Mumps and rubella: a year of enhanced surveillance and laboratory testing

In Victoria (Australia) surveillance for mumps and rubella has historically been passive, with most notified cases clinically diagnosed. In July 2001, the Victorian Department of Human Services implemented an enhanced surveillance system focusing on improved laboratory testing. We tested 85% of notifications and only 9% of all mumps and 27% of rubella notifications were laboratory confirmed. While most notified cases were children who had been clinically diagnosed, we found most laboratory-confirmed cases were in adults. The positive predictive value of the clinical case definition was low: mumps (10%); rubella (22%). These results highlight the value of laboratory confirmation of the diagnosis when mumps and rubella are rare, failure to do so is likely to overestimate disease incidence.