The U.S. measles count keeps climbing into early October. As of Oct. 1, the Centers for Disease Control and Prevention tallied 3,887 cases in 47 jurisdictions, with 42 outbreaks and about 95% of cases tied to those clusters, according to CIDRAP and ContagionLive summaries of CDC data.

Pennsylvania is the standout state this fall. State tallies are approaching 1,000 cases, CIDRAP reported, making it one of the heaviest local burdens in a year that has already set modern records. Outbreaks have also strained clinics and school exclusion rules in several other states.

Measles spreads through the air and can hang in a room after an infected person leaves. Two doses of the MMR vaccine prevent most cases. People born before 1957 are generally considered immune, but anyone unsure of their shots can ask a clinic for titers or a catch-up dose.

Public health officials keep urging travelers and parents of young children to check records before school, sports, and fall trips. Hospitals watch for fever and rash after international travel, because late confirmations still move the national total day to day.

Some background: The United States declared measles eliminated in 2000, meaning the disease was no longer constantly spreading here. That status has been under pressure in years with large outbreaks fueled by gaps in vaccination. This year's case count already dwarfs typical recent seasons.

Families can call their pediatrician or a local health department about MMR catch-up. Pharmacies and clinics often give the shot the same day as a flu visit when schedules allow.

School nurses still send exclusion letters when unvaccinated students are exposed. Parents should read those notices carefully for return dates rather than relying on hallway rumors.

What we know: CDC counted 3,887 U.S. measles cases through Oct. 1, with Pennsylvania near 1,000.
What we don't: Whether late October will push the national total past 4,000.