Measles in the U.S., January–April 2019: 704 Cases, the Most Since 1994

By April 26, 2019, CDC had counted 704 measles cases in the United States since the start of the year — the most in a single year since 1994 (963 cases), and since measles was declared eliminated in 2000. Elimination means no continuous spread for 12 months or more in a defined area.

Measles is a highly contagious, acute viral illness with fever and a maculopapular rash. It can lead to pneumonia, encephalitis and death.

At a glance

• 704 cases in 22 states; the busiest week, ending March 23, brought 87.
• 503 (71%) were unvaccinated; 76 (11%) had had at least one dose of MMR (measles, mumps and rubella) vaccine; for 125 (18%) it was unknown.
• 689 (98%) were U.S. residents.
• 66 (9%) were hospitalized and 24 (3%) had pneumonia. No deaths or encephalitis were reported.
• Median age: 5 (half between 1 and 18.5 years).

Reported measles cases by state, January 1–April 26, 2019 (preliminary). CDC / MMWR

Cases by week of rash onset, January 1–April 26, 2019. The last week is partial. CDC / MMWR

Outbreaks

An outbreak is a chain of three or more linked cases, as local and state health departments determine.

• 13 outbreaks accounted for 663 cases (94%), in 12 states — California, Connecticut, Georgia, Illinois, Maryland, Michigan, Missouri, New Jersey, New York, Oregon, Texas and Washington — and New York City. Four spread across state lines.
• Six were in underimmunized, close-knit communities, and they alone accounted for 88% of all cases.
• New York state and New York City had 474 cases (67%), with spread continuing since October 2018.

Imported cases

A case is imported when at least part of the exposure period — 7 to 21 days before the rash — was spent abroad, the rash appeared within 21 days of arriving, and there was no known exposure in the United States.

• 44 cases came directly from other countries; 34 (77%) were in U.S. residents travelling abroad.
• 40 (91%) were unvaccinated or of unknown status — and all 40 were old enough to be vaccinated, including two infants aged 6–11 months.
• 23 imports led to no known further cases.

Of 245 cases (35%) sequenced, the only genotypes were B3 and D8 — the most common worldwide over the previous 12 months.

Why it is happening

The previous post-elimination high was 2014: 667 cases, 383 (57%) of them from an outbreak in an underimmunized Amish community in Ohio. Worldwide an estimated 7 million people get measles each year, and since 2016 it has risen in five of the six World Health Organization regions — more chances for it to reach the United States.

Most imports do not start outbreaks, because state and local health departments act fast, and U.S. measles vaccination coverage among children aged 19–35 months is over 91%. But unimmunized or underimmunized groups are at risk of large, long outbreaks that take great effort to control, and recent outbreaks have been driven by misinformation about measles and the MMR vaccine.

What health care providers should do

• Vaccinate before any international travel everyone without contraindications and without acceptable evidence of immunity:
• • infants aged 6–11 months: one dose of MMR — then two more, one at 12–15 months and another at least 28 days later;
  • adults: a second dose.
• Accept as evidence of immunity only written records of age-appropriate vaccination (not what the person remembers), lab evidence of immunity, lab confirmation of disease, or birth before 1957.
• Report every suspected case quickly — measles is nationally notifiable — so control measures start in time.

High MMR coverage is the most effective way to limit spread and keep measles eliminated.

Sources

Based on Patel M, Lee AD, Redd SB, et al., "Increase in Measles Cases — United States, January 1–April 26, 2019," MMWR Morbidity and Mortality Weekly Report, volume 68, posted as an Early Release on April 29, 2019, Centers for Disease Control and Prevention; a work of the United States government in the public domain. The figures are preliminary as of April 26, 2019.