Infantile hypertrophic pyloric stenosis after pertussis prophylaxis with erythromycin: a case review and cohort study

Background In February, 1999, a local US health department identified a clu ster of pertussis cases among neonates born at a community hospital and rec ommended oral erythromycin for post-exposure prophylaxis for about 200 neon ates born at that hospital between Feb 1 and Feb 24, 1999, We investigated a cluster of seven cases of infantile hypertrophic pyloric stenosis (IHPS) that occurred the following month among the neonates who had received eryth romycin. Methods We obtained a masked, independent review of the IHPS ultrasonograph y diagnoses, calculated the monthly IHPS incidence, and compared index and historical (1998-99) IHPS cases with respect to several characteristics inc luding erythromycin exposure. We used a retrospective cohort of infants bor n in January and February, 1999, to investigate further erythromycin exposu re and development of IHPS. Findings An independent review confirmed the ultrasonographic diagnoses of all seven index IHPS cases. All index cases versus none of the historical I HPS cases had been given erythromycin for pertussis prophylaxis. The IHPS r ate for infants born in the hospital in February, 1999, was 323 per 1000 li veborn infants, representing nearly a seven-fold increase over 1997-98 (rel ative risk 6.8 [95% CI 3.0-15.7]). Among infants born in January and Februa ry, 1999, erythromycin was associated with IHPS (absolute risk 4.5%, relati ve risk infinity [1.7-infinity]). Interpretation Neonates receiving oral erythromycin may have an increased r isk of IHPS. The risks and benefits of erythromycin for neonatal pertussis prophylaxis should be re-evaluated, and caution should be used in defining risk groups for prophylaxis.