Viral infections predisposing to bacterial infections.

Epidemiological and experimental evidence support the hypothesis that primary viral infection increases host susceptibility to secondary microbial invasion. The evidence is most compelling for a correlation between upper respiratory tract viruses and bacterial sinopulmonary disease; and cytomegalovirus and opportunistic fungal, bacterial and protozoal pathogens invading multiple sites. While a number of virus-induced alterations in host defenses have been described, the determinants of virus pathogenicity are still poorly understood.