Ontario got hit by SARS so you can assume people there are interested in face masks.
This trial compared the simple surgical masks with the fitted N95. In theory the surgical mask might let a cough or sneeze in through the side, whereas the fitted mask should not. In practice however (always do the trial) there was no difference.
The trial used laboratory confirmed influenza as the outcome. Nurses were randomised to use either the surgical mask or the N95 when caring for patients with acute respiratory symptoms. In both groups about 23% of the nurses caught flu. As the authors say this implies that droplet transmission is not a major route of infection. (It's also a frightening high infection rate once you start to think about a pandemic.)
The trial is called a 'non-inferiority' trial. Don't worry too much about this - it's still a randomised trial with an outcome in two group. The 'non-inferiority' bit affects how the study power is calculated since what you are interested in is the lower confidence interval: we need to be confident that the intervention is no worse (or 'not more than 9% worse') than the control group.
Halfway through the trial H1N1 flu reached Ontario and the health ministry ordered everyone onto the N95. Sometimes politics trumps evidence.
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