P1549: high prevalence of respiratory syncytial virus in haematological patients after covid19 waves.

Topic: 30. Infections in hematology (incl. supportive care/therapy) Background: Respiratory syncytial virus (RSV) is one of the most common respiratory viruses that can affects not only infants but also elderly and immunocompromised patients (pts). After the emergence of SARS-CoV-2, a reduction of RSV spread was documented probably due to the implementation of public health measures and social distancing. Reports from European Center for Disease Prevention and Control (ECDC) highlight the intensified circulation of RSV in many European countries, with an increased transmission rate in all population groups and an earlier start to the RSV 2022-23 season. The impact of RSV infection is assessed as very low in general population contrary to what happens in high-risk groups such as immunocompromised pts. Aims: We aim to analyse the prevalence of RSV in high-risk pts affected by haematological diseases. Methods: This retrospective, single‐centre study was conducted to evaluate RSV infection at Hematological Department in San Raffaele Hospital, Milan in the last 2 years. All consecutive pts affected by symptomatic RSV infection were reported: cohort-1 refer to season 2021-22 (1st Oct 2021-10th Feb 2022) and cohort-2 refer to season 2022-23 (1st Oct 2022-10th Feb 2023). We collect all clinical information and outcomes for each pts. The immunodeficiency scoring index (ISI) score (low, moderate, high) was calculated for each pts to predict the risk of evolution from upper respiratory tract infection (URTI) into lower respiratory tract infection (LRTI) and poor outcomes (Shah DP, et al. Blood. 2014 May 22;123(21):3263-8). Treatment was administered according to institutional policy, upon written informed consent for off-label therapies (ribavirin and palivizumab) and use of medical records for research. Results: 252 nasal swab were collected in the 2 seasons: RSV positivity was documented in 5/72 (7%) swabs in cohort 1 and 36/180 (20%) in cohort 2. Pts’ characteristics are summarized in table 1. Median follow up from infection in cohort 2 is 36 days (range 14-101 days). In cohort-1 all pts experienced URTI while in cohort-2, 12 pts progressed from URTI to LTRI: 3 required oxygen therapy, 5 non-invasive respiratory support and 3 needed invasive mechanical ventilation. According to ISI score, no pts at low risk progressed from URTI to LTRI and all pts resolved the infection; 4/18 pts (22%) in cohort-2 at moderate risk progressed to LTRI and required hospitalization. All the 8 pts at high-risk progressed to LTRI and 3 deceased due to RSV infection after 10 to 24 days from first positive swab. All pts (8) with high ISI score were treated with both intravenous infusion of immunoglobulin (dosage 0.5-2g/kg) and ribavirin 600mg/q8h; 2 patients received also palivizumab. Immunoglobulin were used in 2/10 and 5/18 pts with low and moderate risk, respectively. Only 1 pt with moderate ISI was treated with immunoglobulin and ribavirin. All therapies were well tolerated with no adverse events. Twenty pts had not received any specific therapies. At data cut off, 7/36 patients still have an ongoing infection. Summary/Conclusion: In season 2022-23, RSV circulation in Europe has intensified with an increased number of severe acute respiratory infections. We confirmed a high prevalence of RSV infection in a cohort of high-risk haematological patient (mortality rate 8%). ISI score is confirmed to be an important tool to identify patients at higher risk of progression from URTI to LTRI. Further investigations are requested to implement preventive, prophylactic and therapeutic measures to reduce the impact of RSV among frail patients.Keywords: Infection, Stem cell transplant