Human sentinels for arbovirus surveillance and regional risk classification in South Australia

To assess the use of human sentinels to monitor arbovirus activity in South Australia and to use age-specific seroprevalence data from the same sentinels to classify regions according to risk from Ross River virus (RRV).

Between 1 January 1992 and 15 August 1992, 4776 serum samples were obtained from Red Cross blood donors in the State. All sera were tested for the presence of total antibody (IgA, IgG and IgM) by indirect enzyme immunoassay. To test for recent infection, positive sera were further tested for IgA and IgM specific antibody to Ross River virus with a view to initiating public health interventions if necessary. The age, sex and postcode of residence of each donor were also recorded for seroepidemiological studies.

Of the 4776 sera, 2952 were tested to the end of May (the end of the arbovirus season in South Australia). There was evidence of RRV infection in 248 sera (8.4%) but none had serological markers consistent with recent infection. The arbovirus season was considered non-epidemic, and no reactive public health interventions were introduced. Analysis of age-specific seroprevalence by post-code in the full bank of 4776 sera indicated that the Riverland is endemic for RRV, the Murray Mallee and Upper South East epidemic for RRV, and the remaining regions of the State at variable risk, depending on their proximity to these regions.

The ongoing use of human sentinels is a new public health surveillance system for this disease. In the first year of operation of this surveillance system, a suboptimal number of sera was collected from some areas, and sera were tested only for RRV. However, the number of sera tested could easily be increased, as could the range of arboviruses covered by the testing.