Figure 1. Seriologically confirmed cases of Ross River virus
disase, by month of onset, in the southwest of Western
Australia, July 1995 to February 1996, as reported by doctors to
the Health Department of Western Australia (when possible, case
follow-up questionnaires were administered by environmental
health officers from relevant local authorities). Only a small
number of cases diagnosed by state and private laboratories,
although the patient was not notified, have been included.
Consequently, the number of cases shown is almost certainly an
underestimate of the true number of serologically confirmed
cases. Almost 65% of cases have dates of onset in January 1996.
However, further notifications and analysis of follow-up
questionnaires that have not yet been carried out for many
January/February cases may alter this pattern. Previous
southwest outbreaks also peaked in January or February but were
considerably less acute.