Disease Outbreaks


Disease outbreaks are occurrences of more cases of a disease in a particular area or among a certain group of people than normally expected.


Most often, a disease outbreak is caused by an infection. The infection is spread by person-to-person contact, animal-to-person contact, or by the environment. The outbreak can be confined to a single community or can spread among countries. The disease might be an unknown one, or a new disease in a community. The terms outbreak and epidemic can be used to mean the same thing, but an epidemic usually applies to larger numbers of people over wider geographic areas than implied by the term outbreak.

Disease outbreaks also can occur because people in a certain area are exposed to environmental factors such as chemicals or other toxic materials, or because of bacteria or fungi. Legionnaire's disease is an example of an outbreak that can be caused by bacterial exposure.

Risk factors

Many environmental risk factors, such as natural disasters, can lead to disease outbreaks. When tsunamis, hurricanes, or other events cause flooding, water supplies and sanitation suffer. A lack of safe water can lead to poor hygiene, inadequate drinking supplies and waste disposal, and unsafe food. These conditions can lead to outbreaks of diarrhea and other gastrointestinal disease.

There are many pathogens, or disease-carrying agents, that occur naturally in the world. It often requires a combination of a naturally occurring pathogen and human error or intervention to cause a disease outbreak involving the pathogen. For example, a foodborne disease outbreak occurs when several infections are caused by the same pathogen or toxin and linked to the same food. This might happen when a food worker transmits hepatitis A by not properly washing his or her hands before handling food. Diseases such as Salmonella or E. co li can be spread by food that is not prepared, stored, or handled properly. The people exposed to these diseases may or may not be able to take steps to lessen their risk, but those who control the foods, drugs, and other products that make people sick in an outbreak certainly can help prevent them.

Risk factors for disease outbreaks also include being in crowded conditions following natural disasters. For example, an outbreak of typhus, which is caused by a tiny microbe, reduced Spanish forces trying to seize Granada in 1489 from 25,000 to 8,000 soldiers in a month's time. A disease outbreak also can come from manmade causes, such as the unleashing of biological contaminants, sometimes called bioterrorism. Some would argue that even natural disasters have manmade aspects to their risk because global warming might be leading to increased risk of certain natural disasters.

Risk for acquiring diseases during an outbreak can be a combination of exposure to the disease and a vulnerability to infection or illness. For example, acquiring Legionnaire's disease first involves being exposed to water contaminated with the bacterium that causes it, but also requires that the person have compromised lung function. Some individuals are generally more at risk during disease outbreaks. Children and pregnant women are more susceptible to illness during outbreaks. The elderly are particularly at risk when disease outbreaks such as influenza occur, and people who already are ill, are malnourished, or have compromised immune systems have higher risk of contagion, serious illness, or death when disasters and disease outbreaks strike.


It is difficult to know exactly when disease outbreaks first began because not all outbreaks likely were recorded. Among some of the largest early disease outbreaks were the Black Death that struck Europe in 1348, the typhus epidemic that began in the fifteenth century, and the Spanish influenza outbreak that began in the early 1900s and eventually became a pandemic, killing more than 40 million people.

Perhaps the most important early outbreak was the nineteenth century cholera outbreak in London, which was an important contributor to the advancement of public health and how we study infectious disease. Cholera can be traced to India in 1816, and the disease eventually spread through Bengal, China, and Europe. Cholera broke out four times in London neighborhoods between 1831 and 1854, and each time, nothing was done to stop the disease. Officials simply did not understand what caused the outbreaks or how to halt them. When the disease hit particularly hard in an area of Broad Street, a physician named Dr. John Snow traced the problem to a pump that supplied drinking water to the neighborhood. The pump had been contaminated by waste from nearby cesspits.


Costs to society

It is difficult to estimate the cost of each outbreak, but in general, disease outbreaks can disrupt the economies of individuals, families, companies, communities, and even countries. Aside from the cost of medicine and hospitalization that might be required to care for people who become ill, there are societal costs such as lost wages and productivity. If a disease outbreak heavily impacts a group of people, the effects are more severe. For example, if everyone in a factory comes down with the same illness, production stops and the entire company suffers. If the company is the largest employer in the community, the effects spread to families and other businesses. Studies have shown that the cost of preventing disease outbreaks with strategies such as early detection can ease monetary and social burdens.

Common diseases and disorders

Some diseases have been all but eradicated by efforts such as vaccinations and early detection. New disease outbreaks also can occur, and researchers identify new causes or strains of viruses such as influenza regularly. The following are some of the common diseases that tend to occur in outbreaks:

Effects on public health

When an outbreak occurs, and even when a few cases of a disease that could become an outbreak are detected, public health can be at risk. Outbreaks threaten the health of people in groups or geographic areas and threaten the health of the world population in the event that the disease continues to spread. Disease outbreaks can create public health emergencies, have socioeconomic effects on families and communities, and cause a great deal of illness, suffering, and death. When disease outbreaks spread to vulnerable populations, such as children or the elderly, the consequences can be even more severe.

Public health role and response

Continuous reporting, monitoring, and surveillance can help minimize disease outbreaks, as can programs aimed at preventing diseases. These efforts include education of people and community leaders, vector control programs (such as pest management to control mosquito populations), and widespread immunizations. New approaches to data collection can help identify potential disease outbreaks earlier, as can improved communication between public health workers, departments, and their partners. Timeliness of response once a potential outbreak occurs is essential in containing a disease outbreak.

Efforts and solutions

Vaccinations and education efforts by public health teams have nearly ended or completely eradicated some diseases, even when there has been no effective treatment or cure for the illness. An example is smallpox, which is caused by a virus. A worldwide cooperative effort of vaccinations led to official eradication of the disease in 1979.


The CDC's Tracking Network is an example of a continuous collection of data that is assessed to help prevent disease. With federal funding of state and local health departments, local data can be integrated into a national tracking network that helps public health workers at the local level, but also provides information on regional and national disease occurrences. Many public health departments also have developed early warning systems for disease outbreaks to hasten response and helps minimize incidence of disease.

See also Bioterrorism ; Cholera ; Foodborne illness ; Malaria ; Pandemic ; Sanitation ; Typhus ; Viruses .



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Wagner, Michael M., et al. “The Emerging Science of Very Early Detection of Disease Outbreaks.” Journal of Public Health Management and Practice (Nov. 2001): 51–59.


Centers for Disease Control and Prevention. “Emergency Preparedness and Response: Recent Outbreaks and Incidence.” http://www.bt.cdc.gov/recentincidents.asp (accessed November 8, 2012).

Centers for Disease Control and Prevention. “EXCITE: Introduction to Investigating an Outbreak.” http://www.cdc.gov/excite/classroom/outbreak/objectives.htm (accessed November 8, 2012).

Lamb, Robert. “10 Worst Epidemics.” Discovery. http://dsc.discovery.com/tv-shows/curiosity/topics/10-worstepidemics.htm (accessed November 8, 2012).

World Health Organization. “Environmental Health in Emergencies: Disease Outbreaks.” http://www.who.int/environmental_health_emergencies/disease_outbreaks/en/ (accessed November 8, 2012).

World Health Organization. “Global Alert and Response.” http://www.who.int/csr/en/ (accessed November 8, 2012).


World Health Organization, Avenue Appia 20, 1211 Geneva 27, Switzerland, 41 22 (791) 2111, Fax: 41 22 (791) 3111, publications@who.int, http://www.who.int/en .

Teresa G. Odle

  This information is not a tool for self-diagnosis or a substitute for professional care.