Skip to main content
Advertisement
Browse Subject Areas
?

Click through the PLOS taxonomy to find articles in your field.

For more information about PLOS Subject Areas, click here.

  • Loading metrics

Role of CD4/CD8 ratio on the incidence of tuberculosis in HIV-infected patients on antiretroviral therapy followed up for more than a decade

  • Dawit Wolday ,

    Roles Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Supervision, Validation, Writing – original draft, Writing – review & editing

    dawwol@gmail.com

    Affiliation Mekelle University College of Health Sciences, Mekelle, Ethiopia

  • Yazezew Kebede,

    Roles Formal analysis, Investigation, Writing – original draft

    Affiliation Mekelle University College of Health Sciences, Mekelle, Ethiopia

  • Dorsisa Legesse,

    Roles Data curation, Project administration, Supervision

    Affiliation Hayat General Hospital, Addis Ababa, Ethiopia

  • Dawd S. Siraj,

    Roles Conceptualization, Formal analysis, Funding acquisition, Investigation, Methodology, Writing – review & editing

    Affiliation Division of Infectious Diseases, Department of Medicine, University of Wisconsin, Madison, Wisconsin, United States of America

  • Joseph A. McBride,

    Roles Formal analysis, Investigation, Writing – review & editing

    Affiliation Division of Infectious Diseases, Department of Medicine, University of Wisconsin, Madison, Wisconsin, United States of America

  • Mitchell J. Kirsch,

    Roles Data curation, Formal analysis, Investigation

    Affiliation Division of Infectious Diseases, Department of Medicine, University of Wisconsin, Madison, Wisconsin, United States of America

  • Robert Striker

    Roles Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Supervision, Validation, Writing – review & editing

    Affiliation Division of Infectious Diseases, Department of Medicine, University of Wisconsin, Madison, Wisconsin, United States of America

Abstract

Background

The role of CD4/CD8 ratio on the incidence of tuberculosis (TB) in patients on antiretroviral therapy (ART) is unknown. Thus, we sought to determine whether the CD4/CD8 ratio was associated with development of TB in a cohort of HIV infected individuals on ART followed up for more than a decade in the setting of sub-Saharan Africa (SSA).

Methods

The cohort comprised adult patients who started ART between 2001 and 2007 and followed for up to 15 years. Clinical data were collected in retrospective manner. Patients with an AIDS defining illness or a CD4 count <200 cell/μL were started with a combination of ART. The participants have clinic visits every 6 months and/or as needed. Poisson regression models were used to identify factors associated with development of incident TB. Kaplan-Meier curves were used to estimate the probability of incident TB while on ART.

Results

A total of 347 patients with a median duration of follow-up on ART of 11.5 (IQR: 10.0–12.5) years were included. Incident TB developed in 47 patients during the 3259 person-years of follow-up, the majority (76.6%) occurred within five year of ART initiation. On univariate analysis, poor ART adherence (RR:2.57, 95% CI: 1.28–5.17), time-updated CD4 cell count of lower than 200 (RR: 4.86, 95%CI 2.33–10.15), or CD4 cell count between 200 and 500 (RR: 4.68, 95% CI: 2.17–10.09), time-updated CD8 cell count lower than 500 (RR: 2.83 95% CI 1.31–6.10), or CD8 cell count over 1000 (RR: 2.23, 95% CI: 1.12–4.45), time-updated CD4/CD8 ratio of less than 0.30 (RR: 6.00, 95% CI: 2.96–12.14), lack of normalization of CD4 T-cell count (RR: 6.13, 95% CI: 2.20–17.07), and virological failure (RR: 2.35 (95% CI: 1.17–4.71) were all associated with increased risk of incident TB. In multivariate analysis, however, time-updated CD4/CD8 ratio of less than 0.30 (adjusted RR: 4.08, 95% CI: 1.31–12.68) was the only factor associated with increased risk of developing incident TB (p = 0.015). Similar results were obtained in a sensitivity analysis by including only those virally suppressed patients (n = 233, 69% of all patients). In this group, CD4/CD8 ratio of less than 0.30 was associated with development of incident TB (adjusted RR: 4.02, 95% CI: 1.14–14.19, p = 0.031). Overall, the incidence rate of TB in patients with an updated CD4/CD8 ratio of less than 0.30 was more than 5-fold higher when compared with those with a ratio more than 0.45.

Conclusion

Low CD4/CD8 ratio is independently associated with an increased risk of incident TB despite viral suppression. CD4/CD8 ratio may serve as a biomarker for identifying patients at risk of TB in patients on ART in the setting of SSA.

Introduction

Cumulative findings have demonstrated that antiretroviral therapy (ART) reduces the risk of developing tuberculosis (TB) significantly [118]. Despite the advent of ART, however, TB remains the major cause of death and morbidity among patients co-infected with HIV-1 in sub-Saharan Africa (SSA) [1922]. The mechanism(s) related to the development of TB in patients taking ART, however, remains to be elucidated.

Effective ART suppresses HIV replication allowing progressive CD4+ T-cell recovery that is usually accompanied by persistent expansion of CD8+ T-cells. As a consequence, there is an incomplete restoration of the CD4/CD8 T-cell ratio, which very often remains inverted [2326]. While it is well established that HIV, and specifically low CD4 cells in patients with HIV increase the susceptibility to TB [27], this strong relationship becomes obscured once patients start ART and their CD4 count rises. While CD4 counts rise fairly fast on HIV medications, the CD4/CD8 ratio does not rise or at best rises quite slowly and new evidence suggests this may be a marker for continuing HIV related immune dysfunction even when on ART [28].

We hypothesized that HIV positive patients on ART with low CD4/CD8 ratios are more likely to be diagnosed with incident TB than HIV positive patients with higher ratios. The CD4/CD8 ratio may serve as a marker of chronic immune activation, and may be clinically useful in identifying HIV-1 infected patients at risk for TB. Therefore, we sought to determine whether the CD4/CD8 ratio was associated with development of TB in a cohort of HIV infected individuals on ART followed up for more than a decade in the setting of SSA.

Methods

Study population

This retrospective cohort was enrolled at Hayat General Hospital’s ART Clinic in Addis Ababa, Ethiopia, which delivers HIV treatment and care. The cohort consists of adult patients who started ART between 2001 and 2007 and have been followed until 2017. Patients with an AIDS defining illness or a CD4 count <200 cell/μL were started on with a combination of ART, based on National ART Guidelines [29]. First-line ART comprised of zidovudine (AZT) or stavudine (d4T) or tenofovir (TDF) in combination with lamivudine (3TC) plus non-nucleoside reverse transcriptase inhibitors, nevirapine (NVP) or efavirenz (EFV). All patients were offered isoniazide preventive therapy (IPT) for preventing TB as of 2010. The participants had clinic visits every 6 months and/or as needed for monitoring treatment outcomes. Laboratory tests performed during each visit included complete blood cell count, clinical chemistry, urine analysis, and immune-profiles (as measured by CD4 cell count, CD8 cell count and CD4/CD8 ratio). HIV-1 viral load was done for patients after suspecting virological failure. The diagnosis of TB was based on the National Tuberculosis and Leprosy Control Guidelines of Ethiopia [30]. Accordingly, TB was diagnosed based on either one or a combination of the following: sputum microscopy, culture, chest radiography, fine-needle aspiration for lymphadenopathy, histopathology, or high index of clinical suspicion followed by response to treatment.

Definitions

Patients presenting with TB at time or within one month of ART initiation were considered as prevalent TB. The development of TB following one month of ART initiation until censoring the study (death, loss to follow-up, transfer-out, or termination of the study) was considered as incident TB.

CD4+ T-cell count is considered normalized if above 500 cells (lower limit value of healthy adult Ethiopians [31, 32]), and CD4/CD8 ratio was considered normalized if above 1.0 [33, 34]. Viral suppression was defined as the attainment of HIV-1 plasma viral load of <400 copies/mL on two subsequent measurements. Poor adherence was defined as intake of prescribed medications <95%, based on National ART Guidelines [29].

Statistical analysis

Baseline characteristics for continuous variables were expressed as the median with interquartile range (IQR), and for categorical variables as proportions. Chi-square test was used to compare categorical variables and Wilcoxon rank-sum test for not normally distributed variables.

The overall incidence rate of TB was calculated per 100 person years at risk. Patients were censored at the time of incident TB event or at the time of death, transfer to other clinic, loss to follow-up, or the last visit date before December 2017. Risk factors associated with the development of incident TB were analyzed using Poisson regression analysis. We opted to use Poisson regression analysis based on the small frequency of TB events in the cohort [1].

We first analyzed the association between the development of incident TB and baseline demographic (age, gender), clinical (HIV disease stage) characteristics, and baseline laboratory biomarkers including CD4 cell count, CD8 cell count, CD4/CD8 ratio and viral load in univariate analysis. The CD4 cell counts were built in three categories (<200, between 200 and 500, and >500 cells/μL), the CD8 cell counts in three categories (<500, between 500 and 1000, and >1000 cells/μL), and the CD4/CD8 ratio in three categories (<0.30, between 0.30 and 0.45, and >0.45). The cut-offs were chosen based on previous reports showing association of the biomarkers with AIDS-related events [33, 34].

In addition, time-dependent variables including ART adherence, toxicity, ART switching as well as updated CD4 cell count, CD8 cell count, CD4/CD8 ratio, normalized CD4 cell count (>500 cells), normalized CD4/CD8 ratio (≥1.0), and plasma viral load were included in the initial bivariate analysis. Then a multivariate analysis of predictors of incident TB was done including all variables that were significant in univariate analysis. Sensitivity analysis was done to examine the effect of viral suppression by excluding those who failed to attain viral suppression (<400 copies/mL) following initiation of ART.

Kaplan-Meier curves were used to estimate the probability of incident TB in patients on ART across explanatory variables and statistical differences were tested using log-rank test. P values <0.05 were considered statistically significant. Data was entered on excel and exported for analysis by STATA (Statistical package v. 14.0, StataCorp, Texas, USA).

Ethical considerations

The study was reviewed and approved by the Addis Ababa City Administration Health Bureau Research Ethics Review Committee, Addis Ababa, Ethiopia and the Institutional Review Board (IRB) of the University of Wisconsin, Madison, USA.

Results

Characteristics of study participants

Socio-demographic and baseline clinical features are shown in Table 1. A total of 347 (of which 36.3% were female) fulfilling recruitment criteria were included in the study. The median age at ART initiation was 40 (IQR: 33–46) years, the majority (61.4%) being Stage III and IV WHO clinical stage. We compared baseline characteristics between patients who developed TB and those who remained free from incident TB. We found that, there was no statistically significant difference in all of the characteristics between the two groups.

thumbnail
Table 1. Baseline characteristics of study participants at initiation of ART.

https://doi.org/10.1371/journal.pone.0233049.t001

The CD4 cell count increased from baseline median of 127 cells (IQR: 60–197) to 411 cells (IQR: 225–602) after a median of 11.5 (IQR: 10.0–12.5) years of follow up on ART (p<0.0001). Overall, only 36.3% of the cohort has normalized CD4 cell count (>500 cells) at censoring the study. CD8 cell counts remained somewhat stable through-out treatment. In contrast CD4/CD8 ratio trends revealed continuous increase throughout the course of ART, and increased from a median baseline of 0.13 (IQR: 0.08–0.22) to a median of 0.49 (IQR: 0.26–0.72, at the time of censoring the study (p<0.001). In addition, only 9.7% of the cohort has normalized ratio (≥ 1.0) at censoring the study.

TB incidence rates

Incident TB developed in 47 patients during the 3259 person-years of follow-up, accounting for an incidence rate of 1.44 per 100 person-year follow-up (95% CI: 1.08–1.92). The majority were extra-pulmonary tuberculosis (72%). The median time to developing TB was 1.5 years (IQR: 0.5 to 5.0). The median age of individuals who developed incident TB was 38 (IQR: 31–50) years. Of the 47 incident TB cases, the majority (76.6%) occurred within five year of ART initiation, accounting for an incidence rate of 53.03 per 100 person-year follow-up (95% CI: 38.25–73.51). On the contrary, the remaining incident TB cases occurred within 10 years and 15 years of follow-up, resulting in the incidence rate of 1.63 (95% CI 0.82–3.27) and 0.11 (95% CI 0.04–0.34) per 100 person-years of follow-up, respectively [S1 Table]. The incidence rate of TB in patients with an updated CD4/CD8 ratio of more than 0.45 was 0.47 per 100 person-year follow-up (95% CI: 0.25–0.87) and those with ratio between 0.30 and 0.45 was 0.85 per 100 person-year follow-up (95% CI: 0.35–2.05). However, when the ratio was less than 0.30, the incidence rate of TB was significantly higher (6.055 per 100 person-years of follow-up, 95% CI 4.28–8.55; p<0.0001) when compared with those with a ratio more than 0.45 (Fig 1).

thumbnail
Fig 1. The incidence rate of tuberculosis (TB) in the different CD4/CD8 ratio group.

https://doi.org/10.1371/journal.pone.0233049.g001

We did further sensitivity analysis by excluding those who failed to achieve viral suppression. In this group, incident TB developed in 28 patients during the 2492 person-years of follow-up, accounting for an incidence rate of 1.12 per 100 person-year follow-up (95% CI: 0.78–1.63). The incidence rate of TB in this virally suppressed group with an updated CD4/CD8 ratio of more than 0.45 was 0.46 per 100 person-year follow-up (95% CI: 0.23–0.92) and those with ratio between 0.30 and 0.45 was 0.87 per 100 person-year follow-up (95% CI: 0.33–2.31). On the contrary, the incidence rate of TB was significantly higher (5.41 per 100 person-years of follow-up, 95% CI 3.32–8.83; p<0.001) in those with a ratio less than 0.30 compared to those with a ratio more than 0.45. In addition, patients with a ratio less than 0.30 and with viral failure did not exhibit significantly higher TB incidence (5.05 per 100 person-years of follow-up, 95% CI 2.52–10.09) [S2 Table]. The results suggest that viral suppression did not alter significantly the incidence rate of TB.

CD4 cell count, CD8 cell count, CD4/CD8 ratio and viral load at time of TB diagnosis in patients on ART who developed incident TB to those who remained free from TB is shown in Fig 2. The median baseline CD4 cell count among those who developed TB was not significantly different than that of patients who remained free from TB (p = 0.336). In addition, the median CD4 count at the time of TB diagnosis was significantly higher than at baseline (213 cells/μL; IQR: 76–325 vs. 103 cells/μL; IQR: 68–190, respectively (p = 0.002). Likewise, among the patients who remained free from TB, the time-updated CD4 cell count increased significantly compared to baseline (450 cells/μL; IQR: 280–626 vs. 132 cells/μL; IQR: 60–197, respectively (p<0.0001). However, among the patients who developed incident TB, the median CD4 cell count at the time of TB diagnosis (213 cells/μL; IQR: 76–325) was significantly lower than the time-updated cell count (450 cells/μL; IQR: 280–626) in those who remained free from TB (p<0.0001). The CD4/CD8 ratio increased significantly in both patient group irrespective of developing TB (Fig 2C). Nevertheless, despite similar baseline CD4/CD8 ratio in the patients who developed TB compared to those who remained free from TB (0.14; IQR: 0.09–0.21 vs. 0.13; IQR: 0.08–0.22, respectively; p = 0.612), the median CD4/CD8 ratio at the time of TB diagnosis was significantly lower than the time-updated ratio of those who remained free from TB (0.17; IQR: 0.11–0.37 vs. 0.52; IQR: 0.31–0.78, respectively; p<0.0001). Both CD8 cell count (Fig 2B) and viral load levels (Fig 2D) in patients who developed TB were not different than the values in those who remained free from TB.

thumbnail
Fig 2. CD4 cell count (A), CD8 cell count (B), CD4/CD8 ratio (C) and viral load levels (D) at time of TB in patients who developed incident TB vs. those who remained free from TB.

Data are presented as medians (IQR).

https://doi.org/10.1371/journal.pone.0233049.g002

The probability of TB-free survival in the cohort with an updated CD4/CD8 ratio of more than 0.45 was significantly higher than in the patients with a ratio less than 0.30, including only those with viral suppression (Fig 3). In addition, a similar pattern was noted among those who exhibited virological failure [S1 Fig].

thumbnail
Fig 3. Kaplan-Meier estimates for incident TB in patients on antiretroviral therapy.

Time-updated CD4/CD8 ratio in all cases (A), and in those with virological suppression.

https://doi.org/10.1371/journal.pone.0233049.g003

Risk factors associated with incident TB

On the univariate analysis (Table 2), poor ART adherence (RR:2.57, 95% CI: 1.28–5.17), time-updated CD4 cell count of lower than 200 (RR: 4.86, 95%CI 2.33–10.15), or CD4 cell count between 200 and 500 (RR: 4.68, 95%CI: 2.17–10.09), time-updated CD8 cell count lower than 500 (RR: 2.83 95% CI 1.31–6.10), time-updated CD8 cell count over 1000 (RR: 2.23, 95% CI: 1.12–4.45), time-updated CD4/CD8 ratio of less than 0.30 (RR: 6.00, 95% CI: 2.96–12.14), lack of normalization of CD4 T-cell count (RR: 6.13, 95% CI: 2.20–17.07), and viral failure (RR: 2.35 (95% CI: 1.17–4.71) were all associated with increased risk of developing TB. On the other hand age, gender, WHO stage, adverse drug events and not switching ART were not associated with risk of TB. In multivariate analysis, however, time-updated CD4/CD8 ratio of less than 0.30 (adj. RR: 4.08, 95% CI: 1.31–12.68) was the only factor associated with increased risk of developing TB (p = 0.015).

thumbnail
Table 2. Relative risk of tuberculosis in HIV-infected patients on antiretroviral treatmenta.

https://doi.org/10.1371/journal.pone.0233049.t002

In sensitivity analysis, we only included those virally suppressed patients (n = 233, 69% of all patients). The results are shown in Table 3. On univariate analysis, time-updated CD4 cell count of lower than 200 (RR: 12.22, 95%CI 4.52–33.05), CD4 cell count between 200 and 500 (RR: 5.99, 95% CI: 2.21–16.18), time-updated CD8 cell count lower than 500 (RR: 2.84, 95% CI: 1.14–7.06), time-updated CD4/CD8 ratio of less than 0.30 (RR: 7.77, 95%CI: 3.38–17.86), and lack of normalization of CD4 T-cell count (RR: 6.49, 95% CI: 1.96–21.49) were associated with increased risk of developing TB. However, multivariate analysis revealed that time-updated CD4/CD8 ratio of less than 0.30 (adj. RR: 4.02, 95% CI: 1.14–14.19) was the only independent risk factor associated with development of TB (p = 0.031).

thumbnail
Table 3. Relative risk of tuberculosis in HIV-infected patients on antiretroviral treatmenta.

https://doi.org/10.1371/journal.pone.0233049.t003

Discussion

The overall TB incidence rate in our study is 1.44 (95% CI: 1.08–1.92) per 100 person years of follow-up. A more recent meta-analysis from Ethiopia reported a pooled TB incidence rate of 3.79 (95% CI: 2.03–5.55) per 100 person years based on 7 studies in patients who received ART and IPT [35]. Several reports have shown the complementary effects of ART and IPT in preventing the development of TB [15, 17, 36, 37]. All our cohort participants received IPT and this could also contribute to the lower incidence of TB. Overall, our result demonstrated about 2.6-fold lower incidence of TB than the previous studies reported from Ethiopia. However, longer treatment duration in our cohort might have resulted in a lower TB incidence rate, which is consistent with previous studies undertaken elsewhere in SSA [47]. Another important consideration is the fact that the cohort was followed in a private health-care facility. Thus, better management of TB in the private sector might have contributed to the findings of lower incidence rate of TB, as has been reported from India [17].

We noted that CD4 count at initiation of ART was not associated with risk of developing TB. This is consistent with the findings that ART significantly reduces the risk of TB across all CD4 count strata [7, 20]. We have shown previously that low CD4+ T-cell count precedes the development of TB in a cohort of HIV-positive Ethiopians before the advent of ART [27]. Likewise, in the current study, we found that the median CD4 cell count at the time of TB diagnosis was significantly lower than the counts in those who remained free from TB. Overall, these findings suggest that incident TB developed in the patients whose immunological responses to ART were suboptimal [38, 39].

Previous reports related to viral suppression and risk of developing TB produced conflicting reports. Some authors reported an increased risk of TB in patients on ART who did not achieve viral suppression [40], whereas others have demonstrated that achieving viral suppression is not associated with risk of TB development [3, 5, 41]. In our study, viral load levels did not differ significantly between those who developed TB and those who remained free of TB. In addition, we have demonstrated that there was no statistically significant difference on the incidence rate of TB in those who achieved viral suppression when compared with those who failed to attain viral suppression. Taken together, the findings suggest that, despite effective viral suppression after initiation of ART, CD4 recovery is suboptimal and eventually resulting in a residual risk of developing TB [38, 39]. Indeed, we and others have previously reported that incomplete restoration of Mycobacterium tuberculosis-specific CD4 T-cell responses despite ART [42, 43] contributes to increased incidence of TB.

Median CD4/CD8 ratio at time of ART initiation in patients who developed incident TB in our cohort was similar to recent reports [18, 44]. However, no significant difference in the average change of ratio over time on ART was seen in patients developing TB compared to patients remaining free of TB [44]. The investigators did not analyze the role of time-updated CD4/CD8 ratio on the incidence of TB. In our cohort, however, CD4/CD8 ratio at the time of TB diagnosis was significantly lower than those who remained free from TB. In our cohort followed-up for more than a decade, only few patients (≈10%) had normalized their CD4/CD8 ratio despite long-term viral suppression. Indeed, low CD4/CD8 ratio was strongly associated with risk of development of incident TB. Particularly, the incidence rate of TB when the CD4/CD8 ratio was less than 0.30 was more than 4-fold higher than that when the ratio was more than 0.45.

M. tuberculosis-mediated immunosuppression is a known phenomenon observed among TB patients resulting in low CD4 cell counts in both HIV-negative and HIV-positive patients [4547]. The fact that our patients who developed TB had significant increase in CD4/CD8 ratio at the time of TB diagnosis compared to the ratio at enrolment suggests that the patients indeed responded immunologically to ART. Nonetheless, the increases in CD4/CD8 ratio among the patients who developed TB was significantly lower and suboptimal when compared to those who did not develop TB, resulting in their increased risk of developing TB. To the best of our knowledge, this is the first report demonstrating the impact of time-updated CD4/CD8 ratio on the incidence of TB in patients on ART. The strong association between a low CD4/CD8 ratio and the risk of TB might reflect the fact that a low ratio is a marker of a chronic immune activation. This suggestion is consistent with our previous studies conducted in Ethiopia whereby non-HIV infected adults exhibit CD4/CD8 inversion (<1.0) coupled with higher frequencies of activated effector memory cells [32, 48].

Strengths of our study include long duration of follow-up more than a decade, availability of immune profile data comprising of time-dependent change in CD4 cell count, CD8 cell count and CD4/CD8 ratio, and also the availability of viral load determinations for a large proportion (≈78%) of our cohort. Nonetheless, limitations related to our study include that our findings cannot be generalized to the entire population as the data is generated from the private sector and included only one study site. The diagnosis of TB in SSA setting is challenging as it is not definitive being without microbiological confirmation for all patients [14,15,21,47,49,50], as is for our cohort. All our patients received IPT for preventing TB as of 2010. IPT adherence data, however, were not available—which is another limitation of the study. Furthermore, the retrospective design of the study has limitations in respect to data completeness.

In conclusion, long-term ART confers a significant risk reduction in the development of TB, and in combination with IPT, it may contribute more to TB control in low-income countries. The fact that TB risk is independently associated with time-dependent CD4/CD8 ratio suggest that monitoring ratio levels may serve as a biomarker risk for TB among patients receiving ART.

Supporting information

S1 Table. Incidence of tuberculosis in HIV-infected patients on antiretroviral treatment followed for up to 15 years.

https://doi.org/10.1371/journal.pone.0233049.s001

(DOCX)

S2 Table. Incidence of TB vs. time-updated CD4/CD8 category.

https://doi.org/10.1371/journal.pone.0233049.s002

(DOCX)

S1 Fig. Kaplan-Meier estimates for incident TB in patients on antiretroviral therapy with updated CD4/CD8 ratio category.

Data are from those with virological failure.

https://doi.org/10.1371/journal.pone.0233049.s003

(TIF)

Acknowledgments

We thank all patients for participating in the study. We would like to thank the management and staff of Hayat General Hospital, College of Health Sciences, Addis Ababa, Ethiopia for their technical support and allowing us to conduct this study.

References

  1. 1. Badri M, Wilson D, Wood R. Effect of highly active antiretroviral therapy on incidence of tuberculosis in South Africa: a cohort study. Lancet 2002; 359: 2059–2064. pmid:12086758
  2. 2. Dean GL, Edwards SG, Ives NJ, Matthews G, Fox EF, Navaratne L, et al. Treatment of tuberculosis in HIV-infected persons in the era of highly active antiretroviral therapy. AIDS. 2002; 16:75–83. pmid:11741165
  3. 3. Girardi E, Sabin CA, Monforte A, Hogg B, Phillips AN, Gill MJ, et al. Incidence of tuberculosis among HIV-Infected patients receiving highly active antiretroviral therapy in Europe and North America. Clin Infect Dis 2005; 41: 1772–1782. pmid:16288403
  4. 4. Seyler C, Toure S, Messou E, Bonard D, Gabillard D, Anglaret X. Risk factors for active tuberculosis after antiretroviral treatment initiation in Abidjan. Am J Respir Crit Care Med 2005; 172: 123–127. pmid:15805184
  5. 5. Lawn SD, Badri M, Wood R. Tuberculosis among HIV-infected patients receiving HAART: Long term incidence and risk factors in a South African cohort. AIDS 2005; 19: 2109–2116. pmid:16284460
  6. 6. Gupta A, Wood R, Kaplan R, Bekker L-G, Lawn SD. Tuberculosis incidence rates during 8 years follow-up of an antiretroviral treatment cohort in South Africa: Comparison with rates in the community. PLoS ONE 2012; 7: e34156. pmid:22479548
  7. 7. Lawn SD, Myer L, Edwards D, Bekker LG, Wood R. Short-term and long-term risk of tuberculosis associated with CD4 cell recovery during antiretroviral therapy in South Africa. AIDS 2009; 23:1717–25. pmid:19461502
  8. 8. Moore D, Liechty C, Ekwaru P, Were W, Mwima G, Solberg P, et al. Prevalence, incidence and mortality associated with tuberculosis in HIV-infected patients initiating antiretroviral therapy in rural Uganda. AIDS 2007; 21:713–719. pmid:17413692
  9. 9. van Rie A, Westreich D, Sanne I. Tuberculosis in patients receiving antiretroviral therapy: incidence, risk factors and prevention strategies. J Acquir Defic Syndr 2011; 56: 349–355. pmid:20926954
  10. 10. del Amo J, Moreno S, Bucher SC, Furrer H, Logan R, Sterne J, et al. Impact of antiretroviral therapy on tuberculosis incidence among HIV-positive patients in high-income countries. Clin Infect Dis. 2012; 54:1364–1372. pmid:22460971
  11. 11. Dembélé M, Saleri N, Carvalho AC, Saouadogo T, Hien AD, Zabsonre I, et al. Incidence of tuberculosis after HAART initiation in a cohort of HIV-positive patients in Burkina Faso. Int J Tuberc Lung Dis. 2010; 14:318–323. pmid:20132623
  12. 12. Nicholas S, Sabapathy K, Ferreyra C, Varaine F, Pujades-Rodriguez M. Incidence of tuberculosis in HIV-infected patients before and after starting combined antiretroviral therapy in 8 sub-Saharan African HIV programs. J Acquir Immune Defic Syndr. 2011;57:311–318. pmid:21423023
  13. 13. Liu E, Makubi A, Drain P, Spiegelman D, Sando D, Li N, et al. Tuberculosis incidence rate and risk factors among HIV—infected adults with access to antiretroviral therapy. AIDS. 2015; 29:1391–1399. pmid:26091295
  14. 14. Jerene D, Næss A, Lindtjørn . Antiretroviral therapy at a district hospital in Ethiopia prevents death and tuberculosis in a cohort of HIV patients. AIDS Research Therapy 2006;3:10–15. pmid:16600050
  15. 15. Semu M, Fenta TG, Medhin G, Assefa D. Effectiveness of isoniazid preventative therapy in reducing incidence of active tuberculosis among people living with HIV/ AIDS in public health facilities of Addis Ababa, Ethiopia: a historical cohort study. BMC Infectious Diseases 2017;17: 5–12. pmid:28049455
  16. 16. Ahmed A, Mekonnen D, Shiferaw AM, Belayneh F, Yenit MK. Incidence and determinants of tuberculosis infection among adult patients with HIV attending HIV care in north-East Ethiopia: a retrospective cohort study. BMJ Open 2018;8: e016961. pmid:29437750
  17. 17. Dravid A, Natarajan K, Medisetty M, Gawali R, Mahajan U, Kulkarni M, et al. Incidence of tuberculosis among HIV infected individuals on long-term antiretroviral therapy in private healthcare sector in Pune, Western India. BMC Infectious Diseases 2019;19:714–726. pmid:31409289
  18. 18. Wong NS, Leung CC, Chan KCW, Chan WK, Lin AWC, Lee SS. A longitudinal study on latent TB infection screening and its association with TB incidence in HIV patients. Sci Reports 2019;9:10093–10100. pmid:31300686
  19. 19. Lawn SD, Myer L, Bekker LG, Wood R. Burden of tuberculosis in an antiretroviral treatment programme in sub-Saharan Africa: impact on treatment outcomes and implications for tuberculosis control. AIDS. 2006;20:1605–1612. pmid:16868441
  20. 20. Suthar AB, Lawn SD, del Amo J, Getahun H, Dye C, Sculier D, et al. Antiretroviral therapy for prevention of tuberculosis in adults with HIV: A systematic review and meta-analysis. PLoS Med 2012; 9: e1001270. pmid:22911011
  21. 21. Naidoo K, Karim QA, Bhushan A, Naidoo K, Yende-Zuma N, McHunu PK, et al. High rates of tuberculosis in patients accessing HAART in rural South Africa. J Acquir Immune Defic Syndr 2014;65:438–446. pmid:24256629
  22. 22. World Health Organization. Global Tuberculosis Report, 2018.
  23. 23. Lu W, Mehraj V, Vyboh K, Cao W, Routy JP. CD4:CD8 ratio as a frontier marker for clinical outcome, immune dysfunction and viral reservoir size in virologically suppressed HIV-positive patients. J Int AIDS Soc. 2015;18:20052. pmid:26130226
  24. 24. Plana M, Garcia F, Gallart T, et al. Immunological benefits of antiretroviral therapy in very early stages of asymptomatic chronic HIV-1 infection. AIDS 2000;14:1921–1933. pmid:10997396
  25. 25. Helleberg M, Kronborg G, Ullum H, Ryder LP, Obel N, Gerstoft J. Course and clinical significance of CD8 counts in a large HIV cohort. J Infect Dis 2015;211:1726–1734.
  26. 26. Buggert M, Frederiksen J, Noyan K, Svärd J, Barqasho B, Sönnerborg A, et al. Multiparametric bioinformatics distinguish the CD4/CD8 ratio as a suitable laboratory predictor of combined T cell pathogenesis in HIV infection. J Immunol 2014;192: 2099–2108. pmid:24493822
  27. 27. Wolday D, Hailu B, Girma M, Hailu E, Sanders E, Fontanet AL. Low CD4+ T-cell count and high HIV viral load precede the development of tuberculosis disease in a cohort of HIV-positive Ethiopians. Intern J Tubercle Lung Dis 2003; 7:110–116.
  28. 28. Serrano-Villar S, Gutiérrez C, Vallejo A, Hernández-Novoa B, Diaz L, Abad Fernández M, et al. The CD4/CD8 ratio in HIV-infected subjects is independently associated with T-cell activation despite long-term viral suppression. J Infect 2013;66:57–66. pmid:23046968
  29. 29. Federal Ministry of Health (MoH). HIV/AIDS Prevention and Control Office. National Guidelines for Use of Antiretroviral Drugs in Ethiopia. MoH, Addis Ababa, Ethiopia, 2001.
  30. 30. Federal Ministry of Health. National Tuberculosis and Leprosy Control Program Manual, MoH, Addis Ababa, Ethiopia, 2002.
  31. 31. Tsegaye A, Messele T, Tilahun T, Hailu E, Sahlu T, Doorly R, et al. Immunohematological reference ranges for adult Ethiopians. Clin Diag Lab Immunol 1999;6:410–14.
  32. 32. Kassu A, Tsegaye P, Petros B, Wolday D, Hailu E, Tilahun T,et al. Distribution of lymphocyte subsets in healthy human immunodeficiency virus-negative adult Ethiopians from two geographic locales. Clin Diag Lab Immunol 2001; 8: 1171–76.
  33. 33. Mussini C, Lorenzini P, Cozzi-Lepris A, Lapadula G, Marchetti G, Nicastri E, et al. CD4/CD8 ratio normalisation and non-AIDS-related events in individuals with HIV who achieve viral load suppression with antiretroviral therapy: an observational cohort study. Lancet 2015;2:e98–106. pmid:26424550
  34. 34. Tinago W, Coghlan E, Macken A, McAndrews J, Doak B, Prior-Fuller C, et al. Clinical, immunological and treatment-related factors associated with normalized CD4+/CD8+ T-cell ratio: effect of naive and memory T-cell subsets. PLoS One 2014; 9: e97011. pmid:24816636
  35. 35. Geremew D, Endalamaw A, Negash M, Eshetie S, Tessema B. The protective effect of isoniazid preventive therapy on tuberculosis incidence among HIV positive patients receiving ART in Ethiopian settings: a meta-analysis. BMC Infectious Diseases 2019;19:405–414. pmid:31077133
  36. 36. Khawcharoenporn T, Apisarnthanarak A, Manosuthi W, Sungkanuparph S, Mundy LM. Isoniazid preventive therapy and 4-year incidence of pulmonary tuberculosis among HIV infected Thai patients. Int J Tuberc Lung Dis 2012;16:336–341. pmid:22230143
  37. 37. Sabasaba A, Mwambi H, Somi G, Ramadhani A, Mahande MJ. Effect of isoniazid preventive therapy on tuberculosis incidence and associated risk factors among HIV infected adults in Tanzania: a retrospective cohort study. BMC Infect Dis 2019;19:62. pmid:30654753
  38. 38. Bock P, Jennings K, Vermaak R, Cox H, Meintjes G, Fatti G, et al. Incidence of tuberculosis among HIV-positive individuals initiating antiretroviral treatment at higher CD4 counts in the HPTN 071 (PopART) trial in South Africa. J Acquir Immune Defic Syndr 2018;77:93–101. pmid:29016524
  39. 39. Lawn SD, Bekker LG, Wood R. How effectively does HAART restore immune responses to mycobacterium tuberculosis? Implications for tuberculosis control. AIDS 2005;19:1113–1124. pmid:15990564
  40. 40. Fenner L, Atkinson A, Boulle A, Fox MP, Prozesky H, Zürcher K. HIV viral load as an independent risk factor for tuberculosis in South Africa: collaborative analysis of cohort studies. J Int AIDS Soc. 2017;20:21327. pmid:28691438
  41. 41. Martin-Echevarria E, Serrano-Villar S, Sainz T, Moreno A, Casado JL, Dronda F, et al. Development of tuberculosis in HIV-infected patients receiving antiretroviral therapy. Int J Tubercle Lung Dis 2014;18:1080–1084.
  42. 42. Kassa D, Gebremichael G, Alemayehu Y, Wolday D, Messele T, van Baarle D. Virological and immunological outcome of HAART in HIV-infected patients with and without tuberculosis (TB) and latent TB infection (LTBI) in Addis Ababa, Ethiopia. AIDS Res Therapy 2013;10:18–28.
  43. 43. Hsu DC, Kerr SJ, Thongpaeng P, Iampornsin T, Pett SL, Zaunders JJ, et al. Incomplete restoration of Mycobacterium tuberculosis-specific CD4 T-cell responses despite antiretroviral therapy. J Infect 2014;68:344–354. pmid:24325926
  44. 44. Karo B, Krause G, Castell S, Kollan C, Hamouda O, Hass W, et al. Immunological recovery in tuberculosis/HIV co-infected patients on antiretroviral therapy: implications for tuberculosis preventive therapy. BMC Infect Dis 2017;17:517–526. pmid:28743248
  45. 45. Kony SJ, Hane AA, Larouze’ B, Samb A, Cissoko S, et al. Tuberculosis associated severe CD4+ T-lymphocytopenia in HIV-seronegative patients from Dakar, SIDAK Research Group. J Infect 2000; 41: 167–171. pmid:11023763
  46. 46. Andersen AB, Range NS, Changalucha J, Praygod G, Kidola J, et al. CD4 lymphocyte dynamics in Tanzanian pulmonary tuberculosis patients with and without HIV co-infection. BMC Infect Dis 2012; 12: 66–73. pmid:22436147
  47. 47. Hermans SM, Kiragga AN, Schaefer P, Kampuga A, Hoepelman AM, et al. Incident tuberculosis during antiretroviral therapy contributes to suboptimal immune reconstitution in a large urban HIV clinic in Sub-Saharan Africa. PLoS ONE 2010; 5:e10527. pmid:20479873
  48. 48. Kassu A, Tsegaye A, Wolday D, Petros B, Aklilu M, Sanders EJ, et al. Role of incident and/or cured intestinal parasitic infections on profile of CD4+ and CD8+ T cell subsets and activation status in HIV-infected and uninfected adult Ethiopians. Clin Exp Immunol 2003;132:113–119. pmid:12653845
  49. 49. Mupfumi L, Moyo S, Molebatsi K, Thami PK, Anderson M, Mogashoa T, et al. Immunological non-response and low hemoglobin levels are predictors of incident tuberculosis among HIV-infected individuals on Truvada-based therapy in Botswana. PLoS ONE 2018;13:e0192030. pmid:29385208
  50. 50. Yirdaw KD, Teklu AM, Mamuye AT, Zewdu S. Breakthrough tuberculosis among people with HIV—Should we be worried? A retrospective longitudinal study. PLoS ONE 2019;14:e0211688. pmid:30716126