Co-infections are bad news for flu patients. The risk posed by the novel coronavirus is generating headlines, but secondary infections caused by Streptococcus pneumoniae and other common bacteria have stalked flu patients for centuries. The combination is associated with more severe symptoms and a greater risk of pneumonia, hospitalization and death. Flu, particularly in patients who also have bacterial respiratory infections, remains a leading cause of illness and death worldwide.

How flu works in your nose

The last decade has seen a flurry of research from St. Jude Children’s Research Hospital scientists and others on the intersection of flu and bacteria. The findings include evidence that S. pneumoniae (pneumococcus) and other common respiratory bacterium and flu work together in the upper respiratory tract of humans and animals to spread the infections. S. pneumoniae can live in the nasal passages and upper respiratory tract of humans without causing disease. “Most people carry pneumococcus at some point in their lives without any associated disease,” said Jason Rosch, PhD, of the St. Jude Infectious Diseases department.

Rosch and Stacey Schultz-Cherry, PhD, also of Infectious Diseases, recently added key details about the alliances these infectious agents form. The findings appeared in the journal mSystems.

The researchers showed that direct interaction between S. pneumoniae bacteria and influenza A promoted airborne transmission of the virus in ferrets. Ferrets are a model of human flu infection. The investigators reported that when bound to bacteria, the flu virus survived longer in the environment and remained infectious.

A new way to slow flu transmission

The scientists also identified a possible way to block the flu’s spread. Antibiotic ointment inside the nasal passages of flu-infected ferrets blocked flu from spreading through the air. When S. pneumoniae was reintroduced into the ferrets’ noses, flu transmission was restored. The antibiotic ointment had no effect on the flu virus or symptoms.

“While antibiotics have no effect on the flu itself or flu symptoms, this study suggests that targeting common respiratory bacteria, possibly with vaccines, offers a possible new way to slow flu infections,” Rosch said. He and his colleagues have developed an experimental vaccine designed to block pneumococcal transmission.

Studies of flu transmission in households suggest that the respiratory microbiome of flu patients may influence viral spread. The microbiome includes bacteria and other organisms that live on tissue lining the nose and airways. “This study suggests that modifying the make-up of the respiratory microbiome, including through vaccination, may profoundly affect flu transmission,” Schultz-Cherry said.