Heavy precipitation, drinking water source, and acute gastrointestinal illness in Philadelphia, 2015-2017

Abstract

Runoff from heavy precipitation events can lead to microbiological contamination of source waters for public drinking water supplies. Philadelphia is a city of interest for a study of waterborne acute gastrointestinal illness (AGI) because of frequent heavy precipitation, extensive impervious landcover, and combined sewer systems that lead to overflows. We conducted a time-series analysis of the association between heavy precipitation and AGI incidence in Philadelphia, served by drinking water from Delaware River and Schuylkill River source waters. AGI cases on each day during the study period (2015-2017) were captured through syndromic surveillance of patients' chief complaint upon presentation at local emergency departments. Daily precipitation was represented by measurements at the Philadelphia International Airport and by modeled precipitation within the watershed boundaries, and we also evaluated stream flowrate as a proxy of precipitation. We estimated the association using distributed lag nonlinear models, assuming a quasi-Poisson distribution of the outcome variable and with adjustment for potential confounding by seasonal and long-term time trends, ambient temperature, day-of-week, and major holidays. We observed an association between heavy precipitation and AGI incidence in Philadelphia that was primarily limited to the spring season, with significant increases in AGI that peaked from 8 to 16 days following a heavy precipitation event. For example, the increase in AGI incidence related to airport precipitation above the 95 th percentile (vs no precipitation) during spring reached statistical significance on lag day 7, peaked on day 16 (102% increase, 95% confidence interval: 16%, 252%), and declined while remaining significantly elevated through day 28. Similar associations were observed in analyses of watershed-specific precipitation in relation to AGI cases within the populations served by drinking water from each river. Our results suggest that heavy precipitation events in Philadelphia result in detectable local increases in waterborne AGI.

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

“…Epidemiological research undertaken in high-income nations like the United States, Canada, Taiwan, France, England, and Australia have shown a link between heavy precipitation and an increased risk of AGI [ 3 , 4 , 7 , 10 , 35 , 36 ]. This association raises a significant public health concern since it may indicate microbial contamination of drinking water supplies that have evaded treatments by water systems or could indicate exposure from direct contact with floodwater or residential sewage backups resulting from heavy rainfall events.…”

“…Individuals could then be exposed by consuming contaminated water or having direct contact with river water, floodwater, or sewage backups. For instance, numerous studies have linked cryptosporidiosis (a frequent cause of waterborne gastroenteritis) to high rainfall, most likely as a result of runoff and flooding contaminating water sources [ 10 , 11 , 37 , 43 ]. A study in New Jersey discovered that Cryptosporidium concentration rose after rainfall and was even more closely connected with other factors like streamflow and turbidity than rainfall [ 42 ].…”

Predicting Fecal Indicator Bacteria Using Spatial Stream Network Models in A Mixed-Land-Use Suburban Watershed in New Jersey, USA

“…In fact, more than 400,000 cases of acute gastrointestinal illness (AGI) were attributed to a drinking water treatment plant overwhelmed by high turbidity load after a period of heavy precipitation in Milwaukee, Wisconsin in 1993 [ 67 ]. Downstream of the Musconetcong River in Philadelphia, where the Delaware River serves as the drinking water source, a significant increase in waterborne AGI following precipitation above the 95th percentile was documented [ 68 ]. Under the current trend of global climate change, the National Climate Assessment projected an almost 50% increase in the total annual precipitation falling in the heaviest cases (1%) by the late 21st century under the higher scenario (RCP 8.5) in the northeastern United States [ 69 ].…”

A population-based survey of the prevalence of self-reported acute gastrointestinal illness in Zhejiang Province, China

“…First, in summer, climate warming and weather changes exacerbate the challenges of nutrition and clean water. Moreover, owing to the increase in rainfall events in summer, enteric infections and inflammatory bowel disease (IBD) rise accordingly [ 33 , 34 ]. In addition, respondents living in Jiaxing and Quzhou were more likely to report AGI compared to respondents at other sites.…”