A pandemic is the outbreak of a disease on a global scale.


When a disease occurs in higher numbers than expected, it often is referred to as a disease outbreak. Epidemiologists and other public health officials continuously monitor disease incidence to watch for outbreaks. If an infectious disease outbreak spreads to a high number of people in a given region, it might be termed an epidemic. A pandemic differs from an epidemic in that a pandemic spreads beyond a geographic region, affecting different areas around the world. The pandemic might involve a number of separate epidemics around the globe or a progressive, systematic spread of the disease throughout the world.

Perhaps the most well-known example in the twentieth century is the HIV/AIDS pandemic, which reached 65 million infections and 2.5 million deaths at its peak. Probably the first recorded pandemic was the Antonine Plague, which occurred sometime between 165–180 B.C.E. In this plague, soldiers from Asia might have brought measles or smallpox to Europe. The pandemic eventually killed as many as 5 million people.

A cholera outbreak in London was an important contributor to the advancement of public health and how people study infectious disease. But cholera can be traced to India in 1816. The disease spread through Bengal, China, and Europe.

Progress in science and public health efforts has eradicated or slowed many of the diseases that used to result in pandemics. Influenza, or flu, pandemics have caused many health problems throughout past and recent history, however. Between 1918 and 1920 the Spanish influenza probably killed more than 40 million people worldwide and 100,000 people in the United States. However, by the time the Asian flu struck in the 1950s, identification and response methods had improved.

Effects on public health

A pandemic can have major effects on community health, social structures, and economies. The effects might be felt more strongly in certain parts of the world or in certain people who are more vulnerable. For example, some countries are not as well equipped to handle massive immunizations and other practices to stem pandemics. Plus some people, such as the elderly, are more vulnerable to severe illness or death from diseases such as the flu than are others. Though most pandemics now can be predicted and often averted with actions such as immunizations, there remains the chance that a flu virus could emerge to which humans have little or no immunity. In that case, there would be serious health ramifications, and communities and countries might have to resort to travel restrictions and other methods to prevent transmission of the virus.

Cost to society

Influenza pandemics caused millions of deaths around the world in the twentieth century. The outbreak of severe acute respiratory syndrome (SARS) in 2003 caused economic losses and social disruption that reached far outside the borders of the affected countries. Pandemics can cause enormous healthcare costs and disrupt normal services that are essential to communities and regions.

Public health role and response

Public health professionals should prepare for a pandemic in advance and with a comprehensive pandemic preparedness guide or checklist. The planning includes preparing for emergencies and disease surveillance. Also involved is determining how cases will be investigated and treated and how further spread of the disease in the community can be prevented. Determining how to maintain essential community services during the pandemic is essential. Surveillance should assist with early warning and prevention strategies at the time the pandemic occurs. Case management might include improved hygiene, immunizations, distancing of social groups, and even travel restrictions and quarantines.

If public health professionals are involved in helping a community during a pandemic, they often will study and evaluate the response that occurred after the pandemic has passed. This evaluation helps to improve response in that community and in other areas in the event of a future pandemic. Public health professionals also learn from response to epidemics and disease outbreaks and any mistakes made.

See also Cholera ; Disease outbreaks ; Measles ; Plague ; Severe acute respiratory syndrome (SARS) ; Smallpox .



Doshi, Peter. “The Elusive Definition of Pandemic Influenza.” Bulletin of the World Health Organization. 89 (2011): 532–38.


National Council of Teachers of Mathematics. “The History of Pandemics.” .aspx?id=10826 (accessed October 14, 2012).

World Health Organization. “WHO Checklist for Influenza Preparedness Planning.” (accessed October 14, 2012).


Centers for Disease Control and Prevention—Bioterrorism Preparedness & Response Program (CDC), 1600 Clifton Rd., Atlanta, GA, 30333, (404) 639-3534, (888) 246-2675,, .

World Health Organization, Avenue Appia 20, 1211 Geneva 27, Switzerland, 2241 791 21 11, Fax: 2241 791 31 11,, .

Teresa G. Odle

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