Weekly measles cases hit new record amid worst outbreak since 1990s

Weekly measles cases have set a new record, according to figures published Friday by the U.S. Centers for Disease Control and Prevention, topping the peak of an outbreak in 2019 that ranked as the worst since the 1990s.

The number of cases that had their symptoms start during the week of March 30 has grown to 111, according to the agency's latest update. Authorities backdate newly reported measles cases based on when their rash began, to account for delays in reporting and diagnosis.

That tops the 102 cases reported for the week of March 23, 2019, at the height of that year's wave. By the end of 2019, measles cases that year added up to the largest annual tally since endemic spread of the virus was declared eliminated in 2000.

This year, the majority of cases are from an ongoing outbreak in Texas and neighboring states, which is now larger than any other single outbreak since the virus was eliminated. Between Texas and New Mexico, at least 750 of the measles cases reported this year have been linked to that outbreak. Cases in Oklahoma and other states have also been linked to the outbreak.

There have been 11 other local outbreaks of measles within the U.S. this year, up from 10 last week.

While the pace of new cases looks to have declined in Texas, officials caution it is too soon to say whether the outbreak is truly ending.

"We look at the trends over time and we'd want to see several weeks of decline. New cases sometimes get reported to public health up to a week after someone was tested, especially if the test was done at a commercial lab," Lara Anton, a spokesperson for the Texas Department of State Health Services, told CBS News in a statement.

Anton said authorities are also watching to see if travel from the Easter holiday weekend last month will result in an increase.

"Cases from travel that weekend would likely start to be reported in the next week or two," Anton said.

This year's tally of cases is likely an undercount, officials and experts have said, citing anecdotes of unreported infections. The unusually high severity of this year's wave also suggests many mild cases of spread are going undiagnosed.

For example, authorities in Canada have confirmed more than 1,000 measles cases so far this year, after record outbreaks there. The U.S. has tallied at least 935 this year, according to the CDC.

In Canada, 7% of cases have resulted in hospitalizations, less than the 13% of cases that have resulted in hospitalizations in the U.S. Three Americans have also died from measles so far this year, compared to none in Canada.

In:
• Centers for Disease Control and Prevention
• Measles