The present study showed that OA, including its subtypes, was associated with an increased risk of subsequent UTI in older patients. The impact of OA on subsequent UTI was most prominent in the age subgroup of ≥85 years. In addition to OA, older age, female sex, a history of UTI, an indwelling urinary catheter, cerebrovascular disease, diabetes, dementia, and urolithiasis were also independent predictors for any UTI.
A possible explanation for UTI’s increased risk is that patients with OA have decreased physical activity and even immobilization due to pain. This reduced activity predisposes them to inferior body function, sarcopenia and frailty, diabetes, and immune deficiencies related to UTI[10, 15, 21-23]. A study by Rosemann et al. reported that patients with OA of the lower limb had decreased physical activity than those without OA. Another study by Hirata et al. found that more than 40% of women with hip OA were physically inactive and lacked moderate-intensity activity. A national study by Zhu et al. reported that a greater number of bedridden days was an independent risk factor for UTI. A study by Shang et al. about patients in home health care reported that limited physical function status was a risk factor for infections, including UTI. In contrast to decreased physical activity, a large cohort study by Roger at al. reported that avoiding immobilization and an ability to walk were associated with a 69% lower hospitalization rate for UTI in older adults admitted to a skilled nursing facility. Even in residents with severe mobility problems, including being in a wheelchair or having a missing limb, maintaining or improving mobility (in bed or when transferring) could reduce the risk of hospitalization for UTI by 38% to 80%.
A decrease in physical activity may cause the inability to urinate frequently, urinary retention, and urolithiasis, and then increase UTI risk[15, 25]. Decreased physical activity may decrease the abdominal organs’ pressure on the urinary bladder and decrease the urge to urinate, even when the bladder is full. The bone will turnover to create hypercalciuria, and urine will collect in the lower portions of the renal calyces when the body is immobilized or in the supine position, which increases the risk of renal calculi formation even further. Physical inactivity is also a major contributing factor for sarcopenia, frailty, and adverse outcomes[22, 29]. Sarcopenia and frailty are also associated with impaired bladder function, which may increase UTI risk. Therefore, the impact of OA is broad. Also, many adverse outcomes associated with OA affect each other and result in a vicious circle.
The increased risk of UTI was more prominent in the age subgroup of ≥85 years and suggested that this older population is more sensitive to the effects of OA on developing subsequent UTI. In addition to OA, the present study found that older age, female sex, a history of UTI, an indwelling urinary catheter, cerebrovascular disease, diabetes, dementia, and urolithiasis were also independent predictors of UTI, which is compatible with previous studies[14, 15]. All subtypes of OA, including the upper limbs, lower limbs, spine, and other areas, were associated with increased UTI risk. There was no study about comparing subtypes of OA and subsequent UTI. The results suggest that the influence of pain and decreased physical activity are specific to older adults, regardless of OA type.
The present study’s major strengths are its nationwide design, large sample size, and the clarification of an uncertain issue. The limitations are as follows. First, detailed information related to UTI, including activities of daily living, was not available in the NHIRD, which may confound the present results. However, we had matched age, sex, and adjusted the potential risk factors for UTI. Thus, we believe that the confounding effect is minimal. Second, although we found an association between OA and UTI, the causal relationship between OA and UTI could not be entirely clarified because there is a complex interaction among OA, UTI, and other comorbidities. Third, the present result may not be generalized to other nations because of the differences in race, culture, and medical insurance, and, therefore, further studies in other nations are warranted.