One of the four people confirmed to have measles had come into contact with up to 150 people before being contained, meaning the infection could have spread dramatically, the Milwaukee Journal Sentinel reported Saturday.

Health officer Darren Rausch said officials have been able to locate and contain a 37-year-old man, a 23-month-old girl and two boys, ages 5 months and 1 year, who were found to have measles.

"We believe we have limited the exposure," he said.

As a precaution due to the potential exposure from one of the patients, city officials offered free immunization vaccinations Saturday.

The newspaper said those wanting such immunizations should contact their local public health office immediately.

Milwaukee Health Department medical director Geoffrey Swain said one immunization shot is 95 percent effective.