Genetic analysis of measles viruses isolated in the United States, 1995-1996.

Genetic analysis was conducted on 28 wild type measles viruses isolated from outbreaks or cases in the United States during 1995-1996. These viruses were members of at least 6 distinct genetic groups. However, none of these viruses was related to the group 2 viruses that were associated with the resurgence of measles in the United States between 1989 and 1992 except for a single importation from the Philippines. The sequence data support and extend previous findings showing that transmission of group 2 viruses within the United States was interrupted after 1993. The data also suggest that all measles cases that occurred in the United States in 1995-1996 were the result of importation of virus, even in instances when the source was unknown. Molecular epidemiologic studies can provide a means to measure the success of measles control programs by helping to identify the transmission pathways of the virus.