Pneumococcal mastoiditis in children and the emergence of multidrug-resistant serotype 19A isolates.

OBJECTIVE: We review the impact of pneumococcal conjugate vaccine on pneumococcal mastoiditis in children at Texas Children's Hospital.

METHODS: The medical charts (including the number of pneumococcal conjugate vaccine doses) for children with pneumococcal mastoiditis treated at Texas Children's Hospital between January 1995 and June 2007 were reviewed retrospectively. Isolates were serotyped with the capsular swelling method. Pulsed-field gel electrophoresis was performed on the 19A isolates and multilocus sequence typing on selected 19A clones.

RESULTS: Forty-one pneumococcal mastoiditis cases were identified, and 19A (n = 19) was the most common serotype. Before the introduction of pneumococcal conjugate vaccine (from 1995 to December 1999), 0 of 12 cases were 19A. Between April 2000 and October 2006, 15 cases of pneumococcal mastoiditis occurred, and 5 were 19A. Fourteen cases of pneumococcal mastoiditis occurred between November 2006 and June 2007, all of which were 19A. Mastoiditis caused by 19A isolates was more likely to present with subperiosteal abscess and was more likely to need intraoperative mastoidectomy than was mastoiditis caused by non-19A isolates. Multidrug resistance was also common among the 19A isolates; 13 (68%) of the 19A isolates were resistant to all antibiotics tested routinely. Pulsed-field gel electrophoresis analysis placed 14 (74%) of the 19 serotype 19A isolates into a highly related group; 12 isolates were classified as closely related, and 2 were possibly related. Multilocus sequence typing analysis placed the pulsed-field gel electrophoresis cluster isolates into clonal complex 271 (sequence types 320 and 1451).

CONCLUSIONS: At Texas Children's Hospital, 19A has become the predominant serotype causing pneumococcal mastoiditis, partly related to the emergence of multidrug-resistant clonal complex 271 strains. Subperiosteal abscesses and the need for mastoidectomy were more common in children with mastoiditis caused by serotype 19A isolates, compared with isolates of other serotypes.