Association between Ambient Fine Particulate Matter and Hospital Admissions for Ophthalmic Diseases in Upper Northern, Thailand: A Time-stratified, Case-crossover Study
Authors:   , Kasikam Nichaphan 
Published: February 2025

Fine particulate matter poses problematic worldwide pollution and has been a major health concern in upper northern Thailand. The eye and its adverse effects are one of the most obvious complaints as a frontline organ is directly exposed especially when ambient PM₂.₅ is acute. Yet, epidemiological studies to investigate the acute association between PM2.5 and the eye and adnexa diseases have been lacking. This work analyzed inpatient cases (n = 192,545) of the eye and adnexa diseases (code H00 - H59) in 118 hospitals across 9 upper north provinces of Thailand, 2016 to 2020, given by the Information and Communication Technology Center, Ministry of Public Health. For PM₂.₅ exposure assessment, 15 monitoring stations of the Pollution Control Department were acquired for air pollutants and meteorological indicators. Their hourly measurements were then aggregated to daily average lagged days 0 - 7 and were assigned to their neighborhood hospitals for inpatient exposure. A time-stratified casecrossover design controlling for the day of the week and season trend and multivariate conditional logistics regression adjusted for PM₁₀, O₃, temperature, and relative humidity were performed by the R® program. The associations were analyzed and stratified for the season, sex, age, and sub-diseases. The association of PM₂.₅ exposure below the daily standard was also examined. Results showed significant correlation coefficients of PM₂.₅ and others: PM₁₀, O₃, and relative humidity at 0.92 (p < 0.001), 0.71 (p < 0.001) and -0.62 (p < 0.001) respectively. Adjusted odds ratios and their confidence intervals (ORs and CIs) disclosed statistically significant risk for the increase in PM₂.₅ level per interquartile range (IQR) rising of 26 μg/m³. An increase in PM₂.₅ was found associated with the increment of the eye and adnexa inpatient visits (1.04, 95% CI: 1.02 - 1.07, p < 0.001, lag 6). The association was riskiest in the hot (1.23, 95% CI: 1.17 - 1.29, p < 0.001, lag 6) following by the wet raining season (1.10, 95% CI: 1.08 - 1.12, p < 0.001, lag 0) and no positive association observed in the cold season. For the subgroup, risks of the eye and adnexa diseases were slightly higher in males (1.05, 95% CI: 1.03 - 1.07, p < 0.001, lag 6) than females and also in younger cases (≤65 y) (1.05, 95% CI: 1.01 - 1.09, p = 0.010, lag 6) than older cases (>65y). Sub-disease risks were elevated significantly such as disorders of refraction and accommodation (1.63, 95% CI: 1.16 - 2.29, p = 0.005, lag 6), conjunctivitis (1.34, 95% CI: 1.21 - 1.48, p < 0.001, lag 2), keratitis (1.22, 95% CI: 1.00 - 1.47, p = 0.043, lag 6), other diseases of the eye and adnexa (1.13, 95% CI: 1.01 - 1.25, p = 0.026, lag 1), cataract (1.05, 95% CI: 1.02 - 1.09, p = 0.003, lag 6), and blindness (1.03, 95% CI: 1.02 - 1.05, p < 0.001, lag 6). For age-sub disease analysis, the increased risk was observed for glaucoma (aged > 50y, 1.10, 95% CI: 1.00 - 1.21, p = 0.040, lag 1) and strabismus (aged < 50y, 95% CI: 1.01 - 1.62, p = 0.038, lag 7). For exposure below the PM₂.₅ standard, there was no threshold for exposure level to PM₂.₅. Thus, PM₂.₅ exposure prevention is essential to alleviate the vulnerability of the upper-northern population. Stratified risk result is an indication for PM2.5 abatement strategy development in upper northern Thailand for the season- and identified sensitive population-specificity. Future research is still in great need for bettering control of other co-pollutants when more available and for estimating other inpatient risk factors.