Randomized, Double-blind, Placebo-controlled Clinical Trial to Evaluate the Efficacy of a Probiotic Preparation in the Prevention of Upper Respiratory Tract Infections in a Healthy Adult Population

Randomized, double-blind, placebo-controlled, parallel-group, clinical trial. The study aims to demonstrate the efficacy of the intake of a probiotic product composed of Lacticaseibacillus rhamnosus CRL1505 strain in reducing or preventing upper respiratory tract infections in a healthy adult population.

The study will be focused on a healthy population, so the exclusion criteria will rule out individuals with major acute or chronic illnesses and an immunocompromised state. In addition, those subjects with a regular pharmacological treatment or consumption of food supplements that could influence the outcome of the study in the last 4 weeks prior to inclusión will be excluded. If patients could discontinue this treatment after a washout period and during the intervention period, they would be able to participate in the study. However, the usual medication that is considered not to influence the results of the study will be allowed. Subjects recently vaccinated against influenza will also be excluded, but as the study focuses on a healthy population, a priori vaccination is not recommended and there would be no problem in finding subjects with these characteristics because there is no contradiction.

In addition, subjects included will be asked not to modify their diet or physical activity during the study.

An important data that is not usually recorded in many studies is the use of medication to alleviate the symptoms of URTI, either non-prescription or prescribed by the physician. Only antibiotic medication to treat or prevent bacterial upper respiratory tract coinfections or complications is usually established as a variable (the use of antibiotics is established as a secondary variable in the present study). The investigators consider that it is very important to record the use of these treatments to evaluate if any study group is unbalanced in this regard and/or whether it is a confusion factor when interpreting the results. The investigators could consider the possibility of performing a post hoc analysis of this topic and present it in the final report if the results are interesting.

Similarly, it is important to collect baseline data related to the type of work or continuous contact with people with risk factors such as children or elderly to assess whether the groups are balanced. It will also be collected data about the number of URTIs in the study subjects since 3 months prior to inclusion.