Tuberculosis (TB) remains a significant global health challenge, with millions of people affected by the disease every year. While active TB has garnered substantial attention in public health discussions, latent tuberculosis infection (LTBI) has emerged as a critical concern due to its potential to progress to active disease [1]. LTBI refers to a condition where an individual is infected with Mycobacterium tuberculosis but does not exhibit any symptoms or signs of active disease [2]. The immune system effectively controls the infection, keeping it dormant. However, in certain conditions, such as immunosuppression, malnutrition, or co-existing health issues like HIV, the bacteria can become active, leading to the development of TB disease [3]. Approximately one-quarter of the global population is believed to harbor LTBI, though most individuals will never progress to active TB. This dormant infection poses a risk, particularly in individuals with weakened immune systems, who are more likely to develop active TB. Identifying individuals with LTBI, especially those in high-risk settings, is crucial for effective TB control and prevention [4]. In regions with a high burden of TB, close contacts of active TB patients are at elevated risk for acquiring LTBI. Close contact with someone who has active TB increases the likelihood of LTBI transmission, especially in areas with overcrowded living conditions and limited healthcare resources [5]. The prevalence of LTBI among close contacts varies across different regions and populations. Studies have shown that the prevalence of LTBI in close contacts can range from 30% to over 50%, depending on factors such as exposure duration and intensity. Because they are in constant contact with the infected person, household members of active TB patients are particularly at risk [6]. Age, gender, and overall health status are additional factors that influence the risk of LTBI. Due to their compromised immune systems, children and the elderly frequently face an increased risk of LTBI progressing into active TB [7]. In areas with a high TB prevalence, regular screening and preventative treatment are essential due to the high prevalence of LTBI among close friends and family. Identifying contacts with LTBI can help cut down on the spread of the disease and prevent these individuals from developing active TB [8]. In addition, designing more targeted interventions, such as preventative therapy and raising awareness among populations at risk, can be aided by comprehending the factors that lead to the development of LTBI [9]. The duration and intensity of exposure to the source case, as well as the presence of comorbid conditions, are risk factors for acquiring LTBI [10]. Individuals who are immunocompromised, such as those with HIV, diabetes, or other chronic conditions, are at a higher risk of developing active TB following LTBI [11]. The risk of progressing from LTBI to active TB is further exacerbated by malnutrition, smoking, and alcohol use. In addition, more research is required to evaluate the long-term benefits of the BCG vaccination in high-risk populations. The effectiveness of the BCG vaccination in preventing the progression of LTBI is still a subject of ongoing debate [12]. Objective This study aims to assess the prevalence of LTBI among close contacts of active TB patients in high-burden communities and identify the risk factors associated with its acquisition.

This was a cross-sectional analytical study conducted at Sri Siddhartha Medical College Hospital, Tumkuru from October 2024 to March 2025. A total of 220 close contacts of active TB patients were enrolled in the study. These individuals were selected based on their direct contact with active TB patients, which included household members, co-workers, and others who had frequent exposure to the index case. Inclusion Criteria: 1. Adults and children aged 5 years and above. 2. Close contacts (household or non-household) of active TB patients. 3. Willingness to participate in the study and provide informed consent. 4. Individuals without a history of active TB or previous TB treatment. Exclusion Criteria: 1. Individuals who have previously been diagnosed with active TB. 2. Individuals who have been treated for LTBI in the past. 3. Those with medical conditions that may interfere with the study outcomes (e.g., severe immunocompromised states such as active cancer or HIV). 4. Pregnant women. Data Collection Data for this study were collected through a combination of clinical screening, medical examination, and structured questionnaires. LTBI was diagnosed using either the tuberculin skin test (TST) or interferon-gamma release assays (IGRAs), depending on the resources available in the study area. A positive TST result was defined as an induration of 10mm or more, while a positive IGRA result was considered based on the established cutoff value. All individuals who tested positive for LTBI were subsequently enrolled in the study group. Participants completed a structured questionnaire designed to gather demographic information (e.g., age, gender, occupation) and details regarding their medical and lifestyle history. The questionnaire also assessed the nature of their contact with the index TB case, including the duration and frequency of exposure, as well as environmental factors like living conditions and overcrowding, which are known to influence TB transmission. Participants also underwent a physical examination to assess their overall health and check for any signs or symptoms of active TB, such as persistent cough, weight loss, or fever. Those with symptoms suggestive of active TB were referred for chest X-rays to rule out active disease. Statistical Analysis Data analysis was carried out using statistical software SPSS v21. Descriptive statistics, including means, medians, and percentages, were used to summarize the demographic characteristics of the study population and the prevalence of LTBI. The chi-square test was used to compare categorical variables, while logistic regression models helped identify potential risk factors associated with LTBI acquisition. A p-value of less than 0.05 was considered statistically significant for all tests.

The study involved 220 close contacts of active TB patients. 57% were male (126 participants), and 43% were female (94 participants). The age distribution showed that 16% (36 participants) were between 5-14 years, 19% (42 participants) were in the 15-24 years age group, 21% (46 participants) were in the 25-34 years group, 15% (32 participants) were 35-44 years, 13% (28 participants) were 45-54 years, 8% (18 participants) were 55-64 years, and another 8% (18 participants) were 65 years or older. A majority (68%) of participants resided in urban areas (150 participants), while 32% (70 participants) lived in rural areas. Table 1: Demographic Characteristics of Participants (n=220) Characteristic Frequency (%) Total Participants 220 (100%) Gender Male 126 (57%) Female 94 (43%) Age Group (years) 5-14 36 (16%) 15-24 42 (19%) 25-34 46 (21%) 35-44 32 (15%) 45-54 28 (13%) 55-64 18 (8%) 65+ 18 (8%) Residence Urban 150 (68%) Rural 70 (32%) The overall prevalence of LTBI among the close contacts was 45.5%. The prevalence of LTBI among males was 48% (60 out of 126 males), while in females, it was 42% (40 out of 94 females). Among the different age groups, the highest prevalence was found in the 25-34 years age group (52%, 24 out of 46 participants), followed by the 15-24 years group (43%, 18 out of 42 participants), and the 35-44 years group (50%, 16 out of 32 participants). The lowest prevalence was found in the 5-14 years age group (28%, 10 out of 36 participants). Regarding residence, urban dwellers had a higher prevalence of LTBI (48%, 72 out of 150 participants) compared to rural dwellers (40%, 28 out of 70 participants). Table 2: Prevalence of Latent Tuberculosis Infection (LTBI) by Demographic Factors Characteristic Total (%) LTBI Positive (%) Prevalence (%) Gender Male 126 (57%) 60 (48%) 48% Female 94 (43%) 40 (42%) 42% Age Group (years) 5-14 36 (16%) 10 (28%) 28% 15-24 42 (19%) 18 (43%) 43% 25-34 46 (21%) 24 (52%) 52% 35-44 32 (15%) 16 (50%) 50% 45-54 28 (13%) 13 (47%) 47% 55-64 18 (8%) 8 (44%) 44% 65+ 18 (8%) 8 (44%) 44% Residence Urban 150 (68%) 72 (48%) 48% Rural 70 (32%) 28 (40%) 40% Duration of exposure to the active TB case significantly influenced LTBI prevalence. Among those exposed to the TB patient for less than 6 months (120 participants), 35% (42 out of 120 participants) tested positive for LTBI. However, among those with 6 months or more of exposure (100 participants), 55% (58 out of 100 participants) tested positive, indicating that prolonged exposure is a significant risk factor. Table 3: Prevalence of LTBI by Duration of Exposure to Active TB Case Duration of Exposure Total (%) LTBI Positive (%) Prevalence (%) Less than 6 months 120 (55%) 42 (35%) 35% 6 months or more 100 (45%) 58 (55%) 55% Among those living in overcrowded conditions (≥5 people per household, 110 participants), 60% (66 out of 110 participants) tested positive for LTBI, whereas only 39% (34 out of 110 participants) living in less crowded conditions (<5 people per household) tested positive. Smoking was also associated with a higher prevalence of LTBI, with 50% (35 out of 70 smokers) testing positive compared to 43% (65 out of 150 non-smokers). Alcohol consumption was similarly linked to higher LTBI prevalence, with 54% (27 out of 50 alcohol consumers) testing positive compared to 44% (73 out of 170 non-drinkers). In terms of ventilation, participants living in homes with poor ventilation (115 participants) had a higher LTBI prevalence (53%, 61 out of 115) compared to those with good ventilation (105 participants), who had a prevalence of 38% (39 out of 105). Table 4: Prevalence of LTBI by Living Conditions and Risk Factors Risk Factor Total (%) LTBI Positive (%) Prevalence (%) Living Conditions Overcrowded (≥5 people/house) 110 (50%) 66 (60%) 60% Not Overcrowded (<5 people/house) 110 (50%) 34 (39%) 39% Smoking 70 (32%) 35 (50%) 50% Alcohol Consumption 50 (23%) 27 (54%) 53% Ventilation Poor ventilation 115 (52%) 61 (53%) 53% Good ventilation 105 (48%) 39 (38%) 38% Health conditions also influenced the likelihood of LTBI. Among participants with respiratory conditions such as asthma or chronic obstructive pulmonary disease (COPD, 50 participants), 54% (27 out of 50) tested positive for LTBI, compared to 43% (73 out of 170) in those without respiratory conditions. For participants with diabetes (40 individuals), 48% (19 out of 40) tested positive for LTBI, while 45% (81 out of 180) of those without diabetes tested positive. Table 5: Prevalence of LTBI by Health Conditions Health Condition Total (%) LTBI Positive (%) Prevalence (%) Respiratory Conditions Asthma/COPD 50 (23%) 27 (54%) 54% No respiratory conditions 170 (77%) 73 (43%) 43% Diabetes 40 (18%) 19 (48%) 48% No diabetes 180 (82%) 81 (45%) 45% Among the 100 LTBI-positive participants, 72% (72 participants) were offered preventive therapy, and 88% (63 out of 72) of those who received therapy completed the full treatment course Table 6: Preventive Therapy and Adherence among LTBI Positive Individuals Preventive Therapy Status LTBI Positive (%) Treatment Offered (%) Adherence (%) Received therapy 100 (100%) 72 (72%) 88% Did not receive therapy 0 (0%) 0 (0%) 0%

This study aimed to evaluate the prevalence of latent tuberculosis infection (LTBI) among close contacts of active TB patients in high-burden communities and identify the associated risk factors. The findings revealed a high prevalence of LTBI (45.5%) among close contacts, with several demographic, environmental, and health-related factors contributing to increased risk. These results underscore the importance of targeted TB control interventions, particularly in communities with a high TB burden. The prevalence of LTBI among close contacts in this study (45.5%) is consistent with findings from other studies conducted in high-burden TB settings, where LTBI prevalence among close contacts ranges from 30% to 60%. Our study also highlights the increased risk of LTBI among individuals living in urban areas, where overcrowding and poor living conditions are more common. Urban areas, especially in developing countries, often face challenges such as inadequate housing, poor ventilation, and high population density, all of which contribute to the transmission of TB [14]. The higher LTBI prevalence observed in these areas reinforces the need for TB prevention efforts that target close-contact networks and improve living conditions in densely populated regions. Several risk factors were found to be significantly associated with LTBI prevalence. Duration of exposure to active TB patients was a key factor, with prolonged exposure significantly increasing the risk of acquiring LTBI [15]. This finding is supported by previous research, which suggests that people who have had prolonged or intense contact with an infectious individual are more likely to suffer from LTBI. In addition, there was a higher rate of LTBI among people who lived in overcrowded households, which is consistent with previous research that emphasizes the significance of overcrowding in TB transmission [16]. Consistent with the well-established link between living conditions and TB spread, study participants were more likely to test positive for LTBI in households with more than five people. In this study, environmental factors, particularly living conditions that are too crowded, were significantly linked to a higher prevalence of LTBI. There was a higher risk of LTBI transmission among participants who lived in overcrowded housing because they were more likely to be exposed to the active TB source case for longer periods of time. Additionally, the study found that smoking and alcohol consumption were associated with increased LTBI prevalence, which may be because these lifestyle factors can impair the immune system, making individuals more susceptible to infections [17]. It has been demonstrated that smoking increases the risk of tuberculosis by impairing lung function and reducing the body's capacity to fight infections, and that drinking alcohol can contribute to inadequate nutrition and immune suppression. The presence of respiratory conditions such as asthma and chronic obstructive pulmonary disease (COPD) was also found to be associated with a higher prevalence of LTBI [18]. This suggests that people who already have lung conditions are more likely to get LTBI and go from it to active TB. These findings highlight the need for heightened surveillance and TB screening among individuals with chronic respiratory diseases. In a similar vein, diabetes was found to be a significant risk factor for LTBI. This finding is in line with previous research that found a link between diabetes and an increased risk of tuberculosis [19]. Diabetes is known to weaken the immune system and make it more likely that an infection will progress from LTBI to active TB. Among the participants who tested positive for LTBI, 72% were offered preventive therapy with isoniazid, and 88% of those offered treatment completed the full course. This high rate of adherence is encouraging because it indicates that this population generally accepts preventive therapy for LTBI. Nevertheless, it is important to note that some participants declined treatment due to concerns about side effects and a lack of awareness of the treatment's benefits [20]. This demonstrates the need for improved counseling and education regarding the advantages of preventive therapy in order to increase uptake and adherence. Ensuring that individuals understand the importance of treating LTBI to prevent the progression to active TB is critical to achieving long-term TB control goals [21]. Limitations One of the limitations of this study is its cross-sectional design, which does not allow for causal inferences. While the study identifies associations between risk factors and LTBI, it cannot definitively determine whether these factors directly cause LTBI acquisition. Another limitation is the reliance on TST and IGRA for LTBI diagnosis, which may not detect all cases, particularly in populations with prior BCG vaccination or those with altered immune responses. Additionally, the study was limited to close contacts in specific high-burden communities, which may not be representative of all TB-endemic areas.

It is concluded that a significant proportion of close contacts of active TB patients in high-burden communities are affected by latent tuberculosis infection (LTBI), with a prevalence rate of 45.5%. The study identifies several key risk factors that contribute to the acquisition of LTBI, including prolonged exposure to active TB patients, overcrowded living conditions, smoking, alcohol consumption, and underlying health conditions such as diabetes and respiratory diseases.

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