Associations between extreme precipitation, drinking water, and protozoan acute gastrointestinal illnesses in four North American Great Lakes cities (2009–2014)

Abstract

Climate change is already impacting the North American Great Lakes ecosystem and understanding the relationship between climate events and public health, such as waterborne acute gastrointestinal illnesses (AGIs), can help inform needed adaptive capacity for drinking water systems (DWSs). In this study, we assessed a harmonized binational dataset for the effects of extreme precipitation events (≥90th percentile) and preceding dry periods, source water turbidity, total coliforms, and protozoan AGI – cryptosporidiosis and giardiasis – in the populations served by four DWSs that source surface water from Lake Ontario (Hamilton and Toronto, Ontario, Canada) and Lake Michigan (Green Bay and Milwaukee, Wisconsin, USA) from January 2009 through August 2014. We used distributed lag non-linear Poisson regression models adjusted for seasonality and found extreme precipitation weeks preceded by dry periods increased the relative risk of protozoan AGI after 1 and 3–5 weeks in three of the four cities, although only statistically significant in two. Our results suggest that the risk of protozoan AGI increases with extreme precipitation preceded by a dry period. As extreme precipitation patterns become more frequent with climate change, the ability to detect changes in water quality and effectively treat source water of varying quality is increasingly important for adaptive capacity and protection of public health.

Relationship between extreme precipitation and acute gastrointestinal illness in Toronto, Ontario, 2012–2022

“…Prolonged dry spells cause the soil to become compact and retain contaminants, which when followed by an intense rainfall event, allows for overland runoff into sources of drinking water, increasing turbidity and pathogen loads [57][58][59]. Such events have the potential to overwhelm drinking water treatment processes, allowing pathogens to pass through to the distribution system and ultimately to residents' homes where they are ingested [12,60]. The findings of our study suggest this could be a possible route of exposure in Toronto, given that summer has relatively longer dry periods than other seasons.…”

“…Additionally, AGI patients typically visit the emergency department (ED) after having symptoms for an average of 2–3 days; as such, these selected lag days were suitable to cover the duration from the onset of the illness to the time a clinical visit was made [ 2 ]. Furthermore, some previous literature have revealed significant associations between AGI and heavy precipitation about 1–6 weeks after a precipitation event [ 2 , 3 , 11 , 12 , 30 ]. Using the cross-basis, we then developed several base models (with precipitation and other covariates in separate models and combined into one model) to determine the suitable functional forms as well as the lag function for the non-linear relationship between the precipitation and AGI ED visits.…”

“…Several studies have revealed the impact of extreme precipitation on drinking water in Canada [7,[10][11][12]. For instance, Chhetri et al found a significant increase in acute gastrointestinal illness (AGI) due to cryptosporidiosis and giardiasis 4-6 weeks after extreme precipitation events, with extreme precipitation having greater effects on AGI following a dry period [11].…”

“…For instance, Chhetri et al found a significant increase in acute gastrointestinal illness (AGI) due to cryptosporidiosis and giardiasis 4–6 weeks after extreme precipitation events, with extreme precipitation having greater effects on AGI following a dry period [ 11 ]. Another study found an increased risk for AGI between 1 and 5 weeks after a heavy precipitation event [ 12 ]. However, of the studies executed so far, none took into consideration the explicit effects of other flooding indicators (stream discharge, sewer backup), especially indicators related to direct flooding exposures in homes.…”

Investigating the relationship between extreme weather and cryptosporidiosis and giardiasis in Colorado: a multi-decade study using distributed-lag nonlinear models

“…Precipitation extremes have been more frequently studied in relation to cryptosporidiosis and giardiasis transmission (Keeley and Faulkner 2008, Chhetri, Takaro et al 2017, Lal and Konings 2018, Brunn, Fisman et al 2019, Chhetri, Galanis et al 2019, Forbes, Hosking et al 2021, Ma, Destouni et al 2021, Graydon, Mezzacapo et al 2022, though the magnitude of the relationships tend to be highly dependent on background conditions, and subsequently, how variables and lags are defined and measured. Both periods of drought and heavy rainfall can cause inefficiencies and reduced effectiveness of water treatment systems, which can subsequently impact the risk of cryptosporidiosis and giardiasis transmission (Curriero, Patz et al 2001, Thomas, Charron et al 2006, Nichols, Lane et al 2009, Luber and Lemery 2015, Chhetri, Takaro et al 2017, Schreiber, Heinkel et al 2019.…”