Pertussis vaccination has reduced the number of notified cases in industrialized countries from peak years by more than 95%. The effect of recently recommended adult and adolescent vaccination strategies on infant pertussis depends, in part, on the proportion of infants infected by adults and adolescents. This proportion, however, remains unclear, because studies have not been able to determine the source case for 47%–60% of infant cases.
A prospective international multicenter study was conducted of laboratory confirmed infant pertussis cases (aged ≤6 months) and their household and nonhousehold contacts. Comprehensive diagnostic evaluation (including PCR and serology) was performed on all participants independent of symptoms. Source cases were identified and described by relationship to the infant, age and household status.
The study population comprised 95 index cases and 404 contacts. The source of pertussis was identified for 48% of infants in the primary analysis and up to 78% in sensitivity analyses. In the primary analysis, parents accounted for 55% of source cases, followed by siblings (16%), aunts/uncles (10%), friends/cousins (10%), grandparents (6%) and part-time caretakers (2%). The distribution of source cases was robust to sensitivity analyses.
This study provides solid evidence that among infants for whom a source case was identified, household members were responsible for 76%–83% of transmission of Bordetella pertussis to this high-risk group. Vaccination of adolescents and adults in close contact with young infants may thus eliminate a substantial proportion of infant pertussis if high coverage rates can be achieved.
From the *Department of Epidemiology, School of Public Health, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina; †Centre National de Référence de la Coqueluche et autres Bordetelloses, Unité de Prévention et Thérapie Moléculaires des Maladies Humaines, FRE CNRS 2849, Institut Pasteur, Paris, France; ‡Hôpital Robert Debré, Paris, France; §Université Claude Bernard Lyon, Cedex, France; ∥Hôpital Jean Verdier, Bondy, France; ¶Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio; #Hôpital Armand Trousseau, Paris, France; **Children's Hospital of Pittsburgh, Pittsburgh, Pennsylvania; ††Dalhousie University and the IWK Health Centre, Halifax, Canada; ‡‡Ludwig-Maximilians-Universitaet, Munich, Germany; §§Baylor College of Medicine and Texas Children's Hospital, Houston, Texas; and ∥∥Sanofi Pasteur, Lyon, France.
Accepted for publication January 12, 2007.
Address for correspondence: Annelies Van Rie, MD, PhD, Department of Epidemiology, School of Public Health, The University of North Carolina at Chapel Hill, 2104F Mc Gavran Greenberg Hall, Chapel Hill, NC 27599-7435. E-mail: firstname.lastname@example.org.
Dr. Greenberg is a current employee of sanofi Pasteur, Swiftwater, PA.