Serum vitamin D level in children with bronchiolitis

Acute bronchiolitis is the most common lower respiratory tract infection during the first year of life. Vitamin D is an important contributing factor to the increasing incidence and severity of bronchiolitis over the past three decades. Numerous international studies have suggested that low vitamin D levels are associated with the severity of bronchiolitis. This study aimed to determine serum vitamin D levels in infants hospitalized with acute bronchiolitis in Myanmar. A cross-sectional analytical study was conducted in medical units of Yankin Children's Hospital from August 2022 to July 2023. A total of seventy-five children aged one to twelve months old were included and the Wang clinical severity score was assessed for severity categorization. A total of 75 children, 86% of the study population, were in the one-to-six-month- old age group and only ten children, 13.3%, were in the six-month to one -year-old age group. According to the Wang clinical severity score, severe bronchiolitis was found in 64% of the study population, and non-severe bronchiolitis was detected in 36%. In this study, the mean vitamin D level in the studied population was 44.29 ± 19.55 nmol/L in non-severe bronchiolitis patients and 35.31 ± 15.83 nmol/ L in severe bronchiolitis patients. In the present study, it is found out that 16 children with severe bronchiolitis cases were vitamin D deficient, and only one child with non- severe bronchiolitis cases were vitamin D deficient. Among the 54 vitamin D insufficient children, 59.3% were severe bronchiolitis, 40.7% were non-severe bronchiolitis cases. Among the 48 cases of severe bronchiolitis, none of them had sufficient vitamin D level. A non-parametric Spearman's rank correlation analysis demonstrated a statistically significant, moderate inverse correlation between serum vitamin D levels and the Wang clinical severity score level ([Formula: see text] = -0.41; P < 0.001), establishing that lower vitamin D concentrations strongly correlate with greater clinical severity. It was noted that each one-point increase in the Wang clinical severity score was independently associated with a decrease of 2.95 nmol/L in serum vitamin D concentration (B = -2.95; 95% CI: -4.97 to -0.93; P = 0.005). Neither age (B = -0.21 per month; 95% CI: -1.96 to 1.54; P = 0.814) nor gender (female versus male, B = 2.84; 95% CI: -5.87 to 11.55; P = 0.518) achieved statistical significance in the analysis of the study. In this study, lower serum vitamin D levels were associated with a higher Wang severity score, but the clinical significance is limited by small sample size, lack of confounder control, and absence of seasonality data. Causal inference cannot be made.