Is the etiological agent of Severe Acute Respiratory Syndrome (SARS) the SARS-CoV (Severe Acute Respiratory Syndrome Coronavirus) or can it also be a bacterium?

SARS is Exclusively Caused by the SARS-CoV Coronavirus, Not Bacteria

Severe Acute Respiratory Syndrome (SARS) is definitively caused by the novel coronavirus SARS-CoV, and not by any bacterial pathogen. 1 This is a critical distinction in understanding the etiology, pathogenesis, and appropriate management of this serious respiratory illness.

Etiological Evidence

The causative agent of SARS has been conclusively identified through multiple lines of evidence:

• Multiple laboratories identified an identical strain of novel coronavirus in patients with SARS through various methods including:

  • Culture of respiratory secretions and lung tissue specimens
  • Electron microscopy
  • RT-PCR
  • Seroconversion 1

• Koch's postulates were fulfilled when macaques inoculated with the novel coronavirus (but not with human metapneumovirus) developed a severe respiratory illness similar to SARS in humans 1

• The viral genome has been completely sequenced, confirming the agent belongs to the coronavirus family 1

Distinguishing Features of SARS-CoV

SARS-CoV has several distinctive characteristics:

• It belongs to the cluster of Betacoronavirus in the family of Coronaviridae 1
• The virus particles have distinctive spikes of 9-12nm in length, giving the appearance of a solar corona 1
• The diameter varies from about 60-140 nm 1
• The virus can be cultured in human respiratory epithelial cells within about 96 hours 1
• It is sensitive to ultraviolet light, heat (inactivated at 56°C for 30 min), ethyl ether, 75% ethanol, chlorine disinfectant, peracetic acid, and chloroform 1

Transmission and Clinical Features

Understanding the viral etiology of SARS is crucial for managing its transmission:

• SARS-CoV spreads primarily through respiratory droplets and close/direct contact 1
• Aerosol transmission is possible with prolonged exposure in closed environments 1
• The incubation period ranges from 1-14 days, typically 3-7 days 1
• Common symptoms include fever, weakness, dry cough, with potential progression to dyspnea and hypoxemia in the second week 1

Ruling Out Bacterial Causes

While initial investigations considered various pathogens including Chlamydia pneumoniae, the evidence clearly established SARS-CoV as the sole etiologic agent:

• Although some bacterial pathogens like Mycoplasma pneumoniae, Chlamydophila pneumoniae, and Bordetella pertussis can cause acute bronchitis with cough, they are not associated with SARS 1
• The specific clinical, radiological, and epidemiological pattern of SARS is distinctly associated with SARS-CoV infection 1

Diagnostic Confirmation

The diagnosis of SARS relies on identifying the viral pathogen:

• Laboratory confirmation includes culture of SARS-CoV, detection of antibodies to SARS-CoV, or positive PCR test 2
• RT-PCR assays and serological testing are used to confirm SARS-CoV infection 1
• Chest imaging typically shows multiple ground glass shadows and infiltration in both lung fields 1

Clinical Implications

Understanding that SARS is caused exclusively by a coronavirus has important clinical implications:

• Antibiotics are ineffective against the primary viral infection 3
• Treatment focuses on supportive care, including oxygen supplementation and management of complications 2
• Infection control measures are critical, including standard precautions (hand hygiene), contact precautions (gowns, goggles, gloves), and airborne precautions (negative pressure rooms and high-efficiency masks) 2

Conclusion

The scientific evidence conclusively demonstrates that SARS is caused by the novel coronavirus SARS-CoV, not by bacteria. This understanding is fundamental for proper diagnosis, treatment, and prevention strategies for this serious respiratory illness.