NONCLASSIC MEASLES INFECTIONS IN AN IMMUNE POPULATION EXPOSED TO MEASLES DURING A COLLEGE BUS TRIP

This study investigated the frequency of mild or asymptomatic measles infections among 44 persons exposed to a student with measles during a 3-day bus trip using two buses. Questionnaires and serum samples were obtained 26-37 days after the trip. All participants had detectable m easles-neutralizing antibodies, and none developed classic measles sym ptoms. Ten persons (23%) were IgM positive for measles, indicating rec ent infection. Among previously vaccinated IgM-negative persons, those who rode on bus A with the index case-patient had significantly highe r microneutralization titers than those on bus B (P = .001), suggestin g that some persons on bus A were infected but were IgM negative at th e time of the study. Mild or asymptomatic measles infections are proba bly very common among measles-immune persons exposed to measles cases and may be the most common manifestation of measles during outbreaks i n highly immune populations. (C) 1998 Wiley-Liss, Inc.(dagger)