* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Infectious Disease
Rocky Mountain spotted fever wikipedia , lookup
Foodborne illness wikipedia , lookup
Neglected tropical diseases wikipedia , lookup
Onchocerciasis wikipedia , lookup
Brucellosis wikipedia , lookup
Sarcocystis wikipedia , lookup
Bovine spongiform encephalopathy wikipedia , lookup
Meningococcal disease wikipedia , lookup
Trichinosis wikipedia , lookup
Bioterrorism wikipedia , lookup
Hepatitis C wikipedia , lookup
Chagas disease wikipedia , lookup
West Nile fever wikipedia , lookup
Hospital-acquired infection wikipedia , lookup
Hepatitis B wikipedia , lookup
Sexually transmitted infection wikipedia , lookup
Ebola virus disease wikipedia , lookup
Schistosomiasis wikipedia , lookup
Oesophagostomum wikipedia , lookup
Coccidioidomycosis wikipedia , lookup
Henipavirus wikipedia , lookup
African trypanosomiasis wikipedia , lookup
Middle East respiratory syndrome wikipedia , lookup
Leptospirosis wikipedia , lookup
Marburg virus disease wikipedia , lookup
Back to Basics, 2011 POPULATION HEALTH: Infectious Diseases and Outbreak Investigation E. Ellis, MD Epidemiology & Community Medicine April, 2011 1 78-5 Outbreak Management 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 diarrhea. 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. 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. April, 2011 2 Infectious Disease Summary • Terminology • Nature of diseases • Outbreaks/epidemics – Identification – Methods of control April, 2011 3 April, 2011 4 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 April, 2011 Person-to-person spread • Aseptic meningitis • Hepatitis B and C • Respiratory Infections (e.g., influenza) • Herpes simplex • Streptococcal disease • Tuberculosis • Leprosy 5 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 April, 2011 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 6 Terminology (1) • Infectivity – The ability of an agent to invade and multiply in a host (an infection). – (# infected / # susceptible) X 100 – Dose of organism required to establish infection in 50% of animals. • Pathogenicity – The ability of an agent to produce clinically apparent illness. – (# with clinical disease / # of infected) X 100 April, 2011 7 Terminology (2) • Virulence – The proportion of clinical cases which produce severe disease and/or permanent sequelae. – (e.g., # hospitalized or in ICU ‘ $ with disease) X 100 • 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 April, 2011 8 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 such as rodents. April, 2011 9 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 • Source Case – Source of infection for the index case • Contacts – Possibly infected due to relevant contact with an infectious case April, 2011 10 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, 2011 11 Terminology (6) • Case Fatality Rate (CFR) – The probability of death in people with an infection. April, 2011 12 April, 2011 13 April, 2011 14 April, 2011 15 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 April, 2011 16 Reservoirs (examples of transmission patterns) • Human Human Human • Animal Animal Human Animal Animal Vector Vector Human April, 2011 17 Mechanisms of Spread (1) Direct transmission • • • • Touch (scabies) Bite (rabies) Kiss (mononucleosis) Sexual contact (Chlamydia) • Droplet, over 5 u, spread 1-2 metres (resp. virus) • Soil (tetanus) • Transplacental (hepatitis B) April, 2011 Indirect transmission • Vehicle-borne (inanimate): organism may or may not multiply or develop (E. coli in hamburger) • Vector-borne (animate): Mechanical: organism does not multiply or develop (house flies) Biological: organism multiplies or develops (malaria, West Nile) 18 Mechanisms of Spread (2) Airborne transmission • Droplet nuclei (tuberculosis, measles, varicella, smallpox, ? Influenza) • Dust (anthrax) April, 2011 19 Epidemics (1) • Epidemic (called ‘outbreak’ 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 substance capable of producing tissue damage or initiating a process which can lead to a disease. April, 2011 20 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, 2011 21 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 April, 2011 22 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, 2011 23 Epidemic Curves: point source (1) April, 2011 24 Epidemic Curves: propagated (2) 10 days April, 2011 25 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 April, 2011 Exposure Units of Time 26 Distribution of cases by onset of symptoms Continuous Source type Number of cases 20 15 10 5 0 Exposure begins & continues April, 2011 Units of Time 27 Distribution of cases by onset of symptoms. Intermittent outbreak Number of cases 20 15 10 5 0 Time April, 2011 28 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 April, 2011 Index case Units of Time 29 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 April, 2011 5 10 15 20 25 30 35 Days 30 April, 2011 31 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 April, 2011 32 Develop disease Immune April, 2011 33 Epidemic Control (1) Twin goals: • Understand the cause and mode of transmission • 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, 2011 34 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 – we expect some who are quarantined to get sick; but if none of their contacts get sick, then quarantine was useful Immunization • passive or active Chemoprophylaxis April, 2011 35 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 April, 2011 36 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. April, 2011 37 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. April, 2011 38 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 April, 2011 39 Infectious Disease Control Multiple Choice Questions for discussion April, 2011 40 11) A group of 50 people are exposed to virus “A”. Of those 50 people, 9 develop a mild infection, 10 become seriously ill, and 3 die. The attack rate of virus “A” in the population would be: a) 22/50 b) 9/50 c) 10/50 d) 19/50 e) 13/50 April, 2011 41 15) Examples of secondary prevention would include all of the following EXCEPT: a) Pap smear for cervical cancer b) chemoprophylaxis in a recent TB converter c) proctoscopy for rectal cancer d) immunization for Haemophilus influenzae B e) mammography for breast cancer April, 2011 42 23) Which of the following is the most important justification for mounting a population screening program for a specific disease? a) early detection of the disease of interest is achieved b) the specificity of the screening test is high c) the natural history of the disease is favorably altered by early detection d) effective treatment is available e) the screening technology is available April, 2011 43 25) Active immunization was important in control of each of the following childhood communicable diseases EXCEPT: a) diphtheria b) polio c) measles d) scarlet fever e) pertussis April, 2011 44 29) Differentiation between a point-source epidemic and a progressive (propagated) epidemic is made by: a) considering the characteristics of the infectious agent b) determining the level of immunity in the community c) determining the number of persons infected and calculating the attack rate d) plotting the distribution of cases by time onset e) none of the above April, 2011 45 30) The occurrence of an illness at a rate of above that expected is called: a) hyperendemic b) epidemic c) endemic d) enzootic e) pandemic April, 2011 46 42) Each of the following is an example of primary prevention EXCEPT: a) genetic counselling of parents with one retarded child b) nutritional supplements in pregnancy c) immunization against tetanus d) chemoprophylaxis in a recent tuberculin converter e) speed limits on highways April, 2011 47 43) The classical “epidemiological triad” of disease causation consists of factors which fall into which of the following categories: a) host, reservoir, environment b) host, vector, environment c) reservoir, agent, vector d) host, agent, environment e) host, age, environment April, 2011 48 45) The difference between a common point source outbreak and a propagated outbreak of illness is that: a) all cases in a common point source outbreak occur within one incubation period of the exposure b) the attack rates in propagated outbreaks are higher c) person-to-person transmission is a feature of common source outbreaks d) case fatality rates in common source outbreaks are generally higher e) the source of infection in propagated outbreaks is more easily contained than in common source outbreaks April, 2011 49 Differentiation between a point-source epidemic and a progressive (propagated) epidemic is made by: a) considering the characteristics of the infectious agent b) determining the level of immunity in the community c) determining the number of persons infected and calculating the attack rate d) plotting the distribution of cases by time onset e) none of the above April, 2011 50 April, 2011 51 More MCQs • Here are some more questions that students can use to test their own knowledge: http://www.medicine.uottawa.ca/sim/data/Sel f-test_Qs_Outbreaks_e.htm • (The questions contain comments on the answers, to illustrate why a given response is not correct) April, 2011 52