Impact of Maternal Postpartum Tetanus and Diphtheria Toxoids and Acellular Pertussis Immunization on Infant Pertussis Infection

MAJOR ARTICLE Impact of Maternal Postpartum Tetanus and Diphtheria Toxoids and Acellular Pertussis Immunization on Infant Pertussis Infection Luis A. Castagnini,1 C. Mary Healy,1,3 Marcia A. Rench,1 Susan H. Wootton,4 Flor M. Munoz,1,2 and Carol J. Baker1,2,3 1Department of Pediatrics and 2Department Molecular Virology and Microbiology, Baylor College of Medicine; 3Center for Vaccine Awareness and Research, Texas Children's Hospital; and 4Department of Pediatrics, University of Texas Health Science Center at Houston (See the Editorial Commentary by Libster and Edwards, on pages 85–7.) Despite high infant immunizations rates, pertussis is the only vaccine-preventable disease in the United States for which the incidence reached a nadir in the late 1970s, subsequently increased, and remains high. Although the greatest number of pertussis cases reported to the Centers for Disease Control and Prevention (CDC) Received 30 March 2011; accepted 17 August 2011; electronically published 10 November 2011. Correspondence: Carol J. Baker, MD, Department of Pediatrics, Baylor College of Medicine, 1102 Bates St, Ste 1120, Houston, TX 77030 (). Clinical Infectious Diseases 2012;54(1):78–84 Ó The Author 2011. Published by Oxford University Press on behalf of the Infectious Diseases Society of America. All rights reserved. For Permissions, please e-mail: . DOI: 10.1093/cid/cir765 78 d CID 2012:54 (1 January) d Castagnini et al annually occur in adolescents and young adults, the highest age-specific attack rate is among infants aged ,6 months, in whom rates are up to 20-fold higher than in other age groups [1, 2]. The highest rate of pertussisassociated complications, hospitalizations, and deaths also occurs in young infants who have not yet completed their 3-dose pertussis immunization series at 6 months of age [2–6]. For reasons that are poorly understood, Hispanic infants have substantially higher rates of pertussisassociated complications and death than infants of other ethnicities [2, 5]. The 2010 pertussis epidemic in California, which afflicted more persons than in the previous 65 years, powerfully illustrates the vulnerability of young infants and the disparity in pertussis rates for Hispanic infants [7]. Background. Mothers often are the source of pertussis illness in young infants. The Centers for Disease Control and Prevention recommend tetanus and diphtheria toxoids and acellular pertussis (Tdap) vaccine for postpartum women before hospital discharge. In January 2008, this recommendation was implemented in a predominantly Hispanic, medically underserved population at Ben Taub General Hospital (BTGH) in Houston (hereafter the intervention population). Methods. A cross-sectional study compared preintervention (July 2000 through December 2007) and postintervention (January 2008 through May 2009) periods. Pertussis diagnosis was determined using International Classification of Diseases, Ninth Revision (ICD-9) codes and microbiology reports from 4 major children’s hospitals in Houston. Only those infants #6 months of age with laboratory-confirmed pertussis illness were included. The proportions of pertussis-infected infants born at BTGH in the pre- and postintervention periods were compared. Results. Of 514 infants with pertussis, 378 (73.5%) were identified during preintervention and 136 (26.5%) during postintervention years. These groups were similar in age (mean, 79.3 vs 72 days; P 5 .08), sex (males, 55% vs 52%; P 5 .48), length of hospitalization (mean, 9.7 vs 10.7 days; P 5 .62), mortality (2 deaths each; P 5 .29) and hospital of pertussis diagnosis. After adjustment for age, sex, and ethnicity, the proportions of pertussis-infected infants born at BTGH and potentially protected through maternal postpartum Tdap immunization were similar for the 2 periods (6.9% vs 8.8%; odds ratio, 1.06; 95% confidence interval, 0.5–2.2; P 5 .87). Conclusions. Immunizing only postpartum mothers with Tdap vaccine did not reduce pertussis illness in infants #6 months of age. Efforts should be directed at immunizing all household and key contacts of newborns with Tdap, not just mothers. METHODS Study Design and Subjects We performed a cross-sectional study comparing 2 time intervals: preintervention (July 2000 through December 2007) and postintervention (January 2008 through May 2009). The intervention was a routine standing order for maternal postpartum Tdap immunization at Ben Taub General Hospital (BTGH), Houston, Texas. The majority of pertussis cases in infants in Houston (and a substantial proportion of cases in infants who are not hospitalized) are diagnosed and treated in 1 of 4 Texas Medical Center hospitals: Texas Children’s Hospital, Children’s Memorial Hermann Hospital and 2 Harris County Hospital District Hospitals, BTGH, and Lyndon B. Johnson Hospital. We identified infants #6 months of age with pertussis as a primary or secondary diagnosis at 1 of these 4 hospitals using International Classification of Diseases, Ninth Revision (ICD-9) codes (033.0, 033.1, 033.8, 033.9, and 484.3) and hospital microbiology laboratory reports. We included only laboratoryconfirmed pertussis cases in whom Bordetella pertussis was detected by culture, direct fluorescence assay, or PCR. PCR was performed using standard techniques to amplify the insertion sequence IS481 in B. pertussis (GenBank accession No., M28220). PCR testing employed the same methods and reagents from Roche Diagnostics in each of the participating hospital laboratories. The electronic medical record system was used to identify which of these pertussis-infected infants had been born at BTGH, the likely beneficiaries of the maternal postpartum Tdap vaccine intervention program. The study was approved by the institutional review boards of all participating institutions and hospitals. Intervention Beginning in January 2008, postpartum Tdap immunization was implemented at BTGH as a standing order [23]. Briefly, physicians and nursing personnel caring for women in the peripartum period were educated about the severity of pertussis in very young infants, the need for pertussis booster immunization (Tdap) in adolescents and adults, and the rationale behind cocooning. This was achieved through obstetrical grand rounds and multiple small group in-service sessions. Pertussis education was incorporated into childcare and breastfeeding classes. Mothers were provided with packets containing bilingual information about pertussis and Tdap vaccine. Nursing personnel and physician directors of the cocooning program were available to answer any questions that arose. All women were offered Tdap vaccine before hospital discharge unless there was a medical contraindication (history of anaphylaxis or current unstable neurological condition) or the woman had received a tetanuscontaining vaccine within the previous 2 years [24, 25]. From January 2008 through May 2009, 5223 of 7782 (67%) postpartum women received Tdap. Acceptance rates of .95% (...truncated)