OUT BREAK INVESTIGATIONS BM Hamooya, PhD Students’ learning objectives ■ By the end of the lecture, the student will be able to: – Define the following terms; epidemic, case, and cluster as it relate to epidemiology – Identify and describe elements used to ascertain the existence of an outbreak – List ways used to detect an outbreak – Delineate the importance of investigating outbreaks – Itemize and describe the basic components of an outbreak investigation – Relate the outbreak investigation by following the example from John Snow’s groundbreaking study of London’s 1854 cholera outbreak Introduction ■ We often use the words “outbreak” and “epidemic” in our general vocabulary – For example: – “a flu epidemic”, – “outbreak of bloody diarrhea”, – “an epidemic of failed marriages”, – ”HIV epidemic” etc. ■ The moment we hear the word outbreak it indicates that something is amiss ■ However, the question is “what is an outbreak from the epidemiological point of view?” ■ An outbreak is an increase often sudden in the observed number of cases of a disease or health problem compared with the expected number for a given place or among a specific group of people over a particular period of time. ■ Essentially the definition of epidemic is identical to that of outbreak ■ Epidemic is the occurrence in a community or region of cases of an illness, specific health-related behavior, or other health related events clearly in excess of normal expectancy ■ In real sense, Outbreak and Epidemic can be used interchangeably ■ But public health specialists prefer to use Outbreak for localized epidemics “the one limited to a village, town, or specific institution. ■ Investigators determine the occurrence of an epidemic (or outbreak) by looking at the numbers whether they have increased for a given place or season or geographic area. ■ If an outbreak or epidemic occurs over a very wide area thereby affecting a large proportion of the population in several countries or continents the it is known as a pandemic (pan=all and demos=people) – Example: influenza pandemic of 1918 which killed an estimated 50 million people in North America, Europe, Asia, Africa, Brazil and south pacific – Asian flu pandemic of 1957-1958 – Hong Kong flu pandemic of 1968 – Influenza A (H1N1) pandemic of 2009 ■ Question: Is HIV an epidemic or pandemic? ■ In epidemiology, the term “case” describes a particular disease, health disorder, or condition under investigation – It is also used to describe a person in a population/study group who has the disease, disorder, or certain condition – Cases may also be referred as patients in the case group or case patients ■ Investigators classify cases or case patients based on the case definition they develop as they explore a potential outbreak. – For instance, in case of cholera outbreak; how will cholera be defined? Combine clinical and laboratory diagnosis or just one of them? ■ A case takes into account; – Signs and symptoms of the disease or condition – Important epidemiologic characteristics of the patient “such as the what, who, where, and when” of a disease outbreak ■ Epidemiological definition of a case is not the same as the normal clinical definition that physicians or other healthcare providers might use, although it may be similar. ■ Outbreak investigation usually begins when investigators observes a suspected cluster of cases of a disease. ■ A cluster is a geographical or temporal collection of cases that seem to be greater than the expected number for a particular place or time. When does a number of cases become an outbreak? To understand whether an outbreak underway is more than just counting cases ~quite complicated. Potential outbreaks may arise from the same cause or unrelated cases of the same disease. ■ In general, the key determinant that an outbreak is underway is whether the number if cases is “unusually high” or falls within the expected range of cases for that population at that time of the year ■ Before declaring an outbreak, investigators must take many factors into account: – The etiologic agent – The size and composition of the population – The previous occurrence of the disease in the community – The season ■ Etiologic agent : is the pathogen that is causing the disease. – Investigators need to know the agent’s identity, and further determine whether it is rare or common – If the disease is relatively common such bloody diarrhea or seasonal influenza, then you may need to have a large number of cases or the cases may need to be uniquely related before public health officials considers it an outbreak. – In case of rare diseases such as polio or Ebola health officials may treat even a single case as an outbreak and institute immediate health action. ■ Size and composition of the population: investigators need to know how many and which groups of people are becoming ill. – For example 1,000 of bloody diarrhea in a population of 4000 is of public health concern than in a population of 1, 000,000 – In looking at size, changes in the population should be taken into account. – Population characteristics such as age distribution and socioeconomic status can influence disease rates ■ Previous occurrence of a disease in the community: before ascertaining that a certain number of cases constitute an outbreak, investigators must know whether and how often the disease has been diagnosed in the community in the past. – For example in a certain community with a past history of an average 12 cases of disease per month and 50 or 100 cases have been recorded, this can be called an outbreak if all the laboratory tests have done correctly. ■ The season: incidence of many infectious diseases rises and falls seasonally, hence investigators must take the time of the year into consideration when exploring a potential outbreak. ■ Note: Determining an outbreak requires a well-thought process. – What might look like an outbreak sometimes it might not be the case – Sometimes public health officials might think that a number of cases of severe respiratory illness signals influenza outbreak meanwhile these cases might be arising from different causes e.g severe cold, bronchitis or pneumonia. How are potential outbreaks detected? There are various ways to identify an outbreak and these include: Surveillance or health information system Clinical laboratories Affected citizens Health care providers Outbreaks are detected through the routine and timely analysis of health information systems. ■ Health department staff may detect increase or unusual patterns of disease from weekly tabulations of case reports by time and place ■ Hospital administrators may detect unusual increase in the number of possible hospital-acquired infections through weekly analysis of microbiologic isolates from patients by organism and ward or unit ■ Affected group is another source of information for apparent clusters of both infectious and non-infectious disease ■ Many outbreaks come to the attention of public health officials because of alert clinicians, infection control nurse, or laboratory workers ■ There is need for proper routine health systems in order to detect an outbreak ■ The procedures should be able to determine the “what”, “who”, “when”, “where”, and “why” (or “how”) – What is the problem? Does the clinical description of the illness exist including signs and symptoms, diagnosis, and duration? Was a physician consulted? Were any tests performed or any treatment given? – Who is sick and what those individual characteristics (e.g name, age, occupation) – When did the affected person get sick? – Where are the affected person located, including residential area or work locations? – Why (or how) do patients think they get ill? ■ What are the relevant risk factors, suspected exposures, and suspected mode of transmission? ■ Are there clues on who did and did not become ill? Why investigate outbreak? ■ There are many reason as to why outbreaks should be investigated: – To prevent others from getting infected – To prevent future occurrence – Identification of risk factors – Identification of new pathogens that infect people – To give appropriate treatment to those who are infected – Provides a new research insight into a disease – Provides opportunities for public health practitioners to practice the process and methods of epidemiologic investigation that are essential to protect the public health Applicability of “what”, “who”, “when”, “where”, and “why” ■ On 6 October 2017, the Minister of Health declared an outbreak of cholera in the Zambian capital, Lusaka. From 28 September through 7 December 2017, 547 cases including 15 deaths (case fatality rate = 1.8%), have been reported since the beginning of the outbreak. The initial outbreak period was from 28 September through 20 October. From 21 October through 4 November 2017 there were less than five cases reported each week. However, from 5 November 2017 an increase in the number of cases was observed with a total of 136 cases reported in the week beginning 26 November (sourcehttps://www.who.int/csr/don/11-december-2017-cholerazambia/en/) ■ What: infection with Vibrio cholerae ■ Who: 547 people and 15 of them died ■ When: September and December 2017, after drinking and eating contaminated water and food ■ Where: Lusaka (Chipata, Kanyama, Chawama, Matero, Chilenje and Chelsto) ■ Why: contaminated water supplies, contaminated food, inadequate sanitation and poor hygiene practices The components of an Outbreak investigation ■ When an outbreak is discovered, investigators should take a systematic approach ■ Although the components are listed sequentially, they may occur simultaneously or get repeated as new information is received or uncovered. ■ Some outbreak investigations may just require a phone and others may require assembling a multidisciplinary team Basic components of an outbreak investigation 1. Verify the disease and confirm the outbreak 2. Define a case and conduct case finding 3. Tabulate and orient data: time, place and person 4. Take immediate control measures 5. Formulate and test hypothesis 6. Plan and execute additional studies 7. Implement and evaluate control measures 8. Communicate findings 1. Verify the disease and confirm the outbreak ■ This is the first essential step in confirming an outbreak ■ Investigators need to learn more about the disease and review the existing baseline surveillance data to determine whether the cluster of cases are unusually high ■ Confirm the disease using laboratory testing ■ Reviewing Medical records, talking to health providers and patients themselves can help confirm an outbreak 2. Define a case and conduct case finding ■ Investigators create an operation definition of the case and begin identifying cases associated with the outcome ■ The definition may evolve as the investigation continues ■ Initially it might be broad to include many cases as possible and late on narrowed to exclude false positives 3. Tabulate and orient data: time, place and person ■ Investigators should organize information obtained for medical records or patient interviews – and sort it by person, place and time ■ That is who is getting sick, where and when. ■ “who, where and when“ are essential questions investigators should first answer before generating a hypothesis about the cause of the outbreak 4. Take immediate control measures ■ If the source of contamination has been identified , the health department should take immediate control measures ■ Make public announcement about preventive and control measures (steps) 5. Formulate and test hypothesis ■ As the information gathered and organized, investigators should develop hypotheses ■ It can be essential to review previous outbreaks and studying the epidemiology and microbiology of the pathogen ■ Additional insight can be obtained by interviewing case patients ■ Hypotheses can be tested by analytic studies (e.g retrospective cohort studies and case-control studies) 6. Plan and execute additional studies ■ In addition to epidemiologic investigation, environmental investigation maybe undertaken that includes environmental sampling ■ In case of foodborne outbreak, investigators should collect and test food and beverage samples as soon as possible 7. Implement and evaluate control measures ■ Investigators later on need to work with government regulators, industry, and health educators to undertake control measures to prevent further illness and future outbreaks ■ The team should design mechanisms to evaluate the short- and long term success of the investigation, summarize the investigation and prepare and disseminate specific recommendations. 8. Communicate findings ■ Investigators should prepare health promotion messages for the general public ■ New media can be play a major role in disseminating the information to the public ■ The team should agree on the information to be released and should choose one member who should talk to the media Snow on cholera ■ John Snow identified mode of transmission of Cholera (London 1854) ■ Mostly referred as first modern infectious disease epidemiology ■ Using the 8 steps of outbreak investigation, Snow determined the outbreak of deadly disease caused by contamination of water ■ He used analytic studies to determine the source of infection and convinced local authority to take appropriate action Assignment 2 – Describe how John Snow applied the 8 basic components of an outbreak investigation to determine the outbreak of cholera in London – Due date: 29/03/2021 12pm Conclusion ■ The terms “epidemic” and “outbreak” describe an increase in the observed number of cases of a disease or health problem compared with the expected number for given a place or time in a specific group of people. ■ ”Outbreak” is usually used to describe localized epidemic ■ Outbreak investigation usually begins with information from surveillance or health information systems, clinical laboratories, affected citizens, or astute health care practitioners ■ To determine a potential outbreak, investigators gather such information as what pathogen is causing the infection, who is becoming ill, and where and when the cases are occurring. ■ Investigators take 8 steps to investigate an outbreak Reference ■ https://www.who.int/csr/don/11-december-2017-cholerazambia/en/ ■ Pia D.M.M, Methods in Field Epidemiology: copyright @ 2012 by Jones & Bartlett Learning, an Ascend Learning Company
