Laboratory diagnosis of acute measles infections in hospitalized children in Zambia.

Laboratory diagnosis of measles infection is rarely performed in developing countries and tends to depend on clinical symptoms alone. We evaluated detection of immunoglobulin M (IgM) antibodies for confirmation of acute measles infection in Zambia. In 149 hospitalized children with clinical diagnosis of measles, IgM antibodies were detected in 88.6% (132/149). The IgM-positive rate increased with time after onset of skin rash and all samples were positive after 4 days. In addition to IgM antibody test, virus isolations from throat swabs using B95a cells were also performed. These were positive in only 20.9% (14/67), and both IgM and virus isolation in combination increased the positive rate to 92.5% (62/67). Vaccinated children had higher neutralizing (Nt) antibody responses and, among IgM-negative patients, all 4 vaccinated children had high Nt antibodies while all 10 unvaccinated children had negative or low Nt results. The IgM antibody test was proved to be a sensitive method for laboratory confirmation of measles virus infection in developing countries.