This presentation has been prepared by the Harvard School of Public Health Center for Public Health Preparedness to provide an overview of epidemiology and surveillance. This presentation is intended for use by individuals for personal education, or by educators and trainers to present to a class of students. The content has been developed for public health professionals, but should prove beneficial to hospital personnel, first line-responders, and the general public interested in learning more about epidemiology and surveillance.

•Upon completion of this presentation, we hope to accompany the following seven learning objectives

Epidemiology & Surveillance can be broken down into 5 fundamental components, the 5 progressive steps you must take in order to detect and respond to an outbreak. These 5 steps are the framework for this presentation:

•It is defined as “the study of the distribution and determinants of disease in populations”.  Note that this is not just applicable to infectious diseases, but any conditions or attributes of a population •Distribution refers to the frequency and pattern of health-related characteristics and events in a population: Who gets the disease? How old are they? Where do they live? Where do they work? What are their race and gender? •Determinants are any factors that bring about a change in health condition: a particular exposure, characteristic, behavior, or event •Rothman KJ & Greenland S. Modern Epidemiology, 2nd edition. Philadelphia: Lippincott – Raven; 1998.

•Descriptive epidemiology summarizes health-related characteristics according to person, place, and time •It provides the important information regarding who has disease, the geographic distribution of those affected, and when they were affected •Performing descriptive epidemiology is important to describe the clinical characteristics of illness and the demographic characteristics of those affected •Descriptive epidemiology also allows one to identify particular populations at risk for illness •Finally, it can provide clues about the cause of the disease and the mode of transmission

•The first component of epidemiology and surveillance is to practice routine public health surveillance •We will begin by discussing the importance of surveillance and the types of surveillance used in public health

•In order to practice routine surveillance, we must understand what surveillance is and why it is important. Furthermore, we must be able to identify types of surveillance

•Public health surveillance is defined as the systematic collection, analysis, interpretation, and dissemination of health data on an ongoing basis, to gain knowledge of the pattern of disease occurrence and potential in a community, in order to control and prevent disease in the community •Teutsch SM & Churchill RE. Principles and Practice of Public Health Surveillance, 2nd edition. New York: Oxford University Press; 2000.

•Surveillance is important because it provides an accurate baseline assessment of the status of health in a given population •The primary purpose of surveillance is to collect, analyze and disseminate data for use in public health action to reduce morbidity and mortality and to improve health •Surveillance can be used to measure trends in the burden of disease - it allows for the detection of an outbreak – the occurrence of more cases of disease than expected in a given area or among a specific group of people or over a particular period of time •For practical purposes, the term “outbreak” is often used synonymously with “epidemic” or “cluster”. However, some epidemiologists consider the term “outbreak” to refer to a more localized situation, and “epidemic” to refer to a more widespread and perhaps prolonged situation. The term “cluster” may be defined as the occurrence of a group of cases in a circumscribed place and time, in amounts that are suspected to be greater than expected. The cluster is usually based on anecdotal evidence, and often the first task of epidemiologists is to determine whether a cluster is indeed an outbreak.

The following are types of public health surveillance, and will be described on the following slides

•This slide shows the Notifable Conditions List from Maine Department of Human Services, Bureau of Health, Division of Disease Control •Category 1 conditions include Tuberculosis, acute Hepatitis A, B, and C, foodborne outbreaks, and diseases that are potential indicators of bioterrorism. All cases and suspected cases must be reported immediately by telephone on the day of recognition or strong suspicion of disease. •Category 2 conditions include HIV, AIDS, bacterial meningitis, and Lyme Disease. All cases and suspected cases must be reported within 48 hours or recognition or strong suspicion. •Maine law states that “any person who knowingly and willfully fails to comply with reporting requirements for notifiable diseases commits a civil violation for which forfeiture of not more than $250 may be adjudged. A person who knowingly or recklessly makes a false report…is civilly liable for actual damages suffered by a person reported upon and for punitive damages and commits a civil violoation for which a forfeiture of not more than $500 may be adjudged.” [22 M.R.S. § 825 (2003)]

•Active surveillance is the directed identification of cases of a particular disease •It is typically initiated by a public health department during an epidemic, when public health officials are concerned with identifying as many cases as possible so as to obtain an accurate picture of the magnitude of the epidemic, and to best guide control and prevention measures •Active surveillance may also be event-based. For example, during important events such as the Olympics where security is elevated, epidemiologists will conduct active surveillance of anything out of the ordinary in order to detect a possible bioterrorist event •Unlike routine surveillance, active surveillance is typically finite, not ongoing beyond resolution of the epidemic or completion of the event

•Syndromic surveillance is a form of public health surveillance that uses data on symptoms that precede diagnosis and signal a sufficient probability of a case or an outbreak to warrant further public health response •Syndromic surveillance is typically automated by computer, and often uses hospital medical records or health insurance data •In theory, syndromic surveillance is beneficial because it allows for surveillance of symptoms instead of diagnoses, thus resulting in earlier detection

•The second component of epidemiology and surveillance is to identify potential outbreaks

An outbreak, or the occurrence of more cases of disease than expected, can be detected in a number of ways: •By review of routinely collected surveillance data – as we discussed previously, this in one of the main reasons we conduct surveillance •Astute observation of something out of the ordinary by a health care provider, such as an unusual sentinel event or cluster of events. In September 2001, the first anthrax case was detected in Florida by an astute physician; West Nile virus was originally detected in New York City by a neurologist who saw a cluster of patients with an unusual encephalopathy •Members of the community observe unusual trend in illness – recent NYT article about woman who noticed from reading local obituaries that many of the people who were reported to have died from variant Creutzfeldt-Jakob disease in New Jersey had connections to a local race track. As a result of this woman’s observation, two U.S. Senators have asked the CDC to investigate this possible cluster •Max DT. The Case of the Cherry Hill Cluster. New York Times. 2004 March 28; Sect. 6:50 (col. 1).

•The top figure shows a typical epidemic curve from a Hepatitis A outbreak, the bottom figure shows the epidemic curve from the anthrax attacks that occurred during Fall 2001. •An epidemic curve is a histogram that shows the course of a disease outbreak by plotting the number of cases by time of onset •You can often tell a great deal about the infectious agent and the source of the infection from looking at an epidemic curve: if a disease is transmitted person-to-person, you will likely have a wide epidemic curve as people continue to become infected over time. A point-source infection will likely result in a more narrow epidemic curve as people were likely all exposed at the same time. If the infectious agent has a long incubation period (the period of time between exposure and onset of symptoms) the epidemic curve will likely be wider. •All of this information can assist in the process of investigating the outbreak. An epidemic curve can help to identify a cluster of people who got sick at the same time, and from there you can determine what those people had in common. Once you identify a common event, for example, eating at a particular restaurant, you can work backwards to figure out how long the incubation period was. This information will make it easier to identify the infectious agent.

•The third component of epidemiology and surveillance is to investigate each outbreak in a systematic manner

•A typical outbreak investigation starts with an unexpected event that requires immediate investigation. There is often pressure for answers from the public and local officials, multiple agencies are involved and the media are covering the investigation. On top of that, the public health officials conducting the investigation are likely required to work away from their offices out in the field. •All of these factors illustrate the need for a systematic approach to outbreak investigation

•The main goal of investigating an outbreak is to control further spread of disease, and these data informs the decision of what control and prevention measures to employ •During an outbreak investigation, one typically hopes to determine the following: •Characteristics of the outbreak (who is at risk of disease, what exposures increase risk of disease) •This information is often obtained using a three-pronged approach: epidemiology, laboratory, and environmental assessment •The image shows an electron micrograph of the Hepatitis A virus (HAV), an RNA virus that can survive up to a month at room temperature

•Make necessary administrative arrangements such as travel arrangements, obtain local contact information for all involved parties •Consult with coordinating agencies to determine roles & responsibilities during the investigation

•Before proceeding with the investigation, one must confirm that the suspected outbreak is a real outbreak •This is done by comparing observed number of cases to the historically expected number of cases •This is what surveillance data are for – the collection of baseline data to use historically in order to determine if there is any deviation from the norm

•In order to verify the diagnosis one must identify the illness as accurately as possible •This process requires thorough review of clinical findings and laboratory results •Additionally, it is useful to talk to case-patients about their illness, as they may have insights that the clinicians involved may have missed

•The next step is to establish a case definition: a set of standard criteria for deciding whether a person has a particular illness •The case definition should include clinical information about the disease, characteristics about the people who are affected, information about the location or place, and a specification of the time during which the outbreak occurred

•The case definition should be specific enough to avoid false positives but also sensitive enough so that cases are not missed “The CDC defines a confirmed case of anthrax as 1) a clinically compatible case of cutaneous, inhalational, or gastrointestinal illness that is laboratory confirmed by isolation of B. anthracis from an affected tissue or site or 2) other laboratory evidence of B. anthracis infection based on at least two supportive laboratory tests” •Note that during an outbreak, the case definition would be more complex, and include elements of time and place.

•This slide shows the interim case definition for Severe Acute Respiratory Syndrome (SARS) in the United States as of April 29, 2003 •Note that this case definition includes all necessary components: clinical criteria, epidemiologic criteria specific to person, place and time, laboratory criteria, and criteria for case classification •Centers for Disease Control and Prevention. Updated Interim Surveillance Case Definition for Severe Acute Respiratory Syndrome (SARS)—United States, April 29, 2003.  MMWR. 2003;52:391-393.

•Once the case definition is established, there are many ways to use this to identify additional cases from as many sources as possible. Investigating epidemiologists may contact health care facilities, use the media to alert the public, and even contact potential case-patients using restaurant patrons’ telephone numbers from their credit card receipts in the event of a food borne illness

•Once data have been collected, the epidemic can be described in terms of person, place, and time •This is done in an attempt to determine what the case-patients might have in common, for example, do they live in the same area? Did they eat at the same restaurant? Did they recently travel to the same destination? •An epidemic curve can be drawn to provide further information about the agent and source

•Based on what you know you can “Round up the usual suspects” – for example, if the agent is typically transmitted via an oral-fecal route, you may suspect an infected food handler at a  particular restaurant may be the source

•Recall, analytic epidemiology is the study of the causal relationships between exposures and outcomes

•Even when your analytic study identifies an association between exposure and disease, you may need to refine your hypotheses and conduct additional, more specific studies •An initial study may implicate a particular restaurant in a food-borne outbreak, while a second study may narrow the cause down to a particular menu item

•Even though implementing control and prevention measures is listed as step 9, this should be done as soon as possible •Contaminated food should be destroyed, contaminated water should be sterilized, infectious food handlers should be prohibited from work •Control and prevention measures will likely be dynamic, adapting as the investigating epidemiologists learn more about the outbreak and agent

•Oral briefing for health authorities and people responsible for implementing control and prevention measures •Written scientific report that can serve as a record of performance, a reference for others encountering a similar outbreak, and a document for potential legal issues

•Risk communication can benefit the public by bringing to light the potential risks implicated in an outbreak and preventing further cases •Risk communication can also benefit public health authorities, as publicity of an outbreak will often stimulate case reporting that can serve to provide additional information about the outbreak

•The fourth component of epidemiology and surveillance is to determine if bioterrorism was the cause

•The next few slides show the 17 CDC criteria for determining whether bioterrorism is the suspected cause of an outbreak •One may observe a number of these criteria in the event of a naturally occurring outbreak. However, the more of these criteria that are met, the more likely bioterrorism is a possible cause •Public Health Training Network, Centers for Disease Control and Prevention. Biological Warfare & Terrorism: The Military and Public Health Response. Satellite Broadcast, September 21-23, 1999.

•The final component of epidemiology and surveillance is to understand interagency coordination

•This slide shows the interagency coordination during a naturally occurring outbreak

•This slide shows the interagency coordination required during a suspected bioterrorism event •Note how much more complicated this becomes, as federal agencies and law enforcement get involved

•In review, we have covered these 5 fundamental components of epidemiology and surveillance