TORONTO — Serogroup 22 is emerging as an important cause of pediatric meningitis, Dr. Carrie L. Byington and her associates reported in a poster at the Pediatric Academic Societies annual meeting.
Serogroup 22 appears to have a greater propensity to cause meningitis than other vaccine or nonvaccine serotypes, according to an analysis of 300 cases of pediatric invasive pneumococcal disease (IPD) among patients under age 18 years in Utah.
Serogroup 22 is not included in the licensed 7-valent pneumococcal conjugate vaccine (PCV-7) or in higher-valent vaccines under investigation.
Of the 300 cases of pediatric IPD that occurred from 1997 to 2005 at Primary Children's Medical Center in Salt Lake City, 52 were meningitis with or without bacteremia.
During the period prior to the licensure of the PCV-7 vaccine from 1997 to 2000, serotypes 14 (24%), 19F (16%), and 6B (12%) most often caused meningitis.
During the post-PCV-7 period from 2001 to 2005, serogroup 22 (19%), 14 (11%), 18C (11%), and 3 (7%) were the most common groups.
When analyzed by serogroup, 7 of 11 serogroup 22 isolates (64%) were recovered in blood and cerebrospinal fluid from children with meningitis, reported Dr. Byington, professor of pediatrics and associate chair for clinical research at the University of Utah, also in Salt Lake City, and her associates.
When compared with other non-PCV serotypes that caused meningitis (types 3, 7, 15, and 33), serogroup 22 was more likely to be associated with meningitis (64% vs. 20%), with a relative risk of 3.8.
Serogroup 22 also was more often associated with meningitis than the PCV-7 vaccine serogroups 14, 19F, and 6B (64% vs. 42%), with a relative risk of 2.14.
The findings may be related to the fact that individual serotypes of Streptococcus pneumoniae have differing propensities to colonize and cause invasive disease, Dr. Byington said in an interview.
“For example, in Utah, we have not documented a single pediatric isolate of serotype 1 that has resulted in colonization,” she said. “Rather, all isolates of serotype 1 have been from children with invasive disease, specifically complicated pneumonia.
“As we continue our surveillance, we undoubtedly will learn more about serogroup 22 and its propensity to cause IPD.”
Although meningitis cases nationally have declined significantly since the PCV-7 vaccine was approved, the trend was not significant in the Utah data.
Meningitis made up 20% of invasive pneumococcal disease cases in the prelicensure period (25/127) and 16% (27/173) in the postlicensure period, Dr. Byington and her associates reported
The gains experienced by the rest of the United States were not seen in Utah because prior to the introduction of PCV-7, Utah had a high proportion of invasive pneumococcal disease caused by nonvaccine serotypes, Dr. Byington explained.
“This mismatch may then have allowed for more rapid serotype replacement than what has been seen in other parts of the U.S., including the emergence of serogroup 22,” she said.
It is hoped that these pneumococcal serogroup data may inform future vaccine design, Dr. Byington and her associates concluded.