The quality of evidence is downgraded by study limitations (unclear allocation concealment), and by inconsistency (unexplained variability in results).
A Cochrane review [Abstract] 1 included 17 studies with a total of 3 488 children (mean age 2.4 years). Twelve studies included children who were not prone to acute otitis media (AOM), and 5 studies included children prone to AOM. The definition of 'otitis-prone' was not clear and may have involved a subjective element. Probiotic strains varied: 11 studies evaluated Lactobacillus-containing probiotics, and 6 evaluated Streptococcus-containing probiotics. Also probiotic dose, frequency, and duration of administration varied considerably across studies (duration of administration ranged from 20 days to 2 years).
Probiotics decreased the proportion of children experiencing 1 or more episodes of acute otitis media (AOM) during the treatment (NNTB=10).Post hoc subgroup analysis found that this effect was evident only in children who were not otitis-prone (NNTB=9); the effect was not observed for otitis-prone children (test for subgroup differences was significant, p=0.007). Probiotics decreased the proportion of children having other infections (NNTB=12) and the proportion of children taking antibiotics for any infection (NNTB=8; table T1). There was no difference in the mean number of school days lost (MD −0.95, 95% CI −2.47 to 0.57, statistical heterogeneity I2 =54%; 5 studies, n=1 280). There were no differences in adverse events between probiotic and comparator groups.
| Outcome | Relative effect (95% CI) | Risk with placebo | Risk with probiotic (95% CI) | Participants (studies) |
|---|---|---|---|---|
| Proportion of children with AOM (overall) | RR 0.77(0.63 to 0.93), I2 = 72% | 390 per 1000 | 300 per 1000(246 to 362) | 2 961(16) |
| RR 0.64(0.49 to 0.84), I2 = 59% | 295 per 1000 | 189 per 1000(145 to 248) | 2 227(11) |
| RR 0.97(0.85 to 1.11) | 660 per1000 | 641 per 1000(561 to 733) | 734(5) |
| Difference in proportion of children with other infections | RR 0.75(0.65 to 0.87), I2 = 64% | 363 per 1000 | 272 per 1000(236 to 316) | 3 610(11) |
| Difference in the use of antibiotics | RR 0.66(0.51 to 0.86), I2 = 70% | 397 per 1000 | 262 per 1000(203 to 342) | 1 768(8) |
| Adverse events | OR 1.54(0.60 to 3.94), I2 =56% | 186 per 1000 | 260 per 1000(121 to 474) | 395(4) |
The clinical significance of the observed positive effect is reduced by the unexpected finding that probiotics prevent AOM only in children who were not otitis-prone, and the effect was not observed for otitis-prone children. In addition, there are uncertainties about the optimal strain, as well as the duration, frequency, and timing of probiotics administration.
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