Group B streptococcal colonization and serotype-specific immunity in healthy elderly persons

Abstract

Background. The burden from group B streptococcal (GBS) disease in elderly persons (age, ≥65 years) has increased. Rates of colonization and prevalence of antibodies against capsular polysaccharides (CPS) that might confer protection against invasive GBS disease in such persons are not defined. Methods. A cross-sectional survey was conducted in an outpatient setting in Houston. GBS colonization rates in this convenience sample were assessed by self-obtained vaginal and rectal specimens (for women) and rectal and urine specimens (for men). The CPS type distribution among GBS isolates was determined, and CPS-specific antibodies against GBS types Ia, Ib, II, III, and V were quantified by enzyme-linked immunosorbent assays. Results. The GBS colonization rate among 254 healthy elderly participants (mean age, 73 years) was 21.7%. CPS types Ia (22.8%), III (12.3%), and V (47.3%) predominated, and 12.3% of colonizing isolates were nontypeable. Random selection of 1 member of 33 participating married couples did not alter the overall colonization rate (21.7%) or GBS serotype distribution. The geometric mean concentrations of CPS-specific IgG in serum specimens were low and were significantly lower for GBS type V, compared with other serotypes (P < .001). Conclusions. Adults ≥65 years of age are colonized with GBS at a rate similar to that of younger persons, but older adults are significantly more likely to carry type V, the leading cause of invasive disease in elderly persons, and to lack type V CPS-specific serum IgG. The CPS of type V GBS should be included in candidate GBS vaccines so that adults ≥65 years of age theoretically could be protected against invasive disease.