I Overview

Before discussing disaster epidemiology and surveillance, it is important to define what is meant by disaster. A disaster is generally considered to be an event that puts an overwhelming stress on a system such that the resources used on a daily basis are inadequate for dealing with the impact of the event. The resources may be inadequate because of the number of people affected by the event, or because the resources themselves have been damaged or limited as a result of the event. Disasters may be further categorized by intent or cause. Whereas natural disasters are events such as tsunamis, hurricanes, tornadoes, earthquakes, and floods, man-made disasters are related to human-developed technology and may be unintentional, such as a train crash, or intentional, such as a terrorist attack or the intentional distribution of a toxic agent (e.g., 1995 sarin gas release in Tokyo subway, 2011 anthrax letters sent in U.S.). In either case, the epidemiology and surveillance needs in a disaster may be impacted by the type of event that has occurred.

Disaster epidemiology and surveillance are rooted in epidemiologic principles that apply to other diseases, but unique challenges and concerns need to be considered in the context of disaster epidemiology. Investigators use disaster epidemiology to assess the short-term and long-term health effects of disasters. In addition, disaster epidemiology is important in allowing epidemiologists to understand how to prevent deaths, injuries, and disease spread in disaster situations. Despite advances in disaster epidemiology, however, there is still a need to refine the approaches to surveillance and epidemiology in disaster situations, as Noji¹ stated in 1992.

Unlike in other types of events, when we perform epidemiologic studies and surveillance in disasters, we focus on not only the inhabitants of a community affected by the disaster, but also the workers and volunteers who respond to a disaster. These responders are often at risk for injury or disease because of their involvement in the response (e.g., an NYC Fire Department chaplain responding on 9/11 was killed by a falling object). In other situations, workers may be exposed to infectious diseases or injury risks.

A Burden of Disaster

The World Health Organization (WHO) reports that 385 natural disasters killed more than 297,000 people in 2010. An additional 217 million people were affected by the disasters, at a cost equivalent to $123.9 billion in economic damages.² In the United States, there has been a steady increase in the number of official disaster “declarations” from 1990 to 2011, with 100 declarations in 2011 (Fig. 27-1).

Figure 27-1 Disaster declarations by year, United States, 1990-2011.

(From http://www.fema.gov/news/disaster_totals_annual.fema.)

II Definitions and Objectives

To have a basis for understanding the issues associated with disaster epidemiology and surveillance, it is important to understand the definitions commonly used in the study of disasters. First, a disaster could be considered to be an event that places a strain on the health or public health system such that additional resources are needed in order to respond. Disasters may occur within an institution, in a community, or on a broader scale. Disasters can be classified in a number of ways, but are usually described as natural or man-made, as previously noted. Natural disasters encompass a range of situations that put people at risk for significant health effects.

Disaster epidemiology is defined as the use of epidemiology to assess the short-term and long-term adverse health effects of disasters and to predict consequences of future disasters. It brings together various topic areas of epidemiology, including acute and communicable disease, environmental health, occupational health, chronic disease, injury, mental health, and behavioral health. Disaster epidemiology provides situational awareness; that is, it provides information that helps responders understand what the needs are, plan the response, and gather the appropriate resources.

The main objectives of disaster epidemiology are as follows:

As with other types of epidemiology, disaster epidemiology focuses on identifying disease and injury patterns and risk factors to the population and community affected by the disaster. This information serves as the basis for developing prevention and mitigation strategies that are driven by three contexts of disasters: time, place, and person. For example, hurricane season on the U.S. East Coast, as well as in the Caribbean, is June 1 through November 30.³ In addition, the geographic area generally at risk is defined. Although people who live on or near the coast are at increased risk of injury or death during a hurricane, evacuation from the hurricane zone minimizes or eliminates this risk. In contrast, the usual season for flu occurrence is over the winter months in the United States, and flu risk is related to exposure, immunization status, and other factors such as age; generally, elderly and very young populations, people with chronic illness or immunocompromise, and pregnant women are at increased risks for complications and mortality, depending on the flu strain that is active in a given year.⁴ Prevention strategies would focus on immunization of highest-risk populations, and depending on the severity of an outbreak, isolation of people who have contracted flu or who have been exposed and are likely to expose others to risk.

In a disaster situation, three types of epidemiology generally are used: descriptive, analytic, and evaluative. Each contributes to the understanding of the disaster event, as well as the prevention and mitigation of harm from future events.

A Descriptive Epidemiology

Epidemiologists use descriptive epidemiology to identify the distribution of disease or injury among the population groups affected by the disaster. This includes identifying the health-related issues that occur among people who are responding to the event.

After the World Trade Center disaster on 9/11, responders to the scene were exposed to various types of particulate matter, as well as larger pieces of debris, some of which fell from the collapsing towers. Other responders have complained of resulting respiratory problems. The epidemiology of the health aftermath of the disaster continues to emerge; longitudinal surveys are providing information on various health outcomes. A study of 2960 disaster workers found that 70% did not meet criteria for posttraumatic stress disorder (PTSD), but at 6 years after the event, 4.2% of nonrescue disaster workers still exhibited symptoms of PTSD or partial PTSD. Risk factors for ongoing PTSD included major depressive disorder 1 to 2 years after the event, history of trauma, and extent of occupational exposure.⁵ Asthma rates are increased in the disaster responders as well, with a lifetime prevalence by 2007 that was almost twice (19% vs. 10%) that of the general population.⁶ On a larger scale, the World Trade Center Health Registry at the New York City Department of Health and Mental Hygiene will provide a 20-year follow-up through periodic contact with the enrollees⁷ (Box 27-1).

Box 27-1 World Trade Center Health Registry Projects

The current survey includes over 41,000 respondents as of February 28, 2012, and is split between survivors (>38,000) and responders (>31,000). Through the overall survey and special surveys, the Registry is being used to investigate the following:

 Cardiovascular disease

 Skin rash

 Alcohol use

 Posttraumatic stress disorder (PTSD) among police

 Unmet mental health care needs

 Cancer rates among enrollees

 Health of Staten Island landfill and barge recovery workers

 Respiratory and behavioral health of children

 Impact of 9/11 injuries on long-term enrollee health

 Coexistence, or comorbidity, of respiratory and mental health conditions experienced by many enrollees

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