April 7, Back to Basics, 2009 POPULATION HEALTH (1): Infectious Diseases and Outbreak Investigation N Birkett, MD Epidemiology & Community Medicine Other resources available on Individual & Population Health web siteIndividual & Population Health web site

April 7, Infectious Disease Summary N. Birkett, Back-to-Basics, 2009 Material relates to MCC objective 78.5 Terminology Nature of diseases Outbreaks/epidemics –Identification –Methods of control

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4 Foodborne  Botulism  Clostridium Perfringens  Salmonellosis  Shigellosis  Staphylococcal disease  Traveler’s disease  Trichinosis Water & Foodborne  Amebiasis  Cholera  Giardiasis  Legionellosis  E Coli Person-to-person spread Aseptic Meningitis Viral hepatitis Respiratory Infections (influenza) Herpes Simplex Streptococcal disease (rheumatic fever) Tuberculosis Leprosy Infections: Sources and agents (1)

April 7, 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 Measles Mumps Poliomyelitis Tetanus Infections: Sources and agents (2) Zoonotic Psittacosis Q fever Rabies Hantavirus Opportunistic fungal/fungal Coccidioidomycosis Candidiasis Prions Kuru vCJD

April 7, 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.

April 7, 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 a host Measles vs. gonorrhea

April 7, 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.

April 7, 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 person (case) who brings the infection to the attention of the medical community or the public agency. Sometimes used to refer to the person who brings the infection into a community. This will often (but not always) be the same person.

April 7, 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 7, Terminology (6) Case Fatality Rate (CFR) –The probability of death in people with an infection.

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April 7, Pathogenic Mechanisms (1) Direct Tissue Invasion Production of Toxins Allergic Host Reaction Resistant/latent infection (carriers) Enhancement of host susceptibility to drugs (e.g. Reye’s syndrome and ASA). Immune Suppression

April 7, Reservoirs (examples of transmission patterns) HumanHumanHuman AnimalAnimalAnimal Human Vector Animal Vector Human

April 7, Mechanisms of Spread (1) kissing sexual intercourse hand shaking droplets spores in soil Vehicle borne fomites (e.g. toys) food IV fluid Vector borne mechanical (e.g. soiled feet of insect) biological (e.g. malaria) Airborne dust droplet nuclei Direct transmission Indirect transmission

April 7, Epidemics (1) Epidemic (now often called ‘outbreak’) –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 Pandemic –an epidemic covering a very wide area and affecting a large proportion of the population Pathogen –Infectious and non-infectious substance capable of producing tissue damage or initiating a process which can lead to a disease.

April 7, 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 7, Epidemics (3) Incubation period and causal agent Time frameExamples HoursFood toxins Heavy metals DaysBacterial infections Salmonella / cholera WeeksMeasles / mumps / Hep A MonthsHep B / Rabies YearsKuru / cancer

April 7, 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 7, Epidemic Curves: point source (1)

April 7, Epidemic Curves: propagated (2) 10 days

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April 7, 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 –Person to person –Common vehicle –Vector-borne –Zoonoses Transmission mechanics –Consider sexual vs. droplet spread

April 7, Develop disease Immune

April 7, Epidemic Control (1) Twin goals: Understand the cause, etc. 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 7, Actions for ‘acute’ outbreak control Isolation separation of infected 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 at least two incubation periods. –More controversial than isolation since it affects people who are not currently ill (and may never get ill). Immunization passive or active. Passive (IGG) is more useful for acute outbreaks. Chemoprophylaxis

April 7, General approaches to outbreak control (1) Reduce host susceptibility Immunization (active and passive) nutrition improved income, etc. 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 7, General approaches to outbreak control (2) Inactivate agent water purification; chlorination Personal hygiene measures hand washing (#1 strategy) protective clothing (masks, gowns) avoid at risk situations Family/community measures preventing sexual abuse of children leads to reduction in STDs Needle exchange and related programmes.

April 7, 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.