Diagnostic performance evaluation of Elecsys anti-SARS-CoV-2 assay against RT-PCR for SARS-CoV-2 detection and surveillance in Ethiopian referral hospitals: cross-sectional study

Accurate diagnosis is vital for controlling viral spread and guiding clinical and public health decisions. This study aimed to determine active (determined by RT-PCR) and past SARS-CoV-2 infection (determined by serology test) and evaluate the Elecsys Anti-SARS-CoV-2 serological assay performance relative to RT-PCR as a reference for COVID-19 diagnosis and surveillance in Ethiopian hospitals. We conducted a cross-sectional study across five hospitals from August 9-23, 2021, enrolling 1,360 consecutive patients. Paired nasopharyngeal swabs (RT-PCR) and blood samples (Elecsys Anti-SARS-CoV-2) were collected from all participants. Data were analyzed using Stata 14 to evaluate diagnostic performance (sensitivity, specificity), test agreement (Cohen's κ), comparative accuracy (ROC analysis), and predictors of infection using logistic regression (p < 0.05 threshold for significance). The mean age of study participants was 36.2 years (SD ± 17.2); 52% were females, with 418 (29.2%) reporting COVID-like symptoms. Seroprevalence was 53.2%, while 18% had active RT-PCR-confirmed infections. Urban residence (AOR = 8.44, 3.92-18.17), fever (AOR = 1.74, 1.02-2.96), myalgia (AOR = 2.62, 1.48-4.64), and cough (AOR = 1.84, 1.01-3.36) were significantly associated with active infection. The Elecsys test showed poor diagnostic accuracy (sensitivity = 14% [12.1-15.8%]; specificity = 77.9% [75.7-80.1%]; AUC = 0.43; the overall agreement 43.9%, κ = 0.078). These findings highlight a high burden of SARS-CoV-2 infection in a resource-constrained setting. While the Elecsys immunoassay demonstrated low sensitivity and poor agreement with RT-PCR, indicating it is not suitable for diagnosing active infection, its high specificity makes it a valuable tool for sero-surveillance to estimate population exposure and inform public health strategy where RT-PCR capacity is limited.