Clinical Research Directory

Inclusion Criteria: * Age \< 6 years, gender not limited; * Meets the clinical diagnostic criteria for recurrent respiratory tract infections (Clinical Diagnosis and Treatment Pathway for Recurrent Respiratory Tract Infections in Children (2022 Edition) 10 ); * Parents or other legal guardians of the child fully understand the trial and voluntarily sign informed consent forms before the start of any research procedure; * Willing to discontinue the use of other probiotics during the trial; * Agree to the collection of fecal biological samples during this trial. Exclusion Criteria: * Those deemed by the investigator to have poor compliance or be unsuitable for participation; * Allergic to the investigational product and its components; * Allergic to respiratory tract infection drugs and their components; * Respiratory infections caused by underlying diseases such as primary immunodeficiency diseases, acquired immunodeficiency syndrome (ADRS), congenital airway malformations, congenital heart disease, gastroesophageal reflux disease (GERD), and pulmonary dysplasia; * Patients with severe malnutrition, rickets, and severe primary diseases of the heart, brain, liver, kidney, and hematopoietic systems; * Use probiotic preparations, antibiotics, immunostimulants, or immunosuppressants 4 weeks before participating in the experiment.