CDC: Airborne risk behind N95s for H1N1

Pandemic causing more severe disease in the young

The Centers for Disease Control continues to reassess its infection control guidelines for pandemic influenza A H1N1, but has held to a controversial N95 respirator recommendation due to the possibility of airborne spread that would make standard surgical masks ineffective, said Michael Bell, MD, associate director for Infection Control in the CDC Division of Healthcare Quality Promotion.

"Much of what we are talking about right now is with the understanding that this is an evolving situation," Bell said recently in Fort Lauderdale, FL, at the annual conference of the Association for Professionals in Infection Control and Epidemiology. A line of research conducted by the NIOSH suggests influenza virus in respirable size could become airborne. "If you were really close enough, it is conceivable to actually inhale virus," he told APIC attendees. "We don't think we can say that [airborne transmission] does not exist."

That potential threat combined with the lack of vaccine and uncertainty about any existing herd immunity to the novel virus, has led the CDC to hold to the N95 recommendations for health care workers even as some hospitals dropped them in favor of standard surgical masks used for seasonal flu. Part of the rationale for that decision has been that H1N1 infections have been predominantly mild, even though the virus has been accorded pandemic status.

"We can't put everyone in moon suits," Bell noted, but added that the CDC decided to take a "conservative" approach as the virus continues to emerge. CDC meetings with expert consultants and stakeholders are continuing and the recommendation may be subject to change, he said. As this issue went to press, the CDC still was recommending that health care workers wear N95 respirators for care of patients under H1N1 isolation precautions. In addition, personnel providing care to or collecting clinical specimens from suspected or confirmed cases should wear disposable nonsterile gloves, gowns, and eye protection such as goggles to prevent conjunctival exposure, the CDC recommends.

Tom FriedenThough a pandemic now has officially been declared, it does not mean the virus is becoming more virulent, emphasized, Tom Frieden, MD, MPH, the new CDC director.

"This is not a surprise," he said at a recent CDC press conference. "It was expected based on the data. [The] WHO waited until they were certain that they had documentation that on multiple continents it was person-to-person sustained transmission, and this basically meets our definition of a pandemic. It's a strain of the flu virus to which most of us don't have immunity, which is spreading from person to person in many parts of the world. This does not mean that there is any difference in the level of severity of the flu. This is not at this point a flu that's anywhere near as severe as the 1918 pandemic, for example."

Frieden balanced his call for calm with a warning against complacency, saying, "The virus is here; it's in all likelihood here to stay, and it's important that we continue our aggressive efforts to prepare and respond. Our key goals are to determine where the virus is spreading and to reduce its impact, particularly on those who are most vulnerable — people with underlying health conditions and infants."

Indeed, it is primarily the young that are being hit hard by the virus, with most of the hospitalizations in children under 5. "This virus can cause very mild self-limited disease that gets better without treatment, but it is also able to cause very severe illness for an individual, hospitalization, intensive care unit, or even death," said Anne Schuchat, MD, director of the CDC National Center for Immunization and Respiratory Disease (NCIRD). "We continue to see a disproportionate amount of illness in hospitalizations [in] younger people compared with the elderly."

In the United States, 57% of the cases have been in people 5 to 24 years of age, and 41% of the hospitalizations are in that same age group, she added at the CDC press conference.

"So, it looks like this is a virus that's disproportionately affecting younger people but there are still lots of infections and hospitalizations in older persons," Schuchat said. "According to the U.S. statistics, 71% of the hospitalized patients have occurred in people who have an underlying condition — respiratory illness like asthma or chronic obstructive pulmonary disease, immune deficiencies, and so forth. As we have noted, there's been a disproportionate amount of pregnant women among those who have had infection."

According to published reports, the Swiss pharmaceutical company Novartis has produced the first H1N1 candidate vaccine.

"We can expect to see continued efforts to develop a vaccine and we hope and anticipate that that may be in place by the fall," Frieden said. "Again, a decision of whether or not to use the vaccine is a separate decision from whether or not to make the vaccine. But obviously, we need to make it in order to make the decision of whether or not to recommend it and use it. We're faced with a situation of uncertainty."