Emma Hitt, PhD

March 15, 2012

March 15, 2012 (Atlanta, Georgia) — Two studies, one conducted in Germany and the other in Thailand, have found conflicting results on the benefits of facemasks and handwashing in preventing the spread of flu.

Both studies were presented here at the International Conference on Emerging Infectious Diseases 2012.

In the German study, led by Udo Buchholz, MD, MPH, epidemiologist at the Robert Koch Institute in Berlin, researchers found that household transmission of influenza could be reduced with nonpharmacologic interventions, such as facemasks and intensified hand hygiene, "when applied early and used diligently."

During the 2009/10 and 2010/11 pandemic seasons, Dr. Buchholz and colleagues compared 84 households in which 1 member had influenza.

The households were randomized into 3 groups: facemask use and intensified hand hygiene; facemask use only; and no intervention (control group).

Among the 218 noninfected contacts in the 84 households, 35 (16%) developed flu. An intention-to-treat analysis found no benefit from facemasks and handwashing, nor from facemasks alone.

However, when the intervention was started within 36 hours of symptom onset in the index case, pooled data from the 2 intervention groups showed an 84% reduction in secondary flu infection. In addition, when facemask alone was considered in a per protocol analysis, there was a 70% reduction in risk.

"If effective, these measures would complement other measures, such as vaccines, which may arrive late and need to be given by medical practitioners, and antivirals, which can be expensive, have side effects, and can lead to the potential development of resistance," Dr. Buchholz told Medscape Medical News.

"Using these measures diligently and very early after the occurrence of the household index case may reduce the risk for influenza infections in households," he said. "Cumulative evidence is not conclusive yet, however."

In the study conducted in Thailand, researchers from the US Centers for Disease Control and Prevention (CDC) who were onsite in Thailand found that facemasks and handwashing were ineffective in preventing transmission — potentially because of overcrowding, the researchers speculate.

Data from 788 households were collected from April 2008 to February 2011. The median age of the household member with flu was 5 years, and 724 (92%) slept in the same room with their parents.

Among the household contacts, 31% became infected. Handwashing was found to have no significant benefit, and facemask use was associated with a modest increase in risk for influenza infection.

Lead author Jens Levy, an epidemiologist at the CDC, noted that several handwashing studies in other populations have found handwashing or hand sanitizer and facemask use to be effective in preventing the transmission of the influenza viruses.

"Although our study did not demonstrate this effect, crowding and shared beds in the Thai setting may have overwhelmed any protective effect from the interventions," he told Medscape Medical News.

He added that the onset of the 2009 pandemic and the general public-health messages reminding people to improve hand hygiene soon after the study began could have reduced the effectiveness of the handwashing education intervention in their study. "Also, adherence to facemask use was low," Levy said.

Independent commentator Ben Cowling, PhD, an epidemiologist from the University of Hong Kong School of Public Health, noted that "these studies are very useful. The German study is consistent with another study from Hong Kong, which also found that these interventions can be effective if implemented early enough, while the Thai study cautions that they may not be sufficient in settings with high levels of exposure."

"The German study supports the use of simple interventions to reduce risk of transmission to family members. However, the Thai study cautions that in some settings there may be overwhelming levels of exposure, which cannot be prevented by these simple interventions."

"During a pandemic, ill people are often advised to stay at home so that transmission might be reduced in the community. However, this can put family members at increased risk of infection," he told Medscape Medical News.

The studies were not commercially funded. The researchers and commentator have disclosed no relevant financial relationships.

International Conference on Emerging Infectious Diseases (ICEID) 2012: Abstract O2 and Board 282. Presented March 14, 2012.

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