Inmate health is a major global concern [1]. Prisoners often lack access to health care and face injustices due to unsafe prison environments, unhygienic living conditions, and a lack of medical resources. All of these factors correlate with the high prevalence of chronic diseases, infectious diseases, and poor mental health in prisoners [2-4]. A burgeon of literature suggests a negative relationship between incarceration and health [5-7]. These health inequalities are associated with potential additional medical expenditure. Prison overcrowding correlates significantly with the spread of infectious and communicable diseases [8]. The close living quarters and limited access to health care in prisons can result in rapid disease transmission among inmates and into the community upon their release [9]. This emphasizes the importance of implementing effective public health measures in correctional facilities to minimize the impact of infectious diseases on both inmates and the general population. Moreover, incarcerated populations may be significantly exposed to extreme temperatures, as indicated by existing cases [10]. Both low and high temperatures are associated with emergency department visits for renal and urinary diseases, with heat having a stronger impact than cold. Furthermore, emergency department visits tend to decrease on days with low temperatures [11].

Urinary tract infections (UTIs) are among the most prevalent types of infectious diseases worldwide [12,13]. Despite their widespread occurrence, they are not currently classified as mandatory reportable conditions. The true frequency and burden of UTIs are likely underestimated due to a lack of comprehensive data on their prevalence and impact [14-16]. UTIs not only have an impact on individuals but also pose a significant public health concern. The overuse and misuse of antibiotics to treat UTIs contribute to antimicrobial resistance, making effective management more difficult. Moreover, untreated UTIs can potentially lead to more serious complications, particularly in vulnerable populations such as older adults or individuals with compromised immune systems [17]. Furthermore, a link has been discovered between early-stage chronic kidney disease (CKD) and higher health care costs over a 5-year period. Therefore, it is important to develop strategies to prevent CKD progression and reduce the associated health care expenses [18].

Understanding the differences in urinary disease epidemiology between men and women are crucial for providing sex-specific patient care. Evidence suggests that there are sex differences in the risk and outcomes of urinary disease, with mixed results depending on the cause [19,20]. Urinary disease is prevalent among individuals from disadvantaged socioeconomic backgrounds. These groups are also disproportionately affected by incarceration, and face barriers in accessing health care. Little is known about the status of urological diseases in imprisoned individuals. Some evidence suggests that the prevalence of self-reported kidney problems among incarcerated individuals varies across correctional settings; however, nuanced data characterizing urological disease trends in this population are lacking [21].

The health of prisoners in Taiwan has become a focal point, and in the past decade, the focus has shifted from solely addressing issues related to HIV, hepatitis, and other notifiable diseases to encompassing a broader range of illnesses. Data on the prevalence of diseases including oral and eye diseases are also available [22,23].

To eliminate inequalities in prisoner health, it is important to understand the specific status of each disease. This study aimed to explore the health status of Taiwanese prisoners with urinary diseases. We evaluated the prevalence of urinary diseases across different sex and age groups among prisoners in Taiwan to comprehensively review their health status, improve the identification of urinary diseases by health care professionals, and provide a basis for health policy decisions.

This cross-sectional study was conducted to determine the prevalence of urinary diseases in Taiwanese prisoners, and to clarify differences in sex and age. In Taiwan, the Ministry of Health and Welfare supervises the medical care of prisoners, ensuring they receive a comprehensive initial assessment of their mental and physical health status—including medical history, current status, and past medical history—by medical professionals upon entry. All medical services accessed by prisoners are covered by the National Health Insurance program. This program in Taiwan aims to ensure the right to access health care for all individuals, regardless of their financial status, education, or race. Since March 1, 1995, the compulsory social insurance system has consisted of public and private insurance, and it covers 23,355,508 (>99%) of the Taiwanese population. The Taiwan National Health Insurance Research Database (NHIRD) records the claims data, including inpatient and outpatient records, investigations, and treatment of insured individuals [24]. The data used in this study were extracted directly from the database to prevent underestimation and bias of the actual prevalence that could occur through self-reported data obtained from incarcerated individuals.

This study used the datasets of ambulatory care expenditures by visits and datasets of inpatient expenditures by admissions from the NHIRD. We have previously investigated the prevalence of oral health and skin diseases among prison inmates in Taiwan [22,25].

We extracted claims data for all inmates from January 1 to December 31, 2013, including 1,122,922 person-times of outpatient data and 15,383 person-times of hospitalization data. We combined the medical records of both outpatient and inpatient visits and summarized the data for each individual. In total, this study includes 83,048 inmates. The ICD-9-CM (International Classification of Diseases, Ninth Revision, Clinical Modification) codes were used to define the diagnosis of urinary diseases [26]. Participants were identified as inmates with urinary diseases, indicated by ICD-9 codes 580‐599 in their medical records, and who had more than one medical visit.

This study was conducted using data from the National Health Research Insurance Database and was approved by the Institutional Review Board Research Ethics Committee of Taizhou Hospital of Zhejiang Province (TZH-IRB: K20240836). The National Health Research Institutes encrypted the names of patients, medical care providers, and institutions, replacing the identity numbers of all insured persons with alternative unique numbers to protect their privacy. All applications for National Health Research Insurance Database access are reviewed by peer experts to ensure the rationality of their use. Researchers must comply with Taiwan’s Computer-Processed Personal Data Protection Law and related regulations when accessing the data, and they must sign an agreement declaring that they will not attempt to retrieve information about patients or medical care providers.

All analyses were performed using SAS (version 9.4; SAS Institute Inc). Prevalence data are expressed as numbers and percentages. The chi-square test and Fisher exact test were used to assess sex- and age-group differences in the disease percentages, and the prevalence ratio was calculated using the GENMOD procedure.

This study included data from 83,048 prisoners (Figure 1), comprising 74,405 (89.59%) men and 8643 (10.41%) women. As shown in Table 1, 2424 male inmates were identified as having urinary system diseases, with an average age of 46.46 (SD 13.07) years and an average of 28.03 (SD 22.08) medical service visits per year. Among female inmates, 574 had urinary diseases, with an average age of 39.25 (SD 12.37) years and an average of 32.79 (SD 23.51) times per year using medical services, including outpatient and emergency services as well as hospitalization.

The prevalence of urinary system disorders among the prisoners was 3.61% (n=2998; n=574, 6.64% and n=2424, 3.26% in women and men, respectively). Diseases with the highest prevalence were other disorders of the urethra and urinary tract (ICD-9-CM: 599), including UTI, urinary obstruction, and hematuria, which occurred in 4.65% (n=402) of women and 1.46% (n=1086) of men. The disease with the second highest prevalence differed by sex; it was cystitis (n=115, 1.33%) in women and calculus of the kidney and ureter (n=629, 0.85%) in men.

The significant sex differences in chronic renal failure (ICD-9-CM: 585), kidney infections (ICD-9-CM: 590), calculus of the kidney and ureter (ICD-9-CM: 592), cystitis (ICD-9-CM: 595), and other disorders of the urethra and urinary tract (ICD-9-CM: 599) are shown in (Table 2).

Age-specific prevalence rates are shown in Table 3. There were significant differences in the prevalences of most disease classifications except for acute glomerulonephritis (ICD-9-CM: 580), nephrotic syndrome (ICD-9-CM: 581), renal sclerosis (ICD-9-CM: 587), hydronephrosis (ICD-9-CM: 591), and urethritis (not sexually transmitted), and urethral syndrome (ICD-9-CM: 597). In prisoners aged ≤40 years, three of the most common diseases were other disorders of the urethra and urinary tract (n=665, 1.56%), calculus of the kidney and ureter (n=223, 0.52%), and cystitis (n=165, 0.39%). Among men, the top three diseases were other disorders of the urethra and urinary tract (n=823, 2.04%), calculus of the kidney and ureter (n=445, 1.10%), and chronic renal failure (n=287, 0.71%).

Age- and sex-specific adjusted prevalence ratios were calculated and are presented in Table 4. Higher prevalence rates adjusted by age were observed in men for acute and chronic renal failure, calculus of the kidney and ureter, and other disorders of the urethra and urinary tract. In contrast, women had higher prevalences of kidney infection and cystitis compared to men. The sex-adjusted prevalence ratios were significantly >1 for most diseases, except for acute glomerulonephritis, nephrotic syndrome, kidney infections, urethritis (nonsexually transmitted), and urethral syndrome. Additionally, the prevalence of cystitis was lower in inmates aged >40 years compared to that in younger individuals.

The provision of adequate medical care for incarcerated individuals is not only a matter of basic human rights but also a public health concern. Ensuring access to necessary health care services and providing a healthy environment can help prevent the spread of infectious diseases within correctional facilities and the broader community, as well as reduce the consumption of medical resources. In addition, addressing prisoners’ health care needs can contribute to their successful reintegration into society. Therefore, we conducted an analysis to determine the prevalence of urinary diseases in Taiwanese prisons.

The results of this study showed that most diseases with high prevalence were related to infection and inflammation of the urinary tract. Approximately 3.6% of the inmates had urinary diseases, and their prevalence differed according to sex and age. To our knowledge, this is the first study to explore urinary system diseases in Taiwanese inmates.

The annual statistics showed that the prevalence of nephritis, nephrotic syndrome, and nephrosis in the Taiwanese general population was 2.32%, with 2.61% in men and 2.03% in women [27]. The community-based screening program also found a higher CKD prevalence in the general population than in prisons [28]. This disparity might reflect that the use of medical services for urinary diseases in prisons differs from the actual prevalence, indicating that many prisoners do not receive appropriate medical care. Consequently, this may overestimate the health status and quality of life of prisoners with urinary diseases, indicating that their conditions could be worse than previously thought.

Consistent with previous research, we found that infections and inflammation of the urinary system are more prevalent in women (women: n=574, 6.64%, men: n=2424, 3.26%), and that the prevalence increases with age (>40 years: n=1815, 4.5% and ≤40 years: n=1183, 2.77%). Biological sex (women or men) widely influences various immune responses, including immune responses to mucosal surface diseases. Sex hormones, sex chromosomes, sexual dimorphism, and sexual differences all affect an organism’s response to urological diseases such as bladder infections or cancer [19,29]. Women are more likely to experience urinary system diseases, particularly infections. We infer the following reasons based on previous literatures. Anatomical differences, such as the shorter female urethra and its proximity to the anus, make women more prone to UTIs [30]. Additionally, pregnancy and menopause can increase the risk of urinary incontinence, pelvic organ prolapse, and other urinary system disorders [31,32]. Furthermore, the female reproductive system, including the uterus and ovaries, can affect the urinary system and contribute to the development of diseases [33]. These conditions can significantly impact a woman’s quality of life, leading to urinary symptoms, sexual dysfunction, and more serious complications. They also place a significant economic burden on health care systems due to costs associated with diagnosis, treatment, and management [34-39]. In contrast, there is a higher risk of severe kidney disease in men than in women [40,41]. One key factor is the higher prevalence of conditions such as diabetes and high blood pressure, which are leading causes of kidney disease [42]. Men are more likely than women to develop these conditions, putting them at greater risk for kidney damage. Additionally, lifestyle factors such as smoking, poor diet, and lack of exercise can also contribute to the higher prevalence of end-stage kidney disease in men [43]. Another key factor is the genetic and hormonal differences between men and women. Research has shown that certain genetic factors may predispose men to kidney disease, while hormonal differences, such as the effects of testosterone, may also influence kidney function [44]. Understanding these biological differences is essential for developing targeted interventions to reduce the risk of different urinary system diseases [45].

As individuals age, the risk of developing urinary system diseases is more likely to increase due to a decline in urinary system function and the presence of other age-related health conditions [46,47]. Older adults face a higher risk of UTIs, stones, benign prostatic hyperplasia, and other urinary system disorders, which may lead to discomfort, urination problems, pain, and complications requiring medical treatment [48,49]. The impact of aging on urinary system diseases can result in higher health care costs and decreased quality of life, ultimately affecting overall health and well-being [50,51].

According to our findings, the prevalence of urinary diseases is mainly attributable to infection. Incarcerated individuals are at a higher risk of developing UTIs due to various factors such as limited access to health care, poor hygiene practices, and overcrowded living conditions [52]. UTIs are common and can affect the bladder, kidneys, ureters, and urethra. Antimicrobial resistance is a growing concern in the treatment of UTIs. The overuse and misuse of antibiotics, along with limited access to medical resources, have contributed to the development of resistant bacteria, making it more difficult to treat these infections [53]. UTIs pose significant challenges for individuals and health care systems regarding personal health and financial resources in the era of antimicrobial resistance [54,55].

Measures to reduce the medical burden of UTIs among prisoners should include prevention, diagnosis, and treatment. Providing a healthy environment, ensuring adequate water intake, and dietary interventions such as the provision of cranberries can help reduce the incidence of UTIs [56-60]. Personal hygiene is also essential in minimizing the risk of UTIs. Regular medical screenings and access to medical care are crucial for identifying and treating UTIs in their early stages, and a well-equipped and adequately staffed health care system within correctional facilities is required to treat them [61]. This is a multifaceted endeavor that requires a combination of education, access to resources, and comprehensive health care services. By adopting a comprehensive approach to UTI prevention—including general hygiene practices and targeted medical interventions—prisoners’ overall health and well-being can be significantly improved.

We used claims data from the NHIRD instead of prisoner questionnaires to prevent underestimation of the prevalence of urinary diseases and to avoid selection bias. The results were based on repeated diagnoses using harmonized ICD codes, minimizing measurement bias and improving the comparability of our findings.

Our study had some limitations. First, this was a Taiwanese population-based cross-sectional study, so our findings may not be generalizable to other regions and races. Additionally, the results were based solely on claims data from the NHIRD in 2013, which could not identify any causality between the incidence of urinary diseases and imprisonment. Second, we could not obtain certain information related to urinary diseases such as socioeconomic status and biochemical factors. Furthermore, we were unable to distinguish between the duration and facility of imprisonment and criminal type to clarify the relationship between urinary diseases and imprisonment. Third, although we used data from the NHIRD instead of self-reports, the prevalence of urinary diseases is still likely to have been underestimated, as discrimination by prison officials may have prevented inmates from receiving medical services. Furthermore, the precision of diagnoses based on ICD codes can differ greatly from diseases, and ICD codes may not always accurately reflect the true clinical status, leading to potential misclassification.

Our study revealed sex- and age-related discrepancies in the prevalence of urinary diseases. We found that the prevalence of urinary system diseases is related to infection and inflammation. These findings emphasize the importance of diagnosis and treatment. Thus, considering these findings, comprehensive medical services that implement specialized intervention strategies or policies are needed in prisons to enhance health equality among Taiwanese prisoners and reduce their overall medical burden. Future studies should include more factors influencing health care use and the incidence of urinary diseases among prisoners to investigate ways to improve their overall quality of life and health in the prison.