Wastewater-Based Tracking SARS-CoV-2 RNA and Estimating Infected Population in Industrial Setting After Songkran Festival-Thailand Traditional New Year in 2023.

Abstract

Monitoring SARS-CoV-2 RNA in industrial wastewater has emerged as a potential approach to indirectly identify infected individuals within workplace populations. However, wastewater-based surveillance of SARS-CoV-2 in industrial settings has not previously been conducted in Thailand. This study aimed to qualitatively and quantitatively detect SARS-CoV-2 RNA in wastewater discharged from onsite wastewater treatment plants (WWTPs) and to estimate the number of infected individuals. A total of 120 wastewater samples were consecutively collected from 40 onsite WWTPs comprising 38 factories and two non-factory buildings with over a three-month period (April to June 2023), after the Songkran festival, Thailand's traditional new year celebration. Wastewater samples were concentrated, and the total nucleic acids were extracted. SARS-CoV-2 RNA concentrations were determined by quantitative reverse transcription polymerase chain reaction (qRT-PCR) targeting the N gene. SARS-CoV-2 RNA was detected in 42.5%, 62.5%, and 40.0% of samples collected in April, May, and June, respectively. The concentrations ranged from 3.5 × 10²-1.1 × 10⁴ copies/L in April, 4 × 10²-1.7 × 10⁵ copies/L in May, and 1.1 × 10³-1.4 × 10⁵ copies/L in June. A higher frequency of SARS-CoV-2 RNA detection was observed in factories having more than 1000 employees. Based on our modified estimation model, the estimated infected individuals were 219, 3145, and 2711 for April, May, and June, respectively. The numbers of estimated infected population closely aligned with the official COVID-19 case trending reported in Pathum Thani province and at the national level during the same period. These findings suggest that wastewater-based epidemiology (WBE) is a reliable tool for measuring, estimating, and assessing COVID-19 dynamics in industrial setting.