Bench-to-bedside review: bacterial pneumonia with influenza - pathogenesis and clinical implications

Abstract

Seasonal and pandemic influenza are frequently complicated by bacterial infections, causing additional hospitalization and mortality. Secondary bacterial respiratory infection can be subdivided into combined viral/bacterial pneumonia and post-influenza pneumonia, which differ in their pathogenesis. During combined viral/bacterial infection, the virus, the bacterium and the host interact with each other. Post-influenza pneumonia may, at least in part, be due to resolution of inflammation caused by the primary viral infection. These mechanisms restore tissue homeostasis but greatly impair the host response against unrelated bacterial pathogens. In this review we summarize the underlying mechanisms leading to combined viral/bacterial infection or post-influenza pneumonia and highlight important considerations for effective treatment of bacterial pneumonia during and shortly after influenza.

Figure 1

Complexity of combined viral/bacterial and post-influenza pneumonia. Severe bacterial pneumonia following influenza can be subdivided into combined viral/bacterial (left) and post-influenza pneumonia (right). During combined viral/bacterial pneumonia, the virus, the bacteria and the host all interact with each other. The severity of post-influenza pneumonia is due to virus-induced changes to the host that affect the course of bacterial infection.