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Background
The gold standard for the diagnosis of coronavirus disease (COVID – 19) has been the detection of severe acute respiratory syndrome coronavirus 2 (SARS – CoV – 2) RNA using nucleic acid amplification tests (NAAT). On the other hand, serologic testing for COVID – 19 may offer advantages in detecting infections possibly missed by NAAT.
Methods
To assess the seroconversion of patients with NAAT negative pneumonia, IgM and IgG targeting the SARS-CoV-2 peak protein were semi-quantified using an immunofluorescence assay. Seroconversion was confirmed by another serological method, targeting the nucleocapsid protein.
Results
Eight patients with suspected but unconfirmed COVID-19 pneumonia (median age, 39 years; 21-55) were included. The mean period between the onset of symptoms and the collection of the NAAT sample was 6 days (2–27 days). None of them had tested positive for SARS – CoV – 2 by NAAT. In contrast, all eight patients were seropositive with both serological methods, indicating true seroconversion against SARS – CoV – 2. The mean period between initiation and blood sampling was 26.5 days (7 -51 days).
Conclution
Eight patients with COVID – 19 pneumonia, who initially tested negative for SARS – CoV – 2 by NAAT, were eventually confirmed of the diagnosis by serological tests. To cover the full spectrum of this heterogeneous infectious disease, serological tests must be implemented in the multi-tiered diagnostic algorithm for COVID – 19.
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