Flu is never fun, especially in hospital, and during outbreaks doctors, nurses and other healthcare providers may be dealing with many patients with the bug. But avoiding catching it is more than just a case of dodging coughs, sneezes and other virus-laden aerosols, according to research published in the Journal of Infectious Diseases. In this study, PCR (polymerase chain reaction) has helped researchers find out more about how influenza (flu) viruses are transmitted, including the rather disconcerting fact that even without obvious aerosols, they can travel more than six feet during routine hospital care.

During the 2010–2011 influenza season, researchers at the Wake Forest School of Medicine (US) identified and screened people in the emergency department and hospital who had symptoms of flu. They took samples of the air one foot (0.3 m), three feet (0.9 m) and six feet (1.8 m) from their heads during routine hospital care (not care that might produce aerosols), recording the number of coughs and sneezes and their severity during this time, and used rapid tests and PCR tests to detect influenza viruses in the air samples.

Of the 61 people who tested positive for the influenza virus, 26 released viruses into the air of the room, and five released up to 32 times as many viruses. These five patients were described as ‘super-emitters’. Patients who emitted more virus unsurprisingly felt worse, and had higher loads of virus in samples taken from their noses and throats.

Whereas it was thought that most flu virus was transmitted in aerosols during certain medical procedures such as bronchoscopy, sputum induction, intubation, or cardiopulmonary resuscitation, in this study the researchers found that patients released most influenza virus into the air in small particles during everyday healthcare activities. What was even more concerning was that these could travel up to six feet away from the patient’s head. However, the concentration of the particles did decrease with distance.

Healthcare providers are recommended to wear fitted respirators during aerosol-generating processes, and non-fitted facemasks during non-aerosol-generating patient care when dealing with people with flu. This study, supported by the PCR results, suggests that this might not be enough to protect against infection, as the methods of spreading infection are not as clear-cut as we thought. It also supports the importance of vaccination to try to avoid flu infection in the first place, for both patients and healthcare workers.