This study investigated the influence of weather changes in tropical and subtropical regions on PT resource utilisation among OA patients. We found that higher temperatures increased PT utilisation among OA patients. Barometric pressure had inconsistent effect on PT utilisation under different analyses, and its impact was smaller than the influence of temperature. Additionally, the effects of other meteorological factors altered with the mean temperature changes. In hotter weather (> 23°C), higher daily temperature differences and humidity resulted in increased PT use. However, in colder weather (< 23°C), reverse effects were observed.
Previous studies have found that cold weather could result in worsened symptoms [17, 18, 26, 28]. In addition to its effect on the musculoskeletal system, temperature drop increased the pain perception of the central nervous system [29]. With regards to the effects of barometric pressure on OA, Peultier et al. compiled relevant articles and found seven articles that revealed that there was a significant correlation between barometric pressure and symptoms. However, the results of these studies were not consistent in that some found that increased barometric pressure resulted in greater symptom severity, while other studies found that low barometric pressure aggravated pain [25]. Another study revealed that an increased relative humidity increased the Western Ontario McMaster Universities Osteoarthritis Index (WOMAC) pain score among OA patients [26]. Moreover, a previous study showed that there were significant associations between joint pain and daily average humidity, and this effect increased during cold conditions [21].
As mentioned above, OA patients should experience worsening symptoms when the weather is colder or when humidity is higher. OA patients require more PT at these times. On the contrary, in our research, we found that patients reduced their use of PT during cold weather as well as high humidity conditions. These findings indicate that the frequency of PT among OA patients may be most affected by medical accessibility, rather than temporary changes in symptoms.
How does weather affect medical accessibility? Previous research has focused on two aspects. First, extreme weather or catastrophic climate increases the difficulty of transportation and affects the convenience of patients to reach medical institutions [30]. Bad weather, such as rainy days and typhoons, may decrease the patients’ desire to go out and seek treatment. Second, under severe weather conditions, the number of people availing medical treatment increases which further hinders other people from being able to access medical resources due to shortage of resources [31]. However, these theories seem to be insufficient to explain why changes in temperature and humidity affect the use of PT in Taiwan.
Due to the extremely high medical density and convenience in Taiwan, patients usually receive PT anytime they want, without an appointment. Therefore, relatively uncomfortable weather may cause patients to choose another day for treatment. In addition, since Taiwan is located at the border of subtropical and tropical regions, most air-conditioning systems in hospitals provide cooling rather than heating functions. In scorching weather, the air-conditioned hospital environment provides patients with a greater incentive to receive treatment. In contrast, cold and clammy weather makes patients less willing to go out, and their discomfort is not relieved by arriving at the medical facility. Therefore, even if patients experience more physical discomfort, they do not utilise PT. Another reason why patients avail their PT treatment on days with higher daily highest temperature during cold weather conditions is that the weather is relatively more comfortable for patients to go outside.
Although pain and joint stiffness decrease the walking ability and endurance, which may reduce accessibility of medical services, worsening symptoms should be a stronger driving force for patients to receive treatment. The PT utilisation, contrary to clinical symptoms, indicates that the greatest influence on the utilisation of PT among OA patients is not based on the severity of symptoms, rather it is external weather conditions. Future studies may explore whether PT utilisation in regions with relatively adequate medical treatment is restricted by medical accessibility or subject to overuse.
Study Limitations
This is a nationwide study with the advantage that health insurance coverage is as high as 99%. Therefore, sufficient patient consultation data were obtained. In addition, this study used a case-crossover design to exclude measurable and unmeasurable confounding variables. However, this study has the following limitations: 1) The environment of patients may not be completely consistent with the environment of the meteorological station. Moreover, we were also unable to confirm whether the patients spent the majority of their time in air-conditioned environments. However, the coverage of meteorological stations in Taiwan is very extensive, and the reliability of the data should be higher than those observed in previous studies. 2) The climate of Taiwan tends to be hotter than most other countries, hence, the results may not be extrapolated to other non-tropical regions. We recommend that future studies investigate the effects of meteorological factors in low temperature conditions, which may provide a better understanding of the effects of various meteorological factors on PT utilisation. 3) The utilisation of medical resources varies greatly among different medical insurance systems. Medical resources are relatively cheaper and easier to obtain for patients in Taiwan. Therefore, our research results should only be analogous to countries with relatively sufficient rehabilitation medical resources.