Sources of Infant Pertussis Infection in the United States.
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.


RESULTS
A total of 1306 infant cases were identified; 24.2% were <2 months old. An SOI was identified for 569 cases. Infants 0 to 1 months old were more likely to have an SOI identified than 2- to 11-month-olds (54.1% vs 40.2%, respectively; P < .0001). More than 66% of SOIs were immediate family members, most commonly siblings (35.5%), mothers (20.6%), and fathers (10.0%); mothers predominated until the transition to siblings beginning in 2008. Overall, the SOI median age was 14 years (range: 0-74 years); median age for sibling SOIs was 8 years.


CONCLUSIONS
In contrast to previous studies, our data suggest that the most common source of transmission to infants is now siblings. While continued monitoring of SOIs will optimize pertussis prevention strategies, recommendations for vaccination during pregnancy should directly increase protection of infants, regardless of SOI.
Centers for Disease Control and Prevention, Atlanta, Georgia; tlh9@cdc.gov.
Tami H
TH
Skoff
Minnesota Department of Health, St Paul, Minnesota;
Cynthia
C
Kenyon
Department of Population Medicine, Harvard Medical School and Harvard Pilgrim Healthcare Institute, Boston, Massachusetts;
Noelle
N
Cocoros
Public Health Division, Oregon Health Authority Portland, Oregon;
Juventila
J
Liko
Colorado Department of Public Health and Environment, Denver, Colorado;
Lisa
L
Miller
Connecticut Department of Public Health, Hartford, Connecticut;
Kathy
K
Kudish
New Mexico Department of Health, Santa Fe, New Mexico; and.
Joan
J
Baumbach
New York State Department of Health, Albany, New York.
Shelley
S
Zansky
Centers for Disease Control and Prevention, Atlanta, Georgia;
Amanda
A
Faulkner
Centers for Disease Control and Prevention, Atlanta, Georgia;
Stacey W
SW
Martin
D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D008875:Middle Aged; D014481:United States / Q000453:epidemiology; D014917:Whooping Cough / Q000453:epidemiology / Q000635:transmission*; D055815:Young Adult