Multnomah County health officials say a second person was diagnosed Friday with measles after being exposed to the virus at a Gresham child care center.

The recent diagnosis comes nine days after measles was found in the initial carrier, who contracted the virus while traveling outside the United States, according to the county's health department. More than 500 people may have been exposed to measles by that person.

The county hasn't publicly identified the Gresham business where this occurred, but said some of the people who were exposed have been notified and offered a vaccine. Anyone with questions should contact the Multnomah County Health Department at 503-988-3406.

After being told of the exposure by county health officials, the second person infected stayed home and reported daily updates on any apparent symptoms until an official diagnosis was made, the health department said.

About 40 other people who also were exposed to the first virus carrier at the Gresham child care center are in contact with health officials to help monitor for signs of symptoms, which may appear by mid-July.

Diagnoses of the virus are rare in the U.S. and pose the highest risk to people who haven't been vaccinated, pregnant women, babies under a year old and people with weakened immune systems. Measles was last diagnosed in the Portland area in 2014.

Symptoms usually appear within two weeks of exposure. The virus can spread through the air when someone sneezes or coughs and can remain in the air after an infected person leaves, the health department said. Symptoms include coughing, fever, runny nose and a rash that typically appears first on the head and spreads to the rest of the body.

The virus can lead to ear and lung infections, diarrhea and possibly brain swelling if it isn't treated.

If you think you are infected, call a doctor or emergency room first before visiting to avoid exposing people in the waiting room to the virus. Questions about the virus can be referred to local county health departments.

-Multnomah County (503-988-3406)

-Clackamas County (503-655-8411)

-Washington County (503-846-3594)

-Clark County (360-397-8182)

-- Everton Bailey Jr.

ebailey@oregonian.com

503-221-8343; @EvertonBailey