The number of pertussis cases in Minnesota has doubled in recent weeks.
The Minnesota Department of Health says the state is approaching 700 cases of the disease, also known as whooping cough.
Claudia Miller, the vaccine preventable disease surveillance supervisor at the Health Department, has been tracking the outbreak and said it was looking like a normal year for pertussis earlier this month.
"We were, until recently, sort of in line with the numbers of cases we were seeing a year ago," Miller said. "Now we have had an increase in recent weeks so that we have at this point exceeded the total number of cases for 2011."
Pertussis is a contagious bacterial infection that causes cold-like symptoms and a persistent cough. It usually clears up without treatment, but the disease can be dangerous for infants and people with weak immune systems.
"For them the disease can be very severe," she said. "We have high hospitalization rates and they are much more likely to have complications and unfortunately we even see deaths in infants due to pertussis on occasion."
Most children get vaccinated for pertussis before enrolling in school. But the vaccine starts to wear off by adolescence. A booster vaccine has been available for adolescents and adults since 2005.