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Providersí influenza risk may be higher than thought

Thursday January 31, 2013
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Patients with influenza can emit small virus-containing particles into the surrounding air during routine patient care, potentially putting healthcare providers at higher risk of exposure to influenza than previously thought.

The findings, scheduled for publication in the Journal of Infectious Diseases, raise the possibility that current influenza infection control recommendations may not always be adequate to protect providers during routine patient care in hospitals.

Werner E. Bischoff, MD, PhD, and colleagues from the Wake Forest Baptist School of Medicine in Winston Salem, N.C., screened 94 patients for flu-like symptoms during the 2010-11 influenza season. Study participants had been admitted to the ED (52 patients) or an inpatient care unit (42) of Wake Forest Baptist, where vaccination for influenza is mandatory for healthcare providers.

Of the patients enrolled, 61 (65%) tested positive for influenza virus, 26 (43%) released influenza virus into the air and five (19%) emitted up to 32 times more virus than others.

The finding of this group of patients with influenza, described by the researchers as "super-emitters," suggested that some patients may be more likely than others to transmit influenza.

High concentration of influenza virus released into the air was associated with high viral loads in nasopharyngeal samples. Patients who emitted more virus also reported greater severity of illness.

The belief is that influenza virus is spread primarily by large particles traveling up to a maximum of three to six feet from an infected person. Recommended precautions for health providers focus on preventing transmission by large droplets and following special instructions during aerosol-generating procedures.

In this study, the researchers discovered that the majority of influenza virus in the air samples analyzed was found in small particles during non-aerosol-generating activities up to a six-foot distance from the patientís head, and that concentrations of virus decreased with distance. The study addressed only the presence of influenza-containing particles near patients during routine care, not the actual transmission of influenza infection to others.

Fitted respirators are required for healthcare providers during aerosol-generating procedures with patients. During routine, non-aerosol-generating patient care, recommendations are for providers to wear a non-fitted facemask. Based on their findings, Bischoff and colleagues expressed concern that providers still may be exposed to infectious dosages of influenza virus up to six feet from patients, with small, wide-spreading particles potentially exceeding the recommended exposure zones.

The findings suggest infection control recommendations may need to be reevaluated, the study authors concluded. The detection of "super-emitters" raises concerns about how individuals with high viral load may affect the spread of influenza, they noted.

"Our study offers new evidence of the natural emission of influenza, and may provide a better understanding of how to best protect healthcare providers during routine care activities," the authors wrote. However, studies of influenza virus transmission will be necessary before the role of super-emitters can be firmly established, they noted.

The study abstract is available at http://jid.oxfordjournals.org/content/early/2013/01/29/infdis.jis773.abstract.


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