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...In a regularly scheduled update this afternoon, the health department said 99 cases were identified since Tuesday, bringing the outbreak total to 310 cases. There are currently 200 people in quarantine and nine in isolation.

However, the outbreak is expanding so quickly and with so many exposure sites that health officials are struggling to trace cases and identify people at risk.

"An increasing number of public exposure sites are being identified with likely hundreds more people exposed who are not aware they should be in quarantine if they are not immune to measles," Dr. Linda Bell, state epidemiologist and the health department's incident commander for the measles outbreak, said in the announcement.

"Previous measles transmission studies have shown that one measles case can result in up to 20 new infections among unvaccinated contacts."

The outbreak is centered in the northwestern corner of the state, with cases concentrated in Spartanburg County. According to state data, in the 2024"2025 school year, only 90 percent of students in the county were fully vaccinated.

That's well below the target of 95 percent vaccination coverage that prevents vaccine-preventable infections from spreading.

However, the county-wide vaccination rate likely obscures pockets where vaccination rates are even lower, making the virus more likely to spread. ...