Terminology

Imaging

Top Differential Diagnoses

Clinical Issues

Diagnostic Checklist

Definitions

• Pulmonary viral infection; affects respiratory epithelium from trachea to terminal bronchioles: Alveolar involvement less common; often severe and rapidly progressive

RNA Virus-Related Diseases

• Influenza
  • Seasonal community infections, endemic infections, and unpredictable pandemics
  • Influenza type A: Most important respiratory virus of general population regarding morbidity and mortality
  • Major cause of respiratory illness in immunocompromised hosts
• Avian influenza (H5N1)
  • Contact with infected birds; usually poultry
  • Overall case fatality rate exceeds 60%
• Swine influenza (H1N1)
  • 1st pandemic of 21st century, originally reported in Mexico (spring of 2009)
  • High transmission among humans, but virulence not greater than that observed with seasonal influenza
• Parainfluenza virus
  • Common cause of seasonal upper respiratory tract infection in adults and children
  • Parainfluenza virus type 3: Respiratory illness in immunocompromised hosts and solid organ transplant recipients
• Respiratory syncytial virus (RSV)
  • Ubiquitous cause of respiratory infection
  • Most frequent viral cause of lower respiratory tract infection in infants
• Human metapneumovirus (hMPV)
  • Implicated in 4-21% of infants with acute bronchiolitis
    • Symptoms indistinguishable from those of RSV
  • 4% of cases in patients with community-acquired pneumonia (CAP) or chronic obstructive pulmonary disease (COPD) exacerbations
• Measles
  • One of 3 major infectious diseases worldwide
    • 1.5 million childhood deaths per year
• Coxsackievirus, echovirus, enterovirus
  • Lower respiratory tract infection may occur sporadically, not always associated with pneumonia
• Human T-lymphotropic virus type 1 (HTLV-1)
  • Etiologic retrovirus of adult T-cell leukemia or lymphoma
    • Associations
      • Myelopathy
      • Sjögren syndrome
      • Lymphoid interstitial pneumonia
• Hantavirus
  • Rodent-borne zoonotic disease
    • Hantavirus pulmonary syndrome: Severe acute respiratory distress syndrome (ARDS), rapid clinical progression, and high mortality
• Severe acute respiratory syndrome (SARS)
  • Atypical pneumonia caused by newly discovered SARS-associated coronavirus (SARS-CoV) in 2012 (Guangdong, China)
  • COVID-19 pandemic (2019)
• Middle East respiratory syndrome (MERS)
  • Acute viral respiratory disease caused by novel virus currently named MERS coronavirus (MERS-CoV)

DNA Viruses

• Adenovirus
  • 5-10% of acute respiratory infections in infants and children, < 1% of respiratory illnesses in adults
  • Swyer-James-MacLeod syndrome: Acquired constrictive bronchiolitis due to childhood Adenovirus infection
• Varicella virus
  • Common contagious infection in childhood; increasing frequency in adults
    • Varicella pneumonia: 1 of every 400 cases of adult chickenpox infection
• Cytomegalovirus (CMV)
  • CMV infection: > 70% of hematopoietic stem cell transplant (HSCT) recipients; ~ 1/3 develop CMV pneumonia
    • Infection during postengraftment period (30-100 days after transplantation)
• Epstein-Barr virus (EBV)
  • Primary infection manifests as infectious mononucleosis
  • EBV pneumonia: Rare in immunocompetent or immunocompromised subjects
  • Associated with development of Burkitt lymphoma, Hodgkin lymphoma, nasopharyngeal carcinoma

Radiographic Findings

CT Findings

Microscopic Features

Presentation

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Natural History & Prognosis

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