this is a double-blind randomized placebo controlled clinical trial. 200 healthy children aged 12-48 months, attending day care or preschool for at least 5 days a week, regularly checked by the family pediatrician (FP) involved in the trial, were considered for the study and consecutively contacted during scheduled medical examinations at the FPs office. study plan is 3-month treatment period. The clinical evaluation will be carried out at enrollment, at 30, 60 and 90 days from the beginning of the treatment by the pediatrician. fecal and nasal mucus samples for immunological and microbiological analysis will be collected before the treatment and at 90 days (end of treatment).

Subjects were supplemented daily for 3 months with cow's skim milk fermented with L. paracasei CBA L74 (group A) or placebo (group B).Enrolled children will be randomly assigned, with the use of a computer-generated randomization list to receive either milk fermented with Lactobacillus paracasei CBA L74 or placebo once. Placebo and fermented milk had the same shape, the placebo's taste, dimension, indication, and appearance. At enrollment the family pediatricians consulted the clinical records of each child for previous diseases and pharmacological treatments. At the baseline, after obtaining informed consent from the parents/tutors of each child, the health status of all the study subjects was carefully assessed, and the presence of infectious diseases or other disease was ruled out by means of a complete physical examination, including vital signs (body temperature, pulse rate, respiration rate, blood pressure); neurological status; body growth status; nutritional status; hydration; skin evaluation; otoscopy; evaluation of oral cavity; respiratory/abdomen/lymphonode examination; and genital examination.

A diary will be given to the parents; on a daily basis, patients will monitor and record the frequency/severity of symptoms, episodes of respiratory and/or gastrointestinal infection and their duration and school absence on the diary.

Fecal Analysis: three fecal samples for microbiological and immunological analysis will be collected before treatment and at 90 days (end of treatment). Nasal mucus samples for immunological analysis will be collected before the treatment and at 90 days (end of the treatment).

The study was approved by the Ethics Committee of the Universities of Bari.

Inclusion Criteria:

• Healthy children aged 12-48 months
• attending day care or preschool for at least 5 days a week

Exclusion Criteria:

The exclusion criteria were:

• age <12 months or >48 months
• concomitant chronic infections, chronic systemic diseases, chronic inflammatory bowel diseases, autoimmune diseases, immunodeficiency, malignancy, metabolic diseases
• chronic respiratory tract diseases including respiratory allergies and cystic fibrosis
• malformations of gastrointestinal or urinary or respiratory tract
• history of respiratory or gastrointestinal or urinary tract surgery
• congenital cardiac defects
• functional bowel disorders
• suspected or challenge-proved food allergy, food intolerances
• severe malnutrition (z-score for weight-for-height <3 standard deviation scores)
• use of antibiotics or pre/pro/synbiotics or immune stimulating products in the 2 weeks before the enrolment
• Siblings of subjects enrolled in the study were not allowed to participate to the trial.

The investigators were blinded to the treatment at all times (i.e., allocation, intervention, laboratory analysis and statistical analysis). The study subjects were allocated to two groups (group A or group B) according to a computer-generated randomization list. The pediatricians, parents, and the children were blinded to the allocated treatment. Subjects were supplemented daily for 3 months with cow's skim milk fermented with L. paracasei CBA L74 (group A) or placebo (group B).

Enrolled children will be randomly assigned, with the use of a computer-generated randomization list to receive milk fermented with Lactobacillus paracasei CBA L74 or placebo