SARS-CoV-2 Clinical Update: Virology, Transmission & Pathogenesis

What you need to know

• SARS-CoV-2 is genetically similar to SARS-CoV-1, but characteristics of SARS-CoV-2—eg, structural differences in its surface proteins and viral load kinetics—may help explain its enhanced rate of transmission
• In the respiratory tract, peak SARS-CoV-2 load is observed at the time of symptom onset or in the first week of illness, with subsequent decline thereafter indicating the highest infectiousness potential just before or within the first five days of symptom onset

Transmission risk depends on factors such as contact pattern, environment, infectiousness of the host, and socioeconomic factors. Most transmission occurs through close range contact (15 minutes face to face and within 2 meters) and spread especially within households and through gathering of family and friends.

Sleeping in the same room as, or being a spouse of an infected individual increases the risk of infection. Dining in close proximity with the infected person, sharing food and taking part in group activities have been identified with high risk.

• Reverse transcription polymerase chain reaction (RT-PCR) tests can detect viral SARS-CoV-2 RNA in the upper respiratory tract for a mean of 17 days; however, detection of viral RNA does not necessarily equate to infectiousness, and viral culture from PCR positive upper respiratory tract samples has been rarely positive beyond nine days of illness

• Symptomatic and pre-symptomatic transmission (1-2 days before symptom onset), is likely to play a greater role in the spread of SARS-CoV-2 than asymptomatic transmission
• A wide range of virus-neutralising antibodies have been reported, and emerging evidence suggests that these may correlate with severity of illness but wane over time

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