[Longitudinal Monitoring of Seroconversion Status in SARS-CoV-2 RT-PCR Positive Healthcare Workers]

The impact of the coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome 2 (SARS-CoV-2) still continues. The duration of the immune response in individuals recovering from COVID-19 and its protection against future SARS-CoV-2 infection are not fully understood. This study aimed to longitudinally evaluate anti-SARS-CoV-2 seroconversion status in healthcare workers with positive SARS-CoV-2 Real-time reverse transcription polymerase chain reaction (rRT-PCR), test in Mersin University Hospital. A total of 68 healthcare workers with positive SARS-CoV-2 rRT-PCR test between 19 April and 27 November 2020 were included in the study. Blood samples were collected from healthcare workers for SARS-CoV-2 antibody testing in the 1st, 3rd and 5th months following PCR positivity. Healthcare workers were classified as symptomatic, asymptomatic and reinfected according to their clinical findings, and rRT-PCR cycle thresholds (Ct) were recorded. Elecsys Anti-SARS-CoV-2 (Roche Diagnostics, Germany) kit was used for antibody testing. Of the 68 healthcare workers; 46 were classified as symptomatic, 15 as asymptomatic, and seven as reinfected. Twenty-seven (39.7%) of the healthcare workers were male and 41 (60.3%) were female, and the mean age was 36.4 ± 9.04. Seroconversion was detected in 45 (66.2%) of 68 healthcare workers in the study, and only one person had sero-negative result at the end of the 5th month. While seroconversion was detected in 78.3% (n= 36/46) of symptomatic healthcare workers, it was observed in 26.7% (n= 4/15) of the asymptomatic healthcare workers. Seroconversion was detected in only one of the seven reinfected healthcare workers after primary infection. After reinfection, seroconversion was observed in five of seven reinfected healthcare workers. Antibody response was not detected in two of them after both infections. According to the rRT-PCR Ct values; the median of Ct value was found significantly lower in healthcare workers with seroconversion (23.26, IQR= 18.45-27.30), than the ones without seroconversion (36.20, IQR= 33.09-37.56) (p< 0.001). In those who had reinfection, the mean Ct value (31.77 ± 6.62) detected during the primary infection period was statistically higher than the Ct value (22.44 ± 5.54) detected during reinfection (p= 0.008). The most frequently recorded symptoms in healthcare workers were myalgia (57.3%), fatigue (51.5%), headache (51.5%) followed by sore throat (36.7%), fever (33.8%), cough (27.9%), diarrhea (23.5%) and dyspnea (16.2%). In addition, fever (52%) and fatigue (80.6%) were found to be significantly higher in seroconversion-positive healthcare workers than in those without seroconversion (p= 0.028; p= 0.005, respectively). As a result, a higher rate of antibody response was detected in healthcare workers who had symptomatic infection than those who were asymptomatic. It has been observed that patients with asymptomatic primary infection and without antibody response were more susceptible to reinfection. In addition, it was observed that the probability of immune response increased when the viral load increased (Ct value decreased) in symptomatic infections. Although these findings provide important information about the short-term seroconversion status of healthcare personnel; longer-term and larger-scale studies are needed to evaluate the long-term effectiveness of seroconversion and to better understand the effectiveness of the immune response developed after SARS-CoV-2 vaccine administrations.