Latent Tuberculosis Infection and Human Leukocyte Antigen Polymorphisms in Pulmonary Tuberculosis Patients and Their Household Contacts

Abstract

TITLE: Latent Tuberculosis and Human Leukocyte Antigen Polymorphisms in Pulmonary Tuberculosis Patients and their Household Contacts in Kenya BACKGROUND: Household Contacts (HHCs) are the primary caregivers of Pulmonary Tuberculosis (PTB) patients at home and, subsequently, have a higher cumulative exposure to Mycobacterium tuberculosis through close physical contact and social interactions. Due to the mode of transmission of this pathogen, HHCs are more likely to be infected since the PTB patients are infectious before and during the early stages of their treatment. Due to underdiagnosis, latent tuberculosis infections (LTBI) are often missed, likely progressing to active TB. Sensitisation on LTBI dynamics and addressing challenges that HHCs face while caring for their PTB patients within the home setup could also help identify LTBI-positive cases for prompt initiation of preventive therapy. Host genetics have been identified as predictors for susceptibility to infectious diseases such as TB. For instance, the Human Leucocyte Antigen (HLA) class II alleles can influence the early immune response to TB by presenting antigenic peptides to CD4+ T cells for destruction. Polymorphisms in these genes could affect the efficiency of the body’s immune response to TB infections, thereby determining the likelihood of progressing LTBI to active TB disease. In Kenya, the prevalence of LTBI diagnosed using IGRA among HHCs of PTB patients is lacking, presenting a knowledge gap. In addition, this population has not elucidated HLA class II allele polymorphism that influences susceptibility to TB and progression of LTBI to PTB. OBJECTIVE: To determine the prevalence and risk factors of latent TB infection among household contacts of PTB patients and the association between frequency of HLA class II allele groups and outcome of exposure to Mycobacterium tuberculosis. METHODS: A descriptive-analytic cross-sectional study of adult PTB patients and HHCs was conducted in outpatient clinics and isolation inpatient wards at Mbagathi County Hospital in Nairobi. The HHCs were recruited as they accompanied the patients to the outpatient clinics or during visiting hours at the inpatient section after the provision of consent. Sociodemographic data were collected using informal interviews and structured, pretested questionnaires, while clinical data were retrieved from patient files. Using a mixed-methods study design, we documented the challenges and experiences of PTB patients and their HHCs. Intravenous blood samples were drawn for Interferon Gamma Release Assay (IGRA) to determine Latent Tuberculosis Infection (LTBI) among HHCs and for extraction of DNA for typing of HLA-DQB1 and HLA-DRB1 allele groups via PCR sequence-specific primer amplification. Data analysis was done using R software version 4.2.0. The prevalence of LTBI was calculated using the Clopper Pearson method. Chisquare and Fisher’s Exact tests were used in identifying potential factors associated with LTBI, while logistic regression was used for further comparative analyses. A linear regression model was used to investigate variation in the concentration of Interferon-gamma amongst those who tested positive for LTBI. RESULTS: We evaluated 166 PTB and 175 HHCs. The overall prevalence of LTBI evaluated among the HHCs of PTB patients using the IGRA test was 55.7% (95% CI: 48-63.2). There wasn’t enough statistical evidence to show an association between the Optical Density value measurements of IFN gamma concentrations and any assessed variables among the LTBI-positive individuals. Statistical evidence showed an association between several covariates and the risk of LTBI. These included the HHC HIV serostatus, relationship status (spousal or other) between the

household contact and the PTB patient, and the HIV serostatus of the index PTB patient. In the analysis, HHCs who were HIV seropositive had 98% fewer odds of testing positive for LTBI (OR: 0.02; CI: 0 - 0.3; p-value 0.006). The non-spouse relationship (OR: 0.09; CI: 0.01 – 0.69; p-value 0.021) and PTB patients positive for HIV (OR:0.41; CI: 0.19 - 0.87; p-value 0.02) were also significantly associated with reduced odds (91% and 59% less odds respectively) of testing positive for LTBI. On the contrary, HIV seropositive HHCs who were not spouses had over 63 times the odds of testing positive for LTBI (OR: 63.24; CI:2.44 – 1637.3; p-value 0.012). There was a significant interaction of terms where the non-spousal relationship seemed to modify the effect of the seropositive HHC. The huge confidence interval can be attributed to the smaller sample size falling in this category. The HLA-DQB1 and HLA-DRB1 allele groups were analysed in 54 participants: 17 PTB patients and 37 HHCs. In this group, 19 HHCs were LTBI positive while 18 were LTBI negative. The frequency of DRB3*1 was 0.17-fold lower [95% CI=0.03-0.83] among PTB patients compared to HHCs before adjusting for HIV status (p=0.048), while the frequency of the DRB5*2 allele was 23.5% higher among PTB patients compared to HHCs (p=0.013) before adjusting for HIV status. After adjusting HIV status, the frequency of DRB1*14 was 12-fold higher [95% CI=1.11-138.2] among PTB patients compared to HHCs (p=0.040). Evaluation of the experiences of the PTB patients and their HHCs revealed adequate access to PTB diagnosis and treatment. However, lack of knowledge on LTBI by the HHCs, psychosocial challenges and inadequate infection control measures at home are significant gaps that need to be addressed. CONCLUSION: The HHCs of PTB patients in this population had a high prevalence of LTBI at 55.7%. Being a spouse of a PTB patient, prolonged co-habitation, and HIV serostatus were potential risk factors. The HIV serostatus of the PTB patient could impact infectiousness and, therefore, the risk of infection to close contacts. The HIV serostatus of the HHC could influence the performance of the IGRA test. The frequency of HLA-DRB5*2 and HLA-DRB1*14 alleles groups were higher among PTB patients, which suggested a possible association with the progression of LTBI to active PTB. The HLA-DRB3*1 allele had a higher frequency among LTBI negative HHCs, suggesting a potential protective role against M. tuberculosis infection. RECOMMENDATIONS: The high prevalence of LTBI emphasises the need for TB control programs to focus more on sensitising household contacts of PTB patients on the importance and availability of screening for LTBI and preventive treatment to avoid reactivation. A proposed toolthe PTB HHC data card, can be evaluated for use in TB diagnostic centres to follow up on this high-risk group for implementation of TB preventive treatment. The TB prevention programs should also address the multifaceted challenges faced by caregivers of TB patients at home. We recommend further studies using higher resolution HLA typing kits to investigate the roles of HLA-DRB3*1, HLA-DRB5*2, HLA-DRB1*14 in TB immunopathogenesis as predictive HLA genetic biomarkers of the likely outcome of exposure to Mycobacterium tuberculosis.