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

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Back to Basics, 2015POPULATION HEALTH:

Infectious Diseases and Outbreak Investigation

Dr. Nicholas BirkettSchool 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

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Infectious Disease Summary

• Terminology• Nature of diseases• Outbreaks/epidemics

– Identification– Methods of control

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Foodborne• Botulism• Clostridium perfringens• Hepatitis A• Norovirus• Salmonellosis• Shigellosis• Staphylococcal disease• Trichinosis

Water & Foodborne• Amebiasis• Cholera• Giardiasis• Legionellosis• E coli

Person-to-person spread• Aseptic meningitis• Hepatitis B and C• Respiratory Infections

(e.g., influenza)• Herpes simplex• Streptococcal disease• Tuberculosis• Leprosy

Infections: Sources and agents (1)

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Arthropod Borne• Encephalitis (West Nile)• Lyme Disease• Malaria• Plague• Rocky Mountain Spotted

Fever

Sexually Transmitted• HIV/AIDS• Gonorrhea• Syphilis• Chlamydia trachomatis

Vaccine preventable• Chickenpox• Diphtheria, pertussis,

tetanus• Hepatitis A and B• HPV• Influenza• Measles, mumps, rubella• Meningococcal• Pneumococcal• Poliomyelitis

Infections: Sources and agents (2)

Zoonotic• Psittacosis• Q fever• Rabies• Hantavirus• West Nile

Fungal• Candidiasis• Coccidioidomycosis• Histoplasmosis

Prions• Kuru• vCJD

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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• 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 Animal

Human

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Vector

Animal

Vector

Human

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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 on-going 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)

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10 days

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Maximum incubation period

Average incubation period

Minimum incubation period

Distribution of cases by onset of symptoms:point source type

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Exposurebegins & continues

Distribution of cases by onset of symptomsPoint source, Continuous exposure type

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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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Develop disease

Immune

Herd Immunity

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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

– 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)• AIDS• food poisoning• encephalitis• STIs• influenza• Lassa fever• SARS• plus many more

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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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