Transmission of Bordetella pertussis to young infants.
BACKGROUND
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.


METHODS
A prospective international multicenter study was conducted of laboratory confirmed infant pertussis cases (aged <or=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.


RESULTS
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.


CONCLUSIONS
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.
Wendelboe
Aaron M
AM
Department of Epidemiology, School of Public Health, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7435, USA.
Njamkepo
Elisabeth
E
Bourillon
Antoine
A
Floret
D Daniel
DD
Gaudelus
Joel
J
Gerber
Michael
M
Grimprel
Emmanuel
E
Greenberg
David
D
Halperin
Scott
S
Liese
Johannes
J
Muñoz-Rivas
Flor
F
Teyssou
Remy
R
Guiso
Nicole
N
Van Rie
Annelies
A
D000293:Adolescent; D000328:Adult; D000368:Aged; D000907:Antibodies, Bacterial / Q000097:blood; D001886:Bordetella pertussis / Q000235:genetics / Q000276:immunology / Q000302:isolation & purification*; D002648:Child; D002675:Child, Preschool; D016358:Contact Tracing; D006801:Humans; D007223:Infant; D008875:Middle Aged; D010290:Parents; D016133:Polymerase Chain Reaction; D035781:Siblings; D014917:Whooping Cough / Q000175:diagnosis / Q000382:microbiology / Q000473:pathology / Q000635:transmission*
D000907:Antibodies, Bacterial