Prevalence of Group B Streptococcal (GBS) Colonization among Pregnant Women in Delhi, India

Background: Low GBS rectovaginal colonization rates in pregnant women have been reported in India. Since 1% to 2% of infants born to women colonized with GBS at delivery develop invasive early-onset GBS disease, underestimating maternal colonization rates impacts global estimates of neonatal GBS disease. We hypothesized that colonization rates in India would be substantial using optimal methods and an adequate sample size.

Methods: Lower vaginal and rectal swabs were collected from third trimester pregnant women at Dr. Ram Manohar Lohia Hospital, a tertiary center serving a diverse population in the Central District of Delhi. Swabs were placed in Strep B Carrot Broth™ selective chromogenic media and subculture was performed on GBS Detect™ plates. GBS was confirmed using StrepPRO™ grouping reagent. Isolates were serotyped using ImmuLex^TM Strep-B latex kits (Statens Serum Institute, Denmark) containing antisera to GBS capsular polysaccharides (CPS) Ia, Ib and II-IX. Demographic and clinical data were collected.

Results: From August 2015 to April 2016, 300 pregnant women (mean age 26.9 [range 19-29] years; mean gestation 34 [range 28-42] weeks) were enrolled. GBS colonization prevalence was 15%. Of these women, 15% had vaginal, 29% had rectal and 56% had colonization at both sites. CPS types were III (22.2%), V (20%), II (20%), Ia (13.3%), VII (6.7%) and Ib (4.4%); 13.3% were nontypable. Rural vs. urban dwelling, crowding, and educational level did not differ in colonized vs. non-colonized women. 20.7% had a history of spontaneous abortion; fetal loss at ≥20 weeks’ gestation was significantly more common in GBS colonized than non-colonized women (15.6% vs. 3.5%; p=0.004). Employing Census of India 2011 data for the annual birth cohort (24.9 million) and estimating that 1% of neonates born to GBS colonized women will develop early-onset disease, at least 18,697 cases of early-onset GBS disease occur yearly in India.

Conclusion: Using optimal methods, 15% of third trimester pregnant women in India are GBS colonized. We provide the first contemporary data regarding GBS serotypes in an Indian population. A multivalent vaccine containing 6 CPS types (Ia, Ib, II, III, V and VII) would encompass ~87% of GBS carried by pregnant women in India.