While children under five are by far the most affected by respiratory syncytial virus (RSV), the over-65s and Indigenous Australians face an increasing health risk from the virus, a study shows.

Hospital stays for older adults have gone up 20-fold in recent years, the research reveals.

Although this likely reflected increased testing for RSV in older adults, this group still face longer hospital stays and higher mortality rates, the researchers say.

In addition, Aboriginal and Torres Strait Islanders are more than three times as likely to be hospitalised with an RSV-associated illness than other Australians, the authors write in the Medical Journal of Australia.