Which etiologies of viral pneumonia are most common in the winter months?

Updated: Mar 24, 2021
  • Author: Zab Mosenifar, MD, FACP, FCCP; Chief Editor: John J Oppenheimer, MD  more...
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Influenza viruses are the most common cause of viral pneumonia in civilian adults. Influenza usually is seen in epidemics and pandemics. Influenza A is the serotype most frequently responsible for major epidemics and pandemics; it is the most frequent cause of viral pneumonia in adults.

Influenza epidemics occur during the winter months and are associated with significant morbidity and mortality. Patients with chronic obstructive pulmonary disease (COPD), heart failure, hemoglobinopathies, and immunosuppression are at increased risk for severe disease, which can lead to death. Influenza virus is transmitted from person to person primarily by droplet and aerosol exposure to the virus. The incubation period is 1-5 days after exposure.

Patients with high-grade fever, myalgias, and cough during the winter months should be suspected to have influenza. If test results are negative for influenza, RSV pneumonia should also be suspected during the winter in patients with coryza, wheezing, low-grade fever, and patchy infiltrates on chest radiographs. Because clinical features and periods of activity for many viruses overlap, laboratory confirmation of influenza is recommended for cases involving patients who are seriously ill or institutionalized.

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