Mumps Outbreak: An Overview
The state of Iowa has been experiencing a large
mumps outbreak that began in December 2005. As of April 12, 2006, 605 suspect, probable, and confirmed cases of mumps have been reported to the Iowa Department of Public Health (IDPH). The majority of these cases are occurring in people 18 to 25 years of age, many of whom were vaccinated.
Additional cases of mumps, possibly linked to the Iowa mumps outbreak, are also under investigation in eight neighboring states, including Illinois, Indiana, Kansas, Michigan, Minnesota, Missouri, Nebraska, and Wisconsin.
The Source of the Mumps Outbreak
The source of the current mumps outbreak in the United States is unknown. However, the mumps strain has been identified as genotype G, the same genotype circulating in the United Kingdom. The mumps outbreak in the United Kingdom that lasted from 2004 to 2005 involved more than 70,000 cases. Most cases in the United Kingdom occurred among unvaccinated young adults. The G genotype is not an unusual or rare genotype, and, like the rest of known genotypes of mumps, it has been circulating globally for decades, if not longer.
History of Mumps Outbreaks in the United States
During the prevaccine era, nearly everyone in the United States experienced mumps, and 90 percent of cases occurred among children who were 15 years of age and younger. During this time, it was estimated that 100,000 to 200,000 cases occurred in the United States each year. Since the
mumps vaccine was licensed in 1967, this number has dropped dramatically. In 2003, fewer than 300 cases of mumps were reported.