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. 2022 May 15:215:118220.
doi: 10.1016/j.watres.2022.118220. Epub 2022 Feb 23.

Detection and quantification of SARS-CoV-2 RNA in wastewater influent in relation to reported COVID-19 incidence in Finland

Ananda Tiwari  1 , Anssi Lipponen  2 , Anna-Maria Hokajärvi  3 , Oskari Luomala  4 , Anniina Sarekoski  5 , Annastiina Rytkönen  6 , Pamela Österlund  7 , Haider Al-Hello  8 , Aapo Juutinen  9 , Ilkka T Miettinen  10 , Carita Savolainen-Kopra  11 , Tarja Pitkänen  12
Affiliations

Detection and quantification of SARS-CoV-2 RNA in wastewater influent in relation to reported COVID-19 incidence in Finland

Ananda Tiwari et al. Water Res. .

Abstract

Wastewater-based surveillance is a cost-effective concept for monitoring COVID-19 pandemics at a population level. Here, SARS-CoV-2 RNA was monitored from a total of 693 wastewater (WW) influent samples from 28 wastewater treatment plants (WWTP, N = 21-42 samples per WWTP) in Finland from August 2020 to May 2021, covering WW of ca. 3.3 million inhabitants (∼ 60% of the Finnish population). Quantity of SARS-CoV-2 RNA fragments in 24 h-composite samples was determined by using the ultrafiltration method followed by nucleic acid extraction and CDC N2 RT-qPCR assay. SARS-CoV-2 RNA signals at each WWTP were compared over time to the numbers of confirmed COVID-19 cases (14-day case incidence rate) in the sewer network area. Over the 10-month surveillance period with an extensive total number of samples, the detection rate of SARS-CoV-2 RNA in WW was 79% (including 6% uncertain results, i.e., amplified only in one out of four, two original and two ten-fold diluted replicates), while only 24% of all samples exhibited gene copy numbers above the quantification limit. The range of the SARS-CoV-2 detection rate in WW varied from 33% (including 10% uncertain results) in Pietarsaari to 100% in Espoo. Only six out of 693 WW samples were positive with SARS-COV-2 RNA when the reported COVID-19 case number from the preceding 14 days was zero. Overall, the 14-day COVID-19 incidence was 7.0, 18, and 36 cases per 100 000 persons within the sewer network area when the probability to detect SARS-CoV-2 RNA in wastewater samples was 50%, 75% and 95%, respectively. The quantification of SARS-CoV-2 RNA required significantly more COVID-19 cases: the quantification rate was 50%, 75%, and 95% when the 14-day incidence was 110, 152, and 223 COVID-19 cases, respectively, per 100 000 persons. Multiple linear regression confirmed the relationship between the COVID-19 incidence and the SARS-CoV-2 RNA quantified in WW at 15 out of 28 WWTPs (overall R2 = 0.36, p < 0.001). At four of the 13 WWTPs where a significant relationship was not found, the SARS-CoV-2 RNA remained below the quantification limit during the whole study period. In the five other WWTPs, the sewer coverage was less than 80% of the total population in the area and thus the COVID-19 cases may have been inhabitants from the areas not covered. Based on the results obtained, WW-based surveillance of SARS-CoV-2 could be used as an indicator for local and national COVID-19 incidence trends. Importantly, the determination of SARS-CoV-2 RNA fragments from WW is a powerful and non-invasive public health surveillance measure, independent of possible changes in the clinical testing strategies or in the willingness of individuals to be tested for COVID-19.

Keywords: Community sewage; Coronavirus; National surveillance; RT-qPCR assay; Wastewater-based epidemiology.

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Conflict of interest statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Image, graphical abstract
Graphical abstract
Fig 1
Fig. 1
Total daily reported COVID-19 cases in the municipalities covered in the national wastewater sample collection (for the list of municipalities, see Table S1).
Fig 2
Fig. 2
Relationship between COVID-19 incidence and the detection and quantification rates of SARS-CoV-2 RNA determined using N2-assay in wastewater (the data points presented in Tables 2 and S6).
Fig 3
Fig. 3
Fourteen-day COVID-19 incidence rate thresholds in the sewer network area covered by national surveillance in Finland required for wastewater-based SARS-CoV-2 detection and quantification estimated with logistic regression (the equations presented in Table S5).
Fig 4
Fig. 4
The trend of SARS-CoV-2 RNA (GC/day/person) in WW samples and COVID-19 incidence (per 100 000 persons). Sample dots with (-) denote SARS-CoV-2 was not detected, (+) denotes that the detection was uncertain, (*) denotes detected, but below quantification limit (LOQ). (A) City areas (Helsinki, Espoo, Turku, Hämeenlinna) with quantification rate (QR) 48–79%. (B) City areas (Jyväskylä, Tampere, Lahti II, Vihti) with QR 30–38%. (C) City areas (Mikkeli, Lahti I, Salo, Vaasa) with QR 18–29%. (D) City areas (Kuopio, Oulu, Rauma, Maarianhamina) with QR 14–17%. (E) City areas (Kokkola, Kouvola, Pietarsaari, Savonlinna) with QR 9–10%. (F) City areas (Kajaani, Kotka, Pori, Lappeenranta) with QR 0–5%. (G) City areas (Rovaniemi, Joensuu, Kemi, Seinäjoki) with QR 0%. Caution: the Y-axis of each graph is different, and the x-axis is the same. Samples with arrival temperature higher than 15 °C (C) and transportation delay more than or equal to three days (D) are shown.
See this image and copyright information in PMC

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