Group B streptococcal infection risk factors

We thank Keith Barrington for his interest in the recommendation statement on GBS infection in newborns.¹ As noted at the end of the article, the statement published in CMAJ is based on a technical report available online at www.ctfphc.org or from the task force office at ctf@ctfphc.org.² In that report, we systematically review the evidence relating to the effectiveness of 3 different strategies for the prevention of early-onset GBS infection in the newborn. We state that 2 strategies reduce the incidence of GBS colonization and early-onset infection: 1) universal screening for GBS at 35–37 weeks followed by selective intrapartum chemoprophylaxis given to colonized women with risk factors and 2) universal screening for GBS at 35–37 weeks and intrapartum chemoprophylaxis of all colonized women. However, based on the number of women who need to be treated, strategy A appears to be more efficient. (To our knowledge, strategy C, which is based on risk factors only, has not been evaluated.)

Barrington misquotes the surveillance study by Factor and colleagues,³ who concede in their discussion section, “We did not have a large enough sample to differentiate between types of policies, such as screening and risk-based approaches.”³ Although the authors show that there was a temporal association between the adoption of guidelines for the prevention of GBS infection in the newborn and a reduction of early-onset infection, the incidence of GBS infection was reduced from 1.29 cases per 1000 live births to 0.58 per 1000 live births (p = 0.006). From this study, one cannot conclude that a given strategy is better than another.

No trial comparing strategy A against B has been conducted to determine which is most effective in reducing early-onset GBS infection. As it is a very rare occurrence, a very large number of pregnant women would need to be enrolled in such a trial.

Vibhuti Shah Arne Ohlsson Canadian Task Force on Preventive Health Care London, Ont.