SARS-CoV-2 Viral Load in Upper Respiratory Specimens of Infected Patients

Zou L, Ruan F, Huang M, et al. SARS-CoV-2 Viral Load in Upper Respiratory Specimens of Infected Patients. N Engl J Med. 2020;382(12):1177‐1179. doi:10.1056/NEJMc2001737

Review written by:

Ariel Pourmorady, edited by Diogo Teles, MD, & Robert Parry

Green - published in NEJM, 1 simple experiment with one logical conclusion

Transmission of SARS, a phylogenetically related lower respiratory tract infection to SARS-CoV-2,  typically occurred several days after symptom onset. SARS was associated with modest viral loads in the respiratory tract that would peak 10 days after symptom onset. The authors were interested in determining whether SARS-CoV-2 followed a similar pattern in its pathophysiology and transmission. They collected 1 to 9 sequential nasal and throat swab samples from 18 patients in Guandong, China, in 2 family clusters. 3 of these patients had symptoms severe enough to require intensive care. 1 of these patients had 3 known close contacts, 2 of whom developed symptoms 3 and 5 days after exposure. The other contact developed a detectable viral load, but was entirely asymptomatic.

The viral load that was detected in the asymptomatic patient was similar to that in the symptomatic patients, which suggests the transmission potential of asymptomatic or minimally symptomatic patients.

Unlike SARS-CoV in SARS-CoV-2  viral load was higher (measured by RT-PCR), in the nose greater than in the throat, and peaked soon after symptom onset, thus transmission may occur early in the course of infection.  The earlier and larger viral load peaks of SARS-CoV-2 compared to SARS, would require us to take a different approach to understand the transmission dynamics of SARS-CoV-2 and to implement proper screening practices.

Review Notes

Small number of patients in the study.

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