Diagnosis and treatment of viral capillary bronchitis in children Capillary bronchitis is a common lower respiratory tract infection in infants and children, and is the most common cause of hospitalization in children under one year of age. What is the etiology and pathogenesis of capillary bronchitis? Is there any association with asthma? How should treatment and prevention be carried out? Capillary bronchitis is a common lower respiratory tract infection in infants and children and is the most common cause of hospitalization in children under one year of age. Capillary bronchitis is typically characterized by acute inflammation, edema and necrosis of small airway epithelial cells. It often starts with symptoms of rhinitis and cough and progresses to shortness of breath, wheezing, pulmonary sternal stabbing and damsel generosity. Etiology Respiratory syncytial virus (RSV) is the most common cause of capillary bronchiolitis and is detected in approximately 50-80% of nasopharyngeal secretions from hospitalized children. Other viruses include human rhinovirus, parainfluenza virus, metapneumovirus, adenovirus, and coronavirus. Clinical differences between different viral infections are difficult to distinguish, and mixed infections may increase the severity of the disease. Pathogenesis The immune response induced by RSV infection has both a defense against infection and a pathogenic role. Usually after an incubation period of 4-6 days, the virus replicates and proliferates in the nasal epithelium, causing nasal congestion, runny nose and feeding difficulties, and fever is seen in 50% of infected young children. At the same time, necrotic shedding of cells in the nasopharynx and transmission of the virus to the lower respiratory tract lead to necrotic shedding of epithelial cells in the lower respiratory tract, inflammatory cell infiltration, edema, increased mucosal secretions, and destruction of cilia. The necrotic shedding of cells accelerates the clearance of the virus on the one hand, but also causes airway obstruction and induces emphysema and pulmonary atelectasis. Risk factors Many hospitalized term infants do not have significant risk factors, and age may be the only significant risk factor for severe capillary bronchiolitis, with approximately 2/3 of hospitalized children being under 5 months of age. children hospitalized with RSV capillary bronchiolitis are primarily infants and children 30-90 days after birth, during which time maternal-derived immunoglobulin concentrations begin to decline and may be the main cause of susceptibility to the disease. The main reason for this is that Full-term infants receive sufficient neutralizing antibodies from their mothers, whereas preterm infants receive fewer IgG antibodies, which explains the fact that prematurity is an important risk factor for the disease. In addition, prematurity accompanied by chronic lung disease and congenital heart disease may also contribute to the development of severe capillary bronchitis. Capillary bronchitis and asthma Severe capillary bronchitis in infancy and early childhood increases the risk of asthma, especially rhinovirus or RSV capillary bronchitis. This may be due to inflammatory lung injury early in life leading to alterations in normal lung development and changes in airway immune response function. It has been suggested that there is a common genetic basis for the development of capillary bronchitis and asthma, including polymorphisms in genes involved in intrinsic immunity, allergic responses, surface active proteins and inflammatory factor-related genes. Supportive treatment There are no definitive drugs to shorten the course of the disease or accelerate symptom relief, and because of the lack of effective antiviral drugs, treatment of capillary bronchitis is based on symptomatic supportive therapy, including oxygen therapy, asthma control, and nutritional support. The prognosis of most children is good and is not related to the treatment itself. The American Academy of Pediatrics has published clinical management guidelines to improve the standardized diagnosis and treatment of capillary bronchitis in children. The guidelines do not recommend routine chest radiographs in children, routine pathogenic testing, or the use of bronchodilators, epinephrine, and glucocorticoids for the treatment of childhood capillary bronchiolitis. Nebulization with 3% hypertonic saline can be considered to improve symptoms in children with mild to moderate disease; routine oxygen therapy is not recommended for children without acidosis and oxygen saturation >90%; routine antibiotics are not recommended, but adequate nutrition and hydration should be ensured. Immunoprophylaxis Palizumab, a humanized monoclonal antibody directly against RSV surface fusion protein, has been shown to reduce hospitalization rates for RSV infection in preterm infants by 5.8% based on a large randomized double-blind clinical trial. Immunization is recommended for preterm infants (<29 weeks), preterm infants with concomitant chronic lung disease (<32 weeks), and children with congenital heart disease in the presence of cyanosis to prevent and reduce recurrent episodes of wheezing and reduce the incidence of RSV infection and hospitalization.