Fine particulate air pollution and occurrence of spontaneous intracerebral hemorrhage in an area of low air pollution

Objectives:The association between short-term ambient particulate matter ≤ 2.5 μm diameter (PM2.5) andspontaneous intracerebral hemorrhage (SICH) occurrence is unclear. We aimed to study the association ofambient PM2.5 with occurrence of SICH in an area of low air pollution in southern Portugal.Patientsandmethods:PM2.5 levels from the 3 days before the SICH event (Lag 1, 2, 3) was compared with onecontrol period (Lag 15–17) using a case-crossover analysis. Conditional logistic regression was used to estimatethe odds ratio (OR) with 95% confidence interval (CI). Analysis was stratified by gender, age, functional neu-rological status, type of SICH, environmental factors (temperature, humidity, time of day and season).Results:Three-hundred and eight patients were included (2010–2015); mean age 70.8 years, 62.8% were males.The mean values (μg/l) of PM2.5 were higher on the case days (Lag1 = 7.76, Lag2 = 7.64, Lag3 = 7.74)compared to control period (Lag14-17 = 6.77). For each 10 μg/l increase, the likelihood of SICH increased 5.7%(95% CI = 1.020-1.095. P = .002). The strength of the association was higher in patients younger than 70 years(OR = 1.064, 95% CI = 1.009–1.122); without prior to SICH neurological disability (OR = 1.061, 95% CI1.022–1.101); with non-lobar type (OR = 1.054, 95% CI = 1.012–1.099). A circadian and circannual patternwas present with increased strength of the association when SICH occurred in the morning time (OR = 1,067,95% CI = 1.012–1.125), in the fall (OR = 1.118, 95% CI = 1.031–1.213) and the in the winter (OR = 1.064,95% CI = 1.002–1.129). The association was also potentiated at lower temperature values.Conclusion:Short-term increases of PM2.5 are associated with occurrence of SICH in Algarve, a region of lowambient pollution. Patient and ambient level factors can influence the strength of this association.Portuguese Stroke Associatio