Big Whoop

Number of pertussis cases climbs in SF and New Mexico

Twelve years ago, Santa Fe-based Dr. Gary Giblin watched a 4- to 6-week-old infant weather one of the worst cases of whooping cough he’s known in his decades-long career.

"He didn't have your classic whoop with the cough, but he would have these episodes where he would stop breathing and coughing and just sort of gulp for air," Giblin recounts. "He deteriorated fairly rapidly. We admitted him at night, and by the next day, he was in the pediatric ICU in Albuquerque. He was there for at least a week, and continued coughing for another month afterwards."

Just a couple months ago, Giblin ran into the mother and her now nearly teenaged son, who doesn't look like the illness set him back, he says. But decades ago, whooping cough, or pertussis, was a leading cause of childhood mortality.

After a vaccine for pertussis was introduced in the 1940s, pertussis rates reached a low in 1980 of one per 100,000 in the US, down from 150 per 100,000. But the number of whooping cough diagnoses has been climbing back up, and Santa Fe County now reports an epidemic-level rate, nearly four times the national average and 10 percentage points above the statewide rate. Some 32 per 100,000 people will be affected each year in Santa Fe County, compared to 9.1 nationally and 22.2 throughout the state, according to New Mexico's Indicator-Based Information System.

"It's probably the biggest resurgence of any vaccine-preventable disease," says Dr. Wendy Johnson, medical director of La Familia. "In an adult, it's usually an annoyance and can be treated. In an infant—mostly infants, but also the very old—it can be fatal, especially unvaccinated infants."

Researchers have tried to tease out an answer to why the highly contagious respiratory tract infection is on the rise. This summer, Santa Fe Institute Fellows Benjamin Althouse and Samuel Scarpino found that the vaccine used now may be preventing those immunized from showing the symptoms—which begin with a runny nose, sneezing, mild fever and cough and lead to uncontrolled coughing spasms that may be followed by a whooping sound—but not from becoming carriers of the bacteria that causes pertussis. Those who have elected not to be immunized, or who are too young to be immunized, can face severe consequences if exposed to that bacteria, which spreads through the air when someone sneezes or coughs.

"There's a large group of individuals who are infected and don't know it, so there have been a number of stories that report adults with a persistent cough that lasts two or three weeks; 30 percent of them may be infected with pertussis, so it may be the case that many of us are affected but never find out," Scarpino says.

Althouse and Scarpino's research suggests that current vaccines may well have contributed to, or even exacerbated, the recent pertussis outbreak by allowing affected individuals to spread pertussis multiple times throughout their lives. The genomic data in the bacteria suggests that far more transmission is occurring than cases are reported, indicating that instances of it are going undetected. The symptoms are what kill people, so the researchers still encourage the use of the vaccine. But the commonly prescribed practice of "cocooning" infants too young to have been immunized by vaccinating all of the adults who spend time with them isn't likely to be effective, because even those vaccinated can get infected and transmit the disease. When Giblin's young patient's family was tested, two teenage children who didn't display any symptoms tested positive for pertussis.

"We really need a new pertussis vaccine that both prevents disease and transmission," Scarpino says.

New vaccines are in trials and may be available in five to 10 years.

Santa Fe's rates have rolled up and down, peaking in 2006 at 47.8 per 100,000 and returning to a rate nearly that high in 2012 after several years with rates hovering below a dozen per 100,000. Preliminary data on 2015 suggests that numbers are again dropping, according to the New Mexico Department of Health, but while that's good news, it doesn't mean the bacteria is disappearing.

"One of the things we see with pertussis are these three- to five-year cycles," says David Selvage, bureau chief for the Infectious Disease Epidemiology Bureau at the Department of Health. "Exactly what underlies that, I don't think is really well described, but it is a trend that's been noticed for quite a while. The other thing we've had in recent years are increases in cases not only in New Mexico but nationally, which we attribute to the use of the pertussis vaccine that came into use in the early 1990s."

As far as protecting infants, health officials recommend women get a pertussis booster during their third trimester of pregnancy to pass on antibodies. Infants aren't considered even minimally protected until they've received their third dose, usually around 6 months of age, according to Selvage; past that point, they are still at risk but less likely to develop complications.

"We're most concerned about infants, because infants that contract pertussis are much more likely to have complications and be hospitalized, and unfortunately even die," Selvage says. "They have the highest rates and are the most vulnerable."

Those diagnosed with pertussis under the age of 1 year made up just 7 percent of cases of pertussis reported in 2013 but comprised 11 of the 19 people hospitalized for the illness.

New Mexico is one of several states working with the Centers for Disease Control and Prevention on an enhanced pertussis surveillance program that collects additional information to better understand the transmission of the disease, its dynamics and its severity in various populations in the state.

"That information can be used to develop a vaccine that's more targeted to what we're seeing circulating in communities," Selvage says, adding that the process is expected to take some time: "None of this is quick."

In March, pertussis experts from around the world will be convening in Santa Fe to discuss the continuing problem of and possible solutions to this disease, which is still responsible for an estimated 195,000 deaths worldwide each year.

There's a large group of individuals who are infected and don't know it ... so it may be the case that many of us are affected but never find out.

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