Long Island Rail Road riders beware: You may have come into contact with measles.

Nassau County’s latest confirmed measles patient rode the LIRR three times last week between Mineola and Penn Station, county health officials said.

The individual took the commuter rail in and out of the city on Sept. 11, Sept. 12 and Sept. 14.

Officials advised that riders should be on the lookout for symptoms, which emerge after seven to 21 days.

Individuals with measles experiences high temperatures, coughing, runny nose and watery eyes — followed by a rash.

Groups with the highest risk of contracting measles include pregnant women, children under 6 months old and individuals who have not or cannot be vaccinated.

The impacted trains have been flagged for deep cleans, the MTA said.

“[Health officials] have advised us that any potential contamination due to this individual would no longer exist, as it has a life of only two hours whether airborne or on surfaces,” said LIRR President Phil Eng.

“We’ve instructed our car cleaning crews and station crews to give a full wipe down on areas where a person may have contact with in advance of the normal cyclical cleaning,” he added.

The case marks Nassau County’s second laboratory-confirmed measles case of 2019.

Earlier this month, Mayor Bill de Blasio declared that New York City’s months-long measles outbreak had ended. Last week was the first time in 11 months without a new reported measles case, according to the Centers for Disease and Prevention.