Investigation of measles IgM-seropositive cases of febrile rash illnesses in the absence of documented measles virus transmission, State of São Paulo, Brazil, 2000-2004.
Among the 463 individuals with febrile rash illness who tested positive for measlesIgMantibodies during the period, 297 (64%) were classified as exposed to the vaccine. Among the 166 cases that were not exposed to the vaccine, 109 (66%) were considered false positives based on the absence of seroconversion, among which 21 (13%) had evidence of rubella virusinfection, 49 (30%) parvovirus B19 and 28 (17%) humanherpesvirus-6 infection.
CONCLUSIONS:
Following the interruption of measles virus transmission, thorough investigation of measlesIgM-positive cases is required, especially among cases not exposed to the vaccine. Laboratory testing for etiologies of febrile rash illness aids interpretation of these cases.