Randomized, Double-Blind, Placebo-Controlled, Clinical Trial Assessing Lacticaseibacillus rhamnosus CRL 1505 Efficacy in Preventing Upper Respiratory Tract Infections in Healthy Adults

The aim of this clinical trial was to probe the efficacy of the probiotic strain Lacticaseibacillus rhamnosus CRL 1505 in preventing the frequency and duration of upper-respiratory tract infections (URTI) in healthy young adults. The trial was conducted according to a randomized, double-blind, parallel, placebo-controlled design, with a treatment duration of 12 weeks and a follow-up of 4 weeks. Probiotic group consumed capsules containing 1 billion of colony forming units/day of L. rhamnosus CRL 1505. Questionnaires regarding URTI occurrence, duration and symptomatology have been collected along the study. Salivary Immunoglobulin A have been quantified at baseline and at the end of treatment. L. rhamnosus CRL 1505 reduced the proportion of subjects with at least 2 or 3 URTI episodes, leading to 2- to 3-day reduction in the duration of common cold episodes and a 3% increase in the URTI-free time rate. Moreover, participants receiving L. rhamnosus CRL 1505 used less self-administered symptomatic medication for URTI. Intervention with L. rhamnosus CRL 1505 could effectively prevent URTI in healthy adults, demonstrating to be particularly effective in more susceptible subjects. This evidence are of particular interest in the context of probiotic efficacy in the management of respiratory diseases in the healthy adult population. Registry: ClinicalTrials.gov, ID: NCT07091955, Registration date: 29 July 2025.