Download Infectious Disease

Back to Basics, 2011
POPULATION HEALTH:
Infectious Diseases and
Outbreak Investigation
E. Ellis, MD
Epidemiology & Community Medicine
April, 2011
1
78-5 Outbreak Management
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 diarrhea.
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.
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.
April, 2011
2
Infectious Disease Summary
• Terminology
• Nature of diseases
• Outbreaks/epidemics
– Identification
– Methods of control
April, 2011
3
April, 2011
4
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
April, 2011
Person-to-person spread
• Aseptic meningitis
• Hepatitis B and C
• Respiratory Infections
(e.g., influenza)
• Herpes simplex
• Streptococcal disease
• Tuberculosis
• Leprosy
5
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
April, 2011
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
6
Terminology (1)
• Infectivity
– The ability of an agent to invade and multiply in a host
(an infection).
– (# infected / # susceptible) X 100
– Dose of organism required to establish infection in
50% of animals.
• Pathogenicity
– The ability of an agent to produce clinically apparent
illness.
– (# with clinical disease / # of infected) X 100
April, 2011
7
Terminology (2)
• Virulence
– The proportion of clinical cases which produce severe
disease and/or permanent sequelae.
– (e.g., # hospitalized or in ICU ‘ $ with disease) X 100
• 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
April, 2011
8
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). Example would be 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.
April, 2011
9
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
• Source Case
– Source of infection for the index case
• Contacts
– Possibly infected due to relevant contact with an infectious case
April, 2011
10
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:
April, 2011
11
Terminology (6)
• Case Fatality Rate (CFR)
– The probability of death in people with an
infection.
April, 2011
12
April, 2011
13
April, 2011
14
April, 2011
15
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
April, 2011
16
Reservoirs (examples of
transmission patterns)
• Human
Human
Human
• Animal
Animal
Human
Animal
Animal
Vector
Vector
Human
April, 2011
17
Mechanisms of Spread (1)
Direct transmission
•
•
•
•
Touch (scabies)
Bite (rabies)
Kiss (mononucleosis)
Sexual contact
(Chlamydia)
• Droplet, over 5 u, spread
1-2 metres (resp. virus)
• Soil (tetanus)
• Transplacental (hepatitis
B)
April, 2011
Indirect transmission
• Vehicle-borne (inanimate):
organism may or may not
multiply or develop (E. coli
in hamburger)
• Vector-borne (animate):
Mechanical: organism
does not multiply or
develop (house flies)
Biological: organism
multiplies or develops
(malaria, West Nile)
18
Mechanisms of Spread (2)
Airborne transmission
• Droplet nuclei (tuberculosis, measles, varicella,
smallpox, ? Influenza)
• Dust (anthrax)
April, 2011
19
Epidemics (1)
• Epidemic (called ‘outbreak’ 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 substance capable of producing
tissue damage or initiating a process which can lead to a
disease.
April, 2011
20
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.
April, 2011
21
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
April, 2011
22
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.
April, 2011
23
Epidemic Curves: point source (1)
April, 2011
24
Epidemic Curves: propagated (2)
10 days
April, 2011
25
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
April, 2011
Exposure
Units of Time
26
Distribution of cases by onset of symptoms
Continuous Source type
Number of cases
20
15
10
5
0
Exposure
begins &
continues
April, 2011
Units of Time
27
Distribution of cases by onset of symptoms.
Intermittent outbreak
Number of cases
20
15
10
5
0
Time
April, 2011
28
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
April, 2011
Index
case
Units of Time
29
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
April, 2011
5
10
15
20
25
30
35
Days
30
April, 2011
31
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
April, 2011
32
Develop disease
Immune
April, 2011
33
Epidemic Control (1)
Twin goals:
• Understand the cause and mode of transmission
• Minimize the impact to the affected community
Goals can conflict:
• Need to collect full information base
• Need to take action in absence of full information
Effective and clear communication with general public
is essential
• SARS outbreak
• designate one spokesperson
• regular press briefings
April, 2011
34
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
– we expect some who are quarantined to get sick; but if none of their
contacts get sick, then quarantine was useful
Immunization
• passive or active
Chemoprophylaxis
April, 2011
35
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
April, 2011
36
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.
April, 2011
37
Surveillance
‘the continuing scrutiny of all aspects of occurrence
and spread of disease that we pertinent to effective
control’
•
•
•
•
•
•
•
•
•
Reportable diseases.
Sentinel practices
Animal/water surveys
Environmental monitoring
Mortality (vital statistics)
Provincial laboratory tests
Epidemic investigations
Disease registries
CIHI and related data.
April, 2011
38
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
April, 2011
39
Infectious Disease Control
Multiple Choice Questions
for discussion
April, 2011
40
11) A group of 50 people are exposed to
virus “A”. Of those 50 people, 9
develop a mild infection, 10 become
seriously ill, and 3 die. The attack rate
of virus “A” in the population would
be:
a) 22/50
b) 9/50
c) 10/50
d) 19/50
e) 13/50
April, 2011
41
15) Examples of secondary prevention
would include all of the following
EXCEPT:
a) Pap smear for cervical cancer
b) chemoprophylaxis in a recent TB converter
c) proctoscopy for rectal cancer
d) immunization for Haemophilus influenzae B
e) mammography for breast cancer
April, 2011
42
23) Which of the following is the most
important justification for mounting a
population screening program for a
specific disease?
a) early detection of the disease of interest is
achieved
b) the specificity of the screening test is high
c) the natural history of the disease is
favorably altered by early detection
d) effective treatment is available
e) the screening technology is available
April, 2011
43
25) Active immunization was important in
control of each of the following
childhood communicable diseases
EXCEPT:
a) diphtheria
b) polio
c) measles
d) scarlet fever
e) pertussis
April, 2011
44
29) Differentiation between a point-source
epidemic and a progressive (propagated)
epidemic is made by:
a) considering the characteristics of the infectious
agent
b) determining the level of immunity in the
community
c) determining the number of persons infected and
calculating the attack rate
d) plotting the distribution of cases by time onset
e) none of the above
April, 2011
45
30) The occurrence of an illness at a rate
of above that expected is called:
a) hyperendemic
b) epidemic
c) endemic
d) enzootic
e) pandemic
April, 2011
46
42) Each of the following is an example of
primary prevention EXCEPT:
a) genetic counselling of parents with one
retarded child
b) nutritional supplements in pregnancy
c) immunization against tetanus
d) chemoprophylaxis in a recent tuberculin
converter
e) speed limits on highways
April, 2011
47
43) The classical “epidemiological triad”
of disease causation consists of
factors which fall into which of the
following categories:
a) host, reservoir, environment
b) host, vector, environment
c) reservoir, agent, vector
d) host, agent, environment
e) host, age, environment
April, 2011
48
45) The difference between a common point
source outbreak and a propagated
outbreak of illness is that:
a) all cases in a common point source outbreak
occur within one incubation period of the exposure
b) the attack rates in propagated outbreaks are
higher
c) person-to-person transmission is a feature of
common source outbreaks
d) case fatality rates in common source outbreaks
are generally higher
e) the source of infection in propagated outbreaks is
more easily contained than in common source
outbreaks
April, 2011
49
Differentiation between a point-source
epidemic and a progressive (propagated)
epidemic is made by:
a) considering the characteristics of the infectious
agent
b) determining the level of immunity in the
community
c) determining the number of persons infected and
calculating the attack rate
d) plotting the distribution of cases by time onset
e) none of the above
April, 2011
50
April, 2011
51
More MCQs
• Here are some more questions that
students can use to test their own
knowledge:
http://www.medicine.uottawa.ca/sim/data/Sel
f-test_Qs_Outbreaks_e.htm
• (The questions contain comments on the
answers, to illustrate why a given
response is not correct)
April, 2011
52