RESUMO
Reverse transcriptionquantitative polymerase chain reaction (RTqPCR) is the gold standard method for the diagnosis of COVID19 infection. Due to preanalytical and technical limitations, samples with low viral load are often misdiagnosed as falsenegative samples. Therefore, it is important to evaluate other strategies able to overcome the limits of RTqPCR. Blinded swab samples from two individuals diagnosed positive and negative for COVID19 were analyzed by droplet digital PCR (ddPCR) and RTqPCR in order to assess the sensitivity of both methods. Intercalation chemistries and a World Health Organization (WHO)/Center for Disease Control and Prevention (CDC)approved probe for the SARSCoV2 N gene were used. SYBRGreen RTqPCR is not able to diagnose as positive samples with low viral load, while, TaqMan Probe RTqPCR gave positive signals at very late Ct values. On the contrary, ddPCR showed higher sensitivity rate compared to RTqPCR and both EvaGreen and probe ddPCR were able to recognize the sample with low viral load as positive even at 10fold diluted concentration. In conclusion, ddPCR shows higher sensitivity and specificity compared to RTqPCR for the diagnosis of COVID19 infection in falsenegative samples with low viral load. Therefore, ddPCR is strongly recommended in clinical practice for the diagnosis of COVID19 and the followup of positive patients until complete remission.
