INTRODUCTION: It is unclear whether the alleged efficacy of probiotics in childhood acute gastroenteritis depends on the duration and severity of symptoms before treatment. METHODS: Preplanned secondary analysis of 2 randomized placebo-controlled trials in children 3-48 months of age was conducted in 16 emergency departments in North America evaluating the efficacy of 2 probiotic products (Lactobacillus rhamnosus GG and a combination probiotic: L. rhamnosus and L. helveticus). Participants were categorized in severity groups according to the duration (<24, 24-<72, and ≥72 hours) and the frequency of diarrhea episodes in the 24 hours (≤3, 4-5, and ≥6) before presentation. We used regression models to assess the interaction between pretreatment diarrhea severity groups and treatment arm (probiotic or placebo) in the presence of moderate-to-severe gastroenteritis (Modified Vesikari Scale score ≥9). Secondary outcomes included diarrhea frequency and duration, unscheduled healthcare provider visits, and hospitalization. RESULTS: A total of 1,770 children were included, and 882 (50%) received a probiotic. The development of moderate-to-severe gastroenteritis symptoms after the initiation of treatment did not differ between groups (probiotic-18.4% [162/882] vs placebo-18.3% [162/888]; risk ratio 1.00; 95% confidence interval 0.87, 1.16; P = 0.95). There was no evidence of interaction between baseline severity and treatment (P = 0.61) for the primary or any of the secondary outcomes: diarrhea duration (P = 0.88), maximum diarrheal episodes in a 24-hour period (P = 0.87), unscheduled healthcare visits (P = 0.21), and hospitalization (P = 0.87). DISCUSSION: In children 3-48 months with acute gastroenteritis, the lack of effect of probiotics is not explained by the duration of symptoms or frequency of diarrheal episodes before presentation.
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