Compared to last year's massive pertussis outbreak, it's shaping up to be a quieter year for the bacterial infection.
But public health officials are concerned the return to school could mean an upsurge in new cases of the infection, even as they try to figure out why it's hitting Minnesota harder than usual.
Last year, there were 4639 confirmed, probable and suspected cases of pertussis in Minnesota. The infection is also known as whooping cough.
There were 657 cases recorded during the first eight months of 2013--a figure that would be considered a high level of disease, if not for last year's extraordinary outbreak.
Adolescents are particularly susceptible to catching pertussis because the effectiveness of the vaccine wanes by the time they turn 10 or 11. That's why pertussis cases often jump when kids return to their crowded classrooms.
In July and August there was a jump in cases --around 30 to 40 additional reports during each two week surveillance cycle, compared to June, according to Cynthia Kenyon who coordinates pertussis surveillance for the Minnesota Department of Health.
"I'm a little bit concerned to see a slight uptick over the last couple of weeks, so I'm cautious about the fall,'' Kenyon said.
Kenyon has been tracking pertussis in Minnesota for more than a decade. She said this year's case count that exceeds 500 is still considered high--especially since the year is not over.
"Back when I first started, our peak years were around 500 and our low years were around 200,'' said Kenyon. ''So to put that in perspective, even though we're seeing less now (than last year), it's still more than we've historically seen."
The Health Department is trying to figure out what is causing higher than usual pertussis numbers in the state. Kenyon said her public health colleagues wonder if it has something to do with a change in the bacterium, or its location in the state.
Kenyon said perhaps it has landed in communities where pertussis hadn't been circulating for awhile, making it much easier for the bacteria to spread. Those are all good theories, according to Patsy Stinchfield, Infectious Disease director at Children's Hospitals and Clinics of Minnesota. She said the problem is a combination of the complexity of the bacteria, imperfect vaccines and the population who does not get vaccinated.
"Our vaccines aren't perfect--they don't last as long as we want them to-- but making sure that we all get vaccinated on schedule is really the best thing to do to prevent pertussis,'' Stinchfield said.
Stinchfield, who is also a nurse liason to the Advisory Committee on Immunization Practices, said public health officials are focusing their vaccination strategy on those who are most vulnerable to complications from pertussis.
The Committee recently recommended that pregnant women get vaccinated during each of their pregancies so they can pass pertussis antibodies to their unborn babies.
Newborns in particular are at the highest risk of death from pertussis because babies can't be fully vaccinated until they are six months old.
But the committee's advice for adolescents, teens and adults remains the same: Only one Tdap booster is recommended for now--even though the vaccine's effectiveness against pertussis will likely wane after a few years.