Effect of measles, mumps, rubella vaccination on pattern of encephalitis in children.

462 patients (269 males, 193 females, aged from 1 month to 16 years) with encephalitis were treated at the Children's Hospital, University of Helsinki, over a 20-year period. The incidence of encephalitis was 8.3/100,000 child-years (range 19.8 in 1974 to 2.5 in 1985 and 1986). The organisms most commonly associated with encephalitis in children were mumps, measles, and varicella viruses, and Mycoplasma pneumoniae. After the start of the nationwide measles, parotitis, and rubella (MPR) vaccination programme in 1982 in Finland, encephalitides associated with these viruses seem to have totally vanished. Currently the pathogens most often associated with childhood encephalitides are varicella-zoster, M pneumoniae, and enteroviruses. 3% of the 462 patients died from their illness, and 7% became severely damaged, with the poorest outcome occurring after multiple infections, and herpes simplex virus, cytomegalovirus or M pneumoniae infections. The decline in the total number of cases of encephalitis was not accompanied by a decrease in number of patients with a poor outcome. Patients with treatable encephalitides due, for example, to M pneumoniae and herpes viruses, need prompt attention.