Tuberculosis (TB) remains one of the leading infectious causes of morbidity and mortality worldwide, particularly in low- and middle-income countries. Despite significant advances in diagnosis, treatment, and public health interventions, TB continues to pose a major global health challenge. According to the World Health Organization (WHO), millions of new TB cases are reported annually, with a substantial proportion occurring in developing nations where overcrowding, poverty, malnutrition, and limited healthcare access contribute to disease transmission [1-3].

Latent tuberculosis infection (LTBI) is a state in which an individual is infected with Mycobacterium tuberculosis but does not exhibit clinical symptoms or radiological evidence of active tuberculosis. Individuals with LTBI are not infectious; however, they remain at risk of progressing to active TB disease, particularly in the presence of immunosuppression, malnutrition, diabetes mellitus, or other comorbid conditions. It is estimated that nearly one-quarter of the global population harbors latent TB infection, representing a significant reservoir for future disease transmission [4, 5].

Household contacts of patients with pulmonary tuberculosis constitute one of the highest-risk groups for acquiring TB infection due to prolonged and close exposure to infectious individuals. The risk of infection is influenced by several factors, including the infectiousness of the index case, duration of exposure, household ventilation, overcrowding, socioeconomic conditions, and host immune status. Children, elderly individuals, and immunocompromised persons are particularly vulnerable to both infection and progression to active disease [6-8].

Early identification of latent TB infection among household contacts is an important component of tuberculosis control programs. Screening of household contacts allows detection of infected individuals before the development of active disease and facilitates the initiation of tuberculosis preventive therapy. Such interventions can significantly reduce the risk of progression to active TB and contribute to interrupting the chain of transmission within the community [9, 10].

The present study was undertaken to screen for latent tuberculosis infection among household contacts of pulmonary TB patients using a community-based approach and to identify demographic and exposure-related factors associated with LTBI. The findings of this study may help strengthen contact investigation programs and contribute to improved tuberculosis prevention and control efforts.

Study Design and Study Population:

This community-based cross-sectional study was conducted at the Department of Community Medicine, Maharajah's Institute of Medical Sciences, Nellimarla, between September 20221 to August 2022. A total of 30 household contacts of sputum-positive pulmonary tuberculosis patients were enrolled in the study after obtaining written informed consent. Ethical approval was obtained from the Institutional Ethics Committee before commencement of the study.

Methods:

Household visits were conducted by the study team to identify eligible contacts and perform screening procedures. Clinical assessment included evaluation for cough, fever, weight loss, night sweats, and other symptoms suggestive of tuberculosis. Participants underwent a Tuberculin Skin Test (TST) using standard Mantoux technique. An induration of ≥10 mm after 48–72 hours was considered positive for latent tuberculosis infection in immunocompetent individuals. Chest radiography was performed whenever clinically indicated to exclude active pulmonary tuberculosis. Individuals with symptoms suggestive of active TB or abnormal radiographic findings were referred for sputum examination and further diagnostic evaluation. Contacts diagnosed with latent tuberculosis infection were counseled regarding preventive therapy according to national tuberculosis control program guidelines.

Inclusion Criteria:

1. Household contacts of sputum-positive pulmonary tuberculosis patients.
2. Individuals aged 5 years and above.
3. Contacts residing in the same household as the index case for at least three months prior to diagnosis.
4. Individuals willing to undergo clinical evaluation and Tuberculin Skin Testing.
5. Participants providing written informed consent.

Exclusion Criteria:

1. Individuals with previously diagnosed or currently active tuberculosis.
2. Household contacts already receiving anti-tubercular therapy or tuberculosis preventive therapy.
3. Contacts with severe acute illness at the time of screening.
4. Individuals with known immunodeficiency disorders requiring specialized LTBI assessment.
5. Persons unwilling to participate or unavailable for TST reading after 48–72 hours.
6. Incomplete clinical or demographic data.

Statistical Analysis:

Data were entered into Microsoft Excel and analyzed using SPSS version 26.0. Continuous variables were expressed as mean ± standard deviation (SD), while categorical variables were presented as frequencies and percentages. Associations between latent tuberculosis infection and potential risk factors such as age, sex, duration of exposure, overcrowding, smoking status, and BCG vaccination were evaluated using the Chi-square test or Fisher's exact test. Continuous variables were compared using the Student's t-test. A p-value <0.05 was considered statistically significant.

A total of 30 household contacts of sputum-positive pulmonary tuberculosis patients were screened during the study period. All participants completed clinical evaluation and Tuberculin Skin Testing (TST). The prevalence of latent tuberculosis infection (LTBI), demographic characteristics, exposure-related factors, and associated risk factors were analyzed.

Table 1. Demographic Characteristics of Household Contacts

The majority of participants were females (56.7%), and the mean age of the study population was 31.8 ± 14.6 years.

Table 2. Prevalence of Latent Tuberculosis Infection

Latent tuberculosis infection was detected in 11 participants (36.7%), while 19 participants (63.3%) tested negative.

Table 3. Association between Duration of Exposure and LTBI

Household contacts exposed to the index case for more than six months had a significantly higher prevalence of LTBI (p < 0.05).

Table 4. Household Environmental Factors

Overcrowded living conditions were significantly associated with latent tuberculosis infection, whereas adequate household ventilation appeared protective.

Table 5. Age-wise Distribution of LTBI

The highest prevalence of LTBI was observed among contacts older than 45 years.

Table 6. Clinical Screening Outcomes

Six contacts reported symptoms suggestive of tuberculosis. Two individuals required further diagnostic evaluation, and no active TB cases were confirmed during the study period.

Tuberculosis remains a major public health challenge, particularly in developing countries where household transmission contributes significantly to disease burden. Household contacts of patients with pulmonary tuberculosis are at increased risk of acquiring Mycobacterium tuberculosis infection because of prolonged and repeated exposure to infectious individuals. Early identification of latent tuberculosis infection (LTBI) among these contacts is essential for preventing progression to active disease and reducing community transmission. The present study evaluated the prevalence of LTBI among household contacts of pulmonary TB patients using a community-based screening approach and identified factors associated with infection [11-13].

In the present study, LTBI was detected in 36.7% of household contacts. This finding is consistent with previous studies reporting a high prevalence of latent TB infection among close contacts of infectious pulmonary TB cases. The relatively high prevalence observed in the study emphasizes the importance of systematic contact investigation and screening programs in high-burden settings. Since individuals with LTBI serve as a reservoir for future active tuberculosis, timely detection and preventive therapy are crucial components of TB control strategies [14-15].

In the previous study reported, duration of exposure to the index case was found to be a significant risk factor for LTBI. Contacts exposed to pulmonary TB patients for more than six months had a higher prevalence of infection compared with those exposed for shorter durations. Prolonged exposure increases the likelihood of inhaling infectious droplet nuclei and acquiring infection. Similar observations have been reported in epidemiological studies demonstrating a direct relationship between exposure intensity and the risk of TB infection [16].

In the previous study reported, household overcrowding was another important factor associated with LTBI in the present study. Contacts residing in overcrowded households showed significantly higher infection rates compared to those living in less crowded environments. Overcrowding facilitates airborne transmission by increasing the frequency and duration of contact with infectious individuals while limiting adequate ventilation. This finding highlights the role of social and environmental determinants in tuberculosis transmission and underscores the need for public health interventions aimed at improving living conditions [17, 18].

In this study also demonstrated that adequate household ventilation appeared to have a protective effect against infection. Well-ventilated environments reduce the concentration of airborne bacilli and lower the risk of transmission. Promotion of simple measures such as improving airflow and reducing indoor crowding may contribute substantially to tuberculosis prevention in resource-limited communities [19-22].

In the previous study reported, age-wise analysis revealed LTBI across all age groups, with a slightly higher prevalence among adults and older individuals. Although children constituted a smaller proportion of LTBI-positive contacts, their identification remains particularly important because of the higher risk of progression from latent infection to active disease. Early detection and preventive treatment in children can significantly reduce future morbidity and mortality associated with tuberculosis [23].

The present study has certain limitations. The sample size was relatively small, and the study was conducted in a single geographical region, which may limit the generalizability of the findings. Additionally, diagnosis of LTBI was based primarily on the Tuberculin Skin Test, which may be influenced by prior BCG vaccination and exposure to non-tuberculous mycobacteria. Future studies incorporating interferon-gamma release assays and larger populations may provide more comprehensive insights [24].

The present study demonstrated that latent tuberculosis infection (LTBI) is highly prevalent among household contacts of pulmonary tuberculosis patients, with more than one-third of screened individuals testing positive for LTBI. Prolonged exposure to the index case and overcrowded living conditions were identified as significant risk factors associated with infection. The community-based screening approach proved effective in identifying high-risk contacts, facilitating early diagnosis, and enabling timely referral for preventive therapy. Strengthening household contact investigation and routine LTBI screening programs can play a crucial role in reducing the progression of latent infection to active tuberculosis and contribute significantly to tuberculosis control and elimination efforts.

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