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To Interpret the SARS-CoV-2 Test, Consider the Cycle Threshold Value

2020; Oxford University Press; Volume: 71; Issue: 16 Linguagem: Inglês

10.1093/cid/ciaa619

1537-6591

Michael R. Tom, Michael J. Mina,

Infection Control and Ventilation

To prevent the spread of coronavirus disease 2019 (COVID-19), it is important to identify and isolate people who are infectious.It is especially important to ensure that those with a high viral load are isolated and not able to transmit to others.Currently, diagnosis, screening, and surveillance depend on a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) reverse transcriptasequantitative polymerase chain reaction (RT-qPCR) test, and results are generally reported to the ordering physician as positive or negative.However, the test does provide a measure of the viral load in the sample, in what is called the cycle threshold (Ct) value.We suggest that reporting this Ct value, or a calculated viral load, can aid in interpretation and clinical decisions.We discuss the merits of PCR tests and other approaches, such as time-since-symptomresolution-based approaches for removing individuals from isolation.In this issue of Clinical Infectious Diseases, Xiao et al [1] report that SARS-CoV-2 RT-qPCR results can remain positive up to 5 weeks after onset of symptoms.