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

Abstract

AbstractBackgroundEnvironmentally-mediated protozoan diseases like cryptosporidiosis and giardiasis are likely to be highly impacted by extreme weather, as climate-related conditions like temperature and precipitation have been linked to their survival, distribution, and overall transmission success.ObjectivesOur aim was to investigate the relationship between extreme temperature and precipitation and cryptosporidiosis and giardiasis infection using monthly weather data and case reports from Colorado counties over a twenty-one year period.MethodsData on reportable diseases and weather among Colorado counties were collected using the Colorado Electronic Disease Reporting System (CEDRS) and the Daily Surface Weather and Climatological Summaries (Daymet) Version 3 dataset, respectively. We used a conditional Poisson distributed-lag nonlinear modeling approach to estimate the lagged association (between 0 and 12-months) between relative temperature and precipitation extremes and the risk of cryptosporidiosis and giardiasis infection in Colorado counties between 1997 – 2017, relative to the risk found at average values of temperature and precipitation for a given county and month.ResultsWe found a consistent, significant increase in the relative risk of cryptosporidiosis and giardiasis infection when the maximum or minimum monthly temperature in the 4-6 months prior were low (1stpercentile) for a given county and calendar month. High precipitation (90thpercentile for a given county and calendar month) 2-12 months prior was associated with a significant decrease in the relative risk of cryptosporidiosis, while high precipitation (90thpercentile) 12-months prior was associated with a significant increase in giardiasis infection risk.DiscussionOur study presents novel insights on the influence that extreme low temperatures can have on parasitic disease transmission in real-world settings. Additionally, we present preliminary evidence that the standard lag periods that are typically used in epidemiological studies to assess the impacts of extreme weather on cryptosporidiosis and giardiasis may not be capturing the entire relevant period.