Serum Vitamin D Levels and Life-Threatening Respiratory Syncytial Virus Infection in Previously Healthy Infants.

<bold>Background: </bold>25-hydroxyvitamin D (VD) effects on lung function and immune-modulation might affect respiratory syncytial virus (RSV) infection outcomes. We aimed to assess VD levels on admission and their association with life-threatening RSV disease (LTD).<bold>Methods: </bold>A prospective cohort study was conducted during 2017-2019. Previously healthy infants aged <12 months, hospitalized with a first episode of RSV infection, were enrolled. LTD was defined by need for intensive care and ventilatory support. Serum VD levels <20 ng/mL were categorized as deficient, and 20-29.9 ng/mL as insufficient.<bold>Results: </bold>Of 125 patients studied, 73 (58%) were male. Median age was 4 months. Twenty-two patients developed LTD. No differences in viral load were seen between cases with LTD and controls (P = .94). Patients who developed LTD had significantly lower VD levels: median 18.4 ng/mL (IQR, 15.1-26.9 ng/mL) versus 31.7 ng/mL (IQR, 23.6-42.0 ng/mL), P < .001; 59% of infants with LTD had VD deficiency compared with 12% in those with better outcome. Multivariable regression analysis confirmed VD deficiency as a risk factor (odds ratio, 11.83; 95% confidence interval, 3.89-35.9; P < .001).<bold>Conclusions: </bold>These findings provide additional evidence for the development of strategies to prevent severe RSV infections. [ABSTRACT FROM AUTHOR]