Frequent handwashing and the wearing of face masks at home can help reduce the transmission of influenza viruses within the household if the measures are implemented in good time, a study in Hong Kong has found.

The findings, published in the Annals of Internal Medicine, are seen as important as patients may need to be quarantined at home in a pandemic if hospitals run short of isolation facilities.

"During a pandemic, resources may not be available to isolate all infected individuals, and home isolation of some patients may be required," the researchers wrote.

"Our results suggest that hand hygiene and facemasks can reduce influenza virus transmission if implemented early after symptom onset in an index patient."

Led by public health expert Ben Cowling at the University of Hong Kong, the researchers recruited patients who tested positive for either influenza A or B.

Along with other household members, they were then randomly assigned to one of three groups - one with some health education, a second that undertook to wash hands frequently and a third undertook to wash hands and wear surgical facemasks.

Of the 259 households completing the study, 60 household members were found infected in the seven days after the measures were introduced. But there were fewer transmissions in households where the two measures were implemented in timely fashion.

"Hand hygiene and facemasks seemed to prevent household transmission of influenza virus when implemented within 36 hours of index patient symptom onset," the researchers wrote.

"These findings suggest that non-pharmaceutical interventions are important for mitigation of pandemic and interpandemic influenza."