2629. Respiratory Syncytial Virus Epidemiology and Factors Associated with Severity among Hospitalized Infants in Four Middle-Income Countries, 2015–2017

Background Respiratory syncytial virus (RSV) is the most commonly identified viral pathogen among young children with acute lower respiratory tract infection. Understanding global RSV epidemiology and risk factors for severe illness in low- and middle-income settings is critical as new vaccine candidates become available. Methods We prospectively enrolled infants aged < 1 year hospitalized with any acute illness from sites in Albania, Jordan, Nicaragua and Philippines during 2015–2017. Standardized parental interviews and medical record review were conducted. Respiratory specimens collected during enrollment were tested for RSV using rRT–PCR. RSV A or B subgroup was determined using a CDC-developed rRT–PCR assay. Very severe RSV illness was defined as requiring ICU admission or supplemental oxygen. Factors potentially associated with severity were assessed using individual logistic regression models to adjust for age and study site. Results Overall, 1,129 (31%) of 3634 enrolled infants had RSV infection. The median age of RSV-positive infants was 2.7 (range: < 1 to 11.9) months, 665 (59%) were male, and 63 (6%) had ≥1 underlying medical condition. RSV subgroup was determined for 1,028 (91%); RSV A and B co-circulated at all sites with alternating predominance by study year (figure). 583 (52%) infants had very severe RSV illness, which was significantly associated with younger age (median: 2.0 vs. 4.3 months; P < 0.01), study site (aOR: Jordan 5.0, Albania 2.9, Philippines 1.2, Nicaragua reference; P < 0.01), birth by cesarean section (aOR: 1.4; 95% CI [CI] 1.0–1.8; P = 0.03), having received ICU care after birth (aOR: 1.6; CI 1.0–2.4; P = 0.03), chronic heart or respiratory tract disease (aOR: 1.9; CI 1.0–3.4; P = 0.04), and a low weight-for-age Z score (aOR: 1.8; CI 1.3–2.7; P < 0.01). RSV subgroup was not associated with severity (aOR: 1.0; CI: 0.7–1.3; P = 0.72). Conclusion RSV was associated with a substantial proportion of acute illness among hospitalized infants in middle-income countries. Subgroups co-circulated across sites and study years with varying predominance and resulted in similar illness severity. Significant comorbidities were uncommon, but factors including younger age, low weight-for-age and chronic heart or respiratory tract disease were associated with more severe illness. Disclosures All authors: No reported disclosures.