A 70-year-old nursing home patient refused the influenza vaccine and subsequently developed influenza. She died of acute pneumonia 1 week after contracting the "flu." The most common cause of acute post-influenzal pneumonia is

Staphylococcus aureus is the most common cause of post-influenzal secondary bacterial pneumonia. It most often affects the elderly, although patients of any age may be afflicted. The pneumococcus as well as group A streptococci and Haemophilus influenzae may also cause pneumonia.