Respiratory Viruses

Viral infections commonly affect the upper or lower respiratory tract. Although respiratory infections can be classified by the causative virus (eg, influenza), they are generally classified clinically according to syndrome (eg, the common cold, bronchiolitis, croup, pneumonia). Although specific pathogens commonly cause characteristic clinical manifestations (eg, rhinovirus typically causes the common cold, respiratory syncytial virus [RSV] typically causes bronchiolitis), each can cause many of the viral respiratory syndromes.

Severity of viral respiratory illness varies widely; severe disease is more likely in older patients and infants. Morbidity may result directly from viral infection or may be indirect, due to exacerbation of underlying cardiopulmonary conditions or bacterial superinfection of the lung, paranasal sinuses, or middle ear.

Viral respiratory infections are typically diagnosed clinically based on symptoms and local epidemiology. For patient care, diagnosing the syndrome is usually sufficient; identification of a specific pathogen is rarely necessary.

Diagnostic testing should typically be reserved for the following:

• Situations in which knowing the specific pathogen affects clinical management
• Epidemiologic surveillance (ie, identifying and determining the cause of an outbreak)

Pathogen identification can be important in the rare instances when specific antiviral therapy is contemplated. Currently, such instances are limited to early or severe influenza, COVID-19, severe adenovirus pneumonia, or RSV infection in severely immunocompromised patients. Identifying the specific pathogen, (particularly the influenza virus or RSV in hospitalized patients or patients residing in a facility) may also be important for identifying and containing potential outbreaks.

Rapid point-of-care antigen-based diagnostic tests are readily available for influenza, RSV, and SARS-CoV-2, but have poorer sensitivity than laboratory tests. Point-of-care tests are typically reserved for cases when clinical diagnosis is uncertain and

• Antiviral therapy is being considered.
• Identification of the viral pathogen would prevent additional evaluation for or treatment of a bacterial infection.

Polymerase chain reaction (PCR)-based detection of viral pathogens in a multiplex panel (or individually for influenza, RSV, and SARS-CoV-2) is available in many clinical laboratories. These tests are rapid and more sensitive than point-of-care tests and, when available, are preferred for clinical purposes.

Cell culture or serologic tests are slower than PCR tests but may be useful for epidemiologic surveillance.

Treatment of viral respiratory infections is usually supportive.

Antibacterial drugs are ineffective against viral pathogens, and prophylaxis against secondary bacterial infections is not recommended. Antibiotics should be given only when secondary bacterial infections develop. In patients with chronic lung disease, antibiotics may be given with less restriction.

Aspirin should not be used in patients aged ≤ 18 years with a suspected viral respiratory tract infection, because Reye syndrome is a risk.

Some patients continue to cough for weeks after resolution of an upper respiratory infection; these symptoms may lessen with use of an inhaled bronchodilator or corticosteroids.

In some cases, antiviral drugs are useful:

• Oseltamivir and zanamivir are effective for influenza.
• Ribavirin, a guanosine analog that inhibits replication of many RNA and DNA viruses, may be considered for severely immunocompromised patients with lower respiratory tract infection due to RSV.
• Palivizumab, a monoclonal antibody to RSV fusion protein, is being used to prevent RSV infection in certain high-risk infants.
• Nirmatrelvir with ritonavir, remdesivir, molnupiravir, or monoclonal antibodies after onset of symptoms of COVID-19 may be considered to prevent progression to severe disease in high-risk patients, and remdesivir and monoclonal antibodies may be considered for severe COVID-19.