Will airborne flu spread undercut IC measures?

Unresolved issues remain as pandemic looms

Though a combination of contact and droplet infection control precautions are recommended in the federal influenza pandemic plans, questions remain about the possibility of airborne flu transmission.

Since infection control precautions for airborne infections (e.g., measles) are fairly elaborate, their practicality in a pandemic flu setting will be severely limited. If avian influenza A (H5N1) becomes easily transmitted between people, hospitals will face severe surge capacity challenges. Placing a flu patient in a negative pressure isolation room as if they had tuberculosis is not going to be feasible in the vast majority of institutions. But real world concessions aside, the question lingers: Could a highly transmissible pandemic influenza strain undercut hospital infection control efforts by spreading via the airborne route?

"We don’t really have terrific data on how flu is transmitted," said Andrew T. Pavia, MD, chair of the pandemic flu task force formed by the Infectious Disease Society of America. "There are data that support contact, droplet, and airborne transmission. The bulk of the data suggest that the droplet is the most important, but under the right circumstances it’s likely that airborne transmission) can occur."

Pavia recently spoke in Chicago at a pandemic flu plenary session at the annual meeting of the Society for Healthcare Epidemiology of America (SHEA).

"The current recommendations are to use standard plus droplet precautions as for annual flu," he said. "That is what is in the HHS plan and the WHO recommendations; plus the use of eye protection when close to a patient and the use of airborne precautions for aerosol-generating procedures."

However, pointing out a bit of a disconnect in the public health response, he noted that the Centers for Disease Control and Prevention guidelines for severe acute respiratory syndrome (SARS) state that "airborne precautions should be used in the setting of a possible novel virus." Presumably, a lethal pandemic flu strain would meet the "novel" threshold, but, as a practical matter, would it be possible to implement airborne precautions for an onslaught of patients? Pavia hinted that the answer may come in the form of respirators, invoking the names of their principal regulators: the Occupational Safety and Health Organization (OSHA) and the National Institute for Occupational Safety and Heath (NIOSH). "There are some controversies that need to be resolved between OSHA, NIOSH, and other health authorities," he told SHEA attendees. "Stay tuned on this."

In addressing the issue, Pavia referenced a review article that thoroughly addresses the complex issue of influenza transmission routes.1 Written by CDC investigators, the article notes that since droplet transmission is the primary means of person-to-person transmission of influenza "the use of many of the less costly precautions, such as cohorting influenza-infected patients and the use of masks and hand hygiene, could offer appreciable benefit. . . . The limited number of beds in negative pressure rooms may be quickly filled during communitywide influenza outbreaks, making implementation of airborne transmission precautions impractical. . . . Nevertheless, given the uncertainty of the clinical importance of airborne transmission of influenza, use of negative-pressure rooms for patients with confirmed or suspected influenza may be prudent if they are housed near severely immunocompromised persons."

Specifically referring to pandemic flu, the authors propose a stopgap measure that essentially advises health care facilities to use airborne precautions for their initial incoming cases. "[Airborne] precautions may also be advisable for initial admissions of persons infected with a newly emergent influenza A subtype with pandemic potential," they conclude "Immunity in the general population to such a virus would be poor, and the viral inoculum necessary for infection may be low."

Of course, once those resources are exhausted, all bets are off. Stay tuned indeed.


  1. Bridges CB, Kuehnert J, Hall CB. Transmission of Influenza: Implications for control in health care settings. Clin Infect Dis 2003; 37:1,094-1,101.