Thursday, July 10, 2008

Mapping Infectious Diseases

A system maps outbreaks culled from Internet news sites.

By Emily Singer

Tracking disease: HealthMap is a freely available, automated surveillance tool used to track outbreaks of infectious disease around the world. Users can search for reports based on both the country and the type of disease that they are interested in. Shown here is a close-up of the eastern portion of the United States, with recent reports of salmonella cases highlighted with colored balloons. The balloons are color-coded based on the time of the report, with red being the most recent. Clicking on the orange balloon in Massachusetts, for example, would open up a July 8 article from a Boston news channel reporting three new cases linked to the salmonella outbreak. Credit: HealthMap

Wonder what state or country has been hit hardest by the salmonella outbreak or where the latest cases have been detected? You can find out on HealthMap, a public-health surveillance system that scours Internet news sites and other sources for real-time information on outbreaks of infectious disease, and then plots that data on a freely accessible world map.

The HealthMap software first collects information from various sources, including alerts from the World Health Organization, discussions on public-health listservs, and breaking news from thousands of websites in six different languages from around the world.

A series of text-processing algorithms then picks out the disease being reported and the location of the event, and tries to determine its relevance. For example, the software must distinguish between a breaking news item on tuberculosis and an article about a TB vaccination campaign. John Brownstein, cofounder of HealthMap and an assistant professor at the Informatics Program at Children's Hospital Boston, says that the algorithms rate reports correctly about 95 percent of the time.

The data is plotted on a world map, with different colors indicating the most recent reports. "It's very helpful to be able to see these things in a spatial representation--it helps us recognize when a disease is spreading, when there's a cluster of cases, and when different cases might be related," says Larry Madoff, a physician at Harvard Medical School, in Boston, and editor of ProMED, a public-health listserv run by the International Society for Infectious Diseases.

One of the benefits to this automated approach is the speed: local news organizations and listserv discussions often detect cases prior to official public-health channels. "We'll pick up a case of avian influenza in Indonesia, and then a few days later see an official confirmation from the World Health Organization," says Brownstein. The site is fully automated and is updated every hour, 24 hours a day.

World travelers can check the map to look for new outbreaks in their vacation destinations. But from a broader public-health perspective, researchers say that the system is likely to be of most use in poorer nations, which have little in the way of public-health monitoring and are often a hotbed of infectious disease. Whereas in countries like the United States, where public-health officials monitor local emergency-room visits and other indicators for signs of outbreaks, "many developing counties don't have the capacity to do surveillance," says Brownstein. "In those cases, the news media tends to be a good source of data." On the downside, areas that carry the greatest burden of infectious disease, including large parts of Africa and South America, have fewer media outlets and thus the greatest gaps in coverage.

These sources become especially important when a country tries to keep public-health information under wraps for economic or political reasons, experts say. "An outbreak of cholera mandates restrictions on trade and tourism that are bad for the country, so they'll err on the side of caution," says Madoff. "But from a public-health perspective, it may be more important to act sooner just on the suspicion [of an outbreak]."