Etiological Agent of Severe Acute Respiratory Syndrome (SARS)
SARS is exclusively caused by the SARS-CoV (Severe Acute Respiratory Syndrome Coronavirus), and not by any bacterial pathogen. The evidence clearly establishes that SARS is a viral disease with a specific coronavirus as its etiological agent.
Definitive Identification of SARS-CoV as the Causative Agent
The clinical practice guidelines from 2003 published in Clinical Infectious Diseases definitively state that a novel coronavirus is the etiologic agent of SARS 1. Multiple independent laboratories identified an identical strain of this novel coronavirus in patients with SARS through various methods:
- Culture of respiratory secretions and lung tissue specimens
- Electron microscopy
- RT-PCR
- Seroconversion studies
Furthermore, Koch's postulates were fulfilled when macaques inoculated with the novel coronavirus developed a severe respiratory illness similar to SARS in humans, while those inoculated with human metapneumovirus did not 1.
Viral Characteristics and Classification
SARS-CoV belongs to the Betacoronavirus cluster in the family of Coronaviridae. The virus has the following characteristics:
- Diameter ranging from 60 to 140 nm
- Distinctive spikes of 9-12 nm in length, giving the appearance of a solar corona
- Sensitive to ultraviolet light, heat (inactivated at 56°C for 30 min)
- Can be inactivated by ethyl ether, 75% ethanol, chlorine disinfectant, peracetic acid, and chloroform 1
The viral genome has been fully sequenced, placing SARS-CoV either as a distant member of one of the three previously described antigenic groups or in a fourth antigenic group 1.
Transmission and Pathogenesis
SARS-CoV is transmitted primarily through:
- Respiratory droplets
- Close/direct contact
- Possible aerosol propagation in prolonged exposure to high concentrations in relatively closed environments 1
The virus enters host cells by binding to angiotensin-converting enzyme 2 receptors (ACE2r) 1, which are expressed by mature lung epithelial cells, enterocytes, kidney proximal tubular cells, and endothelial cells.
Diagnostic Confirmation
SARS is definitively diagnosed when:
- SARS coronavirus is isolated
- Antibodies to SARS coronavirus are detected
- PCR test is positive by appropriate criteria 1
Distinction from Bacterial Pathogens
Although initial investigations of SARS patients identified potential pathogens including Chlamydia pneumoniae, influenza virus B, and human metapneumovirus, subsequent research conclusively established that the novel coronavirus was the sole etiologic agent 1. There is no evidence in the medical literature supporting bacterial etiology for SARS.
Recent Coronavirus Outbreaks
It's worth noting that SARS-CoV is distinct from other coronaviruses that have caused subsequent outbreaks:
- MERS-CoV (Middle East Respiratory Syndrome Coronavirus) 1
- SARS-CoV-2, the etiological agent of COVID-19 1
These are all members of the Coronaviridae family but represent distinct viral entities, each responsible for their respective disease syndromes.
Clinical Implications
Understanding that SARS is exclusively caused by SARS-CoV has important clinical implications:
- Antibiotics are ineffective against SARS and should not be used unless there is evidence of bacterial co-infection
- Infection control measures should be specifically targeted at preventing viral transmission
- Research efforts for treatment and vaccines must focus on viral mechanisms rather than bacterial targets
In conclusion, the scientific evidence unequivocally establishes SARS-CoV as the sole etiological agent of SARS, with no evidence supporting bacterial causation of this disease.