NMA: Nonprescription Medicines Academy

Might Influenza Be Spread by Small Particles Traveling Longer Distances?

April 17th, 2013

A study published in the Journal of Infectious Diseases challenges the prevailing belief that influenza virus is spread primarily by large particles traveling up to a maximum of 3 to 6 feet from an infected person.

The study population encompassed 61 patients who were admitted to the emergency department or an inpatient care unit of Wake Forest Baptist Medical Center in North Carolina during the 2010-2011 influenza season. All of these patients tested positive for influenza virus. Quantitative impaction air samples were obtained by placing three six-stage air samplers within 1 foot, 3 feet, and 6 feet of each patient’s head during routine care. Information about symptom severity, treatment, and medical history were recorded.

Of the 61 patients, 26 (43%) released influenza virus into the air. These patients produced mostly small influenza virus–carrying particles (diameter <4.7 µm), with infectious amounts of virus up to 6 feet from the patient’s head during routine, non–aerosol-generating patient-care activities. High nasopharyngeal viral load and greater severity of illness were linked to dispersal.

Five patients (19%) released influenza virus in exceptionally high concentrations—up to 32 times more than other patients. The presence of these “super-emitters” suggests that some patients may be more likely to transmit influenza than others; additional studies are needed.

J Infect Dis. 2013;207(7):1037-46.