Fourteen RCTs were included (n=3,580 patients). Eleven RCTs were double-blind and two were open label; the remaining trial did not provide details of blinding. Nine RCTs scored more than 2 out of 5 points on the Jadad scale, three scored 2 points and two scored 1 point. Sample size ranged from 47 to 571; only two trials has fewer than 100 patients.
Incidence of respiratory tract infections (14 RCTs): Ten of 14 RCTs reported no significant difference between the probiotic and control groups in the incidence of respiratory tract infections. Four RCTs reported a significantly lower incidence in probiotic treatment groups.
Severity of symptoms (six RCTs): Five out of six RCTs reported a significant reduction in symptom severity in probiotic treatment groups. The other RCT reported no significant difference between probiotics and control.
Duration of symptoms (nine RCTs): Three out of nine RCTs reported a significant reduction in symptom duration in probiotic treatment groups. The other six RCTs reported no significant difference between the probiotic and control groups.
Safety (10 RCTs): None of the RCTs reported any serious adverse events. Six RCTs reported no probiotic treatment related adverse events. Four RCTs reported minor adverse event including nausea, vomiting, bloating, diarrhoea or dyspepsia.