Impact of a Pertussis Cocooning Program on Infant Pertussis
Infants with birth dates between May 1, 2004 and August 31, 2011 and diagnosed with pertussis at ≤6 months of age at 4 hospitals in the Texas Medical Center in Houston, TX [Texas Children's Hospital, Children's Memorial Hermann Hospital and 2 Harris Health System county hospitals, Ben Taub General Hospital (BTGH) and Lyndon B. Johnson Hospital] were included in the study. The majority of severe pertussis cases in young infants in the Houston metropolitan area, and a substantial number of cases in infants who do not need hospitalization, are diagnosed in these hospitals, most at Texas Children's Hospital, which is the largest free-standing pediatric hospital in the United States. These infant birth dates coincided with a 44-month period when pertussis immunization interventions were being offered at BTGH (postintervention; January 2008 through August 2011) and compared it with a 44-month preintervention period (May 2004 through December 2007). The postintervention immunization period further consisted of 2 phases, phase 1 when Tdap vaccine was offered to postpartum women only at BTGH (January 2008 through May 2009) and phase 2 when Tdap was offered to postpartum women and all infant contacts (June 2009 through August 2011), and ended when the recommendation to immunize pregnant women was posted on the CDC website in August 2011. The study was approved by the institutional review boards of participating hospitals and institutions.
Infants with a diagnosis of pertussis were identified from 2 sources: those with a primary or secondary diagnosis of pertussis using International Classification of Diseases, Ninth Revision codes (033.0, 033.1, 033.8, 033.9 and 484.3) and those identified through microbiology laboratory records. Laboratory diagnosis was defined as the detection of Bordetella pertussis by culture, direct fluorescence assay or polymerase chain reaction (PCR). PCR was performed using standard techniques to amplify the IS481 insertion sequence in B. pertussis (GenBank accession no. M28220), and the same methods and reagents from Roche Diagnostics (Indianapolis, IN) were used in each of the hospitals.
The BTGH pertussis immunization program has been previously described. Briefly, free Tdap vaccine was provided to postpartum women through a standing-order protocol and later to other infant contacts. BTGH is 1 of 2 tax-supported hospitals in the Harris Health System and serves a largely underinsured, medically underserved population. Approximately 4000 live-born infants, predominantly of Hispanic ethnicity (>90%), are delivered there annually. The program's success was driven by targeted education of healthcare personnel and families, and by providing Tdap vaccination on-site daily at convenient times for families. More than 90% of eligible postpartum women received Tdap vaccine and approximately 60% of infants for whom detailed information was available had one or more contacts, other than a mother, immunized with Tdap.
The electronic medical record of infants with a diagnosis of pertussis through hospital microbiology records and International Classification of Diseases, Ninth Revision codes were reviewed to ensure they met the following criteria: birth date from May 1, 2004 through August 31, 2011, ≤6 months of age at the time of pertussis diagnosis and microbiologically confirmed infection with B. pertussis. Infants with B. parapertussis infection only were excluded from further analysis. Additional data collected included demographics, hospital of diagnosis, need for hospitalization and admission to an intensive care unit (ICU), duration of hospitalization and outcome. It was determined whether infants had been born at the intervention hospital (BTGH) using their date of birth and electronic database. Infants born at BTGH were then cross-referenced with the BTGH pertussis immunization program database to determine whether their mothers and/or infant contacts had received Tdap vaccine.
Statistical analysis was performed using SPSS version 22.0 (SPSS, Chicago, IL). Descriptive characteristics were assessed. Statistical significance for dichotomous outcomes was determined by χ and Fisher exact tests. Normally distributed data were evaluated by means and the Student's t test or one-way analysis of variance; where positive or negative skewing of data occurred, statistical significance was calculated by medians and the Mann–Whitney U test. A number of analyses were performed. Characteristics of infants diagnosed with pertussis and the severity of illness during the preintervention period were compared first with infants diagnosed in the entire postintervention period, and then infants born during the preintervention, postpartum and family cocooning periods were compared. Where possible, the completeness of an individual infant's cocoon was calculated by assessing the proportion of their contacts who were vaccinated. The proportions of infants born at BTGH during different intervention periods were compared. Multiple logistic regression analysis accounted for potential demographic confounders such as age, sex and Hispanic ethnicity.
Materials and Methods
Patient Population
Infants with birth dates between May 1, 2004 and August 31, 2011 and diagnosed with pertussis at ≤6 months of age at 4 hospitals in the Texas Medical Center in Houston, TX [Texas Children's Hospital, Children's Memorial Hermann Hospital and 2 Harris Health System county hospitals, Ben Taub General Hospital (BTGH) and Lyndon B. Johnson Hospital] were included in the study. The majority of severe pertussis cases in young infants in the Houston metropolitan area, and a substantial number of cases in infants who do not need hospitalization, are diagnosed in these hospitals, most at Texas Children's Hospital, which is the largest free-standing pediatric hospital in the United States. These infant birth dates coincided with a 44-month period when pertussis immunization interventions were being offered at BTGH (postintervention; January 2008 through August 2011) and compared it with a 44-month preintervention period (May 2004 through December 2007). The postintervention immunization period further consisted of 2 phases, phase 1 when Tdap vaccine was offered to postpartum women only at BTGH (January 2008 through May 2009) and phase 2 when Tdap was offered to postpartum women and all infant contacts (June 2009 through August 2011), and ended when the recommendation to immunize pregnant women was posted on the CDC website in August 2011. The study was approved by the institutional review boards of participating hospitals and institutions.
Pertussis Diagnosis
Infants with a diagnosis of pertussis were identified from 2 sources: those with a primary or secondary diagnosis of pertussis using International Classification of Diseases, Ninth Revision codes (033.0, 033.1, 033.8, 033.9 and 484.3) and those identified through microbiology laboratory records. Laboratory diagnosis was defined as the detection of Bordetella pertussis by culture, direct fluorescence assay or polymerase chain reaction (PCR). PCR was performed using standard techniques to amplify the IS481 insertion sequence in B. pertussis (GenBank accession no. M28220), and the same methods and reagents from Roche Diagnostics (Indianapolis, IN) were used in each of the hospitals.
Intervention Hospital
The BTGH pertussis immunization program has been previously described. Briefly, free Tdap vaccine was provided to postpartum women through a standing-order protocol and later to other infant contacts. BTGH is 1 of 2 tax-supported hospitals in the Harris Health System and serves a largely underinsured, medically underserved population. Approximately 4000 live-born infants, predominantly of Hispanic ethnicity (>90%), are delivered there annually. The program's success was driven by targeted education of healthcare personnel and families, and by providing Tdap vaccination on-site daily at convenient times for families. More than 90% of eligible postpartum women received Tdap vaccine and approximately 60% of infants for whom detailed information was available had one or more contacts, other than a mother, immunized with Tdap.
Data Collected
The electronic medical record of infants with a diagnosis of pertussis through hospital microbiology records and International Classification of Diseases, Ninth Revision codes were reviewed to ensure they met the following criteria: birth date from May 1, 2004 through August 31, 2011, ≤6 months of age at the time of pertussis diagnosis and microbiologically confirmed infection with B. pertussis. Infants with B. parapertussis infection only were excluded from further analysis. Additional data collected included demographics, hospital of diagnosis, need for hospitalization and admission to an intensive care unit (ICU), duration of hospitalization and outcome. It was determined whether infants had been born at the intervention hospital (BTGH) using their date of birth and electronic database. Infants born at BTGH were then cross-referenced with the BTGH pertussis immunization program database to determine whether their mothers and/or infant contacts had received Tdap vaccine.
Statistical Analysis
Statistical analysis was performed using SPSS version 22.0 (SPSS, Chicago, IL). Descriptive characteristics were assessed. Statistical significance for dichotomous outcomes was determined by χ and Fisher exact tests. Normally distributed data were evaluated by means and the Student's t test or one-way analysis of variance; where positive or negative skewing of data occurred, statistical significance was calculated by medians and the Mann–Whitney U test. A number of analyses were performed. Characteristics of infants diagnosed with pertussis and the severity of illness during the preintervention period were compared first with infants diagnosed in the entire postintervention period, and then infants born during the preintervention, postpartum and family cocooning periods were compared. Where possible, the completeness of an individual infant's cocoon was calculated by assessing the proportion of their contacts who were vaccinated. The proportions of infants born at BTGH during different intervention periods were compared. Multiple logistic regression analysis accounted for potential demographic confounders such as age, sex and Hispanic ethnicity.
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