Molecular diagnosis of SARS-CoV-2

Diagnóstico molecular de SARS-CoV-2

COVID-19 diagnosis is based on both clinical aspects and screening tests. However, clinical symptoms and signs in infected patients are highly atypical; hence, molecular
tests are essential for diagnosis. RT-qPCR is carried out at BSL II level laboratories; the main molecular targets for viral detection are E gene (envelope), and RdRP gene (RNA-
dependent RNA polymerase). False negatives in this diagnosis are due to sample quality and quantity, transport conditions, storage and handling before and after extraction (RNA
is heat-labile and RNases are abundant); infection phase; virus mutations and presence of CRP inhibitors. Taking into account analytical sensitivity of RT-qPCR (5.2 copies of
RNA / reaction) and the fact that once RNA it is extracted, it progressively degrades and affects test diagnostic sensitivity, a new sample -specifically taken from the lower respiratory
tract in order to increase viral load- is recommended in the abovementioned cases. Timely diagnosis allows optimizing management (isolation and treatment), patient monitoring,
implementing prevention and control measures as well as epidemiological surveillance of the disease.

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