Now Published: Flu Virus Can Spread Up to 6 Feet, No Cough or Sneeze Required

Troy Brown

February 01, 2013

The influenza virus can spread up to 6 feet from a patient's head via submicron particles during routine hospital care, according to a study of patients admitted to the emergency department (ED) and throughout a tertiary care hospital with influenza-like illness during the 2010 to 2011 influenza season. It was previously thought that the virus traveled only a short distance via large particle droplets during coughing or sneezing. Submicron particles are released in the air during talking and breathing.

Werner E. Bischoff, MD, PhD, an assistant professor in the Section on Infectious Diseases, Department of Internal Medicine, Wake Forest School of Medicine, Winston-Salem, North Carolina, and colleagues published their findings online January 31 in Clinical Infectious Diseases.

According to the World Health Organization and the Centers for Disease Control and Prevention, transmission mainly occurs when large-particle respiratory droplets travel a short distance, and face masks worn by healthcare professionals block those particles. Fit-tested respirators are only required when aerosol-generating procedures such as bronchoscopy are performed.

Particle size may affect infection risk and severity on the basis of the virus' ability to travel to the lungs instead of being confined to the upper respiratory tract.

"Protecting [healthcare professionals] against influenza virus requires a clear understanding of how this virus is aerosolized and by whom it is emitted," the authors write.

Investigators enrolled 94 patients with influenza-like illness in the study. They obtained patient history and took nasopharyngeal swab specimens. The researchers then collected quantitative impaction air samples 1 foot or less, 3 feet, and 6 feet from the patient's head during routine care. Rapid test and polymerase chain reaction were used to detect influenza virus.

Of the 94 patients, 61 (65%) were influenza-positive (31 influenza A, 30 influenza B). Of those patients, 26 (43%) emitted influenza virus into room air (13 inpatients and 13 ED patients). Of the emitters, 5 (19%) released up to 32 times more virus than other patients. There were no statistical differences in other characteristics or symptoms.

Higher nasopharyngeal viral loads were found in emitters compared with nonemitters. Patients with increased nasopharyngeal viral load were the only patients in whom coughing and sneezing during air sampling was connected with the release of increased virus into room air (P < .05). Emitters exceeded the airborne 50% human infectious dose of influenza virus at all locations sampled.

All emitters in the study were less likely to report chills and more likely to experience higher illness severity and interference with daily living than nonemitter ED patients (P < .05).

As distance from the patient's head increased (from 1 to 6 feet), the viral load decreased significantly (P < .05). The amount of small particles also increased significantly relative to the amount of large particles. Healthcare professionals were primarily exposed to small influenza virus particles (diameter, < 4.7 μm).

There were no detectable differences between influenza virus types, emitters and superemitters, and patient location.

In an accompanying editorial, Caroline Breese Hall, MD, professor in the Department of Pediatrics and the Department of Medicine at the University of Rochester School of Medicine and Dentistry in New York, notes that more advanced forms of personal protection equipment that effectively block small particles (such as N95 respirators) are expensive and that their use in all influenza-positive patients is "usually not feasible."

"[I]nfection control procedures should be commensurate with the concern generated by the clinical observations of the intensity and severity of the community outbreak. The efficacy of the recommended infection control program, however, is less dependent on which specific procedures are included than on the consistent education of healthcare personnel," Dr. Hall noted. "Included in this should be their vaccination, their compliance with the recommended procedures, and their awareness of the risks of nosocomial infection among patients and personnel."

She concludes, "This study not only adds to our understanding of these risks, but helps define the questions that still need answering."

Dr. Hall died on December 10, 2012, at the age of 73 years. She was internationally known for her work in pediatric infectious diseases.

The study was supported by the Centers for Disease Control and Prevention. The authors have disclosed no relevant financial relationships. Dr. Hall had consulted for GlaxoSmithKline and MedImmune.

Clinical Infectious Diseases. Published online January 31, 2013.