Burden, risk factors, and outcomes respiratory syncytial virus (RSV) infection in pediatric intensive care units in Türkiye (RSVP Study 2020-2024)

Abstract

Background

Respiratory syncytial virus (RSV) is one of the leading causes of respiratory tract infections in infants and young children requiring a pediatric intensive care unit (PICU). This study aimed to characterize the clinical features, complications, co-infections, and risk factors associated with RSV-related morbidity and mortality in a large PICU cohort over five years.

Methods

This is a retrospective multicenter study to evaluate medical records of patients with RSV infection admitted to the PICUs in Türkiye between 2020 and 2024, including the COVID-19 pandemic. Clinical data, co-morbidities, complications, and outcomes were analyzed. Logistic regression was performed to identify factors associated with mortality.

Results

During the study period, medical records of 646 children (360 boys, 286 girls, 70% younger than 12 months; 70.6% previously healthy) were evaluated. Of the total, 388 patients were delivered by cesarean section, and 139 were born preterm (21.5%; mean gestational age: 32.9 ± 2.96 weeks). A history of newborn intensive care unit admission was present in 174 cases (26.9%). Underlying disease was identified in 190 children (29.4%), and congenital heart disease in 58 (9.0%). Most of them had pneumonia (59.8%) or bronchiolitis (38.1%). Complications included pleural effusion (n = 8), pneumothorax (n = 8), central nervous system involvement (n = 19), apnea (n = 10), and myocarditis (n = 5). Pediatric Acute Respiratory Distress Syndrome (pARDS) occurred in 82 patients (12.7%) and eight pARDS cases (9.8%) resulted in death. The number of pARDS admissions was low during the initial phase of the pandemic, and we observed a resurgence in 2022–2024, peaking in November-December every year. Respiratory co-pathogens were detected in 169 patients (26.2%). The most frequent viral co-infections were rhinovirus/enterovirus (n = 57), influenza A (n = 23), coronavirus NL63/OC43/HKU (n = 17), adenovirus (n = 15), and SARS-CoV-2 (n = 12). Bacterial and fungal secondary infections were identified in 49 patients, most commonly Streptococcus pneumoniae (n = 10) and Pseudomonas aeruginosa (n = 10). During PICU admission, 381 patients required high-flow nasal cannula, 57 non-invasive ventilation, and 106 invasive mechanical ventilation (IMV). Over the clinical course, 165 patients (25.5%) required IMV. The median PICU stay was 6 days. Overall mortality rate was 5.4%, mainly in children with the presence of underlying conditions. Logistic regression revealed that the presence of an underlying disease significantly increased mortality risk (OR 3.15, p < 0.01) and this association remained significant in infants under one year (OR 3.57, p < 0.01).

Conclusion

Most children admitted to the PICU due to RSV infection were under one year of age and previously healthy, while mortality was associated with underlying conditions. pARDS is an important clinical picture in the PICU. Secondary infections are common and may complicate disease progression. Monitoring RSV cases in the PICU can be used as a probe for determining the burden of disease and economic cost in the country and for potential treatment and prevention strategies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12887-026-06562-7.

Introduction

Respiratory syncytial virus (RSV) is a leading cause of acute lower respiratory infections and associated hospitalizations in infants and children globally [1]. In 2019, there were 33 million RSV-associated cases of acute lower respiratory airway infection, 3.6 million RSV-associated hospital admissions, and 101,400 RSV-attributable deaths in children under 5 years of age [2]. More than 97% of pediatric RSV-related deaths occur in low- and middle-income countries [1].

Initial RSV infection often occurs in the first year of life, with almost all children infected by their second birthday [3]. RSV causes a wide spectrum of respiratory disease, from mild upper respiratory illness to and life-threatening lower respiratory tract infections (LRTI) including bronchiolitis and pneumonia [1]. RSV-related severe lower respiratory tract infections in infants and young children necessitate pediatric intensive care unit (PICU) admission [4]. Approximately 5% of hospitalized infants with RSV infection require admission to the PICU [5]. The proportion of children aged 1 month to 18 years hospitalized with RSV infections who require admission to a PICU varies based on age, underlying health conditions, and geographic location [6]. For instance, a study focusing on children aged 0–9 years reported an PICU admission rate of 1.8%, with a higher rate of 4.4% among infants aged 0–5 months [6]. Over the last 2 decades, RSV-related PICU admissions have increased in children < 2 years of age in Europe [7]. Previously defined causes of RSV-related PICU admission are severe respiratory distress (hypoxemia, increased work of breathing, apnea), progression to bronchiolitis or pneumonia or complicated secondary bacterial infections, requirement for advanced respiratory support including mechanical ventilation, host-related factors (prematurity, congenital heart disease, bronchopulmonary disorders, neuromuscular disorders, immune deficiency, etc.), inability to feed, neurological complications, or myocarditis [7–13]. A total of 4.2% of patients with RSV infection required readmission to the PICU after discharge, and this was related to the initial PICU admission [4]. RSV infections in early life are linked to long-term respiratory outcomes, such as recurrent LRTI hospitalizations during infancy, persistent wheezing, and potential impairment of lung function in later childhood and possibly adulthood [1]. RSV infections requiring PICU stay also have an impact of parent’s life and 29.2% of parents showed signs or symptoms of post-traumatic stress disorders [4].

Variations between studies and countries may be attributed to differences in study populations, definitions of respiratory support modalities, and clinical practices across institutions. In Türkiye, there is limited data available for RSV hospitalization and PICU requirements, representing the whole country. To understand the full clinical impact of potential RSV prevention, insight into the yet unseen burden of severe RSV disease will be helpful. The aim of this study was to evaluate the distribution of age and risk factors among patients admitted to the PICU due to RSV from 2020 to 2024 and define the clinical course in the PICU.

Patients and method

Study design and setting

This study is a retrospective, multicenter cohort analysis conducted in PICUs across Türkiye. Data were collected from children diagnosed with laboratory-confirmed RSV infection who were admitted to participating PICUs between January 1, 2020, and December 31, 2024. The study included data from multiple tertiary hospitals located in various regions of Türkiye, representing a geographically and demographically diverse pediatric population. Following authorization from the local ethical committee, we collected medical records of patients diagnosed with RSV from 23 centers in 14 different cities.

Patient selection

Patients were eligible for inclusion if they met the following criteria:

• Age between 1 month and 18 years at the time of PICU admission.

• Confirmed RSV infection via polymerase chain reaction (PCR) or rapid antigen testing.

• Admitted to a participating PICU during the study period.

Patients hospitalized in the newborn intensive care unit have not been evaluated. Cases with incomplete medical records or uncertain RSV diagnoses were also excluded.

Data collection

Data were obtained through a structured review of electronic and paper-based medical records. The following variables were extracted:

• Demographics: age, sex, birth history (mode of delivery, gestational age), and neonatal intensive care unit (NICU) history. Prematurity was defined as birth before 37 weeks of gestation. Prematurity was analyzed as a perinatal risk factor and was not classified as an underlying disease unless accompanied by chronic sequelae such as bronchopulmonary dysplasia.

• Clinical history: presence of prematurity, congenital heart disease, chronic respiratory or neurological conditions, genetic syndromes (e.g., Down syndrome), or other underlying illnesses.

• RSV-related diagnosis: bronchiolitis, pneumonia, pediatric acute respiratory distress syndrome (pARDS), and complications such as pleural effusion, pneumothorax, apnea, myocarditis, and seizures. pARDS was diagnosed and graded according to the Pediatric Acute Lung Injury Consensus Conference (PALICC) criteria [14].

• Treatment modalities: type of respiratory support (e.g., high-flow nasal cannula [HFNC], non-invasive ventilation [NIV], invasive mechanical ventilation [IMV], extracorporeal membrane oxygenation [ECMO]), and length of respiratory support.

• Outcomes: PICU length of stay, total hospital stay, and in-hospital mortality.

Outcomes

Primary outcome

• Distribution of age and risk factors among patients admitted to the PICU due to RSV from 2020 to 2024.

Secondary outcomes

• Characteristics of patients who develop pARDS, comparison of patients who develop pARDS and those who do not develop.

• Determining the characteristics of mortality due to RSV infection and comparing them with surviving patients.

• The early period of the pandemic, the easing restrictions period, and the evaluation of changes in the number of RSV infection cases and seasonality after the pandemic.

Statistical analysis

Statistical analyses were performed using JASP (JASP Team, 2025, Version 0.95.3; University of Amsterdam, The Netherlands). Descriptive statistics were used to summarize the data. Categorical variables were reported as frequencies and percentages, and continuous variables as medians and minimum/maximum or means ± standard deviations, according to data distribution. Comparisons between groups (e.g., survivors vs. non-survivors, pARDS vs. non-pARDS) were conducted using chi-square or Fisher’s exact test for categorical variables and Mann–Whitney U or independent samples t-tests for continuous variables, as appropriate. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated for risk factor analysis. For mortality risk analysis, multivariable logistic regression was performed using the backward likelihood ratio method.A p-value < 0.05 was considered statistically significant.

Results

The study evaluated 646 children (360 boys and 286 girls) in intensive care units for RSV infection from January 1, 2020, to December 31, 2024. The ages of the patients varied from 1 month to 214 months, with a median age of 5 months. Infants aged 1–24 months were analyzed as individual monthly categories, while older children were grouped. Of the cases, 149 were between 1 and 2 months old, 358 were under six months old, and 465 were under one year old. A total of 492 cases involved individuals under 2 years of age, while 577 cases involved those under 5 years of age. Seventy cases were identified within the age range of 6 to 18 years (Fig. 1).

Fig. 1.

Age distribution of children with RSV infection requiring PICU admission. The figure shows the distribution of laboratory-confirmed RSV cases admitted to PICU by age. Infants aged 1–24 months are presented as individual monthly categories, while older children are grouped into broader age ranges. The highest burden of severe RSV disease occurred in early infancy, particularly within the first months of life, with a marked decline in cases beyond two years of age

The study included cases as follows: 73 in 2020, 48 in 2021, 130 in 2022, 227 in 2023, and 168 in 2024. In Türkiye, the first COVID-19 patient detected in March 2020, and restriction policies started at this date. There are limited cases that have been seen from March 2020 to September 2022. Since September 2022, in 2022–2023 and 2024, resurgences of RSV infection have been noted, peaking at November to January (Fig. 2).

Fig. 2.

Monthly distribution of RSV cases requiring PICU admission (2020–2024). The figure illustrates the number of laboratory-confirmed RSV infections admitted to PICUs in Türkiye from January 2020 to December 2024. A marked reduction in cases is observed during the early COVID-19 pandemic period, followed by a clear resurgence from late 2022 onward, with consistent seasonal peaks during the winter months (November–January)

Of the cases, 388 were delivered via C-section, while 258 were delivered vaginally. Of the cases, 139 were preterm (21.5%), whereas 507 were term births (78.5%). The gestational week in cases with a history of premature birth was 32.9 ± 2.96 weeks (ranging from 23 to 36 weeks). A total of 174 cases (26.9%) were previously monitored in the neonatal intensive care unit. In 190 instances (29.4%), a history of underlying disease was noted, while 58 instances involved congenital heart disease (Table 1). None of the patients received palivizumab prophylaxis.

Table 1.

Presence of underlying condition in patients with RSV infection in PICU (n = 190)

Underlying Condition
Congenital Heart Disease Type	N = 58
Ventricular septal defect (VSD)	12
Atrial septal defect (ASD)	13
ASD/VSD	9
Patent ductus arteriosus (PDA)	7
ASD/VSD/PDA	2
Aortic Coarctation	2
TOF (Tetralogy of Fallot)	3
VSD + PDA	1
ASD + PS (Pulmonary Stenosis)	1
Bicuspid Aortic Valve	1
Cardiomyopathy	1
Double Aortic Arch	1
ASD + VSD + Aortic Coarctation	1
ASD + PDA	1
Transposition of great arteries	1
Epilepsy/Epileptic Syndrome	22
Cerebral Palsy with Epilepsy	21
Bronchopulmonary Dysplasia (BPD)	20
Down Syndrome	15
Hematologic/Oncologic Disease	12
Genetic Syndromes	12
Neuromotor Retardation	10
Immunodeficiency	8
Spinal Muscular Atrophy (SMA)	7
Asthma	6
Metabolic Disease	6
Allergic Disorders	4
Diabetes Mellitus	3
Esophageal Atresia	3
Chronic Lung Disease/Cystic fibrosis	4
Congenital Infection	2
Cleft Lip and Palate	1
Osteogenesis Imperfecta	1
Congenital Muscular Dystrophy	1
Other	19

Congenital heart disease has been isolated cardiac defects of associated with other underling disorders

A total of 246 cases (38.1%) were hospitalized for bronchiolitis, 386 cases (59.8%) for pneumonia, and 14 cases for other reasons. Eight cases had pleural effusion, eight had pneumothorax, 19 had central nervous system findings and convulsions, and 10 had apnea. Myocarditis was identified in five cases. Two patients required ECMO support: a previously healthy 2-year-3-month-old boy who survived to discharge, and a 5-year-11-month-old boy with an underlying neurological disease who died.

The median length of stay in the PICU for patients was 6 days (range: 1–155 days), while the total hospital stay had a median of 9 days (range: 1–155 days). In 169 patients, RSV was detected with other respiratory pathogens. On PICU admission, 102 patients received oxygen therapy, 381 patients received HFNC, 57 patients received NIV, and 106 patients required IMV. During the PICU stay, 377 required HFNC, 96 required NIV, and 165 (25.5%) IMV.

In this cohort, the most common co-infection was rhinovirus/enterovirus (57 cases), followed by influenza A (23), coronaviruses NL63, OC43, and HKU (17), adenovirus (15), and SARS-CoV-2 (12). Less frequently observed were parainfluenza viruses (including subtypes and combinations), bocavirus, parechovirus, and various multi-virus combinations (Supplementary Table 1). These findings highlight the significant role of respiratory viral co-infections in children with RSV, which may complicate clinical management and outcomes.

In a cohort of 82 cases diagnosed with pARDS, which included 32 girls and 50 boys, ages varied from 1 month to 151 months, with a median age of 6 months. pARDS cases were observed more frequently in December (n = 30) and January (n = 24). Of the cases, 62.2% were delivered via cesarean section (n = 82), including 20 premature cases (24.4%) and 62 term births. Of the cases analyzed, 39 exhibited underlying diseases, accounting for 47.6%, while 16 cases were identified with congenital heart disease. 29 cases are mild pARDS, 27 cases are moderate and 26 cases are severe pARDS. A diagnosis of pARDS was established in 82 cases (12.7%). Girl predominance was observed in the pARDS group (61.0% vs. 41.8%, p = 0.024). Patient age and gestational age were similar between the groups. The prevalence of prematurity was 24.3% (20/82) in the pARDS group, and 21.1% (119/564) in the non-pARDS group (p = 0.498). A history of previous NICU stay history was also similar between the groups (32.9% vs. 26.6%, p = 0.191). Underlying disorders were significantly more common in the pARDS group (47.5%, 39/82) compared to the non-pARDS group (26.7%; 151/564) (p < 0.001). Similarly, the presence of congenital heart disease was higher in pARDS group (19.5%), than non-pARDS group (7.45%) (p < 0.001). PRISM-3 score (p < 0.001), mechanical ventilation duration (p < 0.001), VIS score (p = 0.043), length of PICU stays (p < 0.011), and total hospital stay (p < 0.01) were all higher in the pARDS group. The rate of secondary bacterial infections rate was similar between the groups (8.5% vs. 9.5%, p = 0.764). Mortality was higher in the pARDS group (9.75%) than non-pARDS group (4.78%), but this difference did not reach statistical significance (p = 0.063).

Forty-nine children complicated with bacterial infection. Secondary infections were identified in 49 RSV cases, most commonly involving Streptococcus pneumoniae (n = 10) and Pseudomonas aeruginosa (n = 10, one with BPD, no cystic fibrosis cases), followed by Haemophilus influenzae (7) and Staphylococcus aureus (5). Less frequent pathogens included Klebsiella pneumoniae, Acinetobacter spp., Candida spp., and various other bacteria, such as Stenotrophomonas maltophilia, Streptococcus pyogenes, and E. coli (Supplementary Table 2).

During intensive care monitoring, 35 children (15 boys and 20 girls) died, corresponding to an overall mortality rate of 5.4%. There was no significant gender difference with respect to mortality. Twenty-one of the deceased cases were delivered by cesarean section, while fourteen were delivered vaginally. Ten children were born prematurely and twenty-five were born at term. Thirteen cases had a history of admission to the neonatal intensive care unit. Among the deceased patients, 27 had at least one underlying disease, and 5 had congenital heart disease.

Five children had congenital heart disease, including ventricular septal defect (VSD) in three cases, combined VSD, atrial septal defect (ASD), pulmonary hypertension, and immunodeficiency in one case, and combined ASD and VSD in one case; all had a previous history of cardiac surgery. Other underlying conditions included bronchopulmonary dysplasia (n = 5), neurological disorders (n = 6; one child had spinal muscular atrophy), immunodeficiency (n = 2), Down syndrome (n = 2), inborn errors of metabolism (n = 3), hematological–oncological diseases (n = 6), and other chronic conditions (n = 8).

To identify factors associated with mortality in patients with RSV infection, logistic regression analysis was performed using the backward likelihood ratio method, including age, gender, prematurity, previous neonatal intensive care unit hospitalization, presence of underlying disease, presence of congenital heart disease, and pARDS as covariates. In the overall cohort, only the presence of underlying disease remained significantly associated with mortality (p < 0.01). A subgroup analysis restricted to children younger than one year yielded similar results, with underlying disease again being the only significant predictor (p < 0.01). The risk of mortality in patients with underlying diseases was significantly higher than in those without such conditions (OR 2.22; 95% CI 1.38–3.17; p < 0.001).

Discussion

This is one of the largest clinical studies, including 646 children with RSV in PICUs across Türkiye. Previous studies showed that approximately 5% of hospitalized infants with RSV infection require admission to the PICU. Risk factors for children with RSV infection requiring PICU admission are grouped into patient-specific, socioeconomic, and clinical. Infants under 6 months, especially those < 3 months, are at the highest risk [5]. Premature infants (especially those < 35 weeks gestational age) are particularly vulnerable [7]. Preexisting medical conditions, including congenital heart disease (particularly cyanotic heart disease), BPD, neuromuscular disorders, and congenital and acquired immunodeficiencies [11–13]. Exposure to tobacco smoke, crowded living conditions, and lack of breastfeeding can contribute to increased RSV severity and PICU admission risk [8, 9, 11–13]. In the present study, 76.1% of the patients are below two years of age, 72% are below one year of age, and 55.4% were below 6 months of age. 23% of the patients are 1–2 months of age, and this age period is the peak of PICU stay. In our PICU cohort, 21.5% were preterm births, 8.7% had congenital heart disease, and 70.6% were previously healthy. Our findings are consistent with global patterns, particularly the high burden among infants < 12 months. Halasa et al. [11] showed that 65% of children requiring PICU stay are below 1 year of age, 5–10% have congenital heart disease, and 20% were prematurely born in the US. Another study from United States showed that 63% of patients were below 1 year old, 8% had congenital heart disease, 15–20% were preterm [12]. Regarding the Brick Study, a nationwide, prospective, observational, multicenter study which was performed in the Netherlands, of 423 patients, median age was 46 days, 72.9% were term born and 69% had no comorbidities [4]. Young age (< 6 months) is an independent risk factor even without comorbidities [8]. In our study neurological disorders (cerebral palsy, epilepsies, neuromotor retardation, and spinal muscular atrophy) are important underlying conditions for RSV infection requiring PICU. BPD and other chronic pulmonary disorders, Down syndrome, and immune deficiencies are important risk factors. The presence of underlying disorders increased the risk of pARDS three-fold and was associated with a two-fold higher mortality. A study analyzing data from England estimated RSV hospitalization rates in infants up to 24 months old, highlighting higher rates among those with risk factors such as chronic lung disease and congenital heart disease [15]. While underlying disorders are important for the severity and mortality of the disease, 70.6% of children with RSV who required PICU stays were previously healthy. Preventive strategies are essential for healthy infants as well as infants with underlying disorders.

Many countries experience seasonal peaks in RSV transmission. In temperate climates, RSV causes seasonal epidemics during late fall and winter, lasting on average for 5 months with elevated viral circulation. The RSV season can vary across different geographical regions within the same country and may also shift by a few months from year to year [1]. A nationwide epidemiological study conducted between 2008 and 2010 across 32 hospitals in Türkiye analyzed seasonal patterns of RSV infections in children under two years of age. RSV infections peaked during the winter months, particularly in January and March [16]. In our study, RSV infections in the PICU peaked during the winter months, particularly from November to January in 2022–2023 and 2023–2024 season. In our study we observed a low number of RSV-related PICU stays during early COVID, followed by a resurgence in 2022–2024, echoing trends reported worldwide. Center for Disease Control and Prevention (CDC) noted record-low RSV transmission in 2020–2021 due to non-pharmaceutical interventions [17]. Post-pandemic rebounds were observed globally, especially in 2022 and 2023, often peaking in late fall/winter [18]. There is an increase for children with RSV infection requiring PICU. In Ontario, between 2017 and 2023, annual RSV hospitalizations among children under 5 ranged from 2,008 to 2,421 cases. The proportion of hospitalized children admitted to the PICU increased from 11.4% in 2021–2022 to 13.9% in 2022–2023 [19].

No specific treatment exists for RSV disease. Infants with RSV disease require supportive care, frequently necessitating hospitalization for respiratory assistance, which may include supplemental oxygen, intubation, mechanical ventilation, and intravenous hydration [1]. Among children admitted to the PICU for RSV infection, the need for IMV varies. In our study, on PICU admission, 58.9% of patients received HFNC, 8.8% of patients NIV, and 16.5% of patients required IMV. During the follow-up, patients required IMV. Increased to 25.5%. Previous studies showed different IMV requirements, varying from 24% to 61.1% [11, 12]. Among children hospitalized with RSV, approximately 29.7% required positive pressure ventilation, and 22.3% required IMV in the United States [12]. Differences in IMV rates across studies are influenced not only by disease severity but also by local clinical practice and resource availability. Thresholds for initiating HFNC or NIV versus early intubation vary among institutions and are shaped by clinician experience, staffing levels, and unit-specific protocols. Therefore, comparisons of IMV rates between health systems should be interpreted cautiously, as they reflect both patient severity and organizational factors rather than disease biology alone.

The development of ARDS in children with RSV infection is less common but can occur, particularly in severe cases [20]. In our cohort of 82 cases diagnosed with pARDS, the median age was 6 months. Among these cases, 24.4% were premature, 47.6% had underlying conditions, and 19.5% had congenital cardiac disease. 64.6% of pARDS cases are moderate or severe, and the mortality rate was 9.8%. A study reported that among children under 2 years admitted to the PICU with RSV infection, the incidence of ARDS was approximately 20%, with 7% classified as severe pARDS [13]. Another study observed that 15.9% of children with RSV infection developed ARDS [20]. An earlier study reported a 15.9% incidence of ARDS in children with RSV infection in the Netherlands [21]. The variability in PICU admission rates, mechanical ventilation requirements, and ARDS incidence highlights the need for continued surveillance and targeted preventive strategies.

In addition to severe respiratory distress, different acid-base disorders including respiratory or metabolic acidosis, and need for high oxygen supplementation, co- or superinfection have an increased risk of complications and PICU need [22]. In this cohort, the most common co-infection was rhinovirus/enterovirus, followed by influenza A, coronaviruses NL63, OC43, and HKU, adenovirus, and SARS-CoV-2. These findings highlight the significant role of respiratory viral co-infections in children with RSV, which may complicate clinical management and outcomes. In our study, 7.6% of children were complicated with bacterial and Candida infections, mainly Streptococcus pneumoniae and Pseudomonas aeruginosa. This spectrum indicates that there must be vigilance regarding bacterial and fungal superinfections in children with RSV, which may impact disease severity and management. Some studies suggest higher viral loads correlate with more severe disease [23]; however, we did not perform analysis for viral loads. Prevention strategies against viral, bacterial, and fungal diseases (influenza and pneumococcal conjugated vaccine and infection prevention strategies bundles in PICU) are essential. The median length of PICU stay was 6 days, and comparable with previous international data of 5–8 days. A recent multicenter study conducted across six PICUs in Istanbul evaluated 119 children admitted with RSV infections. Elevated PRISM-3 scores, higher procalcitonin levels, diagnosis of pARDS, use of inhaled steroids, presence of chronic illnesses, and increased heart rate at admission were associated with longer PICU stays [24]. In our study the mortality rate was 5.4%, mostly with comorbidities. The striking overall mortality burden of RSV disease worldwide, with one in every 50 deaths in children aged 0–60 months and one in every 28 deaths in children aged 28 days to 6 months attributable to RSV. In 2019, 21 100 (12 100–39 300) in-hospital deaths for acute lower respiratory infection that could be attributable to RSV in children aged 0–60 months [2]. A systematic review of severe RSV cases reported a case fatality range of 1.9% to 5.9% in hospitalized pediatric patients [25].

In 2023, a total of 203 children were admitted to PICUs in participating centers due to RSV infection, of whom 160 were under the age of 1 year (excluding infants < 1 month). The participating centers are tertiary referral PICUs that predominantly manage children with more severe clinical presentations and complex comorbidities. Referral patterns may therefore enrich our cohort with patients requiring advanced respiratory support, those with underlying disorders, or cases transferred after initial management in secondary hospitals. This case-mix may lead to an overrepresentation of severe RSV disease and pARDS compared with the overall national spectrum of RSV hospitalizations. Consequently, extrapolation to the national level should be interpreted cautiously, as the proportion of critically ill patients in non-tertiary hospitals is likely lower. Nevertheless, tertiary PICUs represent the final common pathway for the most severe RSV cases and therefore provide a realistic estimate of the upper limit of national PICU burden. Participating centers represent approximately 15% of national PICU capacity. Based on this proportion, the estimated total number of RSV-related PICU admissions nationwide in 2023 would be approximately 1,353 cases, of which around 1,067 would be in children under one year of age. Previous studies indicate that RSV hospitalization rates among infants (0–11 months) ranging from 13 to 26 per 1,000 children annually. Given that approximately 953,000 children were born in Turkiye in 2023, an estimated 12,000–25,000 infants may have required hospitalization due to RSV. Our study indicates that 70% of RSV-related PICU admissions occurred in infants under 12 months, and 55% in those under 6 months, corresponding to an estimated 947 PICU admissions for infants < 12 months and 744 infants < 6 months nationwide.

For the prevention of RSV infection including severe forms requiring PICU stays, there are strategies infection control measures (hand hygiene and cohorting in the hospital, maternal RSV vaccination and monoclonal antibodies [1]. The RSVpreF (Abrysvo^®, Pfizer) vaccine, a bivalent prefusion F protein vaccine, is licensed in many countries—including recently in Türkiye—for use in pregnant individuals and at-risk adults [1, 26]. In Argentina, vaccine effectiveness against RSV-associated LRTI leading to infant hospitalisation was 78·6% from birth to age 3 months and 71·3% from birth to age 6 months. Effectiveness against RSV-associated severe LRTI leading to hospitalisation was 76·9% from birth to age 6 months [27]. Palivizumab, while effective in high-risk groups including for premature infants and those with cyanotic CHD, requires monthly injections [28]. Nirsevimab, a long-acting monoclonal antibody, provides passive immunity to infants throughout their first RSV season with a single intramuscular injection. Nirsevimab was associated with a lower odds of RSV-related hospitalisation (odds ratio 0·17; 95% CI 0·12–0·23), a lower odds of ICU admission (0·19; 0·12–0·29), and a lower odds of LRTI incidence (0·25; 0·19–0·33) in infants aged 0–12 months. In the United States hospitalization, rates during the 2024–2025 RSV season, hospitalization rates among infants aged 0–7 months decreased by 28% to 43% compared to pre-pandemic seasons, attributed to the introduction of maternal RSV vaccines and monoclonal antibody treatments [29, 30]. These findings demonstrate the important role of both maternal vaccination and nirsevimab prophylaxis in reducing severe RSV-related outcomes in infants, including the need for PICU admission. Nirsevimab has not started to be used in Türkiye, and our study will be a background for both maternal RSV vaccine and/or nirsevimab use effectiveness in the future, and PICU studies would be a probe for these interventions.

Compared with large PICU RSV studies from Europe [4] and the United States [11, 12], our study provides some additional insights. The BRICK study [4] offers a national, prospective description of RSV-related PICU admissions during infancy and emphasizes broader outcomes beyond the admission itself, including in-PICU adverse events and parental impact [4]. Our multicenter cohort captures a wider pediatric age range and a longer period that spans the COVID-19 suppression phase and the post-pandemic resurgence, providing a detailed characterization of complications in a real-world, middle-income health system. While Halasa et al. [11] describe critically ill US infants during the 2022 seasonal peak and highlight that many are young and previously healthy, our dataset adds additional clinical PICU outcomes, including the frequency and severity distribution of pARDS, the spectrum of viral co-detections and bacterial/fungal secondary infections, and a mortality model showing underlying disease as the dominant predictor of death. Our study provides baseline, pre-implementation national context for Türkiye and an explicit (cautiously framed) extrapolation of PICU burden that can support future evaluation of maternal RSV vaccination and long-acting monoclonal antibody strategies.

Our study has some limitations. As with all retrospective studies, there is potential for missing data, documentation bias, and inconsistency in clinical definitions or reporting practices across centers. The absence of a comparison group (e.g., RSV patients not requiring PICU or patients with non-RSV bronchiolitis) limits the ability to infer risk associations beyond descriptive outcomes. Lack of RSV subtypes (A vs. B), and viral load can influence severity and outcomes. While large, it’s unclear whether centers represent all regions of Türkiye or whether data is skewed toward tertiary/referral hospitals, possibly overestimating severity. In our study cohort, none of the patients received palivizumab prophylaxis. In Türkiye, palivizumab reimbursement is restricted to narrowly defined high-risk groups (e.g., infants < 29 weeks’ gestation, selected infants 29–31 weeks within 90 days of age, and children < 2 years with BPD requiring treatment or hemodynamically significant congenital heart disease); therefore, the absence of prophylaxis in our cohort most likely reflects these limited eligibility criteria rather than missed opportunities for administration.

Our study represents one of the largest multicenter pediatric intensive care analyses of RSV infection in Türkiye and worldwide, covering a period that includes both the COVID-19 pandemic and post-pandemic resurgence. Our cohort includes a broad age range (1 month to 18 years), capturing both typical infant cases and rarer older pediatric cases. Our study provides critical data on age distribution, and underlying conditions, with implications for both clinical risk stratification and health policy. Our study showed that pARDS (12.7%) represents an important clinical entityin PICU and would be an important outcome for prevention strategies. Underlying disease as a significant mortality risk factor for pARDS and mortality highlights the importance of these patients for potential prevention strategies. In 2023, Türkiye likely experienced approximately 1,353 requiring PICU care. Notably, infants under 12 months constituted the majority of severe cases, emphasizing the need for targeted preventive measures in this age group. One of the first detailed, multicenter PICU studies on RSV in Türkiye, providing crucial local epidemiological insight and background data for potential monoclonal antibodies and/or vaccine implementation. We will start the prospective RSV surveillance in PICUs in Türkiye in October 2025 until 2028.

Authors’ contributions

YC, GE, DY and ECD conceptualized and designed the study. YC, GC, DY, NZ, AB, TK, MH, EE, MD, AA, NY, HEKK, MU, EK, GB, MAK, NA, MC, ES, SE, HCT, FA, AA, NA, OD, NUK, AK, MUY, EA, NA, CO, DA, FE, OOH, EET, FI, NYÖ, AEA, MA, MM, RY, AK, ECD collected the data, YC and ECD analyzed the data, YC, DY, ECD wrote the main manuscript and all authors reviewed the manuscript.

Funding

None.

Data availability

The data presented in this study are available on request from the corresponding author.

Declarations

Ethics approval and consent to participate

The study was approved by the Local Ethical Committee of the Mugla Sıtkı Kocman University Faculty of Medicine on 13.01.2025, decision number 5. The methods used in this study complied with the ethical guidelines established by the institutional and/or national research committee, as well as the 1964 Helsinki Declaration and its subsequent amendments or comparable ethical standards. Patient confidentiality was strictly maintained throughout the study by anonymizing all personal identifiers, and only de-identified data were used in the analysis. Access to patient data was restricted to authorized study personnel. The need for consent to participate was deemed unnecessary for retrospective study according to national regulations by the Local Ethical Committee of the Mugla Sıtkı Kocman University Faculty of Medicine.

Consent for publication

Not applicable.

Competing interests

Ener Cagri Dinleyici performs contract work for the Eskisehir Osmangazi University funded by GSK, Pfizer, and Sanofi Pasteur, outside of this publication. Other author have no conflict of interest.

Clinical trial number

not applicable.