Thursday, October 22, 2009

Preventing Influenza Transmission: Is Surgical Mask Comparable To N95 Respirator?

In a new original article reported in JAMA this week (1st October 2009), a randomized trial was conducted to compare the effectiveness of surgical masks and N95 respirators to confer protection against influenza for healthcare workers. This article can be downloaded free here.

As many have known, transmission of influenza can occur by coughing or sneezing through the inhalation route of the infectious particles of variable size, possibly ranging from approximately 0.1 to 100 µm. Nevertheless, the exact nature of transmission of influenza that occurs in nonexperimental settings is not well understood yet.

However, although this is an important issue, especially in the wake of the A(H1N1) pandemic, there has been few comparative studies done on the different types of respiratory devices.

Examples of earlier studies on the effectiveness of respiratory devices:

1. Hand hygiene and face mask has been shown to be important to prevent household transmission in this study done in Hong Kong.
(Cowling BJ, Chan KH, Fang VJ; et al. Facemasks and hand hygiene to prevent influenza transmission in households: a randomized trial [published online August 3, 2009]. Ann Intern Med)

2. The use of masks and goggles was associated with a significant reduction of RSV illnesses in pediatric health care workers, according to this study.
(Agah R, Cherry JD, Garakian AJ, Chapin M. Respiratory syncytial virus (RSV) infection rate in personnel caring for children with RSV infections: routine isolation procedure vs routine procedure supplemented by use of masks and goggles. Am J Dis Child. 1987;141(6):695-697)

But in general, however, how best to protect healthcare workers against influenza remains unresolved.

In this new article, the randomized trial involving eight Ontario, Canada, tertiary care hospitals was conducted during the 2008–2009 winter influenza season.

Participants were 446 nurses who provided care to patients with febrile respiratory illness while working in emergency departments or inpatient medical or pediatric units.

Follow-up (including twice-weekly assessment for signs and symptoms of influenza, and laboratory testing of nasal specimens from participants with influenza-like illness) lasted from January 12 through April 23, 2009.

Influenza infection occurred in 50 nurses (23.6%) in the surgical mask group and in 48 (22.9%) in the N95 respirator group (absolute risk difference, –0.73%; 95% CI, –8.8% to 7.3%; P = .86)

In other words, surgical masks and N95 respirators provided healthcare workers with comparable protection against influenza.

In addition, no significant between-group differences were noted in the incidence of influenza-like illness or infections with respiratory syncytial virus, metapneumovirus, parainfluenza viruses, rhinovirus-enterovirus, or coronaviruses.

However, surgical mask should be properly worn. Download this guideline on wearing surgical mask.

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