probiotics for c.difficileinfection 777
figure 2. Incidence of Clostridium difficile infection.
This analysis suggested that CDI incidence ≥5% interacts with the overall group effect, suggesting that probiotics may be more effective when the baseline CDI risk is moderate to high. Considering the absolute risk reduction (ARR) and corre- sponding number needed to treat (NNT), if the baseline CDI risk is 1.6% (median of all studies), the observed effect (OR, 0.35) corresponds to an ARR of ~1.0% and an NNT of 96. Using the same effect estimate, given the mean baseline, CDI risk across all studies is 4.34%, and the ARR will be 2.8% (NNT, 35). Combining different probiotic species and strains in meta-
analyses is a contentious issue. Some suggested that pooling different probiotic agents is problematic,50 while others sug- gested that pooling probiotics and subsequently assessing any differences using a priori subgroup analysis based on species, strain, and dose is in accordance with standard meta-analysis methods.12 As with previous aggregate-data meta-analyses, we found no significant difference between species or strains, suggesting that specific effects based on the type of probiotic
may not be an important factor to consider when choosing a probiotic. Instead, it is probably more important to consider the quality of the product and credibility of the manufacturer51 and to use a product that has been investigated in RCTs, particularly a multistrain product given our findings. However, as is typical of subgroup assessments, our analysis is likely underpowered. For example, we rated downward for precision for each of our outcomes. For single species and multispecies probiotics, our data suggest that while both reduce CDI compared to no probiotics, multispecies probio- tics demonstrated a statistically significant treatment effect compared to no probiotics, whereas single-strain probiotics did not. One hypothesis is that multiple species may have an additive effect or may be associated with a higher dose. Among studies of multistrain probiotics,29,34,38–41,46 the daily median value was 50 billion CFU per day; in studies with single-strain probiotics,30–33,35–37,42–45 the daily median value was 15.6 billion CFU per day. However, in exploring the impact of dose response, we found no statistically significant trend. Failure to
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