Health officials said yesterday that they are investigating a fourth case of measles at Children's Hospital, where the infection might have occurred.

A news release from the state Department of Health did not offer any information about the age or whereabouts of the latest infected person.

The department announced Tuesday that two Westmoreland County preschoolers and their 33-year-old father had been diagnosed with measles.

The health department said the exposure to measles might have occurred in the Children's Hospital emergency room on March 10, or between 8 p.m. March 21 and 11 a.m. March 22; between 6 p.m. on March 25 and 5 a.m. March 26; or between 5 p.m. on March 28 and 4 a.m. on March 29.

It might also have happened at the hospital's third-floor Ear Nose and Throat Specialty Clinic on March 23, according to the health department.

Anyone known to have been in those areas at those times are "being contacted for evaluation as a precaution," the health department said.

Measles is a highly communicable rash illness caused by a virus transmitted by direct contact with infectious droplets or, less commonly, by airborne spread.

Symptoms include a runny nose, watery eyes, cough and a high fever.

The incubation period is seven to 18 days, but a person is contagious for four days prior to the appearance of the rash and remains contagious four days after the rash appears. The rash will usually last four to seven days.