1. School of Epidemiology, Public Health and Preventive Medicine
Back to Basics, 2015 POPULATION HEALTH: Infectious Diseases and Outbreak Investigation
Dr. Nicholas Birkett
School of Epidemiology, Public Health and Preventive Medicine
03/2015

2. 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.
03/2015

3. 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.
03/2015

4. 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.
03/2015

5. 78-5 Outbreak Management (4)
Enabling Objectives (cont)
Understand key features of communicable diseases
Understand communicable disease epidemiology
03/2015

6. 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
03/2015

7. Infectious Disease Summary
Terminology
Nature of diseases
Outbreaks/epidemics
Identification
Methods of control
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9. Infections: Sources and agents (1)
Foodborne
Botulism
Clostridium perfringens
Hepatitis A
Norovirus
Salmonellosis
Shigellosis
Staphylococcal disease
Trichinosis
Person-to-person spread
Aseptic meningitis
Hepatitis B and C
Respiratory Infections (e.g., influenza)
Herpes simplex
Streptococcal disease
Tuberculosis
Leprosy
Water & Foodborne
Amebiasis
Cholera
Giardiasis
Legionellosis
E coli
03/2015

10. Infections: Sources and agents (2)
Vaccine preventable
Chickenpox
Diphtheria, pertussis, tetanus
Hepatitis A and B
HPV
Influenza
Measles, mumps, rubella
Meningococcal
Pneumococcal
Poliomyelitis
Arthropod Borne
Encephalitis (West Nile)
Lyme Disease
Malaria
Plague
Rocky Mountain Spotted Fever
Zoonotic
Psittacosis
Q fever
Rabies
Hantavirus
West Nile
Prions
Kuru
vCJD
Sexually Transmitted
HIV/AIDS
Gonorrhea
Syphilis
Chlamydia trachomatis
Fungal
Candidiasis
Coccidioidomycosis
Histoplasmosis
03/2015

11. Terminology (1) Infectivity Pathogenicity Pathogen
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.
03/2015

12. Terminology (2) Virulence Immunogenicity
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
03/2015

13. Terminology (3) Reservoir Fomites (Vehicle)
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.
03/2015

14. Terminology (4) Vector Zoonoses
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
03/2015

15. 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
Habitat destruction
War
Famine
Poverty
Climate change
Genetic Drift
03/2015

16. Terminology (6) Carrier Index Case Contacts
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
03/2015

17. Terminology (7) Attack Rate
The probability that people will get ill from the disease. Usually applied in an outbreak situation.
Secondary attack rate is new cases or people minus initial case(s). It is used to estimate to the spread of disease in a family, household, dorm or other group environment.
Measures the infectivity of the agent and the effects of prophylactic agents (e.g. vaccine)
03/2015

18. Terminology (8) Secondary Attack Rate
Similar to ‘attack rate’ but excludes the index case(s). Formula is:
Secondary attack rate is new cases or people minus initial case(s). It is used to estimate to the spread of disease in a family, household, dorm or other group environment.
Measures the infectivity of the agent and the effects of prophylactic agents (e.g. vaccine)
03/2015

19. Terminology (9) Case Fatality Rate (CFR)
The probability of death in people with an infection.
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23. 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
03/2015

24. Reservoirs (examples of transmission patterns)
Human Human Human
Animal Animal Animal
Human
Animal
Vector
Vector
Human
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26. 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
03/2015

27. Epidemics (1) Epidemic Pandemic
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
03/2015

28. Epidemics (2)
Endemic
the occurrence of a disease/condition at a relatively constant level in a given setting, usually with on-going transmission
03/2015

29. 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.
03/2015

30. Epidemics (4) Types of epidemics Epidemic curve Spot maps
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.
03/2015

31. Epidemic Curves: point source (1)
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32. Epidemic Curves: propagated (2)
10 days
03/2015

33. Average incubation period Minimum incubation period
Distribution of cases by onset of symptoms:
point source type
Maximum incubation period
Average incubation period
Minimum incubation period
Exposure
03/2015

34. Exposure begins & continues
Distribution of cases by onset of symptoms
Point source, Continuous exposure type
Exposure begins & continues
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37. 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
03/2015

38. Herd Immunity
Develop disease
Immune
03/2015

39. Outbreak Control (1) Twin goals: Goals can conflict:
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
03/2015

40. 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.
03/2015

41. Outbreak Control (3)
Effective and clear communication with general public is essential
Designate one spokesperson
Regular press briefings
Lessons from the SARS outbreak
03/2015

42. 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
03/2015

43. 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
03/2015

44. Outbreak Control (6) Interrupt Transmission of the Agent
Identify source of outbreak and remove it
Quarantine/isolation
Case treatment
Contract tracing
03/2015

45. 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
03/2015

46. 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
03/2015

47. 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
03/2015

48. 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
03/2015

49. 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
03/2015

50. 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
03/2015

51. Outbreak Control (13) A ‘contact’ Need to treat every ‘contact’
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’
03/2015

52. 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.
03/2015

53. 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.
03/2015

54. 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)
AIDS
food poisoning
encephalitis
STIs
influenza
Lassa fever
SARS
plus many more
03/2015

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59. 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.
03/2015

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