Download Infectious Disease

Back to Basics, 2015
POPULATION HEALTH:
Infectious Diseases and
Outbreak Investigation
Dr. Nicholas Birkett
School of Epidemiology, Public Health and
Preventive Medicine
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78-5 Outbreak Management (1)
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
– 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.
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78-5 Outbreak Management (3)
Enabling Objectives (cont)
• 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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78-5 Outbreak Management (4)
Enabling Objectives (cont)
• Understand key features of communicable
diseases
• Understand communicable disease
epidemiology
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78-5 Outbreak Management (5)
• Physicians are crucial participants in the control of
outbreaks of disease.
• Must be able to
•
•
•
•
Diagnose cases
Recognize outbreaks
Report these to public health authorities
Work with authorities to limit the spread of the outbreak.
• Common example
• Assist in the control of an outbreak of influenza or
diarrhoea in a nursing home
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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
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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.
• 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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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 center.
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Terminology (4)
• 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).
• Usually insects or small mammals such as rodents.
• Zoonoses
– Diseases transmitted to humans from animals (e.g. anthrax)
– Do they develop human-to-human spread
• Bird flu
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Terminology (5)
• Emerging Infectious Disease
– An infectious disease where the incidence in humans has
increased in the past 2 decades or threatens to increase in
the near future (CDC)
– Complex set of diseases and contributing conditions
•
•
•
•
•
•
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Habitat destruction
War
Famine
Poverty
Climate change
Genetic Drift
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Terminology (6)
• Carrier
– 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 (7)
• Attack Rate
– The probability that people will get ill from the disease.
Usually applied in an outbreak situation.
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Terminology (8)
• Secondary Attack Rate
– Similar to ‘attack rate’ but excludes the index case(s).
Formula is:
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Terminology (9)
• 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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Routes for Spread of Infections
Non-Contact
Contact
Direct
Via:
Shaking hands,
kissing
Diseases:
Common cold;
STDs
Precautions:
Wash hands;
condoms;
masks
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Indirect
Droplet
Airborne
Via:
Agent falls on
a surface,
picked up by
susceptible
person.
Via:
Through air:
sneeze, cough.
Droplets > 5µm
Via:
Aerosols
(< 5µm). Can
spread via
ventilation
systems.
Diseases:
RSV; Norwalk;
?influenza
Precautions:
Sterilizing
equipment;
disinfection
Diseases:
Meningococcus;
pertussis;
?influenza
Precautions:
Masks; keep
safe distance
Diseases:
TB; measles;
chickenpox;
smallpox
Precautions:
Respirators
(N95 masks);
neg. pressure
rooms
Vehicle
Via:
“Point source”:
Single
contaminated
item (e.g.
unrefrigerated
food).
“Common
source”:
batch of tainted
items, widely
distributed.
Diseases:
E Coli; tainted
meat; chemical
Vector borne
Via:
Transmission
by animal
or insect
vectors.
Diseases:
Malaria;
bird flu
Precautions:
Barriers; insect
sprays; culling
animals
Precautions:
Disinfection;
hygiene; storage
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Virulence
• Parasite borne diseases are usually more
virulent
• Spread by direct contact requires an alive and
active host
• Agents often lose virulence as an epidemic
passes
– Ebola (previous epidemics)
– Virulent strains kill host and don’t spread
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Epidemics (1)
• Epidemic
– Now often called an ‘outbreak’, especially if localized
– The occurrence (in a community or region) of a
disease/condition/behaviour clearly in excess of normal
expectancy
– Public’s reaction/view differs from technical definition
• Pandemic
– An epidemic covering a very wide area and affecting a
large proportion of the population
– Controversial definition
• Consider H1N1 outbreak
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Epidemics (2)
• Endemic
– the occurrence of a disease/condition at a relatively
constant level in a given setting, usually with ongoing transmission
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Epidemics (3)
• Conditions increasing likelihood of an epidemic
– Agent conditions
• Introduction of a new pathogen
• Increased amount of a pathogen
• Change in the virulence of a pathogen.
– Population conditions
• 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 (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
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Exposure
Units of Time
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Distribution of cases by onset of symptoms
Point source, Continuous exposure type
Number of cases
20
15
10
5
0
Exposure
begins &
continues
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Units of Time
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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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Herd Immunity
Develop disease
Immune
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Outbreak 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
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Outbreak Control (2)
• Establish the diagnosis
– Clinical examination
– History, especially of exposure to:
• other sick people
• travel
• agents
– Laboratory testing
• Rapid response vs. definitive tests
• Determine pattern of spread
– Type of outbreak
– Epidemiological study of exposures ‘in common’, etc.
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Outbreak Control (3)
• Effective and clear communication with
general public is essential
– Designate one spokesperson
– Regular press briefings
– Lessons from the SARS outbreak
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Outbreak Control (4)
• General strategies for addressing outbreaks
– Reduce host susceptibility
– Interrupt Transmission of the Agent
• Strategies can be useful for
– Controlling an active outbreak
– Preventing the onset of an outbreak
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Outbreak Control (5)
• Reduce host susceptibility
– During an outbreak
• Immunization (active and passive)
– Before an outbreak, or during a long outbreak
• Nutrition
• Improve living conditions
• Improve other social determinants of health
– A large part of the reason that infectious outbreaks are now so
uncommon
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Outbreak Control (6)
• Interrupt Transmission of the Agent
–
–
–
–
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Identify source of outbreak and remove it
Quarantine/isolation
Case treatment
Contract tracing
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Outbreak Control (7)
• Interrupt Transmission of the Agent (cont)
– Food inspections
– Environmental clean-up
– Animal population control
• Rabies vaccination of wild animals
– Insect spraying
• Monitor for animal infections
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Outbreak Control (8)
• Isolation
– Applies to propagated epidemics
– Deals with people who are already ill
– Separate the infectious persons or animals from
others during the period of communicability
– Usually isolate for at least two incubation periods
– If incubation period is unknown
• Try and estimate it based on transmission patterns
• Be conservative
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Outbreak Control (9)
• Quarantine
– Applies to propagated epidemics
– Places restrictions on the activities of well people
who (may) have been exposed to a communicable
disease during its period of communicability.
– Quarantine for the longest usual incubation period
– Often at least two incubation periods.
– ‘active surveillance’ is an alternative
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Outbreak Control (10)
• Quarantine (cont)
– More controversial than isolation since it affects
people who are not currently ill (and may never get
ill).
– We expect some people who are quarantined to get
sick
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Outbreak Control (11)
Immunization
• Passive or active
• Passive can be more useful for acute outbreak control
Chemoprophylaxis
• Treat people with disease
• Preventive use of antibiotics for people exposed
– tuberculosis
– meningococcal infection
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Outbreak Control (12)
Harm Reduction (for long term outbreaks)
• Focus on prevent adverse effects from harmful
exposures
– Needle exchange
– Safe Injection sites
Inactivate agent
• water purification; chlorination
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Outbreak Control (13)
Contact tracing
• Done by the Public Health Department
• Applies to diseases with person-to-person spread
– Especially STIs
• A ‘contact’
– Someone who interacted with the index case in
such a way that they may have become infected
• Need to treat every ‘contact’
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Outbreak Control (14)
Contact tracing (cont)
• Index case is given chance to contact his/her
‘contacts’
• If that doesn’t happen, PHU can take proactive action
and contact cases
• For TB, PHU takes the lead in
– contact tracing
– Ensuring preventive treatment using Directly
Observed Treatment methods.
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Outbreak Control (15)
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 (1)
The continuing scrutiny of all aspects of occurrence and
spread of disease that are pertinent to effective control
• Reportable diseases.
– legal obligation to report designated diseases to local public health
department
– list includes (among many others)
•
•
•
•
•
•
•
•
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AIDS
food poisoning
encephalitis
STIs
influenza
Lassa fever
SARS
plus many more
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Number of cases by year
Disease
Acute Flaccid Paralysis
2009
2010
2011
2012
2013
2014
mid-year
-
-
-
-
-
0
AIDS
18
6
8
6
6
1
Amebiasis
2
5
5
0
1
0
Botulism
0
0
0
0
0
0
Brucellosis
0
0
0
1
1
0
Campylobacter enteritis
221
205
222
235
216
86
Chickenpox*
373
279
265
258
65
19
Chlamydia
2024
2317
2531
2533
2403
1319
Cholera
0
0
0
0
0
0
Creutzfeld-Jacob Disease
0
1
0
1
1
0
Cryptosporidiosis
21
31
26
31
12
10
Cyclospora
15
17
8
17
3
3
Diphtheria*
0
0
0
0
0
0
Encephalitis/Meningitis
1
0
1
0
0
1
Encephalitis: Unspecified
2
0
0
1
0
0
Encephalitis: Viral
3
1
2
1
3
0
Giardiasis
150
125
147
88
76
31
Gonorrhea
218
274
217
238
257
159
Haemophilus influenzae b, Invasive (Hib)*
1
0
0
0
0
0
Hepatitis A
7
9
9
14
6
2
Hepatitis B*
3
1
5
2
5
3
Hepatitis C
308
230
231
243
240
120
HIV Infections
66
72
70
57
60
33
Influenza A*
638
13
174
213
429
205
Influenza B*
55
1
16
94
45
104
Legionella Infections
1
2
3
3
7
1
Leprosy
0
0
0
0
0
0
Listeriosis
6
2
4
1
1
0
Lyme Disease (Confirmed and Probable)
6
7
12
19
47
8
Lyme Disease (Confirmed)
5
7
11
15
12
1
Lymphogranuloma venereum (LGV)
chlamydia
-
-
-
-
-
1
#1
Disease
2009
2010
2011
2012
2013
2014
mid-year
Malaria
15
30
18
13
18
7
Measles (Red)*
0
6
1
0
0
4
Meningitis: Bacterial
2
4
1
5
5
1
Meningitis: Viral
11
21
3
10
10
4
Meningococcal Disease*
7
4
2
1
1
0
Mumps*
1
2
4
4
2
0
Ophthalmia Neonatorum
0
0
0
0
0
0
Paratyphoid Fever
0
0
0
0
0
0
Paralytic Shellfish Poisoning
1
1
3
2
2
0
Pertussis (Whooping Cough) *
8
4
17
33
8
3
Polio*
0
0
0
0
0
0
Psittacosis/Ornithosis
0
0
0
0
0
0
Q Fever
0
0
2
1
0
0
Rabies (Human)
0
0
0
0
0
0
Rubella (German Measles) *
0
0
0
0
0
0
Rubella, Congenital Syndrome
0
0
0
0
0
0
Salmonellosis
151
177
177
199
130
100
Shigellosis
16
15
19
19
29
11
Streptococcal Infections, Group A Invasive
34
32
50
33
53
42
Streptococcal Infections, Group B Neonatal
4
4
6
7
5
4
Streptococcus pneumoniae, Invasive
96
60
83
89
68
37
Syphilis, infectious
54
51
49
40
32
24
Tetanus (Lockjaw) *
0
0
0
0
0
0
Tuberculosis of the lung
29
30
35
21
33
20
Tuberculosis: All cases
49
48
48
42
52
29
Tularemia
0
0
0
0
0
0
Typhoid Fever
3
3
4
2
4
0
Verotoxin producing E. coli
9
5
12
12
6
2
West Nile Virus
0
0
0
8
4
0
Yellow Fever
0
0
0
1
0
0
Yersiniosis
16
21
6
9
10
5
Surveillance (2)
The continuing scrutiny of all aspects of occurrence and
spread of disease that are 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.
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