Prevalence and Risk Factors of Latent Tuberculosis Infection among People Living with HIV in Mongolia

Abstract

Background

Tuberculosis (TB) remains the leading cause of death among people living with human immunodeficiency virus (PLHIV). Latent tuberculosis infection (LTBI) poses a serious challenge because immune suppression substantially increases the risk of progression to active disease. In Mongolia, where TB incidence is high, little is known about LTBI prevalence and risk factors among PLHIV. This study aimed to estimate the prevalence of LTBI and identify risk factors for LTBI in Mongolia.

Materials and Methods

A retrospective cohort study was conducted using secondary data from the AIDS/STI Surveillance and Research Department of the National Centre for Communicable Diseases between September 2023 and January 2024. A total of 196 PLHIV without active TB were screened using the QuantiFERON-TB Gold Plus test. Sociodemographic and clinical variables were analyzed with chi-square tests and multivariable logistic regression.

Results

The prevalence of LTBI was 39.3% (77/196). Interruption of antiretroviral therapy was significantly associated with (odds ratio, 27.7; 95% confidence interval, 3.04–252.2). The history of TB contact was also associated with high risk (P=0.047). Viral load level and duration of HIV infection were not significantly associated with LTBI.

Conclusion

These findings indicate that LTBI prevalence among PLHIV in Mongolia is high, comparable to other high-burden settings. Ensuring continuous ART use, implementing systematic LTBI screening, and expanding preventive therapy are critical to reduce progression to active TB and to strengthen TB/HIV control efforts.

Graphical Abstract

Introduction

Tuberculosis (TB) remains a major global health challenge. Caused by Mycobacterium tuberculosis, it spreads through the air and primarily affects the lungs, though it can involve multiple organs [1]. Despite being both preventable and curable, TB continues to cause significant morbidity and mortality worldwide [2,3]. A key feature of TB epidemiology is its ability to persist as latent tuberculosis infection (LTBI). Individuals with LTBI show no symptoms and are not infectious, but they carry a lifelong risk of developing active disease [4,5]. Approximately one in ten will progress during their lifetime, and the risk rises sharply when immunity is compromised. For people living with human immunodeficiency virus (PLHIV), the likelihood of progression is 10–100 times higher than in HIV-negative individuals. As a result, TB is the leading cause of death among PLHIV [6].

The interaction between TB and HIV poses a serious public health threat. HIV weakens host immunity, making individuals more susceptible to TB infection and reactivation, while TB can accelerate HIV progression [7,8,9]. This co-epidemic is particularly damaging in settings with both high TB incidence and rising HIV prevalence. Addressing LTBI in PLHIV is therefore essential to prevent progression, reduce transmission, and improve survival [10,11,12]. Mongolia is recognized as a high TB-burden country. Its incidence rate is several times higher than global and regional averages, with thousands of new cases reported annually [13,14]. Although HIV prevalence is relatively low, the number of cases has steadily increased since the first diagnosis in the early 1990s. Importantly, a significant proportion of HIV cases are complicated by TB coinfection, highlighting the vulnerability of this population [15,16].

Effective prevention requires reliable LTBI diagnosis [17]. The tuberculin skin test has long been used but has limited accuracy, especially among immunocompromised individuals. More recently, interferon-gamma release assays (IGRAs), such as the QuantiFERON-TB Gold Plus (QFT-Plus) test, have been introduced and provide more accurate results. Mongolia has only recently implemented IGRA testing in its national program, presenting an opportunity to generate much-needed data [18]. To date, most research in Mongolia has focused on active TB, while LTBI among PLHIV remains poorly understood. Without evidence on prevalence and risk factors, national programs cannot effectively design or implement preventive strategies. Understanding determinants such as antiretroviral therapy (ART) adherence, treatment interruption, viral load, and sociodemographic conditions is crucial.

This study aims to estimate the prevalence of LTBI among PLHIV in Mongolia and to identify key risk factors. The findings will provide evidence to strengthen TB–HIV programs and support national and global efforts to reduce the burden of TB among vulnerable populations.

Materials and Methods

1. Study design, setting, and population

This study was conducted as retrospective cohort study to determine the prevalence of LTBI and its associated risk factors among PLHIV in Mongolia. The study was conducted between September 2023 and January 2024, using secondary data from the national HIV surveillance system. This registry systematically collects demographic and clinical information on all diagnosed PLHIV and is maintained by the National Center for Communicable Diseases, the country’s central institution for TB and HIV control.

The study population comprised all PLHIV who were actively engaged in care and follow-up services during the study period. Eligibility criteria included confirmed HIV infection and continuous enrollment in monitoring programs, while individuals with a diagnosis of active TB or those undergoing TB treatment were excluded. In total, 196 PLHIV met the inclusion criteria and were analyzed, representing about 80% of Mongolia’s registered HIV population at that time.

2. Ethics statement

The Institutional Review Board approval for the study was obtained from the AIDS/STI Surveillance and Research Department of the National Centre for Communicable Diseases (Date of approval is July 8th 2025, and the reference number is 25/26). This study used secondary data from AIDS/STI Surveillance Department, and the need for informed consent was waived because of the retrospective nature of the study, and the data was anonymized.

3. Data collection

Data for this study were obtained from the AIDS/STI Surveillance and Research Department of the National Centre for Communicable Diseases, which routinely records demographic and clinical information on all registered PLHIV in Mongolia. For each participant, sociodemographic variables included age, sex, education level, sexual orientation, and gender identity. Clinical variables included duration of HIV infection, viral load level, ART status, and ART interruption history. Exposure history was defined as documented household or close contact with a person diagnosed with TB.

LTBI was assessed using the QFT-Plus IGRA, performed between September 2023 and January 2024. Blood samples were collected and processed according to the manufacturer’s instructions, and results were categorized as positive, negative, or indeterminate. Indeterminate results were excluded from the final analysis to ensure the accuracy of prevalence estimates. By combining IGRA test results with sociodemographic and clinical data, the dataset provided a robust foundation for estimating LTBI prevalence and identifying associated risk factors among PLHIV.

4. Variables

The primary outcome in this study was LTBI, defined as a positive result on the QFT-Plus IGRA. Participants with negative results were classified as LTBI-negative.

Independent variables were categorized into three groups:

Sociodemographic factors: age group, sex, education level, sexual orientation, and living condition. The original surveillance dataset categorized “transgender” within the sexual orientation variable, and no corresponding cisgender variable was available, which limited our ability to reclassify participants.

Clinical factors: duration of HIV infection, viral load level, current ART status, and ART interruption.

Exposure factor: history of household or close contact with a person diagnosed with active TB.

These variables were selected to identify potential associations with LTBI among PLHIV. Considering both clinical and sociodemographic characteristics allowed for a comprehensive evaluation of determinants influencing LTBI prevalence in this population.

5. Statistical analysis

Data were cleaned and analyzed using SPSS (version 29.0, IBM Corp., Armonk, NY, USA). Descriptive statistics were performed to characterize the study population. Categorical variables were summarized as frequencies and percentages, while continuous variables were expressed as means with standard deviations or medians with interquartile ranges, depending on their distribution. Bivariate analyses were used to examine associations between LTBI status and independent variables. Chi-square tests were applied for categorical variables, and Fisher’s exact test was used when the data were fewer than five. Variables with a P-value <0.05 in bivariate analysis were included in the multivariable logistic regression model.

Multivariable logistic regression was applied to identify independent risk factors for LTBI. Adjusted odds ratios (aOR) with 95% confidence intervals (CI) were calculated to assess the strength of associations. A P-value <0.05 was considered statistically significant. The final model included sociodemographic, clinical, and exposure variables that met the inclusion criteria.

Results

1. Participant characteristics

A total of 196 PLHIV participated in the study. The mean age was 39.8±10.7 years, and the median age was 39 years, with an age range from 18 to 65 years (Table 1). Of the participants, 12.2% (n=24) were female and 87.8% (n=172) were male. The majority of participants identified as homosexual 58.7% (n=115) followed by heterosexual and bisexual groups were 19.4% and 19.9%, while transgender accounted for least at 2.0% (n=4). The participants with higher education were the lowest at 2.6%, while participants with a high school and bachelor's degree were 49.0% (n=96) and 48.5% (n=95) respectively. Age group 30 to 50 years was the most reported in the age group, accounting for 61.7% (n=121) of the total cases, while ages 50 years and above were the least reported age group. Of total participants, 53.1% were classified living in ger districts, and apartments were 46.9%.

Table 1. Characteristics of study participants with and without latent tuberculosis infection.

Variable		Total (N=196)	LTBI-positive (n=77)	LTBI-negative (n=119)	P-value
Sex					0.483
	Male	172 (87.8)	66 (38.4)	106 (61.6)
	Female	24 (12.2)	11 (45.8)	13 (54.2)
Age, years (mean ± SD)		39.8±10.7	40.8±10.5	39.3±10.9	0.313a
Age group					0.276
	<30	42 (21.4)	12 (28.6)	30 (71.4)
	30–50	121 (61.8)	51 (42.1)	70 (57.9)
	≥51	33 (16.8)	14 (42.4)	19 (57.6)
Sexual orientation					0.532
	Homosexual	115 (58.7)	44 (38.3)	71 (61.7)
	Heterosexual	38 (19.4)	15 (39.5)	23 (60.5)
	Bisexual	39 (19.9)	15 (38.5)	24 (61.5)
	Transgender	4 (2.0)	3 (75.0)	1 (25.0)
History of TB contact					0.047
	Yes	14 (7.2)	9 (64.3)	5 (35.7)
	No	182 (92.8)	68 (37.4)	114 (62.6)
Living condition					0.530
	Apartment	92 (46.9)	34 (37.0)	58 (63.0)
	Ger district	104 (53.1)	43 (41.3)	61 (58.7)
Education level					0.291
	High school	96 (49.0)	43 (44.8)	53 (55.2)
	Undergraduate	95 (48.5)	32 (33.7)	63 (66.3)
	Postgraduate	5 (2.6)	2 (40.0)	3 (60.0)
HIV duration, years (mean±SD)		6.13±4.12	6.47±4.17	5.92±4.09	0.361a
ART interruption, days (mean±SD)		11.5±41.9	20.1±62.3	6.1±18.3	0.022a
ART interruption >2 months					0.002
	No (≤2 months)	187 (95.4)	69 (36.9)	118 (63.1)
	Yes (>2 months)	9 (4.6)	8 (88.9)	1 (11.1)
Viral load at enrollment (mean±SD)		7,063.22±71,837.2	14,165.14±113,936.8	2,467.86±10,622.77	0.267a

Values are expressed as number of subject (%), unless otherwise specified.

^aStudent's t-test.

LTBI, latent tuberculosis infection; SD, standard deviation; TB, tuberculosis; HIV, human immunodeficiency virus; ART, antiretroviral therapy.

The average duration of living with HIV was 6.13 years, with the longest living with HIV was up to 16 years. Participants who tested LTBI -positive had a longer mean duration of ART interruption (20.13±62.32 days) compared to those who tested LTBI-negative (6.07±18.26 days, P=0.022). About 7.2% reported a history of household or close contact with a person diagnosed with TB and 4.6% reported a history of treatment interruption for longer than two months.

2. Prevalence of LTBI

The overall prevalence of LTBI among the study participants was 39.3% (77/196), while 60.7% (119/196) tested negative by the QFT-Plus assay. The prevalence was highest among participants aged 30-50 years (42.1%), compared with 28.6% among those aged <30 years (Table 1). With regard to ART history, LTBI was more frequent among individuals who had experienced ART interruption for longer than two months (88.9%) compared with those who remained on continuous ART (36.9%). Similarly, participants who reported a history of close or household contact with TB patients had a substantially higher prevalence of LTBI (64.3%) than those without such history. There were no statistically significant associations of LTBI prevalence with gender, age group, sexual orientation, living condition or education level.

These findings highlight patterns of vulnerability within the study population. Older adults, individuals with ART interruption, and transgender group showed markedly higher LTBI prevalence, suggesting that targeted preventive interventions for these groups may be warranted.

3. Factors associated with LTBI

Table 2 shows risk factors associated with LTBI among study population. In the univariable analysis, interruption of ART for more than two months was significantly associated with higher odds of LTBI (OR, 13.6; 95% CI, 1.67–111.7; P=0.015), whereas history of TB contact had borderline significance (OR, 3.01; 95% CI, 0.97–9.37; P=0.056). Other factors, such as education level, living condition, sexual orientation and age group were not significant.

Table 2. Risk factor for latent tuberculosis infection among people living with HIV in Mongolia.

Variable		Univariable analysis		Multivariable analysis
		OR (95% CI)	P-value	OR (95% CI)	P-value
ART interrupt
	≤2 months	1		1
	>2 months	13.6 (1.67–111.7)	0.015	27.7 (3.04–252.2)	0.003
Education
	High school	1
	Undergraduate	1.31 (0.20–8.25)	0.772
	Postgraduate	1.59 (0.88–2.86)	0.117
Living condition
	Apartment	1
	Ger district	1.20 (0.67–2.13)	0.530
Contact history
	No	1		1
	Yes	3.01 (0.97–9.37)	0.056	2.9 (0.93–9.34)	0.065
Sexual orientation
	Homosexual	1		1
	Heterosexual	1.05 (0.49–2.23)	0.894	1.0 (0.48–2.35)	0.880
	Bisexual	1.0 (0.47–2.12)	0.982	1.0 (0.45–2.22)	0.980
	Transgender	4.8 (0.48–48.0)	0.178	12.1 (1.08–137.5)	0.043
Age group
	<30 years	1		1
	30–50 years	1.82 (0.85–3.89)	0.122	2.9 (1.13–7.80)	0.027
	≥51 years	1.84 (0.70–4.81)	0.213	3.2 (1.03–10.4)	0.043

HIV, human immunodeficiency virus; OR, odds ratio; CI, confidence interval; ART, antiretroviral therapy.

In the multivariable model, three factors were independently associated with LTBI. Participants who interrupted ART for more than 2 months had significantly higher risk of LTBI compared with those with a shorter duration of interruption (OR, 27.7; CI, 3.04–252.2; P=0.003). Transgender patients are also significantly more likely to have LTBI (OR, 12.1; 95% CI, 1.08–137.5; P=0.043) compared with homosexual participants. Transgender within dataset was recorded under sexual orientation not as a distinct gender identity variable. Older age was also significantly associated with LTBI. Participants aged 30–50 (OR, 2.9; 95% CI, 1.13–7.80; P=0.027) and those aged ≥51 years (OR, 3.2; 95% CI, 1.03–10.4; P=0.043) had higher risk for LIBI compared to those aged <30 years.

Discussion

This is the first study in Mongolia to estimate the prevalence of LTBI among PLHIV using QFT-Plus testing. The prevalence of LTBI among PLHIV in this study was 39.3%, and this finding was relatively higher than the countrywide prevalence of the overall population in Mongolia (33.4%, unpublished data from National TB surveillance report 2023), however, it aligns with those in high TB burden countries. For example, in South Africa, prevalence of LTBI among PLHIV ranges from 40-70%, depending on the diagnostic method, location and epidemiology [19,20].

Among the risk factors investigated, ART interruption days was the most significantly associated with LTBI. Participants who interrupted ART for longer than 2 months were at significantly greater risk of LTBI than participants with shorter or no interruptions. This result suggests that breaks in ART may reduce the immune response and may increase susceptibility to M. tuberculosis infection. However, IGRA positivity may precede HIV acquisition, particularly among older adults, and therefore ART interruption alone cannot explain the association. In addition, ART interruption in PLWH with LTBI may increase risks of active tuberculosis, so this population should be identified and closely cared. This is consistent with findings from Malawi and South Africa which reported significant reductions in TB incidence among PLHIV associated with sustained use of ART [21,22].

Additionally, a study in Northwest Ethiopia found that ART-naive HIV-infected patients were three times more likely to have LTBI than ART-treated patients, not only confirming our findings but also demonstrating that ART treatment has an important impact on the quality of life of people living with HIV [23]. These findings support international guidelines that starting ART early and without interruption reduces TB risk in PLHIV.

In contrast, the viral load levels were not significantly associated with the LTBI status, as it was observed in our study. Although high levels of HIV RNA have been demonstrated elsewhere to be a risk for active TB [24], the association with LTBI is less certain. Our results corroborate those of Kenya and Lithuania where there was not a strong association between viral load and LTBI positivity [25,26]. It is feasible to suggest that viral load may be more important for development of active TB (from LTBI) rather than for acquisition of infection.

HIV duration was not associated with LTBI infection in our study, although the prevalence of LTBI infection was slightly higher in participants with longer HIV duration. HIV duration alone does not predict of LTBI but may interact with other risk factors such as age an TB contact [25,26]. Similarly, older age (>30years) and being transgender were associated with increased risk in multivariable analysis, transgender influenced by small sample size, but it is worth paying attention to targeted interventions.

Sociodemographic factors such as age, educational level, sexual orientation and living condition were no significantly associated with LTBI in our study. However, several studies have shown that higher levels of education are associated with lower risk of LTBI infection [25,27]. This suggests that higher levels of education are associated with greater health awareness and health care. Also, education is associated with income levels. Our study did not include income levels. So further research should examine the relationship between income level and education level and investigate whether it is associated with latent TB infection.

Most studies of latent TB infection among people living with HIV have identified alcohol, drug, and tobacco use, incarceration, comorbidity, and body mass index (BMI). However, some study have shown that incarceration, low BMI, and smoking were associated with latent TB infection [27], whereas in another study, alcohol use and low BMI were not significantly associated with latent TB infection [25].

National HIV surveillance reports indicate that nearly all HIV infections in Mongolia (99.7%) are sexually transmitted and are concentrated among MSM and transgender individuals [28]. These risk exposures frequently coincide with structural vulnerabilities such as poverty, unstable employment, migration, and limited access to health and social services. Such socio-economic factors may contribute to the elevated risk of LTBI among PLHIV. However, our study was unable to collect detailed information on these risk exposures or socio-economic determinants.

Our study results showed that active TB contact was associated with latent TB infection among HIV-infected individuals, which is consistent with the results of all other studies. This aligns with global literature emphasizing that household or close contact with active TB is a major driver of LTBI, particularly among immunocompromised populations. The high prevalence of LTBI among PLHIV in Mongolia highlights the need for integrated TB–HIV services. Routine LTBI screening and timely provision of preventive therapy should be prioritized, especially for those with known TB exposure or a history of ART interruption. Strengthening adherence support programs is equally essential to sustain immune function and reduce vulnerability to opportunistic infections.

In addition, reinforcing contact investigation, community awareness, and linkage to care can help break the chain of TB transmission. Tailored interventions for older adults and marginalized groups, such as transgender individuals, may further enhance program effectiveness and ensure equitable access to TB–HIV preventive services.

This study has several strengths. It represents one of the first systematic assessments of LTBI among PLHIV in Mongolia, providing novel evidence for a population that has been underrepresented in the literature. The study was conducted at the National Centre for Communicable Diseases, which manages the majority of the country’s HIV cases, allowing the sample to capture approximately 80% of the national PLHIV population. Furthermore, the use of a standardized and widely validated diagnostic tool, the QFT-Plus assay, enhanced the accuracy of LTBI detection. By integrating clinical and sociodemographic data, the analysis also provided a comprehensive perspective on potential determinants of LTBI.

Despite these strengths, several limitations should be acknowledged. The relatively small sample size in some subgroups, particularly transgender individuals, limited statistical power and contributed to wide confidence intervals. As a result, certain associations that appeared clinically meaningful may not have reached statistical significance. Another limitation is the misclassification of gender identity within the sexual orientation variable. The dataset includes transgender individuals who are categorized as sexual orientation and does not include the cisgender category. In addition, secondary surveillance data may have lacked detailed information on potential confounding factors such as socioeconomic status, nutritional conditions, and behavioral risks.

This study provided novel evidence on the burden of LTBI among PLHIV in Mongolia. The results revealed that 39.3% of PLHIV had LTBI, highlighting the dual epidemic of TB and HIV in the country. This finding underscores the need for urgent attention to preventive strategies in this vulnerable population. Our findings call for the strengthening of integrated TB–HIV services in Mongolia. Scaling up LTBI screening and provision of preventive therapy should be made a routine part of HIV care. Interventions that promote and support ART adherence are particularly critical to reduce immune deterioration and susceptibility to TB. Contact investigation and community-based outreach should also be reinforced to identify and protect PLHIV at risk of exposure, while targeted strategies for marginalized groups, including transgender individuals, may help address health inequities. Future research should employ longitudinal study designs to establish causal relationships between ART adherence, TB exposure, and LTBI. Expanding sample sizes, especially for underrepresented groups such as older adults and transgender individuals, will improve statistical power and precision. In addition, exploring social, economic, and behavioral determinants will help provide a more comprehensive understanding of LTBI risk in PLHIV. Such evidence can guide more tailored, effective interventions and contribute to Mongolia’s efforts to reduce TB-HIV comorbidity.