Cases of pertussis — or whooping cough — have dropped dramatically this year.
The Minnesota Department of Health has reports of 358 cases so far, compared to 4,485 in all of 2012. The drop-off was expected because the cyclical disease peaks every three to four years.
"I think part of what we're seeing at this point is really sort of that natural drop-off," said Kris Ehresmann, the director of the health department's Infectious Disease Epidemiology, Prevention and Control Division.
Whooping cough is caused by a bacterium that produces a toxin. It irritates the respiratory system and causes a violent cough. Health officials are most concerned about babies and young children getting it.
A vaccine is available, but it's been known to wear off. Last year, there were more cases among children ages nine to 12 than any other age group.
Ehresmann said besides the cyclical pattern of the disease, other factors in the drop in cases could be greater public awareness about getting the vaccine. In addition, people who have had whooping cough recently are less susceptible to it.
Pertussis cases could rise before the end of the year, but Ehresmann said the overall numbers should stay low for 2013.
"School has been a great place for pertussis transmission, and so certainly when the school year starts, we may see an increase in the number of cases," she said. "But our expectation is that the 4,485 cases that we saw in 2012 — that we will not see numbers of that magnitude this year."