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An outbreak of whooping cough has led to a record number of cases in Missoula County — 169 this year so far — according to the Missoula City-County Health Department.

The number of confirmed illnesses is growing as children go back to school, prompting a warning Thursday from the Health Department. So far, just one school-aged child is among the confirmed cases this semester, but the department is anticipating the possibility of a continued increase in the area.

The outbreak sat at 131 cases in May of this year, and new cases cropped up at a rate of around two per week over the summer, according to health promotion director Cindy Farr. There are now 169 confirmed cases of whooping cough — also known as pertussis — in Missoula County in 2019.

“The highest number of cases we’ve seen in the past was 23 cases (in 2012), and that was only in a single school,” Farr said. “This is an unprecedented number of pertussis cases.”

By comparison, the last three years have seen a marginal number of whooping cough cases in Missoula County, with just one in 2018, none in 2017, and four in 2016.

In May, the Health Department hired 10 nurses to help contact people with whooping cough and try to curb the outbreak. Farr hoped once school let out for the summer, decreased contact would end the outbreak, but it held steady.

Aside from three regular nurses, Farr said the health department has six nurses on hand to help screen for whooping cough if needed.

The outbreak isn’t considered over until 42 days have passed with no new cases, she said.

The Health Department encouraged caution for anyone showing symptoms of whooping cough, including runny nose, sneezing, mild to severe cough and a low fever, and especially for children, who are just returning to school.

The school-aged child confirmed to have pertussis wasn't enrolled in Missoula County Public Schools, but district communications director Hatton Littman said over text she would be notifying parents of the outbreak on Sep. 6 and declined to comment further Thursday.

Pertussis begins with cold-like symptoms, later turning into a persistent cough severe enough to cause exhaustion, vomiting or a whooping sound as patients try to catch their breaths.

Some infants with pertussis don’t cough; instead, the illness causes them to stop breathing and turn blue.

Those at high risk include infants, people with respiratory or cardiovascular conditions, pregnant women, and people with compromised immune systems.

Farr said one of the potential reasons for the outbreak is the pertussis vaccine, which may be about 70-80% effective for the first year and then drops off significantly in some cases. The vaccine is administered as part of a sequence throughout childhood. Those becoming parents, grandparents, childcare providers, or educators are encouraged to get the vaccine as well.

Another potential reason for the outbreak is a lack of “herd immunity,” which requires a certain number of the population to be immune to a disease to prevent its spreading. Pertussis needs about an 80% herd immunity, but Farr said it’s not even close to that in Missoula.

“We keep hoping for a better vaccine, or recommendations from the CDC (Centers for Disease Control and Prevention),” Farr said. “Right now we don’t know what’s going to happen, but we might see another uptick in cases.”

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