Respiratory syncytial virus (RSV) causes bronchiolitis and other significant lower respiratory infections. It spreads mainly via droplets, direct contact, and contaminated surfaces. In most of the United States, the prevalence of RSV infection peaks during the winter. Annually, RSV causes approximately 58,000 hospitalizations and more than 2 million outpatient visits among US children younger than 5 years. It also causes up to 160,000 hospitalizations and 10,000 deaths in adults 65 years and older. Prevention comprises hygiene measures, avoidance of infected individuals, and vaccine and antibody strategies. Vaccination is recommended for adults ages 50 to 74 years with chronic health conditions or weakened immune systems or who live in long-term care facilities. Vaccination is also recommended for adults 75 years and older and pregnant women (between 32 weeks’ and 36 weeks and 6 days’ gestation). The long-acting monoclonal antibody nirsevimab is recommended for infants younger than 8 months born during or entering their first RSV season and high-risk infants and young children ages 8 to 19 months. Diagnosis of RSV infection is primarily clinical, with testing used for high-risk or hospitalized patients. Treatment is supportive. Hospitalization is needed for patients with hypoxia, dehydration, respiratory distress, or underlying high-risk conditions. Coinfections, socioeconomic disparities, and environmental factors (eg, tobacco smoke exposure) increase the risk of severe infection.
Azam A, Naik H. Viral Respiratory Infections: Respiratory Syncytial Virus. FP Essent. 2026;569:41-46.
Case 4. DR is a 2-month-old infant brought to your office in December with 3 days of nasal congestion, cough, and difficulty feeding. During the physical examination, you find she has mild subcostal retractions, audible wheezing, and an oxygen saturation of 91%. The parents are worried, noting that their older child recently had a bad cold. Considering DR’s young age and worsening respiratory symptoms, they wonder if this illness can be managed at home or whether she needs to be hospitalized.
Respiratory syncytial virus (RSV) is the most common viral cause of bronchiolitis.1 It is also a leading cause of acute lower respiratory tract infections worldwide, especially among infants and older adults.
RSV spreads mainly through respiratory droplets, direct person-to-person contact, and contact with contaminated surfaces. Standard infection control measures, including hand hygiene, surface disinfection, and avoidance of contact with symptomatic individuals, are generally sufficient to reduce transmission in the general population. However, antibodies are recommended for infants and certain young children, and vaccines are recommended for pregnant individuals and older adults, including those at increased risk for severe illness.1
Early signs of RSV infection include a runny nose, nasal congestion, and low-grade fever. The diagnosis is primarily clinical, although laboratory tests are available for high-risk settings. Treatment is predominantly supportive.
Epidemiology
Circulation of RSV follows a seasonal pattern in the United States, with case numbers increasing in fall, peaking during winter (typically December through February), and decreasing by early spring. Florida experiences an earlier onset of RSV and thus has a longer season.2 The RSV season in Alaska starts later and extends longer than in the rest of the country.3
RSV activity was notably disrupted during the COVID-19 pandemic because of nonpharmacologic infection control measures (eg, masking, distancing), leading to atypical transmission patterns and delayed or shifted peaks in case numbers.4 Recent trends also show increased viral activity outside the traditional RSV season, highlighting the need for year-round vigilance, especially in high-risk populations.
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