In the United States, since 2001, an average of 265 mumps cases (range: 231–293 cases) have been reported each year,* and in Iowa, an average of five cases have been reported annually since 1996. However, in 2006, by March 28, a total of 219 mumps cases had been reported in Iowa, and an additional 14 persons with clinically compatible symptoms were being investigated in three neighboring states (11 in Illinois, two in Nebraska, and one in Minnesota) in what has become the largest epidemic of mumps in the United States since 1988.
Note that it’s spread into all many of our neighboring states. More below…
Of the 219 cases reported in Iowa, the median patient age was 21 years (range: 3–85 years), with 48% of patients aged 17–25 years; 30% (34 of 114) were known to be college students. Of the 133 patients with investigated vaccine history, 87 (65%) had documentation of receiving 2 doses, 19 (14%) 1 dose, and eight (6%) no doses; vaccine status could not be documented in 19 (14%) patients. Among the 114 patients for whom symptomatic information was available, the most common symptoms were parotitis in 94 (83%) patients, submaxillary/sublingual gland swelling in 46 (40%), fever in 41 (36%), and sore throat in 36 (32%); average duration of illness was 5.1 days. Six (5%) patients reported complications (e.g., orchitis); one suspected case of encephalitis is being investigated. As of March 28, 2006, investigators had determined that only 36 (16%) of the 219 cases were linked epidemiologically (i.e., a source of infection was identified), suggesting frequent unapparent transmission.
The source of the Iowa epidemic is unknown; however, the United Kingdom (UK) experienced a recent mumps epidemic that peaked during 2005 with approximately 56,000 cases and a high attack rate among young adults. The mumps strain in the UK epidemic also was identified as genotype G, and the UK epidemic has been linked to a 2005 mumps outbreak in the United States.
The report of the previous introduction of mumps from the UK can be found here, where a counselor at a summer camp apparently brought the virus back from the UK. It’s not known yet whether something like this actually happened with the current outbreak or not, but a more thorough molecular analysis of the strains collected here in Iowa and during the 2005 UK outbreak could show how closely related they are.