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Measles cases exceed 100 in US outbreak

BMJ 2015; 350 doi: https://doi.org/10.1136/bmj.h622 (Published 03 February 2015) Cite this as: BMJ 2015;350:h622
  1. Michael McCarthy
  1. 1Seattle

Since the beginning of the year, 102 cases of measles have been reported in the United States in what has grown to be a multistate outbreak involving 14 states, officials at the Centers for Disease Control and Prevention (CDC) said on 2 February. Of these cases, 92% have been linked to two Disney amusement parks in southern California, they noted.

Investigators believe that an unknown person who had contracted the disease abroad visited the parks in late December, triggering the outbreak.1 Most of the cases affected people who had not been vaccinated against the disease.

Measles had been declared eliminated from the US in 2000, and from 2001 to 2010 the country saw a median of only 60 reported cases a year. Last year, however, the number of reported cases jumped to 644, the largest number since elimination. Most of those cases, 383, occurred in an Amish community in Ohio that had declined immunization for religious reasons. Viruses responsible for the outbreaks since 2000 have been brought into the country either by foreign visitors or by a susceptible US resident returning home from a trip abroad.

Speaking on the CBS news program Face the Nation on Sunday 1 February, Tom Frieden, CDC director, said that he expected the current outbreak to continue. “What we’ve seen is, as over the last few years, a small but growing number of people have not been vaccinated. That number is building up among young adults in society, and that makes us vulnerable,” he said.

Although the US has an overall vaccination rate of 92% some communities’ vaccinations rates are much lower, particularly in affluent neighborhoods where parents who express concerns about the safety of vaccines often obtain exemptions from school vaccination requirements, citing philosophical grounds. A recent study of vaccination rates among 3 year olds enrolled in a health plan in northern California found five statistically significant clusters of vaccine refusal, where the rate of refusal ranged from 5.5% to 13.5%, compared with a rate of 2.6% outside of these clusters.2

Measles is caused by a single stranded, enveloped RNA virus, a member of the genus Morbillivirus in the Paramyxoviridae family. Humans are the only natural hosts. Infections are characterized by fever, rhinitis, conjunctivitis, cough, and an itchy, maculopapular, blanching rash that begins on the face and spreads down the neck to involve the truck and extremities.

The rash usually appears about 14 days after exposure, but the incubation period ranges from 7 to 21 days. Patients are considered to be contagious from four days before to four days after the rash appears. The virus is highly contagious and will infect 90% of susceptible people who come into contact with a case during that period. Immunization with a two dose regimen of the measles, mumps, and rubella (MMR) vaccine, however, is more than 99% effective.

In the US about 28% of young children with measles are hospitalized, and about 3 in 1000 die from it. Serious complications include pneumonia, neurologic involvement, and hearing loss. Worldwide about 20 million measles cases occur each year, with nearly 150 000 deaths.

During a pre-Super Bowl interview on NBC on 1 February, President Barack Obama encouraged parents to get their children vaccinated. “I understand that there are families that in some cases are concerned about the effect of vaccinations. The science is, you know, pretty indisputable. We’ve looked at this again and again. There is every reason to get vaccinated, but there aren’t reasons to not,” he said.

Notes

Cite this as: BMJ 2015;350:h622

References

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