Objective To investigate the clinical characteristics and analyse risk factors for severe respiratory syncytial virus (RSV) infection in hospitalised infants with acute lower respiratory tract infections (ALRIs).

Methods A retrospective review of the medical records of infants with RSV-associated ALRIs between March 1st, 2011 and February 29th, 2012 was done.

Results Among 913 RSV-associated ALRI infants, there were 288 severe infants (31.5%). The severe cases accounted for 4.2% of the hospitalised children and gave a hospital RSV mortality rate of 1.0%. The occurrence of severe RSV infection had a seasonal variation, with a peak in winter (45.6%). The proportions of cases with tachypnea, apnea, cyanosis, and fine rales were significantly higher in the severe ALRIs group (all p < 0.001). The incidences of bronchitis, pneumonia and readmission in the severe group were higher than those in the non-severe infants during the one-year follow-up (all p < 0.001). Multivariate logistic regression determined the factors increasing the risk of severe RSV infection were: low-birth-weight [1.698 (1.028~2.805)], under 3 months of age [3.385 (2.174~5.271)], congenital heart disease [1.667 (1.149~2.418)], bronchopulmonary dysplasia [8.505 (1.731~41.780)], and airway abnormalities [2.246 (1.008~5.005)].

Conclusions Severe RSV infection is associated with a high hospitalisation and mortality. Preventative measures should be targeted against high-risk hospitalised infants, especially those who are low-birth-weight, under 3 months of age, and with underlying diseases.