Abstract: Background The collective living environment during the preschool period is associated with a high incidence of acute upper respiratory tract infections (AURTIs). Objective To explore the effectiveness of physiological saline nasal irrigation (seawater) in preventing AURTIs in healthy preschool children entering childcare centers, providing a theoretical basis for improving hygiene and healthcare in childcare institutions. Design Singlecenter randomized controlled trial (RCT). Methods Healthy children in the middle class of kindergartens were selected as the study subjects, and cluster random sampling was conducted at the class level. The study was not blinded. The intervention group received nasal care with seawater nasal irrigation at room temperature, with one spray before entering and leaving the kindergarten each day, for a semester of kindergarten attendance (192 times over 96 days). The operation was performed according to the recommended methods in the Expert Consensus on Nasal Saline Irrigation in Children with Upper Respiratory Tract Infections (2023). The control group received organized interventions when entering and leaving the kindergarten each day. The kindergarten healthcare doctors recorded nasal irrigation twice daily and adverse reactions. Interrupted nasal irrigation time, the first report of AURTIs, onset time of nasal symptoms, relief time, disappearance time, and withdrawal time were also recorded. Those meeting the following criteria were excluded: children in the intervention group with nasal irrigation interruption ≥1 week (including Saturdays and Sundays); children with absenteeism exceeding 20% of the school days during the study period (19 days); children who withdrew from the study halfway (e.g., transferring schools); children who used antibiotics, antiviral drugs, or antichlamydial infection drugs based on medical records during the study period; children whose first occurrence of AURTI or nasal symptoms was not reported to the kindergarten within 24 hours according to the CRF table. Main outcome measures Incidence of AURTIs (the number of children who developed AURTI within 48 hours of enrollment divided by the number of enrollees). Results A total of 234 children in the middle class of kindergartens who met the inclusion and exclusion criteria were included in the analysis, with 120 in the intervention group and 114 in the control group. There were no statistically significant differences in gender, age, weight, and actual days in kindergarten between the two groups of children. The incidence of AURTIs during the study period ［55 (45.8%) vs. 81 (71.0%)］and the average number of AURTIs ［(0.7±1.0) vs. (1.4±1.3)］ in the intervention group were significantly lower than those in the control group (P<0.05). There were no statistically significant differences in the incidence of AURTIs between boys and girls in the intervention group. It is the same with the control group. However, there were statistically significant differences in the incidence of AURTIs between two groups in both boys and girls. The intervention group showed statistically significant differences in the relief time ［(2.3±1.0 days) vs. (2.8±0.9 days)］ and disappearance time ［(5.4±1.1 days) vs. (5.8±1.0 days)］ of nasal symptoms compared to the control group. Three cases of mild nasal bleeding occurred in the intervention group, but nasal irrigation intervention continued because of the children's tolerance, and no nasal irritation or ear pain was found. Conclusion Physiological seawater nasal irrigation can reduce the incidence and frequency of AURTIs in healthy preschool children entering childcare centers. It can also effectively relieve nasal symptoms associated with AURTIs and shorten the duration of symptoms. The clinical operation is simple and convenient with few adverse reactions.

Key words: Physiological sea salt water, Nasal irrigation, Healthy preschoolers, Acute upper respiratory tract infection