Probiotic administration can protect intestinal microbiota against AID; in 2005, Shamir et al. showed a reduction in the duration of acute gastroenteritis from 1.96 ± 1.24 to 1.43 ± 0.71 days (
p = 0.017), with the addition of 10
9 colony-forming units (CFU) of
Str. thermophilus,
B. lactis, L. acidophilus, 10 mg of zinc and 0.3 g of fructo-oligosaccharide per day [
38]. In addition, several studies have demonstrated the efficacy of
LGG in reducing the duration of acute viral diarrhea and AID, as well as a reduction in length of hospitalization, in both eutrophic and severely malnourished children [
39,
40]. Guarino et al. [
41] also demonstrated a significant reduction in rotavirus shedding. In a prospective European RCT using
LGG (10
10 CFU/250 mL) to supplement ORS in 287 children with acute diarrhea, the results showed a significant decrease in the duration of diarrhea close to 10 % (mean duration of 123 h in the placebo group compared with 110 h in the intervention group) with an improved response in the rotavirus group [
42]. Shornikova et al. [
43] evaluated the efficacy of
L. reuteri
ATCC 55730 in 66 children hospitalized with rotavirus diarrhea randomized into three groups: a placebo group and two groups with different doses of
L. reuteri (10
7 and 10
10 CFU/g once a day for 5 days). The probiotic reduced duration of diarrhea with a dose-dependent effect (2.5 days in the placebo group vs 1.9 and 1.5 in the
L. reuteri groups). In a recent meta-analysis, Szajewska et al. [
44] evaluated two RCTs (
n = 196) using
L. reuteri DSM 17938 and three RCTs (
n = 156) on the evaluation of
L. reuteri ATCC 55730 administration among hospitalized children aged 3–60 months; compared with placebo or no treatment, DSM 17938 significantly reduced the duration of diarrhea (mean difference −32 h, 95 % confidence interval (CI) −41 to −24) and increased the chance of cure on Day 3 (RR 3.5, 95 % CI 1.2–10.8, random effects model). Similar results were obtained with the original strain,
L. reuteri ATCC 55730 [
44].
Other probiotics such as
L. acidophilus LB in a product containing heat-killed
Lactobacillus have also demonstrated effectiveness in reducing the duration of the AID when tested on 73 children with acute diarrhea (50 % rotavirus positive) [
45]. Comparable results were obtained in a double-blind study in 87 Polish children with AID treated with a mixture of three strains of
L. rhamnosus (573L/1, 573L/2, 573L/3) all at a dose of 1.2 × 10
10 CFU twice daily for 5 days;
L. rhamnosus reduced the duration of rotavirus diarrhea (76 ± 35 h vs 115 ± 67 h (
p = 0.03), but not of other types of diarrhea [
46]. Intestinal colonization by administration with these strains was 80 and 41 % at 5 and 14 days, respectively. The intervention also shortened the time required for intravenous rehydration [15 ± 14 vs 38 ± 33 h (
p = 0.006)], although factors such as the variability of care may have influenced the result [
46]. At least three clinical trials in developing countries deny the beneficial effect of
LGG and
L. acidophilus in acute diarrhea or severe diarrhea, probably related to the difference in etiological profile [
47‐
49]. No decrease in the duration of diarrhea with a mixture of
L. acidophilus, B. bifidum (
B. lactis) and
L. bulgaricus was observed [
50]. The strain
L. paracasei ST11 did not reduce the volume of stool in rotavirus infection but improved the results of cumulative stool output (225 ± 218 vs 381 ± 240 mL/kg), stool frequency (27.9 ± 17 vs 42.5 ± 26), and ORS intake (180 ± 207 vs 331 ± 236 mL/kg) in children with less severe non-rotavirus diarrhea compared with those receiving placebo treatment in Bangladeshi children [
51]. Two meta-analyses concluded that most of the studies were conducted in the developed world, and that
LGG, L.
acidophilus and
L. bulgaricus had no efficacy [
52,
53]. In an SR of double blind RCTs, Szajewska and Mrukowicz also found that the duration of viral diarrhea was significantly reduced (by about 17 h or 0.7 days) compared with controls [
54]. The effectiveness of
LGG appears to be connected to the logarithm of the dose (>10
11 as the most effective dose) [
53]. A Cochrane review of 63 RCTs and 8014 participants (56 trials recruited infants and young children) showed the beneficial effect of probiotics in combination therapy with ORS in reducing the duration of diarrhea, although the size of the effect varied considerably between studies [
55]. The average of the effect was significant for mean duration (MD) of diarrhea (MD 24.76 h; 95 % CI 15.9–33.6;
n = 4,555, 35 trials); diarrhea lasting ≥4 days (RR 0.41; 95 % CI 0.32–0.53;
n = 2,853, 29 trials); and stool frequency on Day 2 (MD 0.80; 95 % CI 0.45–1.14;
n = 2,751, 20 trials). The two most commonly studied probiotics were
LGG (13 RCTs) and
S. boulardii (10 RCTs) [
55]. The first double-blind, prospective, randomized study of
S. boulardii (a non-pathogenic yeast) was completed over 15 years ago: diarrhea persisted for more than 7 days in 12 % of the placebo group and in 3 % of the probiotic group [
56]. Since then, several other double-blind, prospective randomized trials conducted on S.
boulardii in children with acute gastroenteritis have consistently shown a significant improvement compared with placebo. A consecutive series of 130 Mexican children with AID from 3 months to 3-years-old were treated with ORS plus placebo or with ORS plus
S. boulardii 600 mg/day for 5 days. A significant decrease in the number of stools occurred from the second day following probiotic use. After 48 h, the percentage of children considered cured was almost 50 % (vs 8 % in the placebo group) and, at Day 4, the percentage cured was up to 95 % (vs 50 % in the placebo group) [
57]. Kurugol and Koturoglu [
58] treated 200 children with acute diarrhea with 250 mg of
S. boulardii or placebo for 5 days: the duration of diarrhea and length of hospitalization was reduced by about 24 h. Villarruel and colleagues [
59] showed similar results in 88 children treated in ambulatory care in Argentina. This study concluded that diarrhea persisted for more than 7 days in 27 % of the control group, compared with 7 % of the group treated with
S. boulardii for 6 days, with a greater effect if treatment was initiated during the first 2 days of diarrhea. In addition, studies of diarrheal parasitic infections showed that
S. boulardii improved feeding tolerance in children with chronic Giardia lamblia [
60]. This probiotic is also shown to be effective in amoebiasis and AIDS-associated diarrhea [
61,
62]. An open RCT in Pakistani children with acute infectious gastroenteritis demonstrated that administration of 500 mg of
S. boulardii for 5 days significantly reduced stool frequency and duration of diarrhea (3.5 vs 4.8 days,
p = 0.001) and resulted, 2 months later, in a 50 % decrease in re-infection rate with a 30 % bodyweight increase [
63].
Regarding the treatment of AID in children, the LATAM consensus estimates that a decrease in the duration of diarrhea, as well as hospitalization length, is an important benefit from the standpoint of social and economic development in acute infectious gastroenteritis in children. While there have been numerous published clinical studies evaluating different probiotics in the treatment of acute gastroenteritis, tests differ in relation to the strains tested, dosages, methodological quality, definitions of diarrhea and the results obtained. Most studies show statistically significant effects in terms of clinical benefit, with greater effect on viral diarrhea [
31]. In general, published meta-analyses conclude that the duration of diarrhea episodes is shortened by approximately 24 h (17–30 h) with the selected strains of lactobacilli and
LGG,
L. acidophilus,
L. bulgaricus, L. reuteri, and
S. boulardii [
31,
33,
52,
54,
55,
67]. In addition, studies have proven the increased effectiveness of probiotics when they were administered in the early stages of the disease; in at least three studies in children with acute diarrhea of different etiologies, probiotic use reduced the average duration of episodes by 57 % (35–71 %) [
44,
64,
68]. Only
LGG and
S. boulardii have Evidence Level 1+ for the treatment of acute diarrhea with ORS in children [
64‐
66]. In developing countries, for varieties of lactobacilli, we found few study-based assays in the community while we observed sufficient data on
S. boulardii.