Disease outbreak
Inepidemiology,anoutbreakis a sudden increase in occurrences of adiseasewhen cases are in excess of normal expectancy for the location or season. It may affect a small and localized group or impact upon thousands of people across an entire continent. The number of cases varies according to the disease-causing agent, and the size and type of previous and existing exposure to the agent. Outbreaks include manyepidemics,which term is normally only forinfectious diseases,as well as diseases with an environmental origin, such as a water orfoodborne disease.They may affect a region in a country or a group of countries.Pandemicsare near-global disease outbreaks when multiple and various countries around theEarthare soon infected.
Definition[edit]
The terms "outbreak" and "epidemic" have often been used interchangeably. Researchers Manfred S. Green and colleagues propose that the latter term be restricted to larger events, pointing out thatChambers Concise DictionaryandStedman's Medical Dictionaryacknowledge this distinction.[1]
Outbreak investigation[edit]
When investigating disease outbreaks, the epidemiology profession has developed a number of widely accepted steps. As described by the United StatesCenters for Disease Control and Prevention,these include the following:[2]
- Identify the existence of the outbreak (Is the group of ill persons normal for the time of year, geographic area, etc.?)
- Verify the diagnosis related to the outbreak
- Create acase definitionto define who/what is included as a case
- Map the spread of the outbreak usingInformation technologyas diagnosis is reported to insurance
- Develop a hypothesis (What appears to be causing the outbreak?)
- Study hypotheses (collect data and perform analysis)
- Refine hypothesis and carry out further study
- Develop and implement control and prevention systems
- Release findings to greater communities
The order of the above steps and relative amount of effort and resources used in each varies from outbreak to outbreak.[3]For example, prevention and control measures are usually implemented very early in the investigation, often before the causative agent is known. In many situations, promoting good hygiene and hand-washing is one of the first things recommended. Other interventions may be added as the investigation moves forward and more information is obtained. Waiting until the end of an investigation to implement prevention and control measures is a sure way to lose ones job. In outbreaks identified through notifiable disease surveillance, reports are often linked to laboratory results and verifying the diagnosis is straight forward. In outbreaks of unknown etiology, determining and verifying the diagnosis can be a significant part of the investigation with respect to time and resources. Several steps are usually going on at any point in time during the investigation. Steps may be repeated. For example, initial case definitions are often established to be intentionally broad but later refined as more is learned about the outbreak. The above list has 9 steps, others have more. Implementing active surveillance to identify additional cases is often added.[4]
Outbreak debriefing and review has also been recognized as an additional final step and iterative process by the Public Health Agency of Canada.[5]
Types[edit]
There are several outbreak patterns, which can be useful in identifying the transmission method or source, and predicting the future rate of infection. Each has a distinctiveepidemic curve,orhistogramof case infections and deaths.[6]
- Common source – All victims acquire the infection from the same source (e.g. a contaminated water supply).[7]
- Continuous source – Common source outbreak where the exposure occurs over multiple incubation periods
- Point source – Common source outbreak where the exposure occurs in less than one incubation period[8]
- Propagated – Transmission occurs from person to person.[9]
Outbreaks can also be:
- Behavioral risk related (e.g.,sexually transmitted diseases,increased risk due tomalnutrition)[10]
- Zoonotic– The infectious agent is endemic to an animal population, infection is transferred to humans.
Patterns of occurrence are:
- Endemic– a communicable disease, such as influenza, measles, mumps, pneumonia, colds, viruses, and smallpox, which is characteristic of a particular place, or among a particular group, or area of interest or activity.
- Epidemic– when this disease is found to infect a significantly larger number of people at the same time than is common at that time, and among that population, and may spread through one or several communities.
- Pandemic– occurs when an epidemic spreads worldwide.
Condition for Declaring an Outbreak Over[edit]
By convention, a communicable disease outbreak is declared over when a period of twice theincubation periodof the infectious disease has elapsed without identification of any new case, however, for organisms with a short incubation period (e.g. fewer than ten days), a period of three times the incubation period is preferred.[11]
Outbreak legislation[edit]
Outbreak legislation is still in its infancy and not many countries have had a direct and complete set of the provisions.[12][13] However, some countries do manage the outbreaks using relevant acts, such aspublic health law.[14] World Health Organizationmember states are obligated byInternational Health Regulationstoreport outbreaks.WHO member states are holding a special session in November 2021 to consider theInternational Treaty for Pandemic Preparedness and Responseto establish further legal obligations in managing disease outbreaks.[15]
See also[edit]
- 1947 New York City smallpox outbreak
- 1993 Four Corners hantavirus outbreak
- 2003 Midwest monkeypox outbreak
- 2007 Yap Islands Zika virus outbreak
- 2014 Democratic Republic of the Congo Ebola virus outbreak
- 2019–present coronavirus pandemic by country and territory
- Superspreading event
References[edit]
- ^Green MS, Swartz T, Mayshar E, Lev B, Leventhal A, Slater PE, Shemer J (2002)."When is an epidemic an epidemic?"(PDF).Israel Medical Association Journal.4(1): 3–6.PMID11802306.
- ^Steps of an Outbreak Investigation,EXCITE | Epidemiology in the Classroom | Outbreak Steps
- ^Perrocheau A, Jephcott F, Asgari-Jirhanden N, Greig J, Peyraud N, Tempowski J (2023)."Investigating outbreaks of initially unknown aetiology in complex settings: findings and recommendations from 10 case studies".International Health.5(15): 537–546.doi:10.1093/inthealth/ihac088.PMC10472873.PMID36630891.
- ^"Principles of Epidemiology in Public Health Practice"(PDF).Centers for Disease Control and Prevention.CDC.Retrieved6 August2016.
- ^Public Health Agency of Canada."Canada's Food-borne Illness Outbreak Response Protocol (FIORP) 2010: To guide a multi-jurisdictional response".Retrieved22 March2013.
- ^"SARS Outbreak Study 2".epiville.ccnmtl.columbia.edu.Center for New Media Teaching and Learning at Columbia University. Archived fromthe originalon March 19, 2009.
- ^Glossary of Epidemiology Terms,Cdc.gov (2007-04-25). Retrieved on 2010-11-25.
- ^Glossary of Epidemiology Terms.Cdc.gov (2007-04-25). Retrieved on 2010-11-25.
- ^Glossary of Epidemiology Terms.Cdc.gov (2007-04-25). Retrieved on 2010-11-25.
- ^"Health Topic: Behavioral Risk Factors".Center for Disease Control.Archived fromthe originalon September 28, 2008.Retrieved30 March2020.
- ^Ghebrehewet S, Stewart AG, Baxter D, Shears P, Conrad D, Kliner M, eds. (October 2016).Health Protection.Vol. 1. Oxford University Press. p. 210.doi:10.1093/med/9780198745471.001.0001.ISBN978-0-19-874547-1.
- ^"Bioterrorism Training and Curriculum Development Program".Archived fromthe originalon 3 March 2016.Retrieved2 August2008.
- ^Star Publications."Outbreak actions protected by law".Retrieved2 August2008.
- ^The State of Queensland Government."Legislation and Powers of Entry".Retrieved2 August2008.
- ^"WHA to hold pandemic treaty talks in November".25 May 2021.
External links[edit]
- Plague of Suspicion,audio hour on media coverage of outbreaks and epidemics