ACT Health said 16 people had gone to the emergency department at Calvary Hospital in the past week, compared with eight at the Canberra Hospital.

The director of respiratory and sleep medication at the Canberra Hospital, Dr Mark Hurwitz, said that while the numbers were similar to this time last year, there were geographical differences.

''In essence, our numbers have slightly increased compared with last year,'' he said. ''But last year there were more at Canberra Hospital than at Calvary.''

Dr Hurwitz said Canberra was fortunate that the traditional flu season didn't coincide with the past week's plummeting temperatures.

''Hopefully background immunity from the flu vaccine will keep it [flu season] down,'' he said.

''We don't want to follow on from the US and the UK, but that's the normal passage of the virus. This past winter in the US, they had a large outbreak, and it came later than it generally does.

''The flu will aggravate asthma, and so does cold, dry air.''

The National Asthma Council Australia said asthma attacks soared in winter and sufferers should be mindful of the risks.

The council's chairwoman, Dr Noela Whitby, said the common cold was the cause of four out of five asthma flare-ups or attacks.

''People with exercise-induced asthma who participate in winter sports are especially susceptible,'' she said.

''During physical activity, people breathe through their mouths, which allows cold dry air to reach the lower airways and lungs without passing through the nose, triggering asthma symptoms.''

Dr Hurwitz said cyclists would benefit from wearing balaclavas on cold days, while others could wrap scarfs around their mouths.

''When you are cycling, the wind chill is greater than if you were walking. Having a balaclava on makes a difference.''