Pertussis, that is. “Sources of Infant Pertussis Infection in the United States” in this month’s Pediatrics:
BACKGROUND: Pertussis is poorly controlled, with the highest rates of morbidity and mortality among infants. Although the source of infant pertussis is often unknown, when identified, mothers have historically been the most common reservoir of transmission. Despite high vaccination coverage, disease incidence has been increasing. We examined whether infant source of infection (SOI) has changed in the United States in light of the changing epidemiology.
METHODS: Cases <1 year old were identified at Enhanced Pertussis Surveillance sites between January 1, 2006 to December 31, 2013. SOI was collected during patient interview and was defined as a suspected pertussis case in contact with the infant case 7 to 20 days before infant cough onset.
Petrussis, which causes whooping cough, is much less of a problem than it used to be because of the vaccines we give infants. But it keeps on trying to come back. We have believed, for a long time, that mothers are the most common source of the transmission of the disease, which is why we try and make sure they, themselves, are immune.
As we are getting better at immunizing monthers, and the disease keeps on roaring back, researchers wanted to see if there might be changing sources of the disease. So they looked at cases identified by the Enhanced Pertussis Surveillance sites from 2006 through 2013. Patient interviews were conducted to identify the source of infection, mainly by trying to identify infected people who might have come into contact with babies 1 to 3 weeks before they got sick.
They identified more than 1300 cases, about a quarter of whom were less than 2 months old (and therefore totally unimmunized). More than two-thirds of the sources of infection were family members. The most common source of infection overall was a sibling (36%) followed by moms (21%) and dads (10%).
This was a new ordering. Mothers were the most common source until 2008, when siblings took over. The median age range for siblings who transmitted pertussis to their newborn brothers or sisters was 8 years old.
Interestingly, this shouldn’t change our prevention strategy too much. There’s debate out there about whether cocooning strategies, where we vaccinate adolescent and adult close contacts of newborns, with a single dose of Tdap on top of pregnancy Tdap boosters, makes much of a difference. What is still believed to be the most impactful intervention is for expecting mothers to get revaccinated somewhere between the 27th and 36th week of pregnancy. This allows them to create antibodies and pass them along to their babies in utero, which can provide some protection until the newborns get their own vaccines starting at 2 months of age.
And, of course, keep sick contacts away from babies. Common sense, people.