mercredi 20 mai 2009

Masks plus handwashing are most effective when their use is started at the first sign of outbreak—before the flu spreads.

From the University of Michigan

What U-M flu studies can tell us about how to deal with swine flu

Plus: Up to date information on U-M flu preparations

Allison Aiello, John G. Searle Professor of Epidemiology in the School of Public Health, led a landmark study in the University of Michigan dorms. The study evaluated the effectiveness of hand-washing and masks in preventing the spread of flu. In this Q and A, plus video, we asked Professor Aiello to explain how best to prepare for swine flu—or any flu outbreak.

Quick Time Video

Michigan Today: Can you describe the flu transmission study you did with UM students?

Allison Aiello: The overall objective of the M-FLU Study was to investigate the feasibility and effectiveness of using non-pharmaceutical interventions, specifically masks and hand hygiene, to prevent the transmission of influenza in residence hall units at the University of Michigan.

The study separated students into two groups. One wore masks and washed hands regularly. The other used masks alone.

We conducted a cluster randomized intervention trial among University of Michigan students living in university residence halls. Students were randomized into one of two intervention groups (face masks with hand hygiene; face masks alone) or a comparison (control) group. Interventions were carried out over two periods of seasonal influenza transmission (2006-2007; 2007-2008) for a six week study period. Students completed electronic surveys, reporting their health behaviors, use of the interventions (if applicable), and occurrence of influenza-like illnesses. In all selected residence halls, when illness symptoms met the criteria for influenza-like illness, specimens were collected for viral isolation.

What conclusions do you draw from the study that would be relevant to the current outbreak of swine flu—or future outbreaks of other strains?

The M-FLU study demonstrated that mask use and hand hygiene (alcohol based hand sanitizer) among university students was associated with a significant reduction in the rate of influenza-like illness of up to 50-65% over the six-week intervention periods.

Our study utilized a unique design by asking participants to begin wearing a mask and use hand sanitizer every day at the very beginning of the influenza season, just after the first case of influenza was identified on campus. This design is in contrast with household study designs that have examined the effect of mask use on secondary transmission where household members may already have been infected by the time mask use was implemented.

The study suggests that masks plus handwashing are most effective when their use is started at the first sign of outbreak—before the flu spreads.

Thus, our study provides evidence that application of masks and hand hygiene interventions prior to outbreak conditions can mitigate transmission of respiratory illness in shared living settings, such as university dorms.

Because there is little or no immunity in the human population against the novel 2009 H1N1 virus and there are currently no available vaccinations, the government has been primarily focusing on non-pharmaceutical mitigation measures to reduce transmission. For this reason, non-pharmaceutical interventions (NPIs) represent our best defense against mitigating 2009 H1N1 transmission in the US.

Do masks really make a difference?

A study conducted in the laboratory setting by van der Sande et al. assessed transmission reduction potential provided by personal respirators, surgical masks and homemade masks. Masks were worn by healthy volunteers and a simulated patient during various activities. All studied masks reduced aerosol exposure, but with a high degree of individual variation. Personal respirators were the most efficient, following by surgical and then homemade masks.

Children were less well protected, regardless of mask type. The researchers concluded that any type of general mask use is likely to decrease viral exposure and infection risk on a population level.

In a laboratory study conducted by Fabian et al., influenza virus nucleic acid was present in fine particle aerosols from influenza patients, in both tidal breathing (14-33%) and coughing (64%).

Preliminary results suggest that face masks limit the generation of influenza virus RNA contained in large droplets. Investigation of the efficacy of face masks to limit the generation of fine droplets virus particles is ongoing.

Our study did not support a significant reduction in influenza-like illness with masks only.

The mask and hand hygiene groups showed the greatest reduction in influenza-like illness, suggesting that a combination of the mitigation measures may work best at reducing transmission.

However, it is unclear whether the protection is related to reduction in aerosol fine particle droplet nuclei or reduction in contact transmission due to less contact of hands with nose and mouth while the masks were being worn by participants.

What would be key events in this or future flu epidemics that you think should trigger new actions or behaviors by ordinary people? At what point, for instance, would you suggest people begin wearing masks when they go out in public?

Sustained human-to-human transmission of disease represents a key feature necessitating behavioral change.

The key to mitigation of an influenza pandemic is adequate surveillance of disease transmission, early implementation of protective measures (i.e., face masks, hand hygiene, school closures, social distancing, quarantine, isolation) in affected communities, and travel restrictions.

Individuals should follow the current recommendations of the CDC, and recognize that peaks of pandemic activity may occur in multiple waves spread over months.

Do you have suggestions for policy makers? What are the most effective public health tools they could deploy now and if the epidemic worsens?

There are many gaps in current pandemic influenza knowledge and effectiveness of mitigation practices. The 2009 H1N1 influenza outbreak may provide a critical window to address many of the gaps in research regarding sociobehavioral response to outbreaks, compliance with NPIs, and effectiveness of NPIs. Support of additional research is essential.

Currently, plans have been developed which describe what needs to occur in the event of pandemic influenza, but they fall short of detailing how to carry out the recommendations. Policy makers must develop consistent laws specifying the authority of public health officials to implement NPI measures across county, state, or national jurisdictions and the responsibility of the federal government in terms of economic compensation for individuals, in the event of compulsory NPI measures which results in lost wages, such as staying home from work.

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