CDI Vol 28 No 2

In the winter of 2003 Western Australia experienced its largest epidemic of infl uenza for at least fi ve years, with activity peaking in August and September. The season was short resulting in very high numbers of cases during the peak weeks. Activity in country areas followed the peak of Metropolitan activity. Infl uenza A virus was detected in 28.3 per cent of the sentinel samples, and infl uenza B in less than one per cent. Both routine and sentinel detections and the overall estimates of infl uenza-like illnesses (ILI) seen by general practitioners at sentinel practices peaked in August and September 2003. The combination of infl uenza detections and an increase in ILI seemed to be the most accurate predictor of the beginning of winter infl uenza activity. There was a shift in age distribution for infl uenza A compared with 2003. Both the sentinel surveillance and routine samples demonstrated an increase of infl uenza in children and young adults. The majority of infl uenza A isolates were identifi ed as A/Fujian/411/2002like, a variant of the A/Moscow strain included in the vaccine. Despite this mismatch there did not seem to have been any noticeable increase in the risk of infl uenza infection in the vaccinated populations from the sentinel practices, nor was there a relative increase in disease among the highly vaccinated elderly population. A number of other respiratory viruses were identifi ed as causes of infl uenza-like illness in the sentinel samples. Rhinoviruses and human metapneumovirus were the most common, the latter occurring mainly in adults. Commun Dis Intell 2004;28:169–174.