Pathogenic partners prompt pneumonia.

Pneumonia can be caused by bacteria or any of a number of respiratory viruses. A report in the August Nature Medicine now suggests that these two classes of pathogens act more closely together in causing pneumonia than scientists had thought. The findings could influence the way in which physicians treat these prevalent lung infections.

The finding emerged from a study of more than 37,000 infants in Soweto, South Africa. Half of the children were immunized with a vaccine against the bacterium Streptococcus pneumoniae, while the other half received a placebo. The researchers tracked the children and examined the records of those who were hospitalized over the following 2.5 years for severe pneumonia. Every hospitalized child was checked for viral and bacterial infections.

Shabir A. Madhi of the University of the Witwatersrand in South Africa and his colleagues found that immunization for bacterial pneumonia had an unexpected payoff: It not only reduced the incidence of bacterial pneumonia but also reduced by nearly a third pneumonia associated with the seven respiratory viruses the researchers tracked. This suggests that viruses often act in tandem with bacterial pathogens in pneumonia, say the researchers.

"We show that in severe pneumonia that requires hospitalization, even when you do identify viral pathogens, the vast majority of diseases are complicated by superimposed bacterial infection," says Madhi. This supports the common practice of treating pneumonia with antibiotics even when the causative agent remains unclear, Madhi adds.--D. P.