Multi-generation measles outbreak with exposures to the general public, Pennsylvania, 2011

Background. Due to ongoing importation and under-immunization, the largest number of reported measles cases in the United States since 1996 occurred in 2011. Each identified case requires significant public health agency efforts to reduce subsequent transmission potential. This was illustrated during a 2011 Pennsylvania cluster. Purpose. To describe a measles outbreak with public venue exposures in Pennsylvania. Methods. Investigators identified locations where infectious measles cases were present and evaluated measles immunity of all identified contacts. Susceptible contacts were offered post-exposure prophylaxis (PEP) or serology and/or were quarantined. Analysis was conducted using SAS 9.2. Results. Four (1 index, 3 secondary) confirmed measles cases occurred. The exposure source for the index case (an unvaccinated two year old) was not identified, but he traveled through two international airports during the likely exposure period. Sixteen subsequent exposure points included three households, three healthcare facilities, a summer camp, a church, four retail stores, three restaurants and a Women, Infants and Children (WIC) center. Two press releases notified the public of possible exposures; one health alert encouraged provider febrile rash illness reporting. Of 403 identified contacts, only 70% were considered immune. Forty-three non-immune contacts received PEP (11 MMR vaccine, 32 immunoglobulin), and 52 were quarantined (45 of whom were exposed at WIC). The secondary cases were siblings and a playmate of the index case. No cases were identified following public venue exposures. Conclusions. This investigation demonstrates even small measles outbreaks require extensive investigations. A large proportion of contacts were non-immune, emphasizing the need for prompt identification and follow-up of exposed contacts.