Risk factors and prognosis for latent tuberculosis infection in dialysis patients: A retrospective cohort study at a single tertiary care center

Recent studies report that latent tuberculosis infection (LTBI) may lead to an increased risk of cardiovascular disease (CVD) that led us to hypothesize that LTBI may play an important role in major adverse cardiovascular events (MACE) in dialysis patients.


| INTRODUCTION
Latent tuberculosis infection (LTBI) is defined as a state of persistent immune response to stimulation by Mycobacterium tuberculosis antigens with no evidence of clinically manifest active tuberculosis (TB). 1 Due to attenuated cellular immunity, dialysis patients are at increased risk of TB, 2 which is mostly developed from LTBI reactivation. 3The extensive vaccination of Bacille Calmette-Guérin (BCG) in China plays a decisive role in reducing the specificity of TST, which is also insensitive in dialysis patients and is not recommended to be used in isolation to diagnose LTBI, 4 leading the choice towards the interferon enzyme-linked immunospot (IFN-γ ELISPOT) only be used to test for LTBI in dialysis patients.The prevalence of LTBI in dialysis population is unclear in China, particularly in those receiving peritoneal dialysis (PD).Meanwhile, not all individuals infected with M. tuberculosis develop active TB, several studies have shown that, on average, 5%-10% of those infected will develop active TB disease over the course of their lives, usually within the first 5 years after initial infection. 5As is well-known, there is high mortality in dialysis patients and significant adverse drug events may influence the willingness for LTBI treatment.The potential benefit of treatment should, therefore, be carefully balanced against the risk for drug-related adverse events, especially in dialysis patients.So, it is necessary to study the natural course and prognosis for LTBI in dialysis patients.
Recently, it has been recognized that LTBI is not a stable condition but rather a spectrum of infections which may lead to not only the progress to active TB disease but also an increased risk of cardiovascular disease 6 and subsequent cancer in general population. 7wever, it has not been reported in uremic population.
The goal of the present study was to investigate the prevalence of LTBI in patients receiving either hemodialysis (HD) or PD and to determine risk factors of LTBI in dialysis patients.At the same time, no studies, to our knowledge, have explored the relationship between LTBI and the incidence of major adverse cardiovascular events (MACE).We focused on assessing whether LTBI is associated with higher incidence of MACE in dialysis patients.The baseline data, including demographic (i.e., age and sex), clinical (i.e., dialysis duration, mean arterial pressure, and diabetes), past history (i.e., smoking, TB, cancer, and cardiovascular disease), as well as related biochemical variables, were recorded.Primary endpoints were MACE, including all-cause death and acute coronary syndrome (ACS).

| Study design and participants
Secondary endpoints were active TB and occurrence of newly diagnosed cancer which were identified based on the International Classification of Diseases Tenth Revision (ICD-10) codes.Follow-up time was calculated as the time from investigation baseline to the occurrence of outcomes or to March 30, 2021 for participants who were censored, whichever occurred first.All methods were carried out in accordance with relevant guidelines and regulations.All procedures related with human participants in this study were conducted in accordance with the ethical standards of the Helsinki Declaration.The study protocol, procedures, and patient informed consent form had been approved by the local ethics committee prior to the study ( 2020[045], Peking University Shenzhen Hospital).

| Statistical analysis
Demographic data are expressed as mean ± standard deviation, median (interquartile range), or number (%).Normally, distributed continuous variables were compared by using independent t-test; Wilcoxon rank A total of 270 subjects (mean age, 52.4 ± 13.4 years; male, 62.6%) with long-term dialysis (mean length of dialysis use, 48.7 months) were enrolled, including 148 HD patients and 122 PD patients.Among these patients, 47 cases were ELISPOT positive, defined as LTBI group, and 223 cases ELISPOT negative, defined as non-LTBI group (Table 1).
Compared with non-LTBI group, patients with LTBI (ELISPOT-positive) were older, lower serum calcium, and more likely had higher tobacco use rate.There were no significant differences in terms of sex, comor- were independent risk factors associated with MACE.In the subgroup analyses (Table 4), no significant effects of gender, older age, tobacco use and anemia, hypoalbuminemia, diabetes mellitus, and cardiovascular disease on the association between LTBI and MACE were observed (p for interaction >0.05).Sensitivity analysis excluding endpoint events within 1 month showed the same result (supporting information Table S1 and Figure 1).In addition, during follow-up, three patients with LTBI developed active TB, a rate of 6.4%, including one case of lymphoid TB and two cases of PD-associated tuberculous peritonitis, while no active TB occurred in the control group.TB incidence was significantly higher in LTBI group (P = 0.005).

| DISCUSSION
In this retrospective cohort study of dialysis patients, our findings showed that the prevalence of LTBI using IFN-γ ELISPOT in dialysis population was 17.4%, which was lower than one third of the world's population of LTBI estimated by the World Health Organization. 11In addition to the declining incidence of TB in Shenzhen China, recent research has also shown low sensitivity of the interferon-gamma release assay (IGRA) in end-stage renal disease (ESRD) cohorts and the positive rate is 18.75%.It was considered that therefore unlikely to be due to poor T cell cytokines secretion and may instead reflect defects in antigen presentation in ESRD patients. 12Traditionally, HD patients are believed to have higher prevalence of LTBI than PD patients due to more frequent hospital visits and longer hospital stay. 13By simultaneously enrolling HD and PD patients in our center, this study demonstrates that LTBI prevalence in patients receiving PD has a similar prevalence of LTBI as those receiving HD (15.6% and 18.9%, respectively), which is consistent with a Taiwan study that revealed that the use of either PD or HD is associated with similar risks of LTBI. 14These observations suggest that transmission of TB to HD patients within crowded dialysis facilities may be similar to PD patients at home, thereby challenging the hypothesis of occult transmission in the HD room.However, a prospective study conducted in King Saud University showed that the prevalence of LTBI in HD population was 45.3%, while that in PD population was only 8.1%. 15It may be related to the degree of the test result discordance, variability in the positive of IGRA sensitivity, and the complexities of different epidemiological backgrounds.
This suggests that reporting of real-world experience is essential to refining local management recommendations for LTBI.
Multivariate logistic regression analysis for LTBI revealed that older patients, smoking behavior, and those with prior TB history were independent risk factors in our study.Older age, especially from the age of 60 years, is also a significant risk factor for LTBI in Japanese dialysis patients; 3 similar results were found in many researches. 16,17Smoking is another key risk factor for LTBI, and studies have shown that cigarette smoke exposure impairs innate barrier defense, as well as alveolar macrophage, neutrophil, dendritic cell, and T-cell functions. 18In contrast to a previous report, 17,19 gender is not an independent factor of LTBI in the present study.Although hypoalbuminemia, which suggest that malnutrition attenuates immune response and compromises the performance of IGRA, was not associated with LTBI in our study, some researches show that nutritional adequacy, especially when assessing nPCR value, was associated with LTBI, while dialysis adequacy was not associated with LTBI. 20These risk factors can be used to select a target group for cost-effective LTBI screening.
Increased incidence of cancer development in LTBI cohort has been revealed by recent population-based research, which was the first cohort study to evaluate cancer risk among LTBI patients. 7However, the relationship between LTBI and subsequent cancer development was not found in dialysis patients in this study.This may be related to the median follow-up period that was 39 months, which might be too short to detect cancer development.Large-scale and long-term follow-up studies are needed to investigate this association in the future.On the other hand, a cross-sectional study in two large national public hospital networks in Lima showed that persons with a first-time acute myocardial infarction had twofold increased odds of having LTBI and revealed that LTBI was independently associated with AMI or subclinical obstructive coronary artery disease (CAD) after adjustment for traditional risk factors. 6,21The same results were also found in our retrospective cohort study; the incidence of MACE was significantly higher in dialysis patients with LTBI.We demonstrated that MACE was independently associated with a

From
August 2017 to March 2018, among 500 dialysis patients in Peking University Shenzhen Hospital were screened.A total of 270 patients were enrolled in this study.Inclusion criteria for participants were as follows: age ≥18 years; undergoing dialysis ≥3 months and clinically stable and able to complete all the measures, as required.Patients were excluded if they had active TB, cancer, HIV infection, steroid, or immunosuppressive therapy within 3 months.The participants underwent testing for M. tuberculosis antigen-specific gamma IFN-γ ELISPOT assay of peripheral blood by the Institute of Hepatology of Shenzhen Third Hospital.Patients with positive ELISPOT results were diagnosed with LTBI after excluding active TB clinically.
sum test was used to analyze other continuous variables, and Chi-square test (or Fisher's exact test) was used to analyze categorical variables.A multivariable logistic regression model was fitted using LTBI as the outcome.In the survival analyses, Kaplan-Meier method was used to generate survival curve, and log-rank test was used to compare the differences between two groups.And multivariate Cox proportional hazards model was used to analyze the association between LTBI and MACE after adjusting for covariates.Additionally, all the data were analyzed by Stata/SE version 15, and statistical significance was set at a 95% confidence interval with p ≤ 0.05.
Baseline characteristics of the study population.
The present study has several limitations.First, it was conducted in a single center and had a relatively small sample size, the number of endpoint were relatively limited, and the statistical power was insufficient to draw a final conclusion about the association between LTBI and MACE in dialysis patients; second, evaluating the accuracy of IFN-γ ELISPOT in diagnosing LBTI remains a problem since there is no "gold standard" for such diagnoses, patients with LTBI may be mis-ACKNOWLEDGMENTSWe thank JYZ from Guangdong Key Laboratory for Diagnosis & Treatment of Emerging Infectious Diseases, the Affiliated Shenzhen Third Hospital for her technical assistance.T A B L E 4Abbreviations: LTBI, latent tuberculosis infection; MACE, major adverse cardiovascular events.XIA ET AL.