Slide 1: What was the most common cause of death in the influenza pandemic of 1918?

Slide 2: Streptococcus pneumoniae superinfection!

Slide 3: Based on postmortem studies, researchers now agree that bacterial superinfection was the most common cause of death during the 1918 influenza pandemic. Importantly, 80 percent of those with lung involvement grew bacteria, with the vast majority, 71 percent, being S. pneumoniae. Graphic showing 20 percent of patient’s lungs had only influenza infection, while 80 percent of patient’s lungs had both influenza and bacterial infection.

Slide 4: If S. pneumoniae was the biggest culprit for superinfection, why is the association between S. aureus and influenza ingrained in today’s medical world? This may have resulted from the initial vivid descriptions of S. aureus superinfection. Clinical features included “cherry-red, indigo-blue cyanosis,” “friable [and] dirty pink” sputum resembling “anchovy sauce,” and numerous micro abscesses on autopsy. Subsequent texts cited these pathognomonic signs in the diagnosis of S. aureus infection, whereas S. pneumoniae lacked specific exam findings.

Slide 5: Interestingly, the microbiologists who isolated H. influenzae from patients believed it was the etiology of the influenza and therefore named it “influenzae.” We know now that the H. influenzae were likely superinfections as well.