Objective: To elucidate the impact of lack of Palivizumab administration during off-season RSV periods on the RSV-related hospitalization among 29-34 weeks of gestational age (wGA) preterm infants. We utilized the summer of 2021 off-season RSV surge during the COVID19 pandemic. Methods: This multi-center retrospective observational study was conducted in 11 medical centers across Israel. We included infants > 1 year-old hospitalized with RSV infection between November 2017-August 2021. Patients were categorized into an in-season admissions group (November-March) and off-season admissions group (April-October). The primary outcome was the proportion of RSV hospitalizations among 29-34wGA infants in relation to total RSV admissions during the same season. Secondary outcomes included clinical severity parameters. Results A total of 3,296 infants were admitted during the RSV season, and 1,044 during the off-season. The proportion of 29-34wGA preemies was significantly higher in the off-season group compared to the in-season group (7% vs 2.1%, p<0.001). In the off-season group, we observed a significantly higher proportion of Jewish individuals (80.1% vs. 59.2%, p=0.001) and higher socioeconomic status (55.1% vs. 45.1%, p<0.001) compared to the in-season group. In the multivariable logistic-regression model, off-season hospitalization odds for 29-34 wGA preemies were significantly higher (2.6-fold, 95% CI:1.8-3.9, p<0.001) compared to in-season, irrespective of demographic covariates. Similar clinical severity parameters was observed between the groups. Conclusions Our results revealed a significantly higher proportion of infants born at 29-34 wGA among those hospitalized during off-season periods compared to in-season periods. These findings highlight the importance of including 29-34 wGA infants into future RSV immunoprophylaxis recommendations.

Objective: Acute bronchiolitis, primarily caused by Respiratory syncytial virus (RSV), is the most common cause of hospitalization in young children. Despite international guidelines supporting clinical diagnosis, laboratory evaluations are often conducted with limited validity. We aim to evaluate the association between C-reactive protein (CRP) levels at admission and disease severity in children hospitalized due to RSV bronchiolitis. Study design: This single center retrospective cohort study included children (0-24 months old) who were hospitalized due to RSV bronchiolitis (January 2018 – March 2022) with CRP levels taken upon admission. Clinical data and severity parameters were extracted using MD-clone platform and the clinical research unit at SUMC. Results: 1,874 children (mean age of 6.7 months, 59% males) with a median CRP level of 1.92mg/dL were included. Children with elevated CRP (>1.92mg/dL) were significantly older (5.1 vs. 3.8 months, p<0.001), had higher rates of pneumonia (9.4% vs. 4.3%, p<0.001 ), urinary tract infection (UTI), (2.2% vs. 0.2%, p<0.001), acute otitis media (AOM), (1.7% vs 0.2%, p<0.001), admissions to pediatric intensive care unit (PICU) (7.4% vs 3.7%, p<0.001), antibiotic treatment (49.8% vs 37.2%, p<0.001) and longer hospitalizations (3.83 vs 3.31 days, p=0.001). Multivariable analysis predicted increased risk for UTI, PICU admission, pneumonia, and longer hospitalization (relative risk of 11.6, 2.25, 1.98, 1.44, respectively, p<0.001)). CRP thresholds of 3.51, 1.9, and 2.81 mg/dL for PICU admission, UTI, and pneumonia, were calculated using Youden’s index with AUC of 0.72, 0.62, and 0.61, respectively. Conclusions: Elevated CRP levels at admission are associated with increased disease severity and higher complication rates in children hospitalized with RSV bronchiolitis.