Pertactin-Negative Bordetella pertussis Strains: Evidence for a Possible Selective Advantage

BACKGROUND: A recent increase in Bordetella pertussis without the pertactin protein, an acellular vaccine immunogen, has been reported in the United States. Determining whether pertactin-deficient (PRN(-)) B. pertussis is evading vaccine-induced immunity or altering the severity of illness is needed. METHODS: We retrospectively assessed for associations between pertactin production and both clinical presentation and vaccine history. Cases with isolates collected between May 2011 and February 2013 from 8 states were included. We calculated unadjusted and adjusted odds ratios (ORs) using multivariable logistic regression analysis. RESULTS: Among 753 isolates, 640 (85%) were PRN(-). The age distribution differed between cases caused by PRN(-) B. pertussis and cases caused by B. pertussis producing pertactin (PRN(+)) (P = .01). The proportion reporting individual pertussis symptoms was similar between the 2 groups, except a higher proportion of PRN(+) case-patients reported apnea (P = .005). Twenty-two case-patients were hospitalized; 6% in the PRN(+) group compared to 3% in the PRN(-) group (P = .11). Case-patients having received at least 1 pertussis vaccine dose had a higher odds of having PRN(-) B. pertussis compared with unvaccinated case-patients (adjusted OR = 2.2; 95% confidence interval [CI], 1.3-4.0). When restricted to case-patients at least 1 year of age and those age-appropriately vaccinated, the adjusted OR increased to 2.7 (95% CI, 1.2-6.1). CONCLUSIONS: The significant association between vaccination and isolate pertactin production suggests that the likelihood of having reported disease caused by PRN(-) compared with PRN(+) strains is greater in vaccinated persons. Additional studies are needed to assess whether vaccine effectiveness is diminished against PRN(-) strains.