(AP) -- A mumps outbreak among Orthodox Jews in New York and New Jersey has now surpassed 1,500 cases and shows no sign of ending soon, health officials said Thursday.
The 7-month-old outbreak began last summer at a boys camp in the Catskills. The campers were from Orthodox Jewish families, and cases multiplied when they returned to their close-knit communities in and around New York City.
Most had a mumps vaccination, but the shots don't prevent all cases, according to the Centers for Disease Control and Prevention. The mumps vaccine is 79 to 95 percent effective if two doses are given, so illnesses will still occur in vaccinated people when the virus spreads, health officials said.
With 1,521 cases, the mumps outbreak is the largest in the U.S. since 2006, when nearly 6,600 cases were reported, mostly in six Midwestern states. Usually fewer than 300 cases are reported annually.
Mumps is spread by coughing and sneezing. Common symptoms are fever, headache and swollen glands. Most cases are in children and teens. It is a mild disease but sometimes can lead to complications such as hearing loss, meningitis and swollen testicles that - in rare cases - can lead to sterility.
In the new outbreak, the first identified case was an 11-year-old boy who got sick in late June. He had just returned from the United Kingdom - where vaccination rates are lower and mumps is more common - before going to the camp in Sullivan County in upstate New York. About 25 campers got sick.
Since then, hundreds of cases have been diagnosed in Orthodox Jewish enclaves in the New York City borough of Brooklyn, in nearby Orange and Rockland counties and in four counties in New Jersey.
Orthodox Jews account for more than 97 percent of the cases, which most likely has to do with the insular nature of their community, said Dr. Guthrie Birkhead of the New York State Department of Health.
Many Orthodox Jewish families are large, and the virus spreads well in packed households, said Kathleen Gallagher, a CDC epidemiologist. She said seating arrangements in religious schools may also be contributing, with students facing each other across tables instead of in rows of desks facing forward.
Since 1989, health officials have recommended that children get two doses of a combination vaccine against measles, mumps and rubella. Birkhead said vaccination rates for Orthodox Jewish kids are about the same as those for other New York schoolchildren.
Among 1,100 from the new outbreak, the CDC said 88 percent had gotten at least one vaccine dose, 75 percent had two doses. Health officials last month began offering a third dose in some schools where the outbreak has persisted. So far, cases are continuing.
"We're not out of the woods yet," said Birkhead.
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More information: CDC report: http://www.cdc.gov/mmwr