Background:PCR (Polymerase Chain Reaction) is generally considered the gold standard for confirming the diagnosis in the early stages of SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) infection. However, in our rheumatology outpatient clinic we observed a significant discrepancy between clinical evidence of COVID-19 and PCR results.Objectives:Aim of this retrospective study was to analyze the significance of PCR and serologic tests in the diagnosis of COVID-19 (Corona Virus Disease 2019) in a cohort of patients with rheumatic diseases.Methods:Between March 2020 and January 2021, 35 patients with a history of established COVID-19 or typical signs and symptoms were identified on the occasion of a routine rheumatology follow-up examination in our institution. Previous diagnostic work-up in external facilities (results of PCR or antibody testing, imaging) was documented. Antibody ELISA-tests (IgG, IgA, IgM, Euroimmun) were performed in patients reporting typical signs and symptoms of COVID-19 in the past.Results:PCR diagnostics had been performed in 15/35 patients (43%), in 13/35 (39%) at the onset of the first symptoms, in 2 subjects only 2 months later. PCR was positive in 7/13 (54%) of those tested early, but negative in the two patients tested later. In 29/35 patients (83%) SARS-CoV-2-ELISA tests were performed on the occasion of the routine rheumatologic examination (interval between first symptoms and testing on average 98 days, median86, range 4-283 days). In two of the initially negative individuals the second PCR was positive. ELISA tests were positive in all patients. SARS-CoV-2 IgM antibodies were positive in only two patients (however 55 and 71 days after disease onset), n=8/29 (28%) IgG only, n=9/29 (31%) IgG and IgA, n=12/29 (41%) IgA only. In these subjects, IgG antibodies did not develop even in the further course. Antibody titers were in part very high, but in part also very low (only just above the normal value), so even low titers were diagnostic obviously. In all patients with negative PCR, ELISA was positive and retrospectively led to confirmation of the diagnosis. Only in 13/35 patients (37%) diagnosis had been made with the onset of the first symptoms or in the course of clinically manifest disease and had led to appropriate quarantine measures and contact tracing by the health authorities. In contrast, in the majority of patients (63%), the diagnosis of COVID-19 infection was only made retrospectively on the occasion of a routine rheumatologic follow-up. However, 5 of these 22 patients (23%) had quarantined themselves during the symptomatic phase. Titer histories were available from 12 patients. The titer became negative in 7 patients, after a mean of 188 days (median 202, min 51, max 296 days), and remained positive in 5 individuals (mean 190 days, median 191, min 122, max 260 days). The change of the titer was independent of disease severity or antirheumatic therapy.Conclusion:The results suggest that the importance of PCR in the diagnosis of COVID-19 may be overestimated. Therefore, antibody testing for SARS-CoV-2 should be performed in cases of clinical suspicion and negative PCR. In antibody diagnostics, special features were observed compared to other viruses, in particular, in some patients only low antibody titers or the absence of seroconversion with lack of development of IgG antibodies. Normalization of antibody titers in some patients supports the recommendation to vaccinate even after expired COVID-19 disease.Disclosure of Interests:None declared
Western blotting studies of IgG antibodies, IgG avidity and IgG subclasses during the follow up of patients with pulmonary tuberculosis, under treatment
