Influenza particles are released simply by breathing. That means, a person does not have to cough or sneeze to spread the flu - just breathing will do it. This has infection control implications.
Why does this matter?
Patients with coughing and sneezing are often asked to wear a mask while awaiting ED bed placement. This study suggests that someone with flu symptoms who lacks significant coughing or sneezing is still contagious simply by breathing.
Breathing out the flu
This was a sample of 142 college volunteers who were symptomatic and diagnosed as influenza positive. They performed paired NP swabs and 30-minute breath samples on days 1 to 3 after onset of illness, with coarse and fine aerosols: >5-µm and ≤5-µm, respectively. They learned that participants did not need to cough or sneeze during the 30-minute period in order to shed infectious virus particles. Simply breathing was enough, though coughing increased shedding. As the illness wore on, they shed fewer particles each day. Ironically, those who were vaccinated the year before and that year shed more flu A particles in breath samples, which "might lead one to speculate that certain types of prior immunity promote lung inflammation, airway closure, and aerosol generation." Ultimately, in times of high influenza prevalence, people with flu symptoms, even those lacking frequent cough, shed up to 2000 infectious flu particles per hour and need to wear a mask while waiting in the ED for a bed.
By the way, if you have full-text BMJ access, the December article on "man flu" was hilarious. The author, "explores whether men are wimps or just immunologically inferior." There is also a free audio section.
Infectious virus in exhaled breath of symptomatic seasonal influenza cases from a college community. Proc Natl Acad Sci U S A. 2018 Jan 18. pii: 201716561. doi: 10.1073/pnas.1716561115. [Epub ahead of print]
Peer reviewed by Thomas Davis, MD.