Influenza-related muscle pain cases no cause for alarm

A rise of influenza B in the community may be to blame for a cluster of cases in Melbourne of flu-related myositis (muscle inflammation and pain), an expert says.

Calf muscle cramps are a well-recognised complication of the B strain of flu, said Professor Robert Booy, head of clinical research at the National Centre for Immunisation Research and Surveillance, Sydney.

A school in the bayside suburb of Sandringham has reported 8 cases of children with the flu experiencing myositis, prompting a public advisory in a bid to allay parental concerns that their children were temporarily unable to walk.

"I’m not surprised ... influenza B normally comes late in the winter," Professor Booy said.

"Myositis ... is transient, and you generally get good recovery within a week or 2 – the problem is that pain in the calves prevents walking, but, as best we know, you recover well."

Latest National Communicable Diseases Surveillance data shows pandemic A (H1N1) influenza (swine flu) has accounted for most influenza transmission this year, with influenza B also circulating (Australian influenza report, 6-19 Aug 2011).

Professor Booy said he expected cases of influenza to tail off within the next few weeks, along with the arrival of warmer weather.

"Some people [with myositis] have an associated [infection-like] syndrome ... but it almost always occurs on its own without any serious complication," he said.

References

1. Australian Government Department of Health and Ageing. Communicable diseases surveillance. Australian influenza report 2011 - current report: 6-19 August 2011. http://www.health.gov.au/internet/main/publishing.nsf/Content/cda-surveil-ozflu-flucurr.htm (accessed Sep 2011).
Medical Observer