Influenza makes people vulnerable to bacterial infection

Influenza is caused by a virus, but the most common cause of death in influenza patients is secondary pneumonia caused by bacteria, rather than the influenza virus itself. While this is well known, what is largely unknown is why influenza infections lead to an increased risk of bacterial pneumonia.

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Key-Points

Pneumococcal infections are the most common cause of community-acquired pneumonia and a leading global cause of death.

A prior influenza virus infection sensitizes for pneumococcal infections, but mechanisms behind this increase susceptibility are not fully understood.

Researchers at Karolinska Institutet have now identified influenza-induced changes in the lower airways that affect the growth of pneumococci in the lungs.

The researchers found that different nutrients and antioxidants, such as vitamin C, leak from the blood. This creates an environment in the lungs that favours growth of the bacteria.

The bacteria adapt to the inflammatory environment by increasing the production of an enzyme called HtrA. The presence of HtrA weakens the immune system and promotes bacterial growth in the influenza-infected airways.