Whooping cough update: outbreak in Montana continues

The Montana Department of Health has reported (pdf) that as of  November 15, 2012, a whooping cough (Bordetella pertussis) outbreak has reached over 500 cases since the beginning of the year, compared to only 129 cases during the same time period in 2011. As of November 15, 33 cases of pertussis were found in infants of less than one year of age. Of these, four have been hospitalized. Because Montana is has a small population (about 1 million people), the overall incidence rate year to date is 50.5 pertussis cases per 100,000 Montana residents. 

This past spring, there was a pertussis outbreak in several Montana counties, but it seemed to abate during the summer. The Department of Health is reporting that Flathead county, a northern county that borders Canada, is currently struggling to contain an outbreak in five school districts. “Since the beginning of October, we have 35 cases,” said Community Health Services Director for Flathead County Jody White. “Usually we won’t even see 35 in a year, so it is definitely unusual to have this many.”

White says nearly all of the victims are school-age children, however the youngest victim in Flathead county is only 13 months old. Infants are especially vulnerable to pertussis as they cannot receive the full vaccine and suffer most from the side effects. Family members of infants are advised to make sure their vaccinations are up to date.

Many would assume that Flathead County’s vaccination rate might be low, but it’s not. White says the vaccination rate of Flathead County students is about average in comparison with other Montana counties.

“Pertussis is always present below the surface in a community,” says White and although the recent explosion is difficult to explain, it appears that one of the main causes for spread in the Flathead is that sick individuals are choosing not to follow the prophylactic procedures the health department advises. The best prevention is immunization, if you have a persistent cough for more than a week make sure you go and see your doctor.”

According to the Centers for Disease Control and Prevention, pertussis (whooping cough) can cause serious illness in infants, children and adults. The disease usually starts with cold-like symptoms and maybe a mild cough or fever. After 1 to 2 weeks, severe coughing can begin. Unlike the common cold, pertussis can become a series of coughing fits that continues for weeks. In infants, the cough can be minimal or not even there. Infants may have a symptom known as “apnea.” Apnea is a pause in the child’s breathing pattern. Pertussis is most dangerous for babies. More than half of infants younger than 1 year of age who get the disease must be hospitalized. Approximately 1-2% of infants who are hospitalized from pertussis will die.

Pertussis can cause violent and rapid coughing, over and over, until the air is gone from the lungs and you are forced to inhale with a loud “whooping” sound. This extreme coughing can cause you to throw up and be very tired. The “whoop” is often not there and the infection is generally milder (less severe) in teens and adults, especially those who have been vaccinated.

Whooping cough can be easily prevented with the Tdap or DTaP vaccine. The problem is that infants are not initially vaccinated until they are 2 months old, and are not fully immunized until they’re 6 months old, so they are susceptible to adults who may be infected. Adults may have lapsed immunity or may have not been vaccinated.

According to the CDC, Montana had one of the highest pertussis vaccination rates in the US at around 95% of the school-aged children. There could be several reasons for the outbreak, including the well-described issueswith the waning of vaccine induced immunity of the Tdap vaccine. And according to the Montana Department of Health, to date, the 5-10 year and 11-18 year age groups represent the greatest number (63%) of pertussis cases. Of course, this doesn’t mean that the pertussis vaccine isn’t working, it is, since the rate of pertussis infection is higher in unvaccinated or partially vaccinated children. 

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