TORONTO - Surgical masks appear to protect health-care workers from catching the flu as well as N95 respirators do in most settings, a new and sure-to-be-debated Canadian study has found.
The work, published online Thursday by the Journal of the American Medical Association, is the latest round in a pitched battle that had gripped many in the scientific, infection control and health-care communities.
It's also, it seems, the first published study of a randomized controlled trial - the gold standard of medical science trials - looking at how well the inexpensive paper masks stack up against the more costly moulded dome-like N95s.
"There's been a great deal of discussion. But the discussion has lacked the incredibly important information to really inform the debate. And what this study will do is it begins to lay what I would call an evidence foundation," said Dr. Arjun Srinivasan, a medical epidemiologist with the U.S. Centers for Disease Control's division of health-care quality promotion.
Srinivasan was not involved in the study, but wrote an editorial on it for the journal with Dr. Trish Perl, an infection control expert at Johns Hopkins University in Baltimore, Md.
They praised the study design, though Srinivasan, others and even the paper's lead author categorized this as a first step, not the last word.
"I think the results are valid. But ... a single randomized control trial isn't sufficient to say this is the end of the story," said Dr. Mark Loeb, lead author and an infectious diseases researcher at McMaster University in Hamilton.
Loeb and colleagues randomly assigned 446 nurses from eight hospitals in Ontario to either wear surgical masks or fit-tested N95s last flu season. Fit-tested means the wearer has undergone a process to learn how to form a seal with the respirator around her or his mouth and nose.
The researchers ensured there was a mix of both in the various units involved, to increase the chances the volunteers in each group had similar levels of exposure to influenza.
They also took blood samples at the beginning and the end of the study to look for antibody changes that would signal whether the nurses became infected over the course of the trial.
Only about 30 per cent of nurses in both groups got a flu shot.
Testing showed 23.6 per cent of the nurses who wore surgical masks got infected with flu during the course of the season, compared to 22.9 per cent of the nurses wearing the N95s. The difference is not statistically significant, meaning the masks were no more or less effective at preventing infection than the N95s.
The results are likely to be hotly debated, especially since a study presented last month at the world's largest annual infectious diseases conference came to a different conclusion. Though not yet published in a journal, that work, done in China, found that N95s cut the risk of catching flu on the job by 75 per cent. It showed no protective effect from surgical masks.
Loeb said he hasn't seen the data and cannot explain the differences.
But a concern raised by infectious diseases expert Dr. Donald Low of Toronto's Mount Sinai Hospital might point to a potential explanation.
He noted that all surgical masks are not created equal. Some are high quality but others are very flimsy, he said, noting there is no regulation of the products. On the other hand, N95s and other respirators have to pass quality control testing. Still, Low praised Loeb's study, and said the findings could give people some confidence that surgical masks will offer protection if supplies of N95s dry up in this or a future flu pandemic.
"This is an important study. It's nice to see these results. It does give some confidence, because there always is the possibility that we could be in that predicament," Low said.
In a report issued last month, the U.S. Institute of Medicine recommended N95 use for health-care workers treating or exposed to patients suffering from H1N1 pandemic flu.
That is also the CDC's recommendation, drawn up in the early days of this pandemic. Srinivasan said the CDC is currently revising its guidelines for the protection of health-care personnel and the new guidelines will be released shortly.
Whatever happens, the debate is likely to continue. Beliefs on both side are deeply entrenched, with some saying that N95s should be standard to prevent influenza transmission in health care and others saying that the less expensive and easier-to-work-in surgical masks are sufficiently protective.
Srinivasan and Perl noted, with apparent regret, that the masks vs. N95 respiratory debate detracts attention from measures that are known to lower the risk of catching flu for health-care workers and their patients alike.
Having sick workers stay home. Urging people who are sick with flu-like symptoms not to visit hospitals. Improving hand hygiene among hospital staff. Persuading more health-care workers to get flu shots.
"This type of personal protective equipment, it's the last line of defence," Srinivasan said. "It comes at the end of all of these other measures that we have."
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