Viruses and rickettsia
  • Mycoses (fungi)
  • Parasites
  • Protozoa
  • Helminths
  • Arthropods

7
AGENTS Bacteria
  • Leading killers in 19th century
  • Examples
  • Tuberculosis
  • Salmonellosis
  • Streptococcal infections
  • Problem emerging bacteria strains resistant to
    current antibiotics

8
AGENTS Viruses and Rickettsia
  • Viral infection include
  • Hepatitis A
  • Herpes simplex
  • Influenza
  • HIV
  • Rickettsial infections include
  • Q fever
  • Rocky Mountain Spotted Fever

9
Mycoses (Fungi)
  • Examples
  • Ringworm
  • Aspergillosis
  • Candidiasis

10
AGENTS Parasites
  • Protozoa
  • Malaria
  • Cyclosporiasis
  • Giardiosis
  • Chagas Disease
  • Helminths (worms)
  • Tapeworms
  • Roundworms
  • Schistosomiasis

11
AGENTS Arthropods
  • Insect vectors including
  • Mosquitoes
  • Ticks
  • Flies
  • Mites
  • Other insects
  • Arthropod-borne diseases include
  • RMSF
  • Malaria
  • Encephalitis
  • Lyme Disease

12
Modes of Transmission
  • Airborne or Contact
  • Food- and Water-borne
  • Blood-borne
  • Sexually Transmitted
  • Arthropod-borne
  • Zoonotic

13
Means of Transmission
14
Means of Transmission
  • Direct person to person
  • Indirect through intermediate sources such as
    vehicles, fomites or vectors
  • Horizontal transmission from one person to
    another (direct or indirect)
  • Vertical mother to fetus either genetic or
    across placenta

15
Characteristics of Infectious Disease Agents
  • Infectivity
  • Pathogenicity
  • Virulence
  • Toxigenicity
  • Resistance
  • Antigenicity

16
Infectivity
  • Capacity of the agent to enter and multiply in a
    susceptible host and thus produce infection or
    disease
  • Examples measles and polio
  • Measure of Infectivity Secondary Attack Rate
    (SAR)

17
Pathogenicity
  • Capacity of the agent to cause disease in the
    infected host
  • Example measles
  • Measure of pathogenicity proportion of
    individuals with clinically apparent disease

18
Virulence
  • Severity of the disease
  • i.e. whether clinical manifestations are produced
  • Example Rabies
  • Measure of Virulence Case Fatality Rate (CFR)

19
Toxigenicity
  • Capacity of the agent to product a toxin or
    poison
  • Examples botulism and shellfish poisoning
  • Disease is caused by toxins produced by the
    agent, rather than by the actual agent

20
Resistance
  • Ability of the agent to survive adverse
    environmental conditions
  • Examples parasite with spores or cysts,
    Hepatitis virus
  • Resistance is also applied to the HOST

21
Antigenicity
  • Ability of the agent to induce antibody
    production in the host
  • Agents may or may not induce long-term immunity
  • Examples Measles re-infection is rare
  • Immunogenicity
  • Related term
  • refers to an infections ability to produce
    specific immunity

22
Host
  • Subclinical infection ? Active Disease
  • Hosts ability to fight off infectious agent
  • Nonspecific defense mechanisms
  • Disease-specific defense mechanisms

23
HOST Non-specific defense mechanisms
  • Age, Sex, Race, Genetics
  • Religion, Customs, Occupation, Nutritional status
  • Skin, Mucosal surfaces, Saliva,
  • High pH of gastric juices
  • Immune system (phagocytes and macrophages)

24
HOST Disease-specific defense mechanisms
  • Immunity resistance of host to an agent
  • Active all or part of organism invokes an
    immunologic response
  • Natural results from an infection
  • Artificial results from immunization
  • Passive preformed antibody invokes short term
    immunity
  • Natural antibodies cross the placenta
  • Artificial immuneglobulin after certain
    exposures

25
ENVIRONMENT
  • Physical weather, temperature, humidity,
    geologic formations, habitat
  • Biological population density, flora, fauna,
    reservoirs
  • Socioeconomical behavioral, personality,
    attitudinal, and cultural characteristics of a
    group of people

26
Endemic vs.Epidemic
  • Endemic constant presence of a disease or agent
    in a defined geographical area
  • Epidemic excessive occurrence of disease (above
    endemic level) in a defined geographical area
  • 2 Types
  • Common Source
  • Propogated Source

27
Epidemic
  • Common Source Epidemic event or exposure comes
    from a single source that all persons in the
    group had a chance to encounter
  • Propogated Epidemic caused by either direct or
    indirect transmission of infectious disease from
    one individual to another and can have multiple
    sources from which disease can be transmitted

28
Endemic versus Epidemic
ENDEMIC
Point EPIDEMIC
Propagating EPIDEMIC
NOTE X axis Time Y axis new cases
29
Reservoir (Niche)
  • Fosters survival of infectious disease agent
  • Types of reservoirs
  • Human
  • Plant
  • Animal
  • Arthropod
  • Physical environment

30
Inapparent infection
  • Subclinical infection absence of clinically
    obvious signs and symptoms
  • Asymptomatic individuals can transmit disease
  • Carrier status
  • Serologic evidence of infection

31
Incubation Period
  • Time interval between exposure to an infectious
    agent and the appearance of the first signs of
    disease
  • During this time, the infectious agent replicates
    within the host
  • Can be hours, days, weeks, or years
  • Applies only to clinically apparent cases of
    disease

32
Generation Time
  • Time between lodgment of an infectious agent in a
    host and the maximal communicability of the host
  • May or may not be equivalent to incubation period
  • Applies to both clinically apparent and
    inapparent cases of disease
  • Utilized for describing the spread of infectious
    agents that have a large proportion of
    subclinical cases

33
Herd Immunity
  • A population may become immune to an infectious
    agent after a large proportion of individuals
    have become immune
  • i.e. through past infections or vaccination
  • Can occur when immune persons prevent the spread
    of disease to unimmunized individuals and confers
    protection to the population even though not
    every single individual has been immunized

34
Effect of Herd Immunity on Spread of Infection
(from Jekel et al. 1996, p. 12)
-

-




-
-
-




-
-
-
-




-
-
-





Absence of Herd Immunity
Presence of 50 Herd Immunity
35
Iceberg Concept of Disease
Death Clinical illness
Visible Cases
Invisible Cases
Asymptomatic cases Carriers
36
Zoonoses
  • World Health Organization (WHO)
  • diseases and infections which are naturally
    transmitted between vertebrate animals and man
  • Examples Rabies, roundworms, Lyme disease,
    Brucellosis, Cryptosporidiosis
  • Epizootic and enzootic but refers to diseases in
    animals

37
Emerging Infectious Diseases
  • Changes in climate global warming
  • Human activities farming, reforestation
  • Technologic changes air travel, organ
    transplantation
  • Demographic changes migration to cities

38
Host Prevention
  • Immunity immunizations
  • Behavioral change
  • Treatment of contact and carriers
  • screening

39
Control
  • Environmental
  • Personal hygiene
  • Food protection and safety
  • Water supplies
  • Sanitation, regulation
  • Vectors
  • Mosquitoes, insecticides
  • Animal population control

40
Measures of Disease Outbreaks
  • Attack Rate
  • Secondary Attack Rate
  • Case Fatality Rate

41
Attack Rate
  • Type of incidence rate
  • AR
  • Ill___ 100 during a time period
  • Ill Well
  • Can calculate food or exposure specific AR

42
Secondary Attack Rate
  • Yields an index of the spread of disease within a
    circumscribed unit, i.e. household, dorm
  • Index case case that first comes to the
    attention of public health authorities
  • SAR
  • new cases in group initial cases 100
  • susceptible persons in group initial cases

43
Case-Fatality Rate
  • Refers to the number of deaths caused by a
    specific disease among those who have the disease
  • Provides index of deadliness of a particular
    disease within a specific population
  • CFR deaths due to disease X 100
  • cases disease X
  • DIFFERENT than crude death rate

44
Centers for Disease Control and Prevention (CDC)
  • National Center for HIV,STD, and TB Prevention
  • National Center for Infectious Diseases
  • AIDS, STD and TB Laboratory Research
  • Division of Bacterial and Mycotic Diseases
  • Division of Parasitic Diseases
  • Division of Vector-borne Infectious Diseases
  • Division of Viral and Rickettsial Diseases
  • National Immunization Program

45
Infectious Disease Information
  • Emerging Infectious Diseases Journal
  • www.cdc.gov/ncidod/eid/
  • Morbidity and Mortality Weekly Report (MMWR)
  • www.cdc.gov/mmwr/
  • Program for monitoring Emerging Diseases (Promed)
  • www.promedmail.org/pls/promed/promed.home

46
THE END!!!
47
EXAMPLE CALCULATIONS
Which food item appears to be the most probable
vehicle for the food-borne infection assocaited
with illness at this picnic?
Write a Comment
User Comments (0)
About PowerShow.com