Originally published by 2 Minute Medicine® (view original article). Reused on AccessMedicine with permission.

1. In a small case-control study comparing infants with and without group B Streptococcus (GBS) infection at age 7-89 days, rates of exposure to breast milk did not differ between groups, indicating that breastfeeding is not a risk factor for late-onset GBS disease.

2. Infants with late-onset GBS disease were more likely to be born to a mother who had tested positive for GBS than infants in the control group.

Evidence Rating Level: 3 (Average)

Study Rundown:

Group B Streptococcus (GBS) causes a large proportion of neonatal sepsis globally. Late-onset GBS infection (LOGBS) occurs from 7 to 89 days of age. Unlike early-onset GBS, LOGBS incidence has not decreased with intrapartum antibiotic prophylaxis. Case reports have described isolation of GBS from breast milk in mothers of infants with LOGBS, raising questions about the safety of breastfeeding for GBS-colonized mothers. This case-control study paired 76 infants treated for invasive LOGBS disease with 368 matched controls. A large majority of infants in both groups (78% of cases, 75% of controls) were breastfed at the studied timepoint. Infants with LOGBS were not significantly more likely to be breastfed at the time of diagnosis than controls. This study was limited to retrospective health record review, and there was no investigation of steps in the potential horizontal transmission pathway — presence of GBS in breast milk was not studied, nor were risk factors identified by past literature such as maternal mastitis. Despite this study’s relatively small size and limitations, it provides a valuable point of reassurance on the safety of breastfeeding for GBS-colonized mothers. Additionally, the results agree with past literature in identifying positive maternal GBS testing as a risk factor for LOGBS, suggesting that the role for mother-to-child transmission does not end at 7 days.

In-Depth [case-control study]:

This study’s cases were infants aged 7-89 days diagnosed with invasive GBS disease, defined as GBS isolated from a sterile site including blood, cerebrospinal fluid, synovial fluid, or pleural fluid, at 4 hospitals in Victoria, Australia. Controls were infants either hospitalized for more than 7 days after birth for any reason or presenting from home with urinary tract infection or bronchiolitis. Cases and controls were matched for chronological and gestational age, presence or absence of a discharge between birth and studied hospitalization, hospital site, and calendar year. Infants who were either exclusively breastfed or received mixed breast and formula feeding were considered to be breastfed. 78.3% of infants with LOGBS were breastfed compared to 74.5% of controls, a statistically insignificant difference (odds ratio 1.2, 95% CI: 0.7-2.3). Patients in the case group were significantly more likely than controls to have a mother who had screened positive for GBS (58.3% and 36.6% respectively, p = 0.003). 9 patients with LOGBS (9.8%) had recurrent GBS disease.

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