Cook County Health officials announced two more confirmed cases of measles Monday night and said they were related to two cases previously announced by the Chicago Department of Public Health.

Chicago confirmed the first case of the disease in the city in five years Thursday. The county’s announcement came hours after Chicago public health officials announced the number of measles patients at the city’s largest migrant shelter had climbed to four.

County health officials said in a news release that the first patient sought medical treatment Feb. 27 at Stroger Hospital, and the second patient visited the department’s Arlington Heights location and the Cook County Health Professional Building in Chicago on Thursday.

Anyone who was at the Arlington Heights Health Center on Thursday should contact Cook County Health, according to the release.

Anyone who was at the Cook County Health Professional Building between 11 a.m. and 3:30 p.m. Thursday or at Stroger Hospital between noon and midnight Feb. 27 should contact the Chicago health department, the release said.

Measles is a serious respiratory infection that causes a rash and high fever, can be particularly severe for young children and can lead to other complications such as pneumonia. The disease travels through the air and is preventable with a two-dose vaccine given to babies at one year and again to young children between the ages of 4 and 6.

Officials said in the news release that they believe department staff are at low risk of contracting measles because of the county’s vaccination requirement. The risk to the public overall is very low because most people in Chicago and across the United States are vaccinated.

The first reported case of measles at the city’s largest migrant shelter on the Lower West Side sent a flurry of city and federal public health workers descending on the shelter Friday and triggered a lockdown for the residents who had not finished with their immunizations. The shelter houses almost 1,900 asylum-seekers.

The Chicago Department of Public Health said late Monday afternoon that two adults at the quarantined facility on Cermak Road and Halsted Street have tested positive, bringing the total number of cases at the shelter to four.