Extreme Environmental Temperatures and Motorcycle Crashes: A Time-Series Analysis

Background: Available studies evaluating the impacts of extreme temperatures on the risk of traffic crashes have mainly focused on car crashes, overlooking the potential differences in ambient and vehicle indoor temperatures due to the use of air conditioners. One way to overcome this limitation is to focus on motorcyclists who are directly exposed to ambient temperature. The aim of this study, therefore, was to evaluate the effect of exposure to extreme cold and hot temperatures on seeking medical attention due to motorcycle crashes in Iran. Methods: The time-series study was conducted in Sabzevar City located in the northeastern part of Iran. Daily counts of medical attendance for motorcycle crashes from March 2011 to June 2017 were collected through emergency departments of all four hospitals of the city and the pre-hospital emergency systems. Data on daily minimum, mean and maximum temperature (°C), relative humidity (%), wind velocity (km/hr.), and precipitation (mm/day) were collected from the Sabzevar meteorological station. We developed semi-parametric generalized additive models following a quasi-Poisson distribution with the distributed nonlinear lag model to estimate the immediate and lagged (0-3 days) associations of indicators of daily thermal stress (one at a time) on daily counts of medical attendance for the motorcycle crash, controlled for the relevant covariates. Results: We found an increased risk of medical attendance for motorcycle crashes at both extremely cold (1 st percentile) and hot (99 th percentile) temperatures and also hot (75 th percentile) temperatures, mainly during lags 0 to 2 days. The risk estimates for extremely hot temperatures were larger than hot and extremely cold temperatures. We also found an increased frequency of medical attendance for motorcycle crashes during heatwave days compared to non-heatwave days. Around 10-11% of the medical attendance for motorcycle crashes was estimated to be attributable to non-optimal temperature. Interpretation : We observed an increased frequency of medical attendance for motorcycle crashes in association with short-term exposure to hot and cold ambient temperature in Sabzevar, a city in a middle-income country. Our findings, if confirmed by future studies, will have important implications for public health messaging, given the considerable burden associated with road traffic injury, particularly in low- and middle-income countries. Funding: This Project mainly was funded by the Shahid Sadoughi University of Medical sciences as a master thesis of Mr. D. Mohammadi. Dr. Gasparrini was supported by the Medical Research Council-UK (Grant ID: MR/M022625/1) and the Natural Environment Research Council-UK (Grant ID: NE/R009384/1). Payam Dadvand is funded by a Ramon y Cajal fellowship (RYC- 2012-10995) awarded by the Spanish Ministry of Economy and Finance and Mark Stevenson is funded by a National Health and Medical Research Council fellowship (ID1136250) Declaration of Interest: None to declare. Ethical Approval: The study was approved by the Ethics Committee of the Shahid Sadoughi University of Medical Sciences (Ethics Committee approval number: IR.SSU.SPH.REC.1396.121).