The Minnesota Department of Health says the pertussis outbreak appears to be slowing.
Pertussis, also known as whooping cough, causes a persistent, severe cough that sometimes lasts for months.
In the past two weeks another 190 cases were confirmed, nearly the same number of cases that were reported for just one week in mid-September.
The drop in cases is a good sign, said Claudia Miller, a section manager at the Minnesota Department of Health.
"On a day-to-day basis we're receiving somewhat fewer reports than we were over the past couple of months," she said.
But she said there is still a lot of disease circulating in the community.
"We're still at what we would consider epidemic levels, so we've got a long way to go," Miller said. "Hopefully we'll see a more dramatic decrease in the not-too-distant future."
In total, the state has confirmed more than 3,700 cases of the bacterial infection. That's the highest number since the 1940s, prior to the development of a vaccine.
Three-quarters of the cases have occurred in vaccinated people. Public health officials say it appears that the pertussis vaccine doesn't offer protection for as long as originally thought.