A mumps outbreak in New York and New Jersey has tripled the expected annual incidence of the disease, according to a report from the CDC.
More than 1,500 cases of mumps were reported from several counties in New York and New Jersey from June 28, 2009 through Jan. 29, 2010. All but 44 cases involved members of the Orthodox Jewish community. Almost half of the cases came from New York City, primarily Brooklyn.
"Anecdotal reports from certain affected areas suggest that the rate of new cases is not decreasing," investigators from the CDC and state and local health departments wrote in the Feb. 12 issue of Morbidity and Mortality Weekly Report. "The appearance of a downward trend in recent weeks is partly a result of reporting delays."
Since 1967, when the MMR (measles-mumps-rubella) vaccine was introduced, the number of reported cases of mumps has declined from 186,000 annually to fewer than 500 cases. Even so, the mumps component of the vaccine is less effective compared with the other components, the authors wrote. Estimates of the mumps vaccine's effectiveness have ranged from 73% to 91% after one dose and from 79% to 95% after two doses.
Investigators traced the index case of the outbreak to an 11-year-old boy who returned June 17, 2009 from a trip to England, where 7,400 laboratory-confirmed cases of mumps were reported in 2009. Upon returning to the U.S., the boy attended a New York summer camp for tradition-observant Jewish boys, where he became symptomatic on June 28.
Subsequently, additional cases of mumps were reported among other camp attendees and staff members. Transmission occurred at multiple locations when the attendees returned home.
By the end of January 2010, 1,521 cases of mumps had been reported, all from counties in New York and New Jersey. Investigators reported that 44% of the cases involved residents of Brooklyn. Additionally, 97% of the cases involved members of the same Orthodox Jewish community.
Among patients with known age, the median is 15, and 76% of cases with known sex are male.
Complications have been reported in 65 cases and include 55 case of orchitis, five cases of pancreatitis, two cases of aseptic meningitis, and one case each of transient deafness, Bell's palsy, and oophoritis. Although 19 patients have been hospitalized, no deaths have been reported.
Of 1,115 patients with known vaccination status, 88% had received at least one dose of mumps-containing vaccine before the outbreak, and 75% had received two doses.
"This outbreak emphasizes that mumps outbreaks can occur in highly vaccinated populations," the authors wrote.
Even so, "maintenance of high two-dose MMR vaccine coverage remains the most effective way to prevent and limit the size of mumps outbreaks," they added.
Public health officials in one of the New York counties involved in the outbreak began offering a third dose of mumps vaccine to students at certain schools, although no data exist in support of the effectiveness of a third dose for reducing the risk of mumps or altering the course of an outbreak, the authors said.
Morbidity and Mortality Weekly ReportSource Reference: Centers for Disease Control and Prevention "Update: Mumps outbreak -- New York and New Jersey, June 2009-January 2010" MMWR 2010; 59: 125-29.