Testing methods to estimate population size for wastewater treatment plants using census data: Implications for wastewater-based epidemiology.

In wastewater-based epidemiology (WBE), wastewater loads are commonly reported as a per capita value. Census population counts are often used to obtain a population size to normalise wastewater loads. However, the methods used to calculate the population size of wastewater treatment plants (WWTPs) from census data are rarely reported in the WBE literature. This is problematic because the geographical extents of wastewater catchments and census area units rarely align perfectly with each other and exist at different spatial scales. This complicates efforts to estimate the number of people serviced by WWTPs in these census area units. This study compared four geospatial methods to combine wastewater catchment areas and census area units to calculate the census population size of wastewater treatment plants. These methods were applied nationally to WWTPs across New Zealand. Population estimates varied by up to 73 % between the methods, which could skew comparisons of per capita wastewater loads between sites. Variability in population estimates (relative standard deviation, RSD) was significantly higher in smaller catchments (rs = -0.727, P < .001), highlighting the importance of method selection in smaller sites. Census population estimates were broadly similar to those provided by wastewater operators, but significant variation was observed for some sites (ranging from 42 % lower to 78 % higher, RSD = 262 %). We present a widely applicable method to calculate population size from census, which involves disaggregating census area units by individual properties. The results reinforce the need for transparent reporting to maintain confidence in the comparison of WBE across sites and studies.

Spatial, temporal and socioeconomic patterns of illicit drug use in New Zealand assessed using wastewater-based epidemiology timed to coincide with the census.

AIMS: A discrete experiment in wastewater-based epidemiology (WBE) timed to coincide with the census was used to investigate the spatial, temporal and socioeconomic patterns of illicit drug consumption in Auckland, Bay of Plenty and Canterbury. METHODS: For seven consecutive days over census week (6 March 2018), wastewater was sampled from seven wastewater treatment plants and analysed for methamphetamine, cocaine (as benzoylecgonine) and 3,4-methylenedioxymethamphetamine (MDMA). Detailed sewer catchment maps were developed and, together with the data, were used to analyse drug consumption. RESULTS: Methamphetamine (mean 22.9 ± 9.9 doses/day/1000 people) was the most consumed drug, followed by MDMA (mean 1.7 ± 1.5 doses/day/1000 people) and cocaine (mean 0.5 ± 0.3 doses/day/1000 people). Methamphetamine consumption (and to a lesser extent MDMA) was high compared to that reported for Western nations, while cocaine consumption was extremely low. Cocaine and MDMA consumption were higher in cities compared to towns. In contrast, methamphetamine was typically higher in towns. Cocaine and MDMA were consumed more at weekends. Methamphetamine use was more consistent throughout the week. MDMA and cocaine were correlated with socioeconomic advantage, whereas methamphetamine was correlated with disadvantage. CONCLUSIONS: This paper contextualises illicit drug use in three New Zealand regions containing 18.3% of the national population and confirms the pervasiveness of methamphetamine consumption in New Zealand towns. This work demonstrates how WBE can be used to explore the socioeconomic dimensions of drug use when duly combined with other data sources like censuses.

Quantifying nicotine and alcohol consumption in New Zealand using wastewater-based epidemiology timed to coincide with census.

INTRODUCTION: Accurate and timely information about nicotine and alcohol consumption is needed to inform effective policy. Wastewater-based epidemiology provides an opportunity to quantify consumption, which can complement traditional data collection methods. METHODS: Wastewater samples were collected from seven wastewater treatment plants on seven consecutive days in three regions of New Zealand during the same week as the national census (6 March 2018). Samples were analysed for nicotine and alcohol metabolites using liquid chromatography-tandem mass spectrometry. Detailed catchment maps were developed and per capita consumption calculated. RESULTS: Observed nicotine consumption (mean 1528 ± 412 cigarettes/day/1000 people) was similar to national sales data. Observed alcohol consumption (mean 1155 ± 764 standard drinks/day/1000 people) was lower than estimated using alcohol availability data. Consumption of nicotine and alcohol was generally higher in the Bay of Plenty and Canterbury compared to Auckland, mirroring trends in the New Zealand Health Survey. Intra-regional differences were observed and the patterns could not be attributed to urbanisation alone. Nicotine consumption was consistent throughout the week whereas alcohol consumption often peaked at the weekend. Nicotine consumption was correlated with neighbourhood-deprivation. There was little correlation for alcohol. DISCUSSION AND CONCLUSIONS: Wastewater-based epidemiology provides a quantitative dataset that complements traditional methods of investigating nicotine and alcohol consumption. Timing data collection to coincide with the census helps to account for the influence of population mobility when normalising consumption.