The Hennepin County measles outbreak grew to 20 cases Monday, after eight new infections were confirmed.
State health officials said all the cases have occurred within the Somali-American community, and they urged parents to get the measles vaccine for themselves and their children if they are unvaccinated.
The outbreak is expected to produce many more cases and could exceed the 2011 outbreak of 26 cases, according to Kris Ehresmann, infectious disease director at the Minnesota Health Department.
So far, all of those who have caught the measles in this outbreak are 5 years old or younger. Exposure has occurred at several day care centers.
Since the first case was detected two weeks ago, health investigators have been trying to identify anyone unvaccinated exposed to the virus, which is highly contagious. It can take up to three weeks for measles symptoms to develop.
Children and parents who have been exposed to active cases are being asked to voluntarily remain at home if they are unvaccinated to avoid exposing others.
There is no drug or cure for the measles, so public health officials say the best way to deal with the disease is to prevent infection through immunization.
The vaccine — known as the MMR vaccine for measles, mumps and rubella protection — is typically given to children around age 1, and a second shot is administered between the ages of 4 and 6.
The Health Department recommended Monday that the schedule for a second dose be accelerated for any Somali-American children who had received the initial shot, which they said is a common practice during outbreaks.
The eight new infections in this outbreak include for the first time at least one baby under 12 months, an age group that has been of concern to public health officials because they typically lack immunity protection.
Investigators have examined the vaccination records of 16 of those infected, and none of them had received the MMR shot. Records for the other four are still being collected.
Measles symptoms include coughing, a sore throat, fever and a blotchy skin rash. It can lead to pneumonia and encephalitis, or swelling of the brain, and in same cases is fatal.