PUBLIC HEALTH PROGRAMS

Disease Tracking and Epidemiology

One branch of public health, epidemiology, studies the incidence of disease in large populations. Epidemiologists study data from public health clinics and private physicians who are required by law to report cases of certain diseases and deaths to public health officials. Using clues about the patterns in which deaths and diseases occur, epidemiologists are able to identify emerging disease patterns that may indicate environmental health hazards, potential outbreaks of existing diseases, or emergence of new infectious diseases.

For example, in the early 1980s a few doctors in New York and California reported an unusually high number of deaths from opportunistic infections—infections by organisms that usually only cause disease in people with weakened immune systems.

These early reports prompted epidemiologists and medical researchers to investigate this new vulnerability to opportunistic infections, which they called acquired immunodeficiency syndrome (AIDS). These efforts led to the identification of the previously unknown human immunodeficiency virus (HIV), the virus that causes AIDS.

Threats to public health concerns change over time and epidemiologists and other officials continuously evaluate epidemiological trends to determine how best to meet future public health needs.

For example, recent epidemiological reports show that tuberculosis, an infectious disease believed to be under control just 30 years ago, is now responsible for more deaths worldwide than any other infectious disease, killing more people per year than AIDS and malaria combined.

This resurgence is due to new drug-resistant strains of the bacteria that cause tuberculosis. The tuberculosis epidemic, or pandemic, has been declared a global public health emergency, prompting intensive international public health efforts to curb its spread.

Epidemiologists and other public health officials attempt to break the chain of disease transmission by notifying people who may be at risk for contracting an infectious disease.

When epidemiologists learn that a restaurant worker has infectious hepatitis, they place announcements in local media, such as radio and newspapers, urging people who ate at the restaurant in recent weeks to be checked for the disease and to seek treatment so that they will no longer risk infecting others.

Organizations such as the World Health Organization (WHO), an agency of the United Nations, monitor infectious diseases and try to prevent outbreaks from spreading worldwide.

In early 2003 WHO epidemiologists learned that a deadly type of pneumonia of unknown cause that originated in mainland China was quickly spreading to other countries.

The disease, known as severe acute respiratory syndrome (SARS), begins with a fever, chills, headache, and malaise. Two to seven days later some people develop a dry cough and difficulty breathing and, in some cases, die.

In March 2003 WHO issued an international alert, designating SARS as a worldwide health threat. The alert triggered public health officials from nations around the world to establish procedures to identify and isolate SARS cases and possibly prevent the illness from reaching epidemic proportions.