"The science has not given us a clear answer, so this is just another piece of the puzzle, another contribution to the body of knowledge," said Artealia Gilliard, adding there is currently a lot of conflicting studies.

"Right now we are not recommending that people who live in a household with someone that is infected with H1N1 wear a face mask within the house," she said.

Hand hygiene and face masks are commonly cited as key actions to prevent the flu, but the article says few studies have been done to show whether they are truly effective in preventing transmission.

Participants in the study were divided three groups: a control group, a group that practised an increased level of hand hygiene and one that combined that measure with wearing a face mask.

Participants were provided with liquid hand soap and told to wash after every washroom visit and when their hands were generally dirty or after sneezing or coughing. They used the hand sanitizer when first entering the home and after touching any potentially contaminated surfaces. Those given masks were told to wear them all the time except when eating or sleeping.

In 154 households out of a total of 259 that participated, transmission from one family member to another was reduced when face masks and hand hygiene were both used within 36 hours.

The study could not distinguish precisely the benefits of the two measures individually -- only the advantages when combined. Home visits were conducted by nurses every three days and some infections may have been missed if the peak of the illness happened in between visits.

Gilliard said another important caveat of the study was that in order for the face masks to be considered effective, they had to be worn properly and at all times.

"The other finding in the study was that most of the time, that doesn't happen," she said.

Throughout the current swine flu pandemic, Canadian public health officials have been hammering the importance of proper hand washing as a protective measure.

Like the CDC, the Public Health Agency of Canada doesn't recommend the general public wear masks. It says evidence shows they are not effective in preventing transmission in community settings and people often use them incorrectly -- and can end up contaminating themselves when putting them on or removing them.

The exception to that advice, though, is when a person is directly caring for someone in their home who has the virus. Similarly, doctors or other health-care workers may wear masks to reduce the risk of infection.