Why does influenza infection increase the risk of secondary Staph aureus pneumonia?

• A. It causes only viral pneumonia
• B. Influenza vaccines increase risk
• C. It prevents bacterial infection
• D. Damages the respiratory tract, impairing immunity, enabling bacteria to invade

Answer: (D)

Influenza injures the lining of the airways, which disrupts the body's ability to defend the lungs. The damage to the respiratory epithelium and the loss of normal ciliary clearance let bacteria that are present in the airway or aspirated into the lungs persist and multiply. The viral infection also alters local immunity by impairing the function of macrophages and neutrophils and creating an inflammatory environment that can help bacteria adhere to and invade tissues. All of this creates a window of opportunity for Staphylococcus aureus to establish infection and cause pneumonia after the influenza illness. Vaccination against influenza reduces this risk by preventing the initial epithelial injury and subsequent susceptibility to bacterial invasion.

The other statements don't fit: the idea that influenza only causes viral pneumonia ignores the well-known risk of a secondary bacterial infection; vaccines do not increase risk; and influenza does not prevent bacterial infection.