Stockpiles of special masks for hospital staff to wear while treating bird flu patients are likely to be inadequate and quickly run out in a pandemic, an Australian study suggests.

Insufficient stocks of protective wear will lead to more people becoming infected, depleting stockpiles of antiviral drugs sooner, it concludes.

The study, to be presented at the http://www.racp.edu.au/asid/ - Australasian Society for Infectious Diseases annual scientific meeting in Hobart this week, shows millions more of the high-filtration masks are needed, and an adequate supply will help reserve drugs for the ill.

"Until now all the fuss has been about drugs but the crucial thing is if there's an epidemic, masks will protect the drug stockpile," says society president and senior investigator Professor Lindsay Grayson.

"The study shows if we run out of masks, a lot more people are going to need drugs," adds Grayson, who is the director of infectious diseases at http://www.austin.org.au/ - Austin Health .

Guidelines recommend high-filtration masks for healthcare workers in close contact with infected patients.

The federal government's national stockpile has at least two million of the masks, plus at least 40 million standard surgical masks for the projected 1-7.5 million people who will attend GPs, clinics and outpatients.

The government projects a maximum 148,000 infected people may be hospitalised.

The study, a collaboration between nine hospitals around Australia, is the first to estimate initial amounts of protective wear and drugs needed per patient by monitoring actors pretending to have avian influenza.

In the initial six hours in hospital, around 20 sets of masks, gowns, gloves and goggles were needed for each 'infected' patient.

This was because each infected patient or their specimens had on average 20 close contacts with on average 12 staff and visitors.

Only 59% of staff always wore protection during contacts, meaning 41% may have required antiviral medication to protect themselves from catching bird flu.

"In an outbreak, it's important that higher rates of compliance than we found in the study are encouraged in healthcare workers," says lead investigator, Dr Ashwin Swaminathan of the Victorian Infectious Diseases Service.

Unlike drugs, masks can be used for other purposes and don't go out of date, researchers say.