The authors of the Canadian Task Force on Preventive Health Care statement on the prevention of neonatal invasive group B streptococcal (GBS) infection1 have reviewed the literature to produce recommendations for prevention. They advocate selective intrapartum chemoprophylaxis based on a combination of screening and risk factors. However, they do not note that only 50% of the mothers of infants with GBS infection have the risk factors that they list. Thus, given the difficulties in following a complex protocol in clinical practice and the fact that many mothers deliver too quickly to benefit from any strategy of intrapartum chemoprophylaxis, the maximum potential benefit of the strategy they propose would be a reduction in neonatal GBS infection of about 40%. The benefit of adding universal screening to the risk-factor approach is to reduce the number of mothers who receive intrapartum chemoprophylaxis while in labour, but this will inevitably also lead to a slight reduction in the program's effectiveness.
The authors concentrate on the “number needed to treat,” which will of course be smaller with a more focused approach, but they do not address the proportion of total cases that will be prevented. Data on over 600 000 deliveries collected through an ongoing US Centers for Disease Control and Prevention surveillance program have shown that the screening-based approach is greater than 50% more effective than a risk-factor approach.2 An approach based on risk factors plus screening cannot be more effective than an approach based on risk factors alone.
Although it is a laudable goal to reduce the number of women receiving intrapartum antibiotics, there is no a priori reason why that goal (efficiency) should take precedence over the goal of preventing the largest number of cases (effectiveness). With the use of penicillin rather than ampicillin, ongoing analysis of resistance patterns and the use of cefazolin instead of erythromycin or clindamycin for penicillin-sensitive mothers, the risks to the population of this very brief course of focused therapy should be minimized.
The strategy suggested by the task force may be one of the most efficient approaches, but it is one of the least effective.
Keith J. Barrington Neonatologist McGill University Montreal, Que.