Exploring the association between knee osteoarthritis outpatient visits and Asian dust storms: a time-series analysis

Exploring the association between knee osteoarthritis outpatient visits and Asian dust storms: a time-series analysis

Research exploring the relationship between air pollution and OA is limited. For example, Chau et al. from Taiwan demonstrated that exposure to air pollutants increased the risk of developing OA24, and Ziadé et al. found that short-term exposure to PM2.5 exacerbated knee OA pain25. An animal study by Peng et al. suggested that high PM exposure could have lasting effects on OA severity, potentially through mechanisms related to systemic inflammation11. Chen et al. found that short-term exposure to PM2.5 might correlate with outpatient visits among adults with knee OA, particularly affecting women and the elderly36. However, no prior research has explored the association between knee OA and ADS, a common environmental pollution during late winter and spring in the East Asian region. This study addresses this gap in the literature.

The findings indicate no significant increase in knee OA outpatient visits on the day of ADS events, however, a delayed effect was observed, with a significant increase in visits on post-event day 1, particularly in female and elder subgroups, and on post-event day 4 in the pediatric group. This delayed effect is consistent with previous air pollution researches30,31,34,37,38. While the pathophysiology of this phenomenon cannot be simply attributed to a cause-effect relationship, since knee OA is a chronic condition. One plausible explanation for the observed flare up is the postponed biological responses resulting from exposure to residual PM after dust storm events. Inhaling air pollutants may lead to increased levels of free radicals within the lungs, initiating oxidative stress. This, in turn, triggers the production of antibodies and pro-inflammatory cytokines like IL-1 and IL-614,15,16, which stimulate inflammatory cells circulating in the bloodstream, potentially migrating toward the knee joint and causing synovial inflammation and hyaline cartilage degradation9,10,11,24,39. This process takes time to progress, which aligns with the delayed outcomes observed in other studies regarding the impact of dust storms on various diseases30,31,34,40.

While the proposed biological mechanisms provide a plausible explanation, alternative hypotheses should also be considered to provide a comprehensive understanding. One potential alternative is the role of systemic inflammation triggered by PM exposure. PM not only increases levels of free radicals and stimulates inflammatory cells within the lungs but also causes various molecular alterations involving systemic inflammation, oxidative stress, endothelial dysfunction, coagulation, and lipid metabolism41. This inflammation might initiate a cascade that does not immediately manifest, potentially exacerbating knee OA symptoms days after exposure as the body continues to process the pollutants. Another area for exploration is the impact of air pollution on the gut microbiome42,43. Environmental stressors such as dust storms could alter gut health, influencing systemic inflammation and pain perception, which might contribute to delayed flare-ups in knee OA. Additionally, psychological stress resulting from environmental changes could affect pain perception and inflammatory processes, potentially leading to a delayed onset of OA symptoms. In addition to physiological characteristics and postponed biological responses, other complex factors must be considered when evaluating the delayed effect, including individual vulnerability, personal exposure to ADS events, the severity of related symptoms, healthcare-seeking behavior, and the adequacy of local medical resources.

The study also identifies gender and age as significant risk factors for the impact of air pollutants on knee OA. Females exhibited a two-fold higher likelihood of experiencing knee OA issues compared to males, with a significant surge in knee OA outpatient visits observed on post-event day 1. Additionally, both the elderly population on post-event day 1 and the pediatric population on post-event day 4 showed a notably higher rise in outpatient visits compared to other adult groups. These findings emphasize the importance of considering both gender and age when assessing the effects of air pollution on knee OA, which is consistent with previous research24,36.

Regarding regional geographic characteristics, a significantly higher number of knee OA outpatient visits was observed in the western part of Taiwan on post-event day 1, a pattern not observed in the eastern region. This difference may be attributed to Taiwan’s Central Mountain Range, which likely blocks dust storms from the Mongolian Plateau, resulting in better air quality in the east. Additionally, the rural nature of the eastern region, combined with limited medical resources and less convenient access to healthcare, may also reduce the likelihood of residents seeking medical attention.

Furthermore, the results indicate a positive association between temperature, SO2 levels, and knee OA outpatient visits. High temperatures and elevated SO2 concentrations were linked to increased knee OA cases across all age groups and genders.

This study is among the first and largest population-based investigation to explore the association between ADS and knee OA. A key strength of the research lies in its use of a large population dataset, NHIRD, which represents the health status of the entire Taiwanese population. Another strength is the comprehensive time-series regression analysis applied to age, gender, and regional subgroups. From a public health perspective, the findings of this study have significant implications for clinical practice and public health policy regarding the impact of ADS on knee OA patients. To mitigate these effects, several recommendations are proposed. First, establish a comprehensive public health alert system to warn vulnerable populations about upcoming ADS events and provide guidance on protective measures. Clinicians should use these results to advise OA patients on specific precautions, such as minimizing outdoor exposure, utilizing air purifiers, and adjusting treatment plans as necessary. Healthcare support during ADS periods should be enhanced through increased access to medical care via mobile clinics, telehealth services, and specialized OA management programs. Urban planning initiatives should prioritize investments in green infrastructure and improvements to indoor air quality. Public health policies should be developed to offer clear guidelines on reducing exposure during ADS events, including public advisories and enhanced emergency health services. Additionally, launch public awareness campaigns to educate the general public on ADS risks and provide targeted training for healthcare providers to better manage OA patients during these events. Finally, ongoing research on the ADS-OA relationship should be supported, encouraging collaboration between scientists, healthcare providers, and policymakers.

Limitations and future prospects

Despite the significant findings, this study has several limitations that require careful consideration when interpreting the results. Primarily, the reliance on outpatient visit data from the NHIRD may not comprehensively capture all individuals affected by knee OA during ADS events, particularly those who do not seek medical care or manage symptoms at home. The accuracy of knee OA diagnoses in the NHIRD may not meet standardized clinical criteria, as the data are solely reliant on claims reported by physicians or hospitals, potentially leading to misclassification and affecting the study’s validity. Furthermore, the observational nature of the study design inherently limits the ability to establish a causal relationship between ADS exposure and knee OA exacerbation. A critical limitation is the inability to control for individual risk factors for knee OA, such as BMI, metabolic diseases, bone deformities, and joint injuries, due to the aggregated nature of the data. The lack of clinical and laboratory information on knee OA disease activity during ADS days compared to non-ADS days further hampers the establishment of a direct correlation between ADS exposure and OA symptoms.

Additionally, the environmental data used in the study present limitations. The uneven distribution of TEPA’s 55 air quality monitoring stations, with denser coverage in urban areas and sparser coverage in rural regions, may lead to inaccurate air quality estimates across different geographical locations. Moreover, the reliance on daily average measurements may fail to capture significant within-day fluctuations in pollutant concentrations, especially during rapidly changing ADS events. This could result in an underestimation of actual exposure levels and their potential health impacts. Personal exposure levels may vary significantly due to factors such as outdoor activities, occupational characteristics, and residential environments, which were not accounted for in this study. This limitation could lead to exposure misclassification and potentially bias the results.

The statistical modeling employed may have inherent limitations, including unaccounted confounding variables and potential model specification errors, which could influence the strength and direction of the observed associations. Moreover, the study did not account for potential biases in data collection or analysis, such as discrepancies in healthcare-seeking behavior among different demographic groups. These factors could influence the observed rates of OA consultations and the accuracy of exposure assessments. Lastly, individual variability in biological responses to air pollution, influenced by genetic factors, existing health conditions, and lifestyle choices, complicates the understanding of delayed effects on knee OA exacerbation and may result in inconsistent findings across the study population.

Future research should address the limitations of this study by incorporating more comprehensive data sources such as inpatient visits, emergency department records, and self-reported symptoms to better capture the spectrum of knee OA cases. Longitudinal studies with larger and more diverse populations are needed to establish a clearer causal relationship between ADS exposure and knee OA exacerbation. Additionally, investigating the underlying biological mechanisms could identify specific components of dust storms that contribute to inflammation and joint pain. Future studies should also focus on precise measurements of particulate matter components during ADS events to determine which pollutants are most associated with worsening knee OA. Exploring individual sensitivity factors, including genetic predispositions and lifestyle, could highlight high-risk groups. Biomarker studies could provide insights into the inflammatory and oxidative stress pathways affected by ADS. Finally, intervention studies evaluating preventive measures such as indoor air purification and personal protective equipment could help mitigate the risk of ADS-related knee OA exacerbations.

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