Acute viral bronchiolitis phenotype in response to glucocorticoid and bronchodilator treatment.

OBJECTIVE: To analyze whether infants admitted to hospital with Acute Viral Bronchiolitis (AVB), who received glucocorticoids and bronchodilators, and who had an atopic phenotype, spent less time in hospital and/or less time on oxygen therapy when compared to those who did not have the phenotype. METHOD: A cross-sectional, retrospective epidemiological study was developed with data from medical records of infants admitted to hospital due to AVB from 2012 to 2019 in a sentinel public hospital. It was verified that the frequency of prescription of glucocorticoids, bronchodilators and antibiotics. Length of stay and oxygen therapy duration were then compared in the group that used glucocorticoids and bronchodilators between those who had a personal or family history of atopy and those who did not. Subsequently, the length of hospital stay was compared among infants who received antibiotic therapy and those who did not. RESULTS: Fifty-eight infants were included. Of these, 62.1 % received an antibiotic, 100 % a bronchodilator and 98.3 % a glucocorticoid. When comparing infants without a family history of atopy, those who received antibiotics had a longer hospital stay (p = 0.01). CONCLUSION: The presence of an atopic phenotype did not interfere with the length of stay and/or oxygen therapy duration of those who received bronchodilators and glucocorticoids. Increased length of stay of infants without a family history of atopy, who used antibiotics without evidence of bacterial co-infection, and the high frequency of prescription of non-recommended drugs call attention to stricter protocol implementation and professional training in AVB diagnosis and care.

Nirsevimab Effectiveness Against Cases of Respiratory Syncytial Virus Bronchiolitis Hospitalised in Paediatric Intensive Care Units in France, September 2023-January 2024.

In September 2023, France was one of the first countries that started a national immunisation campaign with nirsevimab, a new monoclonal antibody against respiratory syncytial virus (RSV). Using data from a network of paediatric intensive care units (PICUs), we aimed to estimate nirsevimab effectiveness against severe cases of RSV bronchiolitis in France. We conducted a case-control study based on the test-negative design and included 288 infants reported by 20 PICUs. We estimated nirsevimab effectiveness at 75.9% (48.5-88.7) in the main analysis and 80.6% (61.6-90.3) and 80.4% (61.7-89.9) in two sensitivity analyses. These real-world estimates confirmed the efficacy observed in clinical studies.

Nirsevimab immunization's real-world effectiveness in preventing severe bronchiolitis: A test-negative case-control study.

BACKGROUND: Several clinical trials have shown that nirsevimab, an antibody targeting the respiratory syncytial virus (RSV), reduces RSV bronchiolitis requiring admission. In 2023-2024, Catalonia and Andorra adopted immunization strategies for children <6 months and those born during the epidemic season. This study evaluates the effectiveness of nirsevimab in preventing hospitalizations from RSV bronchiolitis. METHODS: In the epidemic season of 2023-2024, a test-negative case-control study was conducted in three hospitals from Catalonia and Andorra. Patients <12 months old admitted with bronchiolitis and tested for RSV using molecular microbiology tests were included. The effectiveness in preventing RSV bronchiolitis hospitalization and severe disease was estimated using multivariate models. Comparisons between immunized, non-immunized, and non-eligible patients were made in prospectively collected epidemiological, clinical, and microbiological variables. RESULTS: Two hundred thirty-four patients were included. RSV was detected in 141/234 (60.2%), being less common in the immunized group (37% vs 75%, p < .001). The rate of immunized patients among those eligible was 59.7%. The estimated effectiveness for RSV-associated lower respiratory tract infection was 81.0% (95% confidence interval: 60.9-90.7), and for preventing severe disease (the need for NIV/CMV), 85.6% (41.7-96.4%). No significant differences by immunization status were observed in patients with RSV concerning viral coinfections, the need for NIV/CMV or length of hospital stay. CONCLUSIONS: This study provides real-world evidence of the effectiveness of nirsevimab in preventing RSV-lower respiratory tract infection hospitalization and severe disease in infants during their first RSV season following a systematic immunization program. Immunized patients did not exhibit a higher rate of viral coinfections nor differences in clinical severity once admitted.

Incidental diagnosis of cardiac fibroma in an infant with acute viral bronchiolitis.

OBJECTIVE: Pediatric cardiac tumors are rare and, among them, 90% are benign. Cardiac fibroma is the second most frequent tumor, after rhabdomyoma. The objective of this study is to report a case of cardiac fibroma diagnosed incidentally in a patient admitted with acute viral bronchiolitis. CASE DESCRIPTION: A 5-month-old male infant was admitted to the pediatric emergency department with acute viral bronchiolitis requiring hospitalization. He presented a detectable respiratory syncytial virus in oropharyngeal swab, blood test with lymphocytosis and a chest radiography revealed cardiomegaly. Further cardiologic testing was performed detecting elevation of cardiac biomarkers, an electrocardiogram with alteration of left ventricular repolarization and echocardiogram with a heterogeneous mass in the left ventricular, with areas of calcification. A chest angiotomography suggested rhabdomyosarcoma or cardiac fibroma and a magnetic resonance showed a mass, with characteristics suggesting fibroma. The final diagnosis was made after two cardiac catheterizations for biopsy of the lesion, confirming cardiac fibroma by anatomopathological examination. Because the patient had moderate to severe systolic dysfunction, he was submitted to heart transplant. COMMENTS: One third of cardiac fibromas are asymptomatic, generally diagnosed late through tests ordered for other reasons. The gold-standard test for definitive diagnosis is biopsy. Cardiac fibroma usually does not present spontaneous regression and, in most cases, partial or total surgical resection is necessary. When tumors are unresectable, heart transplantation should be indicated. It is essential to have detailed characterization of the cardiac mass to establish the most appropriate therapeutic approach for each patient.

Does weight influence the course of RSV bronchiolitis in hospitalized infants?

Acute bronchiolitis is among the most common causes of hospitalizations in infants worldwide. Associations between weight and severity of respiratory syncytial virus (RSV) bronchiolitis remain unclear. The aim of this study was to evaluate this association. A single-center, retrospective cohort study of infants aged under 24 months, who were hospitalized between 2018 and 2022 for RSV bronchiolitis. Data from computerized medical records were extracted using the MDclone platform. Participants were divided into three groups according to weight percentiles: underweight (below 5th percentile), normal-weight, and overweight (above 85th percentile). A total of 1936 infants (mean age 6.3 months, 55% males) were included, comprising 274 infants who were underweight, 1470 with normal weight, and 192 with overweight. Underweight infants had a higher rate of admission to the pediatric intensive care unit (PICU) (9.1% vs. 3.5%, P < 0.005) and prolonged length of stay (LOS) in the hospital (3.13 vs. 2.79 days P < 0.001) compared to those with normal weight. Hyponatremia was also more common in the underweight group (23% vs. 15%, P < 0.001). A multivariable model accounting for prematurity and birthweight predicted a relative risk of 2.01 (95% CI 1.13-3.48, P = 0.015) for PICU admission and 1.42 (95% CI 1.17-1.7, P < 0.001) for a prolonged LOS. Being overweight was not associated with a more severe disease.  Conclusion: Underweight infants, hospitalized for RSV bronchiolitis, had a more severe disease course with a higher complication rate, including PICU admission and prolonged LOS. Thus, careful attention and supervision should be given to this subgroup of infants. What is Known: • Established risk factors for severe bronchiolitis include prematurity, BPD, CHD, and compromised immunity. • Abnormal weight status has been associated with an increased risk for morbidity and mortality from infectious diseases, proposedly due to the effects on endocrine and immunologic systems. What is New: • Underweight infants hospitalized with RSV bronchiolitis face an independent risk of PICU admission and prolonged hospital stay. • Conversely, overweight infants did not display associations with severity measures in our study.

Respiratory Syncytial Virus Bronchiolitis Before and After COVID-19 Pandemic: Has the Immunity Debt Been Paid Off?

BACKGROUND: Our aim was to hypothesize that the COVID-19 pandemic influenced the characteristics of viral bronchiolitis by comparing the last 3 epidemics with 3 pre-COVID-19 epidemics in infants hospitalized with bronchiolitis. METHODS: We prospectively enrolled 637 consecutive infants (median age 3.0 ± 2.1 months, 58.5% males), hospitalized for bronchiolitis during 6 consecutive annual epidemic seasons from 2017 to 2023. All parents of the children were given a structured anamnestic questionnaire. A nasopharyngeal aspirate was tested for 15 respiratory viruses. As measures of severity, we evaluated the O 2 supplementation and the admission at the pediatric intensive care unit. RESULTS: A total of 166 were hospitalized with bronchiolitis in 2017-2018, 97 in 2018-2019, 69 in 2019-2020, 0 in 2020-2021, 129 in 2021-2022 and 176 in 2022-2023. Taking together the 332 bronchiolitis cases hospitalized during the 3 prepandemic seasons, they peaked between December and January; after the flat curve in 2020-2021, the cases of bronchiolitis peaked in November 2021 and in December 2022. While the 2021-2022 season registered a less severe clinical presentation, O 2 supplementation and pediatric intensive care unit admissions increased in 2022-2023 with respect to the prepandemic seasons ( P < 0.001). CONCLUSIONS: This study represents an important scientific demonstration of the impact of primary prevention measures on the epidemiology of viral infections; their fluctuations were related to the intensity of restrictive measures and to the changing trend of respiratory viruses. It is essential to predict the real temporal trend of bronchiolitis not to leave high-risk children uncovered and to guide hospitals to maintain a high level of readiness.

Epidemiological shifts in bronchiolitis patterns and impact of the COVID-19: A two-season comparative study.

BACKGROUND: Bronchiolitis is a common lower respiratory tract infection (LRTI) affecting infants and young children. Respiratory syncytial virus (RSV) has historically been the primary causative agent, but other viruses also contribute to the LRTI epidemiology. Recent changes in epidemiology and clinical patterns due to the coronavirus disease 2019 (COVID-19) pandemic have raised concerns. This study aims to analyze the impact of the pandemic on bronchiolitis epidemiology and severity. METHODS: Two consecutive bronchiolitis seasons (October 2021 to March 2022 and October 2022 to March 2023) were compared. Data on viral agents, hospitalization duration, clinical severity, and respiratory support requirements were collected from pediatric patients at San Marco Hospital, University of Catania. RESULTS: In the 2021-2022 season, RSV was the predominant virus (40%), followed by other viruses, with mild clinical outcomes. In the 2022-2023 season, RSV remained prevalent (58.7%), but other viruses, including rhinovirus (RV) and influenza, showed a significant increase (p < .05) in bronchiolitis cases and severity. Notably, RSV-related bronchiolitis did not exhibit greater severity compared to non-RSV cases in the 2022-2023 season, contrary to the previous year. CONCLUSION: The COVID-19 pandemic appears to have shifted the epidemiological landscape of bronchiolitis, with a peak incidence in November instead of January/February. Non-RSV viruses (RV, influenza A and B, as well as metapneumovirus) have gained prominence, possibly due to viral competition and reduced pandemic-related restrictions. Traditionally, RSV has been the primary pathogen responsible for most bronchiolitis cases. Nonetheless, the findings of this study indicate a shifting landscape in bronchiolitis etiology, with RSV gradually diminishing in its role. Contrary to the previous year, RSV-related bronchiolitis did not exhibit greater severity compared to non-RSV cases in the 2022-2023 season.

Azithromycin therapy in infants hospitalized for respiratory syncytial virus bronchiolitis: Airway matrix metalloproteinase-9 levels and subsequent recurrent wheeze.

BACKGROUND: Early life respiratory syncytial virus (RSV) bronchiolitis is a significant risk factor for childhood asthma. In vitro and in vivo studies suggested that decreasing levels of airway matrix metalloproteinase (MMP)-9 during RSV bronchiolitis may be associated with clinical benefits. OBJECTIVE: To investigate whether azithromycin therapy during severe RSV bronchiolitis reduces upper airway MMP-9 levels, whether upper airway MMP-9 levels correlate with upper airway interleukin IL-8 levels, and whether MMP-9 level reduction is associated with reduced post-RSV recurrent wheeze (RW). METHODS: A total of 200 otherwise healthy 1- to 18-month-old infants hospitalized with RSV bronchiolitis were randomized into a double-blind, placebo-controlled trial of oral azithromycin (10 mg/kg daily for 7 days followed by 5 mg/kg daily for 7 days) or placebo. Infants were followed for 2 to 4 years for the outcome of RW (3 or more wheezing episodes). Nasal lavage samples for MMP-9 levels were obtained at baseline, day 14 (end of the study treatment), and after 6 months. RESULTS: Upper airway MMP-9 levels were highly correlated with IL-8 levels at all 3 time points: randomization, day 14, and 6 months (r = 0.80; P < .0001 for all time points). MMP-9 levels were similar between treatment groups at randomization, were lower on day 14 among children treated with azithromycin (P = .0085), but no longer different after 6 months. MMP-9 levels at baseline and change from baseline to day 14 were not associated with the development of RW (P = .49, .39, respectively). CONCLUSION: Azithromycin therapy in children hospitalized with RSV bronchiolitis had a short-term anti-inflammatory effect in reducing upper airway MMP-9 levels. However, the reduction in MMP-9 levels did not relate to subsequent RW post-RSV. TRIAL REGISTRATION: This study is a secondary analysis of the Azithromycin to Prevent Wheezing following severe RSV bronchiolitis-II clinical trial registered at Clinicaltrials.gov (NCT02911935).

ROX (Respiratory rate-OXygenation) index to predict early response to high-flow nasal cannula therapy in infants with viral bronchiolitis.

INTRODUCTION: High-flow nasal cannula (HFNC) is commonly used as first step respiratory support in infants with moderate-to-severe acute viral bronchiolitis (AVB). This device, however, fails to effectively manage respiratory distress in about a third of patients, and data are limited on determinants of patient response. The respiratory rate-oxygenation (ROX) index is a relevant tool to predict the risk for HFNC failure in adult patients with lower respiratory tract infections. The primary objective of this study was to assess the relationship between ROX indexes collected before and 1 h after HFNC initiation, and HFNC failure occurring in the following 48 h in infants with AVB. METHOD: This is an ancillary study to the multicenter randomized controlled trial TRAMONTANE 2, that included 286 infants of less than 6 months with moderate-to-severe AVB. Collection of physiological variables at baseline (H0), and 1 h after HFNC (H1), included heart rate (HR), respiratory rate (RR), fraction of inspired oxygen (FiO2), respiratory distress score (modified Wood's Clinical Asthma Score [mWCAS]), and pain and discomfort scale (EDIN). ROX and ROX-HR were calculated as SpO 2 FiO 2 RR $\frac{\left(\frac{{\mathrm{SpO}}_{2}}{{\mathrm{FiO}}_{2}}\right)}{\mathrm{RR}}$ and 100 × ROX HR $100\times \frac{\mathrm{ROX}}{\mathrm{HR}}$ , respectively. Predefined HFNC failure criteria included increase in respiratory distress score or RR, increase in discomfort, and severe apnea episodes. The accuracies of ROX, ROX-HR indexes and clinical variable to predict HFNC failure were assessed using receiver operating curve analysis. We analyzed predictive factors of HFNC failure using multivariate logistic regressions. RESULT: HFNC failure occurred in 111 of 286 (39%) infants, and for 56 (50% of the failure) of them within the first 6 h. The area under the curve of ROX indexes at H0 and H1 were, respectively, 0.56 (95% confidence interval [CI] 0.48-0.63, p = 0.14), 0.56 (95% CI 0.49-0.64, p = 0.09). ROX-HR performances were better but remained poorly discriminant. HFNC failure was associated with higher mWCAS score at H1 (p < 0.01) and lower decrease in EDIN scale during the first hour of HFNC delivery (p = 0.02). In the multivariate analyses, age and mWCAS score were were found to be independent factors associated with HFNC failure at H0. At H1, weight and mWCAS were associated factors. CONCLUSION: In this study, neither ROX index, nor physiological variables usually collected in infants with AVB had early discriminatory capacity to predict HFNC failure.

Measurement of the interbronchial angle in acute viral bronchiolitis.

BACKGROUND: Acute viral bronchiolitis (AVB) is the most common lower airway infection in children under 2 years. Attempts to determine disease severity based on clinical and radiological manifestations are a major challenge. Measurements of the anatomy of the trachea and main bronchi are not only limited to pure anthropometry, but are also useful for better care of critically ill patients. The purpose of the study is to verify the association between measurements of the interbronchial angle (ITB) and the severity of respiratory disease. METHODS: A cross-sectional study, which included all patients admitted to the Santo Antônio Children's Hospital, over a period of 1 year, with diagnosis of AVB by respiratory syncytial virus (RSV) was designed. ITB angle was measured and clinical characteristics were analyzed. Quantitative variables were compared and correlation analysis was performed using Pearson's correlation coefficient. A receiving operator characteristic (ROC) curve was performed. P-value <0.05 was statistically significant. RESULTS: A total of 425 patients with AVB due to RSV were included. Most of these patients were male and the median age was 130 days, 91.11% of them required oxygen therapy through a nasal catheter, 3.3% used noninvasive ventilation and 4% used mechanical ventilation. Those who required MV or NIV and intensive care unit support were considered severe. The mean ITB was lower for these patients than for those of lesser severity (p < 0.05). CONCLUSION: The present study demonstrates that there is an association between ITB and AVB severity. The smaller the ITB, the greater the disease severity.

Head-to-Head Comparison Between Respiratory Syncytial Virus and Human Metapneumovirus Bronchiolitis in the Setting of Increased Viral Testing.

We compared the epidemiology, severity and management of hospitalized respiratory syncytial virus (n = 305) and human metapneumovirus (n = 39) bronchiolitis in a setting with high respiratory virus testing (95% of admissions tested). Respiratory syncytial virus-positive infants were younger and tended to require more hydration support and longer hospital stays compared to human metapneumovirus-positive infants. Respiratory support requirements were similar between groups despite significant age differences.

Evidentia praxis: nirsevimab y prevención de bronquiolitis en lactantes nacidos a término / Evidentia praxis: Nirsevimab and bronchiolitis prevention in term-born infants

Analizamos la evidencia publicada sobre la eficacia y seguridad de nirsevimab, un anticuerpo monoclonal, empleado para prevenir las infecciones de vías respiratorias bajas (IVRB) por virus respiratorio sincitial (VRS) en el lactante a término. Encontramos un ensayo clínico aleatorizado controlado con placebo doble ciego que incluyó 3012 lactantes, nacidos a término o pretérmino tardío, menores de un año con un seguimiento de al menos 150 días. La calidad de la evidencia se clasificó como baja para IVRB muy grave y moderada para IVRB que precisara asistencia o ingreso. La evidencia se sustenta sobre un escaso número de eventos (para ingresos hospitalarios sólo 29 casos, para IVRB con atención médica 78), por lo que cualquier estimación debe considerarse imprecisa. La eficacia, estimada como reducción relativa del riesgo (RRR) fue del 76,4% (intervalo de confianza del 95% [IC 95]: 62,3 a 85,2) para IVRB por VRS y del 76,8% (IC 95: 49,4 a 89,4%) para ingreso. No se encontraron diferencias en cuanto a seguridad. Existen dudas sobre la importancia clínica, por los criterios de gravedad empleados, y sobre su impacto, con un número necesario a tratar para evitar una IVRB con ingreso de 63 y que requiera asistencia médica de 24. Por la información disponible parece una intervención segura, de la que no esperamos efectos adversos comunes, pero no podemos descartar efectos de baja frecuencia. Asimismo, esperamos contar pronto con estimaciones más precisas de eficacia y seguridad (AU)

We reviewed the published evidence on the efficacy and safety of nirsevimab, a monoclonal antibody, used to prevent respiratory syncytial virus (RSV) associated lower respiratory tract infections (LRTI) in term infants. We have found a randomized double-blind placebo-controlled clinical trial that included 3012 infants, born at term or late preterm, less than one year of age with a follow-up of at least 150 days. The quality of the evidence was classified as low for very severe LRTI and moderate for LRTI requiring medical care or admission. The evidence is based on a small number of events (only 29 cases for hospital admissions, 78 for IVRB with medical care), so any estimate must be considered imprecise. Efficacy, estimated as relative risk reduction (RRR) was 76.4% (95% confidence interval [95 CI]: 62.3 to 85.2) for RSV associated LRTI that required medical care and 76.8% (CI 95: 49.4 to 89.4%) for hospital admission. No differences were found in terms of safety. There are doubts about the clinical importance, due to the severity criteria used, and about its impact, with a number needed to treat of 63 to avoid a LRTI with hospital admission and of 24 to avoid LRTI requiring medical care. Based on the available information, it seems a safe intervention, from which we do not expect common adverse effects, but we cannot rule out low-frequency effects. We also expect to have more precise estimates of efficacy and safety soon. (AU)

Comentario del Comité Asesor de Vacunas de la Asociación Española de Pediatría a Evidencias en Pediatría sobre nirsevimab / Comment by the Advisory Committee on Vaccines of the Spanish Association of Paediatrics on Evidences in Paediatrics about nirsevimab

La bronquiolitis sigue siendo un problema de salud de primer orden en nuestro país, pues genera anualmente miles de consultas en Atención Primaria, colapso en las plantas de hospitalización y cuidados intensivos pediátricas y costes millonarios al Sistema Nacional de Salud. Su interés es máximo, además, porque la mayoría de los que requerirán ingreso hospitalario serán lactantes sanos, sin ningún tipo de factor de riesgo conocido. La altísima incidencia de la enfermedad y la ausencia de un tratamiento específico hace que los pediatras asistamos impasibles a esta epidemia anual, sin poder ofrecer una opción ni preventiva ni terapéutica a nuestros pacientes. En noviembre de 2022, la Agencia Europea de Medicamentos autorizó la comercialización de un anticuerpo monoclonal específico contra la proteína F del virus respiratorio sincitial (VRS), tras los resultados de los ensayos iniciales realizados en más de 3000 lactantes en los que se demostró una eficacia en la prevención de hospitalizaciones por VRS superior al 75%. En mayo de 2023 se comunicaron los resultados preliminares del estudio HARMONIE, llevado a cabo en más de 8000 individuos, representando la primera experiencia en vida real con el uso de nirsevimab y obteniéndose una eficacia superior al 80% en la prevención de hospitalización por bronquiolitis. En este texto se exponen los argumentos del Comité Asesor de Vacunas de la Asociación Española de Pediatría que sustentan la recomendación que hizo este organismo para su uso sistemático en recién nacidos y lactantes menores de 6 meses en España (AU)

Bronchiolitis continues to be a major health problem in Spain, as it generates thousands of consultations in primary care every year, a backlog in paediatric hospitalisation and intensive care wards, and millions in costs to the National Health System. Most of those who require hospital admission are healthy infants, without any known risk factor. The very high incidence of the disease and the absence of a specific treatment means that paediatricians are impassive in the face of this annual epidemic, unable to offer our patients either a preventive or therapeutic option. In November 2022, the European Medicines Agency granted marketing authorisation for a monoclonal antibody specific against respiratory syncytial virus (RSV) F protein, following results from initial trials in more than 3,000 infants that demonstrated greater than 75% efficacy in preventing RSV hospitalisations. Preliminary results from the HARMONIE study, conducted in over 8000 individuals, were reported in May 2023, representing the first real-life experience with the use of nirsevimab and showing greater than 80% efficacy in preventing hospitalisations for bronchiolitis. This text presents the arguments of the Vaccine Advisory Committee of the Spanish Association of Paediatrics to support the recommendation made by this group for its routine use in newborns and infants under 6 months of age in Spain(AU)

Bronchiolitis guidelines: what about the Italian situation in a primary care setting?

Acute viral bronchiolitis is the most common cause of hospitalization in children under 12 months of age. The variable clinical presentation and the potential for sudden deterioration of the clinical conditions require a close monitoring by healthcare professionals.In Italy, first access care for children is provided by primary care physicians (PCPs) who often must face to a heterogeneous disease presentation that, in some cases, make the management of patient with bronchiolitis challenging. Consequently, Italian studies report poor adherence to national and international guidelines processed to guide the clinicians in decision making in acute viral bronchiolitis.This paper aims to identify the potential factors contributing to the lack of adherence to the suggested guidelines derived by clear and evidence-based recommendations among primary care physicians operating in an outpatient setting, with a specific focus on the context of Italy. Particularly, we focus on the prescription of medications such as ß2-agonists, systemic steroids, and antibiotics which are commonly prescribed by PCPs to address conditions that can mimic bronchiolitis.

Multilevel analysis identifying the factors associated with RSV detection in infants admitted for viral bronchiolitis in the era of the COVID-19 pandemic.

OBJECTIVES: To identify factors independently associated with respiratory syncytial virus (RSV) detection in infants admitted for viral bronchiolitis during 3 consecutive years, before and during the COVID-19 pandemic, in Bogota, Colombia, a middle-income country with a subtropical highland climate. METHODS: An analytical cross-sectional study was conducted before and during the COVID-19 pandemic, including patients with a diagnosis of viral bronchiolitis admitted to all the hospitals of the city between January 2019 and November 2021. We evaluated a set of a priori-selected predictor variables that included individual, healthcare system, meteorological, air pollutant, and COVID-19 variables. Since the variables analyzed are hierarchical in nature, multilevel modeling was used to identify factors independently associated with detection of RSV as the causative agent of viral bronchiolitis. RESULTS: A total of 13,177 patients were included in the study. After controlling for potential confounders, it was found that age (odds ratio [OR] 0.86; 95% confidence interval [CI] 0.76-0.97), a third level of medical care institution (OR 3.05; 95% CI 1.61-5.76), temperature (OR 1.60; 95% CI 1.24-2.07), rainfall (OR 1.003, 95% CI 1.001, 1.005), NO2 (OR 0.97; 95% CI 0.95-0.99), CO (OR 0.99; 95% CI 0.99-0.99), and COVID-19 pandemic period (OR 0.84, 95% CI 0.71-0.99) were independently associated with RSV detection in our sample of patients. CONCLUSIONS: The identified factors associated with RSV detection provide additional scientific evidence that may be useful in the development of specific interventions aimed at ameliorating or preventing the impact of RSV in Bogota and probably other similar low- to middle-income countries in high-risk infants.