Health authorities now believe 20 percent of NSW's population will contract swine flu this winter, with the strain now responsible for about 60 percent of all flu cases.

In Victoria, the worst-hit of all Australian states and territories, the H1N1 virus is behind an overwhelming 90 percent of flu cases.

The virus, which has been linked to at least 13 deaths in Australia, is now taking hold of influenza rates — with the number of swine cases rapidly increasing in recent months.

"We expect somewhere around 20 percent of the community will experience [swine flu] this year," the NSW Health Department's chief health officer Kerry Chant told ninemsn.

"A couple of months ago, if you were detected with flu and were tested in a laboratory, we would have said you were most likely to have seasonal flu and very unlikely to have swine flu.

"But now, if you have flu, you are in fact most likely to have swine flu."

Densely populated areas, such as schools and enclosed workplaces, could experience infection rates surpassing 40 percent, health experts say.

While businesses are likely to experience an increase in sick leave, flu-related absentee rates are likely to be inflated due to cases of healthy parents or family members staying home to care for ill children or relatives.

People who have taken to wearing face masks in an effort to protect themselves from the illness may also be wasting their time and money.

Research is currently underway to determine what benefits, if any, a mask can offer a virus-free person.

"We only recommend face masks for people with coughing illnesses to protect others around you," Mrs Chant said.

"We aren't supporting them as a preventative measure — that's not our recommended role of the equipment.

"Sometimes you can inadvertently adjust them and introduce a virus to your eyes and nose, so there's a number of possible negative issues involved with wearing a mask."

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