If you’ve taken the Long Island Rail Road this month, watch out for measles symptoms. The Nassau County Department of Health has issued a warning that it confirmed its second case of measles in the county in recent weeks—and that the infected person rode the LIRR into Manhattan several times earlier this month.

More specifically, the patient traveled on the LIRR on September 11th, September 12th, and again on September 14th. The person also took the MTA shuttle between the Mineola and Hempstead stations on September 14th and ate at the Noches de Columbia Restaurant in Nassau County that same day. “NCDOH is thoroughly investigating this case and has determined there is potential exposure to the public,” the Health Department says in its warning.

Needless to say, measles is highly contagious, and anyone who also visited those sites on those dates should be on alert for symptoms. (The virus is known to remain alive for up to two hours in a location where an infected patient coughed or sneezed.)

Symptoms can appear 10-12 days after exposure. Pregnant individuals and infants are especially high-risk for measles. These are the symptoms to watch out for, per the NCDOH:

Measles is a serious respiratory disease that causes a rash and fever. It is very contagious. You can catch it just by being in a room where someone with measles coughed or sneezed. People usually develop a fever, then may have a cough, runny nose and watery eyes, followed by appearance of a rash. People are considered infectious from four days before to four days after the appearance of the rash. Symptoms usually appear 10-12 days after exposure but may appear as early as 7 days and as late as 21 days after exposure.

This most recent measles patient follows a previous report from September 4th, when health officials confirmed that an infected adult had arrived at John F. Kennedy International Airport after being exposed to measles in a foreign country. At that time, however, there was “minimal risk of exposure to Nassau County residents.”

Meanwhile, New York City recently declared an end to its worst measles outbreak in nearly three decades, which primarily affected ultra-Orthodox Jewish communities in Brooklyn. (Many of those cases involved unvaccinated children.) Health Department officials declared the city measles-free in early September, after nearly a year since the outbreak was first reported last October. During that time, 654 New York City residents got sick, 52 people were hospitalized and 16 of those people were admitted to intensive care units, according to the Health Department.