A pilot study of wastewater monitoring for SARS-CoV-2 in New Zealand

ABSTRACT

Surveillance of municipal wastewater for RNA of SARS-CoV-2, the causative agent of coronavirus disease (COVID-19), is well documented around the world. However, unlike most countries where wastewater surveillance was initially employed during 2020, New Zealand was in the fortunate position of having very few COVID-19 cases, generally confined to Managed Isolation and Quarantine facilities. As such, the prevalence of SARS-CoV-2 RNA in wastewater was likely much lower than seen in other countries. A nine-week pilot study was undertaken to assess the feasibility of detecting SARSCoV-2 RNA in wastewater in New Zealand. Wastewater from 18 catchments across New Zealand was monitored, including six that contained Managed Isolation and Quarantine facilities. Testing both in regions known to have COVID-19 cases and regions where detection was not expected (catchments not containing Managed Isolation and Quarantine facilities) allowed the sensitivity and specificity of detection methods to be assessed. SARS-CoV-2 RNA was detected in seven out of the nine weeks of this study in the Auckland South Western Interceptor catchment, which contained a dedicated isolation facility to which confirmed cases from Auckland, Hamilton and Rotorua were transferred. In weeks two and three of sampling, SARS-CoV-2 RNA was detected in the Christchurch catchment. This coincided with up to 14 COVID-19 cases likely to be shedding high levels of virus (PCR Cq value < 20) in the Managed Isolation and Quarantine facilities. Samples from the seven other weeks were negative despite up to 35 infected cases present at any one time. However, on any of these test dates eight cases or fewer had a PCR Cq value < 30 and were within 10 days of symptom onset or positive PCR test date. Sample inhibition and non-specificity were not observed to be issues. The results of this pilot study underpinned recommendations that wastewater monitoring for SARS-CoV-2 RNA be incorporated as a surveillance tool in New Zealand's COVID-19 response.