Download Infectious Disease

Back to Basics, 2012
POPULATION HEALTH:
Infectious Diseases and
Outbreak Investigation
N. Birkett, MD
Epidemiology & Community Medicine
Other resources available on Individual & Population Health
web site
03/2012
1
78-5 Outbreak Management (1)
• Physicians are crucial participants in the control of outbreaks of
disease.
• They must be able to
•
•
•
•
diagnose cases,
recognize outbreaks,
report these to public health authorities and
work with authorities to limit the spread of the outbreak.
• A common example includes physicians working in nursing homes and
being asked to assist in the control of an outbreak of influenza or diarrhoea.
Key Objectives
• Know the defining characteristics of an outbreak and how to
recognize one when it occurs.
• Demonstrate essential skills involved in controlling an outbreak and
its impact on the public, in collaboration with public health authorities
as appropriate.
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78-5 Outbreak Management (2)
Enabling Objectives
• Define an outbreak in terms of an excessive number of cases beyond that
usually expected.
• Describe and understand the main steps in outbreak management and
prevention.
• Demonstrate skills in effective outbreak management including infection
control when the outbreak is due to an infectious agent.
• Describe the different types of infection control practices and justify which
type is most appropriately implemented for different outbreak conditions.
• Demonstrate effective communication skills with patients and the
community as a whole.
• Describe appropriate approaches to prevent or reduce the risk of the
outbreak recurring.
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Infectious Disease Summary
• Terminology
• Nature of diseases
• Outbreaks/epidemics
– Identification
– Methods of control
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Infections: Sources and agents (1)
Foodborne
• Botulism
• Clostridium perfringens
• Hepatitis A
• Norovirus
• Salmonellosis
• Shigellosis
• Staphylococcal disease
• Trichinosis
Water & Foodborne
• Amebiasis
• Cholera
• Giardiasis
• Legionellosis
• E coli
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Person-to-person spread
• Aseptic meningitis
• Hepatitis B and C
• Respiratory Infections
(e.g., influenza)
• Herpes simplex
• Streptococcal disease
• Tuberculosis
• Leprosy
6
Infections: Sources and agents (2)
Vaccine preventable
• Chickenpox
• Diphtheria, pertussis,
tetanus
• Hepatitis A and B
• HPV
• Influenza
• Measles, mumps, rubella
• Meningococcal
• Pneumococcal
• Poliomyelitis
Sexually Transmitted
• HIV/AIDS
• Gonorrhea
• Syphilis
• Chlamydia trachomatis
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Arthropod Borne
• Encephalitis (West Nile)
• Lyme Disease
• Malaria
• Plague
• Rocky Mountain Spotted
Fever
Zoonotic
• Psittacosis
• Q fever
• Rabies
• Hantavirus
• West Nile
Prions
• Kuru
• vCJD
Fungal
• Candidiasis
• Coccidioidomycosis
• Histoplasmosis
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Terminology (1)
• Infectivity
– The ability of an agent to invade and multiply in a host
(an infection).
– Dose of organism required to establish infection in
50% of animals.
• Pathogenicity
– The ability of an agent to produce clinically apparent
illness.
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Terminology (2)
• Virulence
– The proportion of clinical cases which produce severe
disease and/or permanent sequelae.
• Immunogenicity
– The ability of an agent to produce specific immunity
against the agent
– Can be produced in general body or within specific
sites such as the GI tract.
– Determines the ability of an agent to re-infect the
same host
• e.g., measles vs. gonorrhea
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Terminology (3)
• Reservoir
– Living organisms or inanimate matter in which infectious
agent normally lives and multiplies
• Fomites (Vehicle)
– Inanimate objects contaminated with infectious agent (not
the reservoir).
• E.g. toys in a daycare centre.
• Vector
– An animate source of an infectious agent.
• The vector may be infected with the organism (e.g. mosquitoes
and malaria) or just be a mechanical carrier (e.g. flies).
• There is disagreement about whether vectors are restricted to
insects or can also include small mammals such as rodents.
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Terminology (4)
•
Zoonoses
– Diseases transmitted to humans from animals (e.g. anthrax)
• Carriers
– An infected person without apparent clinical disease who
remains infectious (e.g. Typhoid Mary)
• Index Case
– The first case to be diagnosed in an outbreak
– Sometimes defined as the first case noticed in the outbreak
• Contacts
– People who have possibly been infected due to relevant contact
with an infectious case
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Terminology (5)
• Attack Rate
– The probability that people will get ill from the
disease. Usually applied in an outbreak situation.
• Secondary Attack Rate
– Probability of infection in a closed group who are at
risk but excluding the index case(s). Formula is:
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Terminology (6)
• Case Fatality Rate (CFR)
– The probability of death in people with an
infection.
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Pathogenic Mechanisms (1)
•
•
•
•
•
Direct Tissue Invasion (Group A Strep)
Production of Toxins (Diphtheria)
Allergic Host Reaction
Resistant/latent infection (carriers)
Enhancement of host susceptibility to
drugs (e.g. Reye’s syndrome and ASA).
• Immune Suppression
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Reservoirs (examples of
transmission patterns)
• Human
Human
Human
• Animal
Animal
Human
Animal
Animal
Vector
Vector
Human
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Mechanisms of Spread (1)
Direct transmission
• Touch (many URI’s,
scabies)
• Bite (rabies)
• Kiss (mononucleosis)
• Sexual contact (Chlamydia)
• Droplet, over 5 u, spread 1-2
meters (resp. virus)
• Soil (tetanus)
• Transplacental (hepatitis B)
03/2012
Indirect transmission
• Vehicle borne (inanimate)
• fomites (e.g. toys)
• Food
• IV fluid
• organism may or may not
multiply
• E. coli in hamburger
• Vector borne (animate)
• mechanical (e.g. soiled feet
of insect)
• biological (e.g. malaria)
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Mechanisms of Spread (2)
Airborne transmission
• Droplet nuclei
–
–
–
–
–
tuberculosis,
measles,
varicella,
smallpox,
? Influenza)
• Dust
– anthrax
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Epidemics (1)
• Epidemic (now often called an ‘outbreak’, especially if
localized)
– the occurrence in a community or region of cases of a
disease/condition/behaviour clearly in excess of normal
expectancy
• Endemic
– the occurrence of a disease/condition at a relatively constant
level in a given setting, usually with on-going transmission
• Pandemic
– an epidemic covering a very wide area and affecting a large
proportion of the population (SIM web link)
• Pathogen
– Infectious and non-infectious substances capable of producing
tissue damage or initiating a process which can lead to a
disease.
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Epidemics (2)
• Common conditions increasing likelihood
of an epidemic
– The introduction of a new pathogen or an
increased amount of, or a change in the
virulence of, a pathogen.
– An adequate number of exposed and
susceptible persons.
– An effective means of transmission between
the source of the pathogen and the
susceptible person.
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Epidemics (3)
• Incubation period and causal agent
Time frame
Examples
Hours
Food toxins
Heavy metals
Days
Bacterial infections
Salmonella / cholera
Weeks
Measles / mumps / Hep A
Months
Hep B / Rabies
Years
Kuru / cancer
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Epidemics (4)
• Types of epidemics
– Common source
• Point source
• Ongoing exposure
• Need not be geographically localized
– Propagated/progressive
– Mixed
• Epidemic curve
• Spot maps
• Note that epidemics can arise from behaviour as
well as from traditional infectious sources.
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Epidemic Curves: point source (1)
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Epidemic Curves: propagated (2)
10 days
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Distribution of cases by onset of symptoms:
point source type
Number of cases
20
15
10
Maximum incubation period
Average
incubation period
Minimum
incubation period
5
0
03/2012
Exposure
Units of Time
27
Distribution of cases by onset of symptoms
Continuous Source type
Number of cases
20
15
10
5
0
Exposure
begins &
continues
03/2012
Units of Time
28
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Factors Influencing Spread of
Disease in a Population (1)
• Period of infectivity in relationship to
symptoms
– Includes consideration of carrier states
• Herd immunity
• Type of spread
– Direct
– Indirect
– Airborne
• Transmission mechanics
– Consider sexual vs. droplet spread
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WHO Stages of a Pandemic
1.No virus circulating
in animals has
caused human
disease
2.Animal virus has
caused disease in
humans
3.Some human to
human
transmission but
not enough to
sustain community
outbreak
4.Sustained
human to
human
transmission
leading to
community
level outbreaks
5.Human to
human spread
in at least two
countries of
one WHO
region
6.Phase 5 + a
community
level outbreak
in at least one
other WHO
region
Post peak
period
Incidence is
decreasing
although
waves of
increased
incidence
may occur
Post
pandemic
period
Return to
normal
levels
Time
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Herd Immunity
Develop disease
Immune
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Epidemic Control (1)
Twin goals:
• Minimize the impact to the affected community
• Understand the cause and mode of transmission
Goals can conflict:
• Need to take action in absence of full information
• Need to collect full information base
Effective and clear communication with general public
is essential
• SARS outbreak
• designate one spokesperson
• regular press briefings
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Actions for ‘acute’ outbreak
control
Isolation
• separation of infectious persons or animals from others during the period of
communicability
–
usually isolate for at least two incubation periods.
Quarantine
• restrictions on the activities of well people who (may) have been exposed to a
communicable disease during its period of communicability.
–
–
active surveillance is an alternative
usually quarantine for the longest usual incubation period
•
–
–
Often at least two incubation periods.
More controversial than isolation since it affects people who are not currently ill (and may
never get ill).
we expect some who are quarantined to get sick
Immunization
• passive or active
• Passive (IGG) can be more useful for acute outbreak control
Chemoprophylaxis
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General approaches to outbreak
control (1)
Reduce host susceptibility
• Immunization (active and passive)
• nutrition
• improved living conditions and other social determinants of health
Interrupt transmission of the agent
• quarantine/isolation
• case treatment
• contract tracing
• inspections
• environmental clean-up
• animal population control
– rabies vaccination of wild animals
– insect spraying
– monitor for animal infections
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General approaches to outbreak
control (2)
Inactivate agent
• water purification; chlorination
Personal hygiene measures
• hand hygiene (#1 strategy)
• cough etiquette
• protective clothing (masks, gowns)
• avoid at risk situations
Family/community measures
• preventing sexual abuse of children leads to reduction in STIs
• Needle exchange and related programmes.
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Surveillance
The continuing scrutiny of all aspects of occurrence
and spread of disease that we pertinent to effective
control
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•
•
•
•
•
•
•
•
Reportable diseases.
Sentinel practices
Animal/water surveys
Environmental monitoring
Mortality (vital statistics)
Provincial laboratory tests
Epidemic investigations
Disease registries
CIHI and related data.
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More MCQs
• Here are some more questions that
students can use to test their own
knowledge:
http://www.medicine.uottawa.ca/sim/data/Se
http://www.medicine.uottawa.ca/sim/data/Sel
lf-test_Qs_Outbreaks_e.htm
f-test_Qs_Outbreaks_e.htm
• (The questions contain comments on the
answers, to illustrate why a given
response is not correct)
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Distribution of cases by onset of symptoms.
Intermittent outbreak
Number of cases
20
15
10
5
0
Time
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Distribution of cases by onset date:
Point source with index case and limited spread
Number of cases
20
15
10
Maximum incubation period
Average
incubation period
Minimum
incubation period
5
0
03/2012
Index
case
Units of Time
40
Distribution of cases by onset of symptoms.
Point source, index case with propagated spread
Number of cases
20
15
10
Average
incubation
period
5
0
1
Index
case
03/2012
5
10
15
20
25
30
35
Days
41