Is Airborne Spread of Influenza Possible?

indigo girl · Sep 1, 2009

IOM hears diverse findings on PPE for flu

http://www.cidrap.umn.edu/cidrap/content/influenza/swineflu/news/aug1209iom-jw.html

A task force of the Institute of Medicine (IOM), charged with making recommendations about how to protect healthcare workers against novel H1N1 influenza, today heard a variety of evidence that respirators and masks can shield healthcare workers (HCWs) and others from getting respiratory illnesses.
The IOM panel learned, for example, that N95 respirators—whether fit-tested or not—reduced respiratory illnesses in a recent multiple-hospital study in China, whereas surgical masks were not effective. But other studies, focusing on household transmission of flu, suggested that both surgical masks and N95-type respirators are valuable.
Still another study, involving students at the University of Michigan, suggested that the combination of surgical masks and hand sanitizers may reduce the risk of respiratory illness, but the results didn't achieve statistical significance.
The committee also heard about the problems that some HCWs have with face protection—including a concern among pregnant HCWs in Singapore that wearing an N95 may cause fetal hypoxia.
Evidence on the clinical effectiveness of personal protective equipment (PPE) has been notoriously fuzzy. In the face of the murky science, the IOM has been asked to provide a recommendation to the Centers for Disease Control and Prevention (CDC) and the Occupational Safety and Health Administration (OSHA) by Sep 1.
The CDC currently recommends that HCWs who enter the room of a patient in isolation for suspected or confirmed novel H1N1 flu should wear an N95 respirator or equivalent protection.
Today's day-long workshop, which was streamed over the Web, was dedicated to examining what's known about H1N1 flu and about the effectiveness of masks, gowns, gloves, respirators, and eye protection in preventing H1N1 and seasonal flu transmission.
Hospital study in China
In an afternoon session on preventing flu transmission with PPE, Raina MacIntyre of the University of New South Wales presented a few findings from an as-yet-unpublished study of respiratory protection in hospital workers in Beijing.

The study compared the effectiveness of surgical masks, fit-tested N95 respirators, and non-fit-fit-tested N95s in protecting HCWs from respiratory illnesses. The trial involved 1,936 workers in 24 hospitals, including physicians and nurses, who wore the equipment for 4 weeks last winter. The Chinese location was chosen because the team wanted a site where workers are used to wearing protection, making for high compliance, MacIntyre said.
The researchers looked at several outcome measures, ranging from clinical respiratory illness and influenza-like illness (ILI) to lab-confirmed flu.
She said the detailed results of the trial are being saved for a meeting in September and journal publication, but she revealed a few findings: An intention-to-treat analysis showed that the surgical masks had no efficacy against any outcomes, whereas the N95s provided 75% protection against lab-confirmed flu. She also said the N95s were 42% more effective than the surgical masks overall.
MacIntyre also reported that the fit testing did not improve the effectiveness of the N95s, as there was no difference between the results for the fit-tested and non-fit-tested groups.
Household transmission studies
MacIntyre also reviewed the findings of a recent study that compared the use of surgical masks and P2 respirators (the equivalent of N95s) in households where a child was diagnosed with a respiratory illness. The randomized controlled trial was reported in Emerging Infectious Diseases in February.
The Australian researchers recruited 145 families, who were assigned to wear surgical masks, P2s, or no respiratory protection. The outcome measures were ILI and confirmed respiratory virus infections.
The scientists found no difference in illness rates between the P2 and surgical mask groups overall. However, mask use in the intervention groups was fairly low, and when the team looked only at the families that actually used the respiratory protection, they found a four-fold reduction in clinical illness for both groups, MacIntyre reported. No clear difference between the P2 and surgical mask groups was found.
A somewhat similar study, recently published in the Annals of Internal Medicine, was reviewed by Ben Cowling of the University of Hong Kong. He and his team used rapid flu tests to recruit patients from outpatient clinics and then studied the effects of interventions in their households.
The researchers recruited about 250 households and divided them into three groups: basic health education only, hand hygiene with soap and an alcohol hand rub, and hand hygiene plus surgical face masks.
The study produced some evidence that the interventions made a difference in flu transmission, but it varied depending how soon the interventions were initiated, Cowling reported.
Overall, 10% of contacts in the control group households contracted confirmed flu, versus 5% of contacts in the hand hygiene group and 7% in the hand hygiene plus face masks group. In a subanalysis focusing on households where interventions were started within 36 hours of the index patient's illness onset, the respective proportions were 12%, 5%, and 4%.
Cowling concluded, as stated in a slide, that the study showed "substantial and significant benefits of face masks and hand hygiene if implemented within 36 hours of index case symptom onset." He said it wasn't possible to distinguish which of the two interventions was more effective.
Pregnant women and N95s
The panel also heard Paul Ananth Tambyah of Singapore National University hospital review the SARS (severe acute respiratory syndrome) experience at his hospital, where full PPE, including N95s and gowns, was found to provide good protection.
In a question period, Tambyah revealed that pregnant HCWs in Singapore do not wear N95s. They are exempted from the requirement because gynecologists believe there will be fewer incidents of fetal hypoxia if pregnant workers don't use the devices, he said. Pregnant women appear to be at increased risk for complications from novel H1N1 flu.
"I think the general consensus with university obstetricians is to use surgical masks rather than N95s" in pregnant women, except when they are involved in intubation or other aerosol-generating procedures, Tambyah said.
Dr. Howard J. Cohen, a member of the IOM panel, commented later that, assuming the concern about fetal hypoxia is valid, "It seems the solution is to put them in a PAPR [powered air purifying respirator], where they have plenty of room to ventilate."

oramar · Sep 1, 2009

I am stunned, I thought air born transmission was a given. I didn't know it was in any doubt and that anyone was still trying to prove the effectiveness N95.

indigo girl · Sep 1, 2009

I am stunned, I thought air born transmission was a given.

Nay, nay, there is much controversy over this point, and not nearly enough research. The CDC site, I think was still saying N95 last time I checked. This is what the IOM meeting was all about a few weeks ago. They are going to be recommending updating the guidance based on the testimony of what was heard in those meetings.

This directly impacts how we as caregivers are protected in our facilities because most hospitals are following the droplet precaution protection which means only surgical masks unless there is a procedure such as bronchoscopy or neb tx in use. This is based on the clinical "expertise" of the ID people, not on actual research.

More studies are coming out, but there is little definitive data that tells us for sure how flu is transmitted. We really don't know how.

I suspect that it is in a variety of ways such as fomites, droplets as well as aerosolized. The study done in Chinese hospitals proved to me at least, that the N95 was the way to go. While surgical masks are useful in home care by families, I would rather be wearing the N95 in a hospital setting especially if patients are actively coughing.

One of the float techs that I know, was assigned to provide one to one observation with a patient in isolation recently. He spent 12 hours at the bedside with this patient in a closed room. He wore his surgical mask, and washed his hands, religiously, and he came down with a nasty case of swine flu a few days afterwards. Needless to say, he was very upset. Did he get it at work? Who knows? It is where he spends most of his time.