PITTSBURGH -- University of Pittsburgh infectious disease experts reviewed nearly a century of epidemiology reports to trace the origins of the H1N1 virus, commonly known as swine flu, that emerged in Mexico this spring.

Swine flu has sickened at least 27,000 people and killed more than 100 in the United States.

They have found that, over time, viruses evolve.

The recent swine flu outbreak may even be related to a flu virus from birds that infected humans with deadly results back in 1918.

The National Institutes of Health, which paid for the Pitt research, will use the information to learn more about how to write computer programs that predict the emergence of diseases and the best ways to prevent them from spreading.