Back to Basics, 2013 POPULATION HEALTH: Infectious Diseases and Outbreak Investigation N. Birkett, MD Epidemiology & Community Medicine Other resources available on Individual & Population Health web siteIndividual & Population Health web site 03/20131

78-5 Outbreak Management (1) 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 diarrhoea. 03/20132

78-5 Outbreak Management (2) 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. 03/20133

78-5 Outbreak Management (3) 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. 03/20134

Infectious Disease Summary Terminology Nature of diseases Outbreaks/epidemics –Identification –Methods of control 03/20135

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7 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)

03/20138 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

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. 03/20139

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 03/201310

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 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). Usually insects or small mammals such as rodents. 03/201311

Terminology (4) Zoonoses –Diseases transmitted to humans from animals (e.g. anthrax) 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 03/201312

Terminology (5) Attack Rate –The probability that people will get ill from the disease. Usually applied in an outbreak situation. 03/201313

Terminology (6) Secondary Attack Rate –Probability of infection in a closed group who are at risk but excluding the index case(s). Formula is: 03/201314

Terminology (7) Case Fatality Rate (CFR) –The probability of death in people with an infection. 03/201315

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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 03/201319

Reservoirs (examples of transmission patterns) HumanHumanHuman AnimalAnimalAnimal Human 03/ Vector Animal Vector Human

Mechanisms of Spread (1)Spread Touch (many URI’s, scabies) Bite (rabies) Kiss (mononucleosis) Sexual contact (Chlamydia) Droplet, over 5μ, spread 1-2 meters (resp. virus) Soil (tetanus) Transplacental (hepatitis B) 03/ Vehicle borne (inanimate) fomites (e.g. toys) Food IV fluid organism may or may not multiply E. coli in hamburger Vector borne (animate) mechanical (e.g. soiled feet of insect) biological (e.g. malaria) Direct transmission Indirect transmission

Mechanisms of Spread (2)Spread Airborne transmission Droplet nuclei –tuberculosis –measles –varicella –smallpox –? Influenza Dust –anthrax 03/201322

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 Pandemic –an epidemic covering a very wide area and affecting a large proportion of the population (SIM web link)SIM web link –Controversial definition Consider H1N1 outbreak Endemic –the occurrence of a disease/condition at a relatively constant level in a given setting, usually with on-going transmission 03/201323

Epidemics (2) 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. 03/201324

Epidemics (3) Incubation period and possible causal agents Time frameExamples HoursFood toxins Heavy metals DaysBacterial infections Salmonella / cholera WeeksMeasles / mumps / Hep A MonthsHep B / Rabies YearsKuru / cancer 03/201325

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. 03/201326

Epidemic Curves: point source (1) 03/201327

Epidemic Curves: propagated (2) 03/ days

03/ Exposure Maximum incubation period Average incubation period Minimum incubation period Distribution of cases by onset of symptoms: point source 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 03/201332

03/ Develop disease Immune Herd Immunity

Epidemic 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 Effective and clear communication with general public is essential –Designate one spokesperson –Regular press briefings –Lessons from the SARS outbreak 03/201334

Outbreak control measures (1) 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 –Quarantine for the longest usual incubation period Often at least two incubation periods. –More controversial than isolation since it affects people who are not currently ill (and may never get ill). –we expect some who are quarantined to get sick 03/201335

Outbreak control measures (2) 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 Harm Reduction (for long term outbreaks) Focus on prevent adverse effects from harmful exposures –Needle exchange –Safe Injection sites 03/201336

Outbreak control measures (3) Reduce host susceptibility Immunization (active and passive) nutrition improve 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 03/201337

Outbreak control measures (4) 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. 03/201338

SurveillanceSurveillance (1) The continuing scrutiny of all aspects of occurrence and spread of disease that are pertinent to effective control Reportable diseases.Reportable –legal obligation to report designated diseases to local public health department –list includes AIDS food poisoning encephalitis STIs influenza Lassa fever SARS plus many more 03/201339

SurveillanceSurveillance (2) The continuing scrutiny of all aspects of occurrence and spread of disease that are pertinent to effective control Reportable diseases.Reportable Sentinel practices Animal/water surveys Environmental monitoring Mortality (vital statistics) Provincial laboratory tests Epidemic investigations Disease registries CIHI and related data. 03/201340

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