engleski

Detection of antibodies to severe acute respiratory syndromeCoronavirus 2 (SARS-CoV-2) by electrochemical immunoassay (ECLIA) - one center experience

Introduction. Serological testing by antibodies detection can detect a previously undiagnosed SARS-CoV-2 infection among asymptomatic individuals that could create the immunity even without overcoming the COVID-19 disease. After contact with severe acute respiratory syndrome Coronavirus 2 (SARS-CoV-2) the human immune system produces specific antibodies which appear in serum either of asymptomatic or infected individuals few days to 2 weeks after the onset of infection symptoms. The aim of the study was to investigate the presence of antibodies to SARS-CoV-2 in serum of Merkur University Hospital staff exposed to symptomatic patients with suspected or confirmed SARS-CoV-2 infection by real- time reverse transcription polymerase chain reaction (RT-PCR). Materials and methods. Analytical verification of qualitative total antibody electrochemical immunoassay (Roche Cobas Elecsys Anti SARS-CoV-2, ECLIA method) was performed according to CLSI- EP15A guidelines on Roche Cobas e411 analyzer. Since there were no commercial controls available at the time of verification, in house control samples were prepared – negative control (NC) as a pool of non-reactive serum samples obtained from patients with negative RT-PCR test and positive control (PC) as a pool of serum samples from COVID-19 confirmed by RT-PCR. Stability of the qualitative total antibody electrochemical immunoassay (according to the producer of the immunoassay it is stable for 3 days from calibration) was tested by analyzing the PC samples 6, 9, 12 and 18 days from calibration. The presence of antibodies to SARS-CoV-2 in serum of Merkur University Hospital employees (110 primarly most exposed to symptomatic patients with suspected or confirmed SARS-CoV- 2) was investigated by serological testing in a epidemiological pilot study. Regarding the fact that Roche Cobas Elecsys Anti SARS-CoV-2 is a qualitative test, the results were given as a cutt-off index (COI) for non-reactive samples (COI < 1) and for reactive samples (COI > 1). Results. The control target values were 0, 099 COI for NC and 12, 338 for PC. During 5 verification days NC mean of 0, 10 COI (within- laboratory precision of CV 2, 56%) while PC mean of 12, 01 COI was obtained (within-laboratory precision of CV3, 71%). Results of stability testing showed that COI values of PC were in constant decline as the number of days after calibration rised: COI 90, 3% on day 6, COI 88, 0% on day 9, COI 82, 3% on day 12 and COI 71, 4% on day 18 of the PC mean COI value. 100% of Merkur University Hospital employees (110/110) involved in an epidemiological pilot study had negative serological testing results (non-reactive). Conclusions. Analytical verification of qualitative total antibody electrochemical immunoassay (Roche Cobas Elecsys Anti SARS-CoV-2, ECLIA method) showed results agreeably to literature sources. Results of its stability confirmed that Roche Cobas Elecsys Anti SARS-CoV-2 immunoassay can be used up to 2 weeks after declared calibration deadline which could be important given the large test pack (200 tests). An epidemiological pilot study showed that 4 months after confirmation of the first COVID-19 positive patient in Republic of Croatia none of Merkur University Hospital employees exposed to symptomatic patients with suspected or confirmed SARS-CoV-2 infection involved in the epidemiological study did not develop antibodies or had active immune system without disease development.

serology testing ; immunity

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