Genotyping revealed predominance of the 280M-containing genotypes (M/M or T/M) in cases compared with controls (37.8% versus 20.8%, respectively; odds ratio, 2.03; 95% confidence interval, 1.1-3.9; P = 0.025), demonstrating an association between the common CX3CR1-T280M variations and increased risk of severe RSV bronchiolitis.