The University of Hong Kong is retesting one of its earlier studies on the effectiveness of surgical masks that found they can reduce the spread of viruses by more than 70 per cent. The original study involved HKU, the University of Maryland and Harvard School of Public Health, and was conducted in 2009 in the United States. HKU's School of Public Health is now working to reproduce and extend the study's findings in Hong Kong. "We expect similar findings, but we're interested to see if factors in Hong Kong, such as high humidity and temperature, might play a special role," said Dr Ben Cowling, the principal investigator of the study. We expect similar findings, but we're interested to see if factors in Hong Kong, such as high humidity and temperature, might play a special role Dr Ben Cowling, University of Hong Kong The earlier study found that normal surgical masks, available in pharmacies, were effective in "source control" when people who have the flu wear them, despite earlier debate among health professionals about how useful they were. It used seasonal flu viruses for the testing, but Cowling says the study's findings apply to other flu viruses as well. Local researchers will use a special machine to measure and analyse the amount of exhaled virus in subjects with influenza virus infections, both with and without surgical masks. Cowling does not think the bird flu virus discovered in Shanghai has a high chance of spreading to Hong Kong, but he advises anyone with flu symptoms to wear surgical masks to protect those around them. "I think people in Hong Kong are already very concerned about the idea of spreading infections to others," he said. "What can be improved is that employers should encourage employees to take sick leave when they have the flu. There's still an attitude that adults who are sick should go to work anyway," he said. The preliminary findings from HKU's School of Public Health will be available this summer. The school will continue to research patterns of how much virus people exhale in the early and later stages of illness.