Effects of Meteorological Factors on Daily Outpatient Visits for Skin Diseases: A Time Series Study in a Chinese Population
The relationship between meteorological factors and health outcomes has been a subject of increasing interest in recent years. While previous studies have explored the impact of weather conditions on specific diseases, there has been limited systematic analysis of how meteorological factors influence a broad category of diseases, particularly skin conditions. This study aims to fill this gap by investigating the short-term effects of meteorological factors on the number of daily outpatient visits for skin diseases in a Chinese population.
The study was conducted using data collected from the Affiliated Hospital of Guizhou Medical University, located in the downtown area of Guiyang, China. The data spanned a three-year period from January 1st, 2014, to December 31st, 2016, encompassing 1096 days. The dataset included daily outpatient visits for skin conditions, excluding emergency department visits. Each patient’s identity card (ID), visit date, age, sex, contact number, residential address, and diagnosis (coded according to the International Classification of Diseases, 10th revision) were recorded. Patients who visited the hospital multiple times on the same day were excluded based on their ID to avoid duplication. The study was approved by the Ethics Committee of the Affiliated Hospital of Guizhou Medical University, and the need for informed consent was waived as the data were analyzed anonymously.
Meteorological data, including daily mean temperature (T, °C), mean atmospheric pressure (P, hPa), relative humidity (RH, %), mean wind speed (W, m/s), and total hours of sunshine (ST, h), were obtained from the Guiyang Meteorological Information Center. Additionally, data on the average concentrations of six air pollutants—particulate matter with an aerodynamic diameter less than 2.5 microns (PM2.5), particulate matter with an aerodynamic diameter less than 10 microns (PM10), sulfur dioxide (SO2), nitrogen dioxide (NO2), carbon monoxide (CO), and ozone (O3)—were collected from the Guiyang Environment Monitoring Center.
The analysis employed generalized additive models (GAMs) to estimate the relative risk increase of 10 units for the main meteorological factors. Several independent models were constructed to evaluate the associations between meteorological factors and daily outpatient visits. The models controlled for long-term time trends, seasonal patterns, holidays, and the day of the week using regression spline functions. The degrees of freedom (df) for time trends were selected based on the partial autocorrelation function (PACF), with the Akaike Information Criterion (AIC) and residual analysis used to validate the choice of df. All analyses were conducted using R 3.3.3 statistical software with the “mgcv” package.
The study found that the mean number of daily outpatient visits for skin diseases was 143.0, with adults (18–64 years) constituting the majority at 96.9 visits per day. Preschoolers (≤6 years), school-aged children and teenagers (7–17 years), and the elderly (≥65 years) accounted for 17.8, 15.6, and 12.8 visits per day, respectively. Females had slightly more daily outpatient visits (79.1) than males (63.9). Notably, all descriptive indicators of daily outpatient visits were higher in the warm season compared to the cool season, suggesting that skin diseases are more prevalent or more likely to prompt medical visits during warmer months.
The analysis revealed significant associations between certain meteorological factors and the number of daily outpatient visits. In single-day lag structures, temperature (T) was significantly associated with outpatient visits at lag 0 day, while wind speed (W) showed significant effects at lag 4, lag 5, and lag 6 days. Sunshine hours (ST) were also significantly associated with outpatient visits at lag 2, lag 3, and lag 4 days. However, no significant associations were found for atmospheric pressure (P) or relative humidity (RH) in single-day lag structures.
When examining multi-day lag effects, the study found that the impact of meteorological factors on outpatient visits was generally stronger than for single-day exposures. The effects of temperature, wind speed, and sunshine hours increased from lag 01 day and peaked at lag 06 day. The study also observed positive linear relationships between daily outpatient visits and temperature, atmospheric pressure, wind speed, and sunshine hours. However, the relationship between temperature and outpatient visits was negative below approximately 10°C and positive above this threshold. In contrast, relative humidity showed a negative linear relationship with outpatient visits.
Age-specific analysis revealed that the elderly (≥65 years) were slightly more affected by temperature compared to other age groups. However, all meteorological factors except atmospheric pressure showed significant effects on outpatient visits among school-aged children and teenagers (7–17 years). Wind speed had the strongest association in this age group compared to others. Females were found to be more vulnerable to all meteorological factors, including temperature, atmospheric pressure, relative humidity, wind speed, and sunshine hours. Among males, significant associations were observed for temperature, wind speed, and sunshine hours, but not for atmospheric pressure or relative humidity.
Season-specific analysis showed significant positive relationships between the number of daily outpatient visits and temperature, wind speed, and sunshine hours in the warm season. In contrast, a significant negative association was observed between temperature and outpatient visits in the cool season. Wind speed and sunshine hours showed significant positive associations with outpatient visits in both the warm and cool seasons. Relative humidity was significantly associated with a decrease in outpatient visits in both seasons.
Sensitivity analysis confirmed that the effects of the five major meteorological factors on outpatient visits remained statistically significant even after adjusting for covariates such as weather conditions and air pollutants. This suggests that the findings are robust and not substantially influenced by changes in these covariates.
The study concluded that meteorological factors, particularly temperature and wind speed, have a significant impact on the number of daily outpatient visits for skin diseases. The positive association between wind speed and outpatient visits may be partly explained by the role of airborne allergens, such as pollen, in triggering allergic skin conditions. The relationship between temperature and outpatient visits was found to be positive above a threshold of approximately 10°C and negative below this threshold, which contrasts with findings from studies on cardiovascular diseases. This highlights the different ways in which various body systems respond to meteorological factors.
Despite its robust findings, the study has some limitations. The data were derived from administrative databases, which did not include information on medication use, personal habits (e.g., smoking), or comorbidities. Additionally, daily rainfall was not included as a weather variable due to data access limitations, which may have affected the results.
In conclusion, this study provides statistically significant evidence that meteorological factors have a non-negligible impact on the health of the general population, particularly in relation to skin diseases. Further research with consistent methodology is needed to clarify the magnitude of these effects and their influence on specific skin conditions.
doi.org/10.1097/CM9.0000000000001290
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