REGIONAL- Pertussis, commonly known as whooping cough, is at a ten-year high in both St. Louis County and across the state. The most recent statistics, issued on Nov. 21, show 1,969 pertussis cases have been reported in the state so far this year, with half occurring since mid-October.
Most cases have been reported in the seven counties of the Twin Cities metropolitan area, however, St. Louis County, with 61 cases is the state’s other hot spot. “There is a distinct clustering of cases in the Duluth area, although it is starting to spread north to the Iron Range,” said Cynthia Kenyon, senior epidemiology supervisor at the Minnesota Department of Health, along with Senior Public Health Nursing Advisor Tabitha Hanson. “MDH is also hearing that there may be more cases than are getting reported, so there is likely more pertussis circulating than is reported.”
St. Louis County had no reported pertussis cases in 2021, 2022, and 2023, so the reporting of 61 cases year-to-date in 2024 appears startling. According to Kenyon and Hanson, the zero rate was an unusual situation due to the pandemic, and this trend wasn’t just in St. Louis County — it was national.
Pertussis cases in Minnesota and the rest of the nation fell to historic lows in the three years after the arrival of COVID-19, and it affected all contagious respiratory infections. According to the National Institutes of Health, “The fall in non-COVID-19 respiratory diseases, including seasonal influenza, during the pandemic is well reported. It is thought to be a result of a combination of social distancing, lockdowns, improved hand hygiene, and respiratory protection measures.”
With the lifting of the pandemic protocols, infectious diseases have come roaring back. The U.S. Center for Disease Control and Prevention reported that the current year-to-date cases of pertussis in the U.S. mark a return to pre-pandemic rates. While the spike of pertussis in Minnesota and St. Louis County is at a ten-year high, the increase follows a cyclic trend for the disease.
“Pertussis outbreaks tend to follow a cyclical pattern,” explained Kenyon and Hanson, “with peaks occurring every three to five years. These cycles are influenced by decreasing immunity and the contagious nature of the disease … (with the) regular cyclical pattern disrupted by the COVID-19 pandemic.”
While the current pertussis rate may seem high compared to the rate during the pandemic, it is worth mentioning that in 2012, Minnesota had over 4,000 reported pertussis cases and over 1,500 in 2005.
The decreased immunity the two MDH experts described is due to a drop in the immunity effectiveness provided by the modern pertussis vaccines, which are bundled with tetanus and diphtheria vaccines in one injection. While the tetanus and diphtheria immunity from modern vaccines last several years, the pertussis immunity declines sooner.
Pertussis is often a severe disease for infants and young children. It is famous for its noisy bouts of prolonged and severe coughing. It was a significant cause of childhood death before the introduction of the first tetanus-diphtheria-pertussis vaccine in 1948. While infants and toddlers were once most of this disease’s victims, the age demographics of pertussis have changed to include older children and teens.
“Pertussis vaccine rates in Minnesota are pretty good overall, but pertussis vaccines decrease in protection over time,” Kenyon and Hanson explained. “Additionally, pertussis is endemic in Minnesota, meaning that it is always circulating, and we see peaks of pertussis every three-five years. When we have these peaks, we see the biggest impact in those whose vaccine coverage has decreased, so with over the last couple of peak years, the age group that has been the most impacted are teens with a median age of 13 and 14.”
Kenyon and Hanson emphasized that immunization can prevent pertussis and will mitigate the symptoms when vaccinated individuals do become infected. They recommended a booster shot for adults and teens who haven’t had a tetanus-diphtheria-pertussis vaccine in the last year, and for pregnant women, infants, and children who have not previously been vaccinated.