A research team from the US Centers for Disease Control and Prevention (CDC) today fleshed out the picture of measles activity in the United States, much of it tied to a large Disney-linked outbreak, which highlights the ongoing threat from imported infections and unvaccinated Americans.
Meanwhile, California health officials say the theme park outbreak is nearly over, while the CDC yesterday posted a travel notice about a dramatic spike in measles cases in Kyrgyzstan, one of 10 countries linked to imported cases in the United States this year.
2015 US measles cases
In the CDC's overview of measles activity so far this year, published today in Morbidity and Mortality Weekly Report (MMWR), it said 159 cases were reported between Jan 4 and Apr 2.
The agency said 111 of those cases (70%) are linked to an outbreak that began in December at Disneyland in California, though a CDC update earlier this week placed the Disney-linked cases at 117. Three other smaller outbreaks have been reported in Illinois, Nevada, and Washington.
The total number of overall outbreak cases is 19 fewer and the theme-park cases are 6 fewer than the CDC's previous measles updates. A spokesman from the CDC's National Center for Immunization and Respiratory Diseases told CIDRAP News today that numbers in the updates are provisional and subject to change as states review data. As states review data, they can reclassify cases, add retrospective cases, or identify rashes that occurred during a different time frame.
He added that the drop in cases reflect infections reclassified from 2015 to 2014, all of them Disney-linked cases.
Among the 159 outbreak cases, 22 people have been hospitalized for their infections, 5 of them with pneumonia. No deaths have been reported.
The vast majority of patients (131) were either unvaccinated or didn't know their vaccination status, the MMWR report said. Of the 68 Americans in the unvaccinated group, 29 cited philosophical or religious objections, 27 couldn't be vaccinated because they were too young or had a medical contraindication, and 12 weren't vaccinated for other reasons.
The researchers pointed out that 60 patients were adults who didn't know their vaccination status, showing the lack of immunization data in registries on adults. The CDC recommends that adults born after 1957 who don't have evidence of measles immunity and who are at high risk for the disease—such as health providers or travelers—receive two doses of the measles mumps, and rubella (MMR) vaccine. Other adults without evidence of measles immunity should get at least one MMR dose.
The team also emphasized that vaccine exemptions increase the risk of getting sick and boost the risk of outbreaks in community settings.
Nearly all cases (153) were import-associated, 10 of them in travelers who contracted measles in other countries. Six patients were unvaccinated US residents, including three babies ages 6 to 11 months old who were eligible to receive the vaccine before departure.
Aside from Kyrgyzstan, the other countries linked to measles importations included Azerbaijan, China, Germany, India, Indonesia, Pakistan, Qatar, Singapore, and the United Arab Emirates.
Signs of waning
Meanwhile, the California Department of Public Health (CDPH) said in its most recent measles update that 134 cases have been reported in the state since December, when the Disney-associated outbreak began.
The CDPH added that the outbreak will be considered over when 42 days have passed from the end of the incubation period for the last of the known B3 genotype measles cases that don't reflect a new importation. As of its Apr 10 update, the CDPH said the date the outbreak will be considered over is tomorrow, Apr 17.
The CDC has said the outbreak was probably sparked by a traveler who was infected overseas, then visited the park. However, the source hasn't been identified.
The B3 genotype is identical to the virus that caused a large outbreak in the Philippines in 2014, but it has recently been identified in 14 other countries and six US states that had cases not linked to the Disney outbreak.
Travel notice on Kyrgyzstan
In yesterday's travel notice, the CDC said Kyrgyzstan is experiencing an ongoing measles outbreak, with more than 7,400 cases reported from May 2014 through February 2015. It said a surge of infections have occurred this year, with many hospitalizations and two deaths in children.
The agency recommended that travelers to the country ensure that they have been vaccinated against measles, especially babies ages 6 to 11 months old and other children.
Apr 17 MMWR report
Apr 13 CDC measles update
Apr 10 CDPH measles update
Apr 15 CDC travel alert