Prevalence of latent tuberculosis infection in Sudan: a case-control study comparing interferon-γ release assay and tuberculin skin test

Tuberculosis in Sudan: systematic review and meta analysis

Every year, 10 million people fall ill with tuberculosis (TB). Despite being a preventable and curable disease, 1.5 million people die from TB each year -making it the world's top infectious disease. TB is the leading cause of death of people with HIV and also a major contributor to antimicrobial resistance. Its presumed that TB was the cause of 1% of the total deaths among inpatients in Sudan in 2017. The current study is aimed to provide pooled prevalence of Mycobacterium tuberculosis among Sudanese as well as to determine any socio-cultural risk factors associated. A systematic review of the literature was conducted and regulated in accordance with the PRISMA Statement. After abstract and full text screening only twenty-six articles met our inclusion criteria and passed the quality assessment procedure. Pulmonary tuberculosis prevalence was assessed in sixteen included studies among participants from Khartoum, Gezira, Kassala, Blue Nile, River Nile, White Nile, Gadarif, Red sea, North Kordofan, Northern State, Sennar and West Darfur States, representing a total sample size of 11,253 participants of suspected individuals such as febrile outpatients, TB patients' contacts and other groups such as HIV/AIDS patients, hemodialysis patients, School adolescents as well as pregnant women. The pooled prevalence was 30.72% [CI: 30.64, 30.81]. Moreover, Khartoum State recorded the highest pooled prevalence as 41.86% [CI: 14.69, 69.02] based on a total sample size of 2,737 participants. Furthermore, male gender and rural residence were found to be significantly associated with TB infection. Further research with larger sample sizes targeting prevalence and risk factors of TB among Sudanese population is needed to be conducted.

Latent tuberculosis infection in family members in household contact with active tuberculosis patients in Semarang City, Central Java, Indonesia

A quarter of the world’s population is infected with Mycobacterium tuberculosis (M.tb), 10% of cases develop active tuberculosis (TB), and 90% have a latent TB infection. Family members of TB patients have the highest potential for latent TB infection. This study aims to identify latent TB infection and risk factors in family members within the household contacts of active TB patients. This study used a crosssectional study design with a contact tracing method. The selected subjects were 138 people from 241 total family members of 112 active TB patients. Subjects underwent a tuberculin skin test (TST), using 2 units of tuberculin (TU) purified protein derivative (PPD) 0.1 mL (PT. Bio Farma Persero, Bandung, Indonesia). Data risk factors were collected during home visits. Data were analyzed using the chi-square test and multiple logistic regression. A total of 63.8% (88/138) of family members of active TB patients’ household contacts had latent TB infection. The type of occupation of laborers/ farmers/fishers is the most dominant risk factor associated with latent TB infection (AOR: 7.04; 95% CI: 1.70–29.02), followed by unqualified bedroom density (<8 m2/2 people) (AOR: 5.33; 95% CI: 2.44– 12.71) and contact duration ≥5 hours/day (AOR: 4.70; 95% CI:1.33–16.66). Latent TB infection in family members of active TB patients’ household contacts was quite high. Occupation type, contact duration, and bedroom density were simultaneously confirmed as the main risk factors related to latent TB infection. Therefore, it is recommended to identify and prevent latent TB infection in family members in household contact with active TB patients.

Mycobacterium tuberculosis antigen-specific T cell responses in smear- negative pulmonary tuberculosis patients

Despite recent improvements in microbial detection, smear negative TB remains a diagnostic challenge. In this study, we investigated the potential discriminatory role of polychromatic flow cytometry of M. tuberculosis antigen-specific T cells to discriminate smear negative TB from health controls with or without latent TB infection, and non-TB respiratory illnesses in an endemic setting. A cross-sectional study was conducted on HIV negative, newly diagnosed smear-positive PTB (n=34), smear-negative/Gene Expert negative PTB (n=29) patients, non-TB patients with respiratory illness (n=33) and apparently healthy latent TB infected (n = 30) or non-infected (n = 23) individuals. The expression of activation (HLA-DR, CD-38), proliferation (Ki-67) and functional (IFN-γ, TNF-α) T cell markers using polychromatic flow cytometry was defined after stimulation with PPD antigens. Sputum samples were collected and processed from all patients for Mtb detection using a concentrated microscopy, LJ/MGIT culture, and RD9 typing by PCR. Our study showed CD4 T cells specific for PPD co-expressed activation/proliferation markers together with induced cytokines IFNγ or TNFα were present at substantially higher levels among patients with smear positive and smear negative pulmonary TB than among healthy controls and to a lesser extent among patients with non-TB illness. Our study conclude that Smear negative TB can be distinguished from non-TB respiratory illness and healthy controls with a flow cytometric assay for PPD-specific T cells co-expressing activation/proliferation markers and cytokines.

In vitro responses of multiple cytokines to purified protein derivative in healthy and naturally Mycobacterium tuberculosis-infected rhesus monkeys (Macaca mulatta)

BACKGROUND

As the widely used biomarker of whole-blood stimulation assays for tuberculosis diagnosis, the release of IFN-γ might be affected by multiple factors, such as immunosuppression and some infectious agents. Here, we evaluated additional cytokines as diagnostic biomarkers.

METHODS

Forty-three cytokines were measured by Luminex xMAP technologies in 30 healthy and 10 naturally Mycobacterium tuberculosis (MTB)-infected rhesus monkeys pre- and post-stimulation by purified protein derivative (PPD).

RESULTS

After stimulation, production of 23 and 38 cytokines was markedly increased in healthy and MTB-infected macaques, respectively. A comparison of the stimulation index (SI) between MTB infections and healthy macaques showed that the SIs of 32 cytokines in MTB-infected macaques were significantly higher than those in healthy macaques. Pooling the results, eight cytokines were suggested as ideal biomarkers for a whole-blood stimulation assay for MTB diagnosis.

CONCLUSION

PPD could induce multiple cytokine responses in either healthy or MTB-infected monkeys, and eight cytokines had reliable predictive capacity as diagnostic biomarkers of MTB infection.

Latent tuberculosis infection and associated risk indicators in pastoral communities in southern Ethiopia: a community based cross-sectional study

BACKGROUND

Research pertaining to the community-based prevalence of latent tuberculosis infection (LTBI) is important to understand the magnitude of this infection. This study was conducted to estimate LTBI prevalence and to identify associated risk factors in the Omo Zone of Southern Ethiopia.

METHODS

A community-based cross-sectional study was conducted in six South Omo districts from May 2015 to February 2016. The sample size was allocated to the study districts proportional to their population sizes. Participants were selected using a multi-stage sampling approach. A total of 497 adult pastoralists were recruited. Blood samples were collected from the study participants and screened for LTBI using a U.S. Food and Drug Administration approved interferon-gamma release assay (IGRA). Logistic regression was used to model the likelihood of LTBI occurrence and to identify risk factors associated with LTBI.

RESULTS

The prevalence of LTBI was 50.5% (95% CI: 46%, 55%) with no significant gender difference (49.8% among males versus 51.2% among females; Chi-square (χ2) = 0.10; P = 0.41) and marginally non-significant increasing trends with age (44.6% among those below 24 years and 59.7% in the age range of 45-64 years; χ2 = 6.91; P = 0.075). Being residence of the Dasanech District (adjusted odds ratio, AOR = 2.62, 95% CI: 1.30, 5.28; P = 0.007) and having a habit of eating raw meat (AOR = 2.89, 95% CI: 1.09, 7.66; P = 0.033) were significantly associated with an increased odds of being positive for LTBI. A large family size (size of 5 to 10) has significant protective effect against associated a reduced odds of being positive for LTBI compared to a family size of below 5 (AOR = 0.65, 95% CI: 0.42, 0.99; P = 0.045).

CONCLUSIONS

A high prevalence of LTBI in the South Omo Zone raises the concern that elimination of TB in the pastoral communities of the region might be difficult. Screening for and testing individuals infected with TB, independent of symptoms, may be an effective way to minimize the risk of disease spread.

Comparing tuberculin skin test and interferon γ release assay (T-SPOT.TB) to diagnose latent tuberculosis infection in household contacts

BACKGROUND/AIMS

The tuberculin skin test (TST) and interferon γ release assay are currently used as diagnostic tools to detect latent tuberculosis (TB) infection; however, there are inconsistencies about the degree of agreement between the tests. We aimed to evaluate the concordance rate between the two tests in household contacts of a country with intermediate TB burden, where most people were vaccinated.

METHODS

We recruited household contacts who spent > 8 hours daily with patients with microbiologically confirmed active pulmonary TB, and received both TST and T-SPOT.TB (Oxford Immunotec) simultaneously. The degree of agreement was analysed according to TST cutoff and Bacille Calmette-Guerin (BCG) vaccination status. Relevant factors were analysed to establish the association with TST or T-SPOT.TB.

RESULTS

Among 298 household contacts, 122 (40.9%) were spouses, and 250 (83.9%) had received BCG vaccination. In the contact sources, 117 (39.3%) showed a positive result for acid-fast bacillus (AFB) sputum smear and 109 (36.6%) had cavities. The highest agreement rate of 69.5% and κ value of 0.378 were found with a 10 mm cutoff. Spouse, time interval from TB diagnosis to test, and AFB sputum smear positivity were significantly associated with a positive result for T-SPOT.TB. Sex, BCG vaccination, and cavity on chest computed tomography were related to TST positivity.

CONCLUSIONS

The present study suggested it was not possible for TST and T-SPOT.TB to replace each other because of considerable discrepancy between the two tests in household contacts in a country with intermediate TB prevalence.

Improving T-cell assays for diagnosis of latent TB infection: Confirmation of the potential role of testing Interleukin-2 release in Iranian patients

BACKGROUND

Since gamma interferon release assays (IGRAs) cannot differentiate between active tuberculosis and latent tuberculosis infection (LTBI), development of rapid and specific diagnosis tools are essential for discriminating between active tuberculosis (TB) from LTBI. Both IGRAs are based on Mycobacterium tuberculosis-specific antigens, namely, early secretory antigenic target 6 (ESAT-6) and 10kDa culture filtrate (CFP-10). The aim of this study was to evaluate the potential value of IL-2 secretion by whole blood cells after stimulation with rESAT-6 and rCFP-10 for discriminating between active and latent tuberculosis.

METHODS

Interleukin-2 and IFN-γ were measured after blood stimulation of 90 cases (30 with active TB, 30 with LTBI and 30 healthy controls) with recombinant ESAT-6 and CFP-10. Receiver operating characteristic (ROC) curve analysis was conducted to determine the best IL-2 and IFN-γ result thresholds in discriminating between cases with active or latent TB, and the corresponding sensitivity and specificity were recorded.

RESULTS

The IFN-γ release assay demonstrated a good sensitivity and specificity (sensitivity 83-84% and specificity 92%) for diagnosis of tuberculosis. The discrimination performance of IL-2 assay (assessed by the area under ROC curve) between LTBI and patients with active TB were 0.75 and 0.8 following stimulation with rESAT-6 and rCFP-10, respectively. Maximum discrimination was reached at a cut-off of 11.6pg/mL for IL-2 after stimulation with recombinant rESAT-6 with 72% sensitivity and 79% specificity and 10.7pg/mL for IL-2 following stimulation with rCFP-10 with 75% sensitivity and 79% specificity, respectively.

CONCLUSION

This study demonstrates that rESAT-6 and rCFP-10 can provide a sensitive and specific diagnosis of TB. In addition, it was shown that IL-2 may be serving as a marker for discriminating LTBI and active TB.

Challenges in diagnosing tuberculosis in children: a comparative study from Sudan

OBJECTIVES

The diagnosis of tuberculosis (TB) in children is challenging due to insufficient specimen material and the scarcity of bacilli in specimens. This study aimed to evaluate methods for diagnosing TB in children in Sudan.

METHODS

Patients (N=197) were subjected to the tuberculin skin test (TST). Gastric lavage or sputum specimens were then collected, processed, and cultured as per standard procedures.

RESULTS

Culture on Löwenstein-Jensen medium, the reference standard, revealed growth in 16.2% of the specimens. Comparative analysis showed that 43.7% were positive for the TST (sensitivity 100%, specificity 67.3%), 8.1% were positive by Ziehl-Neelsen stain (sensitivity 43.8%, specificity 98.8%), 11.2% by auramine stain (sensitivity 56.3%, specificity 98.8%), and 17.8% were positive for PCR amplification of the IS6110 sequence (sensitivity 100%, specificity 98.8%).

CONCLUSIONS

It is concluded that whilst TST and IS6110 achieved 100% sensitivity based on the reference standard of culture, the latter was more specific. The TST is recommended for routine diagnosis and the use of PCR for particular cases, depending on the facilities and the urgency.

Comparison of latent tuberculosis infection rate between contacts with active tuberculosis and non-contacts

BACKGROUND

Latent tuberculosis infection (LTBI) rate is usually high in contacts with infectious TB patients. In TB-prevalent country, however, background LTBI rate is already high in general population.

AIM

To compare the LTBI rate between controls and recognized close contacts.

METHOD

Between February 2010 and January 2014, 183 controls and 376 contacts with TB infection were enrolled. The tuberculin skin test (TST) and QuantiFERON-TB Gold In-Tube (QFT-GIT) were used to diagnose LTBI.

RESULTS

Higher TST positivity was found in the control group than in the contact group (37.7% vs. 29.9%, P = 0.073). The positive QFT-GIT rate was higher in contacts than in controls (32.6% vs. 24.1%, P = 0.054). A significantly higher positive QFT-GIT rate was found in contacts under 30 years of age than in controls (16.1% vs. 0%, P = 0.005).

CONCLUSION

In a TB-prevalent country, both TST and QFT-GIT were limited in the diagnosis of recent LTBI in adult contacts probably due to the high background LTBI rate. However, QFT-GIT seems to be better than TST in differentiating LTBI status in contacts younger than 30 year old.

Profile of interferon-gamma response to latency-associated and novel in vivo expressed antigens in a cohort of subjects recently exposed to Mycobacterium tuberculosis

Recently some latency-associated antigens (LAA) of Mycobacterium tuberculosis were described, as Rv2029c, Rv2031c, Rv2034, Rv2628 and Rv3353c. Of which, the Rv2034 and Rv3353c also demonstrated in vivo expression. Therefore evaluating the immune response to these antigens may help to understand their role in latent TB infection. In a 1-year longitudinal study, IFN-γ response by in vitro peripheral blood mononuclear cells stimulation with LAA was investigated in subjects recently exposed to TB, classified by IFN-γ release assay (IGRA) using RD1 antigens (ESAT-6:CFP-10) and tuberculin skin test (TST) response. Except for Rv3353c, all the LAA triggered higher mean IFN-γ response in IGRA-RD1(+) groups (p < 0.05). Combining the IFN-γ-responders to Rv2029c, Rv2031c plus Rv2034 detected 90.3% (28/31) of IGRA-RD1(+) and 66.7% (24/36) of TST(+) contacts, while 95% (19/20) and 11% (2/17) were identified by classifying them according to a TST and IGRA-RD1 double-positive or double-negative response, respectively. In the follow-up, the TST convertors (negative to positive) also demonstrated an IFN-γ conversion to Rv2029c and Rv2031c, whereas the unique TB incident case was exclusively detected via IGRA-Rv2029c and TST before developing TB. A reversion rate to LAA (60%-100%) after prophylactic treatment was observed at TST(+)/IGRA-RD1(+) group. Further studies into the performance of these antigens are thus warranted.

Prevalence of latent tuberculosis infection and associated risk factors in an urban African setting

Background

Nearly one third of the world is infected with latent tuberculosis infection (LTBI) and a vast pool of individuals with LTBI persists in developing countries, posing a major barrier to global TB control. The aim of the present study was to determine the prevalence of LTBI and the associated risk factors among adults in Kampala, Uganda.

Methods

We performed a secondary analysis from a door-to-door cross-sectional survey of chronic cough conducted from January 2008 to June 2009. Urban residents of Rubaga community in Kampala aged 15 years and older who had received Tuberculin skin testing (TST) were included in the analysis. The primary outcome was LTBI defined as a TST with induration 10 mm or greater. Multivariable logistic regression analyses were used to assess the risk factors associated with LTBI.

Results

A total of 290 participants were tested with TST, 283 had their tests read and 7 didn’t have the TST read because of failure to trace them within 48–72 hours. Of the participants with TST results, 68% were female, 75% were 15–34 years, 83% had attained at least 13 years of education, 12% were smokers, 50% were currently married, 57% left home for school or employment, 21% were HIV positive and 65% reported chronic cough of 2 weeks or longer. The overall prevalence of LTBI was 49% [95% CI 44–55] with some age-and sex-specific differences. On multivariable analysis, leaving home for school or employment, aOR = 1.72; [95%CI: 1.05, 2.81] and age 25–34, aOR = 1.94; [95%CI: 1.12, 3.38]; 35 years and older, aOR = 3.12; [95%CI: 1.65, 5.88] were significant risk factors of LTBI.

Conclusion

The prevalence of LTBI was high in this urban African setting. Leaving home for school or employment and older age were factors significantly associated with LTBI in this setting. This suggests a potential role of expansion of one’s social network outside the home and cumulative risk of exposure to TB with age in the acquisition of LTBI. Our results provide support for LTBI screening and preventive treatment programs of these sub-groups in order to enhance TB control.