Tuberculosis (TB) continues to infect an estimated one-third of the world’s population, there were 10.6 million cases of TB in 2022, and 1.4 million deaths (1). India: The total number of incident TB patients (new & relapse) notified during 2021 was 19,33,381 which was 19% higher than that of 2020 (TB Annaul Report- 2022). Current TB control measures mainly focus on the prompt detection as well as treatment of those patients with infectious forms of the disease to prevent further transmission of the organism. The incidence of tuberculosis is greatest among those with conditions impairing immunity (2), such as human immunodeficiency virus (HIV) infection, diabetes mellitus (DM), smoking and malnutrition (3). The association between tuberculosis and diabetes, well established through studies, is a major challenge for global Tuberculosis (TB) control. It is believed that the impairment of immunity in long-term diabetics makes the patients prone to a number of microbial infections including Mycobacterium tuberculosis. Hyperglycaemia in DM is believed to favour the growth of tuberculosis bacilli. The association between TB and DM is bidirectional. One of the first-line anti-tubercular drugs, Rifampicin, is known to interfere with the metabolism of oral hypoglycaemic agents and hence affect glycaemic control (4). The risk of TB is two to three times higher among people with diabetes compared with the normal population (5, 6).

 In this regard, a “Collaborative framework for care and control of tuberculosis and diabetes” has been outlined most recently by WHO and the International Union against Tuberculosis and Lung Diseases.

We, therefore, conducted this study to determine the comparative incidence of pulmonary tuberculosis (PTB) between diabetic and non-diabetic subjects and also to determine the Relative Risk of tuberculosis among diabetic and non-diabetic groups in this area. These findings may provide significant evidence and contribute to a better understanding and proper management of tuberculosis among diabetic patients.

The study conducted in Sambhram Institute of medical sciences and Research, KGF, Karnataka a tertiary care hospital. The study was approved by Institutional Ethical clearance (IEC no:-SIMSAR/Ethics/Proc.No.36/2022).  The database of 761 patients was retrospectively reviewed from medical records from 01-01-2021 to 31-12-2022. The following information was listed in the standardized data collection sheet: socio-demographic profiles, diabetes and ATT status. A total of 761 patients who came to the hospital for suspected pulmonary tuberculosis infection were included. All patients’ data were separated into two groups a) the Diabetic group, b) Non-Diabetic group. Sputum samples of both groups were processed prospectively for MTB detection along with Rifampicin susceptibility using Gene Xpert MTB/RIF assay along with smear examination by Zeihl-Neelsen staining and scored according to RNTCP guidelines.

Statistical analysis

The study participants were classified into “Diabetic TB (DMTB)” and “Non-Diabetic TB (NDTB)” groups. Further analysis of different variables was done for both groups separately. The analysis was done using Open EPI and MS Excel software. The data were analysed and expressed in the form of mean, standard deviation and 95% confidence intervals (CIs) wherever required. Univariate odds ratio (OR) was calculated as an estimate for relative risk (OR) with 95% CI. The chi-square test and t‑test (difference of means) were applied to determine the P value and statistical significance. P <0.05 was considered statistically significant.

A total of 761 patients with tuberculosis symptoms were retrospectively analysed in this study. Among 761 patients 128 (16.82%) patients are known Diabetic and 633 (83.18%) patients were non-diabetic. Diabetic and Non-diabetic group patient’s sputum samples were processed prospectively for MTB detection and Rifampicin susceptibility by Gene-Xpert MTB/Rif assay. Out of 128 Diabetic confirmed patients, 41 patients were positive and 87 patients were negative for Tuberculosis. Among the non-diabetic group 115 patients were positive and 518 patients were negative for tuberculosis.

The prevalence of TB among Diabetic and Non-Diabetic patients was 32% (41/128) and 18% (115/633) respectively.  Among diabetic and TB positive patient’s males were 34 (83%) females were only 7 (17%). In non-diabetic TB patients males were 85(74%) and females were 30(26%)

In both groups (diabetic and non-diabetic TB) males were higher compared to females but no statistically significant difference was found (p-value = 0.244). The male vs female ratio in the diabetic with TB group and Non-diabetic with TB is 4.8:1 and 2.8:1 respectively.

The mean age of diabetes with TB and Non-diabetic with TB from 11 to 90 years was 50 years (Standard deviation (SD) ±16) and 48 years (Standard deviation (SD) ±17) respectively. The 41 to 50 years age patients from the diabetic group were mostly affected by TB while the 51 to 60 age group from the non-diabetic group were mostly affected.

In diabetic with TB patients no Rifampicin resistance was found and only 3 patients from non-diabetic with TB showed Rifampicin resistance. Anti-tubercular Treatment (ATT) already initiated in patients with Diabetic patients, without a prior diagnosis of Tuberculosis (Table 1) is given significant results.

TABLE 1: ATT initiated in patients with Diabetic.

The Relative Risk (RR) of Tuberculosis among diabetic patients was 1.82 (95% CI: 1.31 – 2.53 with p value = 0.0003). This finding stresses the fact that diabetes predisposes to the development of tuberculosis and carries a 3.6 time higher risk compared to non-diabetic patients.

The burden of diabetes is increasing rapidly in India and the prevalence of diabetes remains higher in economically and epidemiologically advanced states. It has increased more rapidly in the less developed states, which are home to a large proportion of India’s population (7). In India, it is now strongly recommended to screen for TB among people with DM (8, 9).

The increased incidence of Tuberculosis infection among Diabetic patients is well known. It is not clear why DM patients, particularly those with poorly controlled disease, are at increased risk of TB, although changes have been found in both their innate and their adaptive immune responses. Diabetes is associated with an increased risk of TB and is known to be a factor that contributes to the progression of latent TB into active disease and increases the risk of latent TB infection (10).

The present study has found a significantly higher prevalence of Tuberculosis in Diabetic patients. One study from Puducherry by Raghuraman et al, in 2014, reported the prevalence of diabetes with TB is 29% (11). A study from Kerala by Balakrishnan et al, in 2012 reported 23% of patients self-reported a previous diagnosis of DM and TB, and 21% of patients were newly diagnosed with DM + TB (12).  A study from Karnataka in 2018 with different diagnostics approaches (RBS and Glycosylated Haemoglobin) for diabetes, reported DM + TB prevalence is 25.3% (13). A study from Tamilnadu by Viswanathan et al, reported prevalence of DM +TB is 25.3% (14).

Studies from north Indian origin, from New Delhi by Khanna A et al, in 2013 reported 14% (15), Nagar V et al, in 2018 reported 15.3% in Bhopal (16), Sharma D et al, in 2018 reported13.1% in Chandigarh (17) and Mansuri S et al, in 2015 reported 15.3% in Gujarat (18). The above studies suggest the prevalence of Diabetic with TB is higher in the South Indian population compared to the North Indian population. Some low prevalence was observed in countries like China (6.3%) and Spain (5.9%) (19, 20).

The most common age group for Diabetes with TB is 41 -50 years similar to the results found in earlier studies in India (12, 13) and the United States (21). This may be related to the fact that Diabetic and TB are seen more frequently in the older age group. In both of our study groups (diabetic + TB and Non-diabetic + TB), males were higher compared to females. The study matched similar studies reported earlier (22, 23). The higher prevalence of TB among diabetic patients especially men than women might be other risk factors such as smoking, tobacco use and alcohol consumption.

The relative risk (RR) of tuberculosis among the diabetic group compared to the non-diabetic group was 1.82 (95% CI: 1.31 – 2.53) and was statistically significant (p-value 0.0003).  The RR of TB in Diabetic were in agreement with similar studies reported earlier (24-26). In a national wide cohort study conducted in 2012 from Australia, the relative risk of TB among DM patients was 1.78 (24).

 The mechanisms behind Diabetes susceptibility to tuberculosis are still not yet well understood. Leung et al. study found that patients who had poor recent glycaemic control (Glycosylated haemoglobin more than seven per cent) were at significantly increased risk of getting tuberculosis, while those with Glycosylated haemoglobin <7% were not (27). Research suggests that individuals who have both tuberculosis (TB) and diabetes experience more adverse outcomes in their TB infection compared to those who have TB alone. (28).

Individuals with diabetes have a 3.6 times higher likelihood of acquiring tuberculosis (TB) infection compared to those without diabetes. The precise mechanisms responsible for this increased susceptibility to TB remain relatively unclear and require further investigation. This study underscores the importance of giving heightened consideration to tuberculosis among individuals with diabetes, which may involve early detection of TB, improved management of glucose levels, and enhanced clinical monitoring and treatment.

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