The goal of this randomized non-pharmacological Intervention study is to evaluate the effects of probiotic supplements (Bifidobacterium breve M-16V, Bifidobacterium lactis HN019, Lactobacillus rhamnosus HN001) on children affected by upper respiratory tract infections.

The main questions it aims to answer are:

• probiotic formulation can reduce intensity and duration of fever in children affected by upper respiratory tract infections
• probiotic formulation can influence the gut microbiota composition in children affected by upper respiratory tract infections

Participants will be asked to take probiotic supplements or placebo for 14 days and to collect three fecal samples: before probiotic supplementation (T0), 14 days after probiotic supplementation (T1), and 12 months after the enrollment (T2).

Inclusion Criteria:

• Access to the Emergency room with fever and upper respiratory tract infection
• Age > 28 days and ≤ 4 years
• Signature of informed consent by parents or guardian

Exclusion Criteria:

• Presence of pathologies associated with immunosuppression or ongoing immunosuppressant treatments
• Hospitalisation/hospitalisation
• Diarrhea at enrollment
• No signed informed consent