Infants most often acquired pertussis from siblings, not their mothers as was previously found, researchers reported online in Pediatrics.
The trend reflects the changing epidemiology of pertussis in the United States as immunity to acellular Tdap vaccination wanes among older children and adolescents, who then develop clinical or subclinical pertussis and infect younger siblings, said Tami Skoff at the Centers for Disease Control and Prevention in Atlanta, and her associates. “Prevention efforts should focus on increasing Tdap coverage during pregnancy, because this is currently our best strategy for providing direct protection to the infant, regardless of the changing source of infant infection.”
Bordetella pertussis infects up to 80% of exposed, naive individuals and is particularly risky for infants, the researchers noted. To examine infection sources for this age group, they studied 1,306 pertussis cases among children less than 1 year old that were reported to the Enhanced Pertussis Surveillance program between 2006 and 2013. The program tracks pertussis in Colorado, Connecticut, Massachusetts, Minnesota, New Mexico, New York, and Oregon. For each case, the researchers attempted to identify the infection source – a person with suspected pertussis who had contact with the infant 7-20 days before cough onset (Pediatrics 2015 Sep 7. doi: 10.1542/peds.2015-1120). A source of infection was identified in 43.6% of cases.
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Siblings were the infection source for 36% of infants, followed by mothers (21%), fathers (10%), grandparents (8%), and aunts and uncles (7%), the investigators reported. The source was unspecified for 6% of cases, while ill day care contacts, cousins, friends, babysitters, and other contacts accounted for less than 5% of infections each.
“Consistent with previous studies, our analysis of 8 years of enhanced surveillance data identified a source of infection for less than half of reported infant pertussis cases,” the researchers emphasized. Such a high proportion of unknown infection sources limits the efficacy of the cocooning strategy, in which a Tdap booster dose is given to adults and adolescents who are in close contact with infants, the investigators added. “The cocooning strategy is less than ideal, and strong support of vaccination during pregnancy is needed to maximize the protection of infants in the first critical months of life.”
The Enhanced Pertussis Surveillance Program is funded through a cooperative agreement with the Centers for Disease Control and Prevention. The investigators reported no financial disclosures.