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.
ABSTRACT
To assist public health responses to COVID-19, wastewater-based epidemiology (WBE) is being utilised internationally to monitor SARS-CoV-2 infections at the community level. However, questions remain regarding the sensitivity of WBE and its use in low prevalence settings. In this study, we estimated the total number of COVID-19 cases required for detection of SARS-CoV-2 RNA in wastewater. To do this, we leveraged a unique situation where, over a 4-month period, all symptomatic and asymptomatic cases, in a population of approximately 120,000, were precisely known and mainly located in a single managed isolation and quarantine facility (MIQF) building. From 9 July to 6 November 2020, 24-hr composite wastewater samples (n = 113) were collected daily from the sewer outside the MIQF, and from the municipal wastewater treatment plant (WWTP) located 5 km downstream. New daily COVID-19 cases at the MIQF ranged from 0 to 17, and for most of the study period there were no cases outside the MIQF identified. SARS-CoV-2 RNA was detected in 54.0% (61/113) at the WWTP, compared to 95.6% (108/113) at the MIQF. We used logistic regression to estimate the shedding of SARS-CoV-2 RNA into wastewater based on four infectious shedding models. With a total of 5 and 10 COVID-19 infectious cases per 100,000 population (0.005% and 0.01% prevalence) the predicated probability of SARS-CoV-2 RNA detection at the WWTP was estimated to be 28 and 41%, respectively. When a proportional shedding model was used, this increased to 58% and 87% for 5 and 10 cases, respectively. In other words, when 10 individuals were actively shedding SARS-CoV-2 RNA in a catchment of 100,000 individuals, there was a high likelihood of detecting viral RNA in wastewater. SARS-CoV-2 RNA detections at the WWTP were associated with increasing COVID-19 cases. Our results show that WBE provides a reliable and sensitive platform for detecting infections at the community scale, even when case prevalence is low, and can be of use as an early warning system for community outbreaks.