* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Infectious Disease
Creutzfeldt–Jakob disease wikipedia , lookup
Sarcocystis wikipedia , lookup
Onchocerciasis wikipedia , lookup
Brucellosis wikipedia , lookup
Neglected tropical diseases wikipedia , lookup
Trichinosis wikipedia , lookup
Meningococcal disease wikipedia , lookup
Foodborne illness wikipedia , lookup
Chagas disease wikipedia , lookup
West Nile fever wikipedia , lookup
Hepatitis C wikipedia , lookup
Bovine spongiform encephalopathy wikipedia , lookup
Bioterrorism wikipedia , lookup
Hepatitis B wikipedia , lookup
Schistosomiasis wikipedia , lookup
Hospital-acquired infection wikipedia , lookup
Coccidioidomycosis wikipedia , lookup
Ebola virus disease wikipedia , lookup
Oesophagostomum wikipedia , lookup
Sexually transmitted infection wikipedia , lookup
Henipavirus wikipedia , lookup
African trypanosomiasis wikipedia , lookup
Leptospirosis wikipedia , lookup
Marburg virus disease wikipedia , lookup
Middle East respiratory syndrome wikipedia , lookup
Back to Basics, 2012 POPULATION HEALTH: Infectious Diseases and Outbreak Investigation N. Birkett, MD Epidemiology & Community Medicine Other resources available on Individual & Population Health web site 03/2012 1 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. 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. 03/2012 2 78-5 Outbreak Management (2) 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. 03/2012 3 Infectious Disease Summary • Terminology • Nature of diseases • Outbreaks/epidemics – Identification – Methods of control 03/2012 4 03/2012 5 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 03/2012 Person-to-person spread • Aseptic meningitis • Hepatitis B and C • Respiratory Infections (e.g., influenza) • Herpes simplex • Streptococcal disease • Tuberculosis • Leprosy 6 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 03/2012 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 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. 03/2012 8 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 03/2012 9 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). • There is disagreement about whether vectors are restricted to insects or can also include small mammals such as rodents. 03/2012 10 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 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 03/2012 11 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: 03/2012 12 Terminology (6) • Case Fatality Rate (CFR) – The probability of death in people with an infection. 03/2012 13 03/2012 14 03/2012 15 03/2012 16 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 03/2012 17 Reservoirs (examples of transmission patterns) • Human Human Human • Animal Animal Human Animal Animal Vector Vector Human 03/2012 18 Mechanisms of Spread (1) Direct transmission • Touch (many URI’s, scabies) • Bite (rabies) • Kiss (mononucleosis) • Sexual contact (Chlamydia) • Droplet, over 5 u, spread 1-2 meters (resp. virus) • Soil (tetanus) • Transplacental (hepatitis B) 03/2012 Indirect transmission • 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) 19 Mechanisms of Spread (2) Airborne transmission • Droplet nuclei – – – – – tuberculosis, measles, varicella, smallpox, ? Influenza) • Dust – anthrax 03/2012 20 Epidemics (1) • Epidemic (now often called an ‘outbreak’, especially if localized) – 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, usually with on-going transmission • Pandemic – an epidemic covering a very wide area and affecting a large proportion of the population (SIM web link) • Pathogen – Infectious and non-infectious substances capable of producing tissue damage or initiating a process which can lead to a disease. 03/2012 21 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. 03/2012 22 Epidemics (3) • Incubation period and causal agent Time frame Examples Hours Food toxins Heavy metals Days Bacterial infections Salmonella / cholera Weeks Measles / mumps / Hep A Months Hep B / Rabies Years Kuru / cancer 03/2012 23 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. 03/2012 24 Epidemic Curves: point source (1) 03/2012 25 Epidemic Curves: propagated (2) 10 days 03/2012 26 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 03/2012 Exposure Units of Time 27 Distribution of cases by onset of symptoms Continuous Source type Number of cases 20 15 10 5 0 Exposure begins & continues 03/2012 Units of Time 28 03/2012 29 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 03/2012 30 WHO Stages of a Pandemic 1.No virus circulating in animals has caused human disease 2.Animal virus has caused disease in humans 3.Some human to human transmission but not enough to sustain community outbreak 4.Sustained human to human transmission leading to community level outbreaks 5.Human to human spread in at least two countries of one WHO region 6.Phase 5 + a community level outbreak in at least one other WHO region Post peak period Incidence is decreasing although waves of increased incidence may occur Post pandemic period Return to normal levels Time 03/2012 31 Herd Immunity Develop disease Immune 03/2012 32 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 • SARS outbreak • designate one spokesperson • regular press briefings 03/2012 33 Actions for ‘acute’ outbreak control 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 usually 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 Immunization • passive or active • Passive (IGG) can be more useful for acute outbreak control Chemoprophylaxis 03/2012 34 General approaches to outbreak control (1) Reduce host susceptibility • Immunization (active and passive) • nutrition • improved 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 03/2012 35 General approaches to outbreak control (2) 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. 03/2012 36 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. 03/2012 37 More MCQs • Here are some more questions that students can use to test their own knowledge: http://www.medicine.uottawa.ca/sim/data/Se http://www.medicine.uottawa.ca/sim/data/Sel lf-test_Qs_Outbreaks_e.htm f-test_Qs_Outbreaks_e.htm • (The questions contain comments on the answers, to illustrate why a given response is not correct) 03/2012 38 Distribution of cases by onset of symptoms. Intermittent outbreak Number of cases 20 15 10 5 0 Time 03/2012 39 Distribution of cases by onset date: Point source with index case and limited spread Number of cases 20 15 10 Maximum incubation period Average incubation period Minimum incubation period 5 0 03/2012 Index case Units of Time 40 Distribution of cases by onset of symptoms. Point source, index case with propagated spread Number of cases 20 15 10 Average incubation period 5 0 1 Index case 03/2012 5 10 15 20 25 30 35 Days 41