Effect modification by high-concentration duration in the association between particulate matters and stroke hospital admissions among hypertension patients in Beijing, China

Abstract

To investigate the associations between particulate matter (PM) and hospital admissions for stroke and its subtypes among hypertension patients. We proposed a new modifier named high-concentration duration (HCD). Data on daily hospital admissions, air pollution, and meteorological factors were collected from 2014 to 2018 in Beijing, China. We included all patients with hypertension who were admitted to hospitals of secondary-level and above for stroke. Time-series analysis was conducted by fitting a generalized additive model. An interaction term of daily concentration and an HCD stratum indicator were included in the model. Sex subgroup analysis was performed in four age groups to detect vulnerable populations. A total of 358,577 admissions were identified. The PM was significantly associated with stroke admissions in patients with hypertension. The maximum excess risk (ER) (%) per 10 μg/m³ increase in fine particulate matter (PM_2.5) was 0.23% (95% confidence interval (CI): 0.15%, 0.31%) for overall stroke, 0.25% (95% CI: 0.16%, 0.33%) for ischemic stroke (IS). The maximum ER (%) per 10 μg/m³ increase in inhalable particle (PM₁₀) was 0.14% (95% CI: 0.06%, 0.23%) for overall stroke, 0.15% (95% CI: 0.06%, 0.23%) for IS. For hemorrhagic stroke, significant associations were also observed among males and patients < 55 years. ER (%) in long-HCD strata was significantly larger than that in short-HCD strata. The effects of PM_2.5 were significant in long-HCD strata, but insignificant in short-HCD strata. HCD might be a modifier in the association between air pollution and health effects. While controlling the daily average concentration, it is also important to reduce HCD on a given day.