BackgroundRSV is the main agent that causes Acute Lower Respiratory Tract Infection(ALRI) in children. Preterm infants(PT) have a higher risk of hospitalization and complications associated with RSV infection. The aim of this study was to describe epidemiology, clinical pattern and risk factors associated to RSV infection in PT infants.MethodsProspective, Cross-sectional study of patients admitted for ALRI, 2000–2017. Virological diagnosis was made by fluorescent antibody assay of nasopharyngeal aspirates or RT-PCR. We compared epidemiological and clinical features, complications and lethality between full term(FT) and PT infants. Logistic regression was performed to establish lethality risk factors in PT.ResultsA total of 15,451 patients included, 13,033 were tested and 45% (5,831) had positive samples; RSV was predominant (81.3%, 4,738) all through the study period showing a seasonal epidemic pattern (May–July); 14% (655) were PT.PT FT OR IC 95% Two-tailed PGender 58.47% 56.19% 1.1 0.9, 1.3 0.274 Age (median) 7 (4–13) 7 (3–12) 0.001 Bronchiolitis 60.15% 61.39% 0.9 0.8, 1.1 0.548 Comorbidities 56.34% 38.75% 2.0 1.7, 2.4 0.000 Perinatal respiratory history 46.56% 5.46% 15.1 12.3, 18.5 0.000 Cardiopathy 8.09% 5.60% 1.5 1.1, 2.0 0.012 Malnourishment 10.09% 3.74% 2.9 2.1, 3.9 0.000Chronic respiratory disease 41.37% 28.96% 1.7 1.5, 2.1 0.000 Bronchopulmonary displasia 5.95% 0.05% 128.8 31.0, 534.9 0.000 Immunosuppression 1.07% 1.97% 0.5 0.2, 1.2 0.114 Previous hospitalization (ALRI) 41.74% 23.94% 2.3 1.9, 2.7 0.000 Chronic neurological disease 7.48% 3.66% 2.1 1.5, 3.0 0.000 Re-admission 4.74% 3.00% 1.6 1.1, 2.4 0.020 Length of stay (median) 7 (5–10) 8 (5–11) 0.000 ICU requirement 10.84% 7.55% 1.5 1.1, 2.0 0.004 Nosocomial infection 7.86% 6.01% 1.3 1.0, 1.8 0.074 Lethality 3.09% 1.54% 2.0 1.2, 3.4 0.005 Congenital cardiopathy OR = 3.41(1.12–10.3), P = 0.003 and perinatal respiratory history OR = 3.1(1.6–6.1), P < 0.001 were the independent predictors for VSR lethality in PT.ConclusionRSV showed an epidemic pattern (May–July) and affected PT with certain comorbidities, with more severe disease, more complications during hospitalization and higher lethality than FT. RSV lethality in PT was more associated with congenital cardiopathy and perinatal respiratory history.Disclosures A. Gentile, Sanofi Pasteur: Consultant, Speaker honorarium.