Pilot Monitoring of SARS-CoV-2 RNA in Influent and Treated Effluent of Municipal Wastewater Treatment Plants Across Slovakia During the Autumn 2020 COVID-19 Wave

Wastewater-based surveillance can track community SARS-CoV-2, but RNA signals at wastewater treatment plants are affected by sampling, analytical recovery and transfer to solids. We quantified SARS-CoV-2 RNA in influent and biologically treated effluent from eight Slovak municipal wastewater treatment plants during the period October–December 2020. Twenty-seven 24 h influent composites and seven same-day effluent samples were analysed by reverse-transcription quantitative PCR targeting ORF1b, S, E and RdRp. RNA was detected in 20/27 influents (74%; 95% CI, 54–89%) and 3/7 effluents (43%; 95% CI, 10–82%). Influent loads ranged from 4.66 × 109 to 5.60 × 1013 copies day−1; the maximum population-normalised load was 5.84 × 105 copies per population equivalent per day. All seven effluent concentrations were lower than paired influents (exact sign test, p = 0.0156). Apparent log10 reductions were 0.18 and 0.76 for quantifiable effluents, approximately 1.75 for one detection at the operational limit of detection, and ≥1.9–≥2.5 for four non-detects. A one-day process profile at the selected plant detected RNA in activated-sludge supernatant, digested-sludge supernatant and reject water. Because solids, infectivity and whole-process recovery were not measured, the results describe RNA occurrence rather than viral inactivation or a mass balance. These pilot data provide a historical baseline for Slovakia and define requirements for repeated sampling, process controls and paired liquid-solid measurements.