The Impact of HIV Infection and CD4 Cell Count on the Performance of an Interferon Gamma Release Assay in Patients with Pulmonary Tuberculosis

BACKGROUND:The performance of the tuberculosis specific Interferon Gamma Release Assays (IGRAs) has not been sufficiently documented in tuberculosis- and HIV-endemic settings. This study evaluated the sensitivity of the QuantiFERON TB-Gold In-Tube (QFT-IT) in patients with culture confirmed pulmonary tuberculosis (PTB) in a TB- and HIV-endemic population and the effect of HIV-infection and CD4 cell count on test performance. METHODOLOGY/PRINCIPAL FINDINGS:161 patients with sputum culture confirmed PTB were subjected to HIV- and QFT-IT testing and measurement of CD4 cell count. The QFT-IT was positive in 74% (119/161; 95% CI: 67-81%). Sensitivity was higher in HIV-negative (75/93) than in HIV-positive (44/68) patients (81% vs. 65%, p = 0.02) and increased with CD4 cell count in HIV-positive patients (test for trend p = 0.03). 23 patients (14%) had an indeterminate result and this proportion decreased with increasing CD4 cell count in HIV-positive patients (test for trend p = 0.03). Low CD4 cell count (<300 cells/microl) did not account for all QFT-IT indeterminate nor all negative results. Sensitivity when excluding indeterminate results was 86% (95% CI: 81-92%) and did not differ between HIV-negative and HIV-positive patients (88 vs. 83%, p = 0.39). CONCLUSIONS/SIGNIFICANCE:Sensitivity of the QFT-IT for diagnosing active PTB infection was reasonable when excluding indeterminate results and in HIV-negative patients. However, since the test missed more than 10% of patients, its potential as a rule-out test for active TB disease is limited. Furthermore, test performance is impaired by low CD4 cell count in HIV-positive patients and possibly by other factors as well in both HIV-positive and HIV-negative patients. This might limit the potential of the test in populations where HIV-infection is prevalent

Anti-tuberculosis drug resistance pattern among pulmonary tuberculosis patients with or without HIV infection in Mwanza, Tanzania

Anti-tuberculosis drug resistance is a major problem in tuberculosis (TB) control, particularly multi-drug resistance TB (MDR-TB). The objective of this study was to determine the prevalence of primary and acquired anti-TB drug resistance among newly diagnosed pulmonary TB (PTB) and relapse cases. Sputa were collected from newly diagnosed and relapse PTB patients. Drug susceptibility tests (DST) were performed on sputum culture positive isolates of Mycobacterium tuberculosis using resistance ratio method on four first-line anti-TB drugs: rifampicin, isoniazid, ethambutol and streptomycin. Demographic and anthropometric information was collected and HIV status was determined. Of the 523 culture positive isolates, DST results were available for 503 (96%), 455 were new and 48 were relapse cases. Resistance to at least one of the four drugs was observed in 7.8% (39/503) of the isolates, 7.3% (33/455) were new and 12.5% (6/48) were from relapse cases. Mono resistance to isoniazid was higher in both among new 45.5% (15/33) and relapse 50.0% (3/6) cases. Resistance to rifampicin and streptomycin alone was equal 4/33 (12.1%) and only among new cases. Resistance to ethambutol alone was only one among new cases. Overall MDR-TB prevalence was 2.4% (12/503), nine were new and three were relapse cases. MDR-TB was 17.9% (7/39) for rifampicin and isoniazid. Prevalence of HIV was 43.3% and was similar among new and relapse cases and not risk factor for drug resistance. Majority of PTB patients (52%) had BMI below 18 kg/m2. Those with BMI greater than 18 kg/m2 were more likely to develop drug resistance than those with BMI below 18 kg/m2  (P=0.004). With the resurgence of TB and the high prevalence of HIV among TB patients, prevalence of drug resistance is still low both among new and relapses cases. Despite the current low drug resistance, there is a need for continuous monitoring of the resistance

Anti-tuberculosis drug resistance pattern among pulmonary tuberculosis patients with or without HIV infection in Mwanza, Tanzania

Anti-tuberculosis drug resistance is a major problem in tuberculosis (TB) control, particularly multi-drug resistance TB (MDR-TB). The objective of this study was to determine the prevalence of primary and acquired anti-TB drug resistance among newly diagnosed pulmonary TB (PTB) and relapse cases. Sputa were collected from newly diagnosed and relapse PTB patients. Drug susceptibility tests (DST) were performed on sputum culture positive isolates of Mycobacterium tuberculosis using resistance ratio method on four first-line anti-TB drugs: rifampicin, isoniazid, ethambutol and streptomycin. Demographic and anthropometric information was collected and HIV status was determined. Of the 523 culture positive isolates, DST results were available for 503 (96%), 455 were new and 48 were relapse cases. Resistance to at least one of the four drugs was observed in 7.8% (39/503) of the isolates, 7.3% (33/455) were new and 12.5% (6/48) were from relapse cases. Mono resistance to isoniazid was higher in both among new 45.5% (15/33) and relapse 50.0% (3/6) cases. Resistance to rifampicin and streptomycin alone was equal 4/33 (12.1%) and only among new cases. Resistance to ethambutol alone was only one among new cases. Overall MDR-TB prevalence was 2.4% (12/503), nine were new and three were relapse cases. MDR-TB was 17.9% (7/39) for rifampicin and isoniazid. Prevalence of HIV was 43.3% and was similar among new and relapse cases and not risk factor for drug resistance. Majority of PTB patients (52%) had BMI below 18 kg/m2. Those with BMI greater than 18 kg/m2 were more likely to develop drug resistance than those with BMI below 18 kg/m2 (P=0.004). With the resurgence of TB and the high prevalence of HIV among TB patients, prevalence of drug resistance is still low both among new and relapses cases. Despite the current low drug resistance, there is a need for continuous monitoring of the resistance

Association of risk factors with an indeterminate QuantiFERON-TB® Gold In-tube result.

<p>A total of 23 out of 161 patients (14%) had a QFT-IT indeterminate result. No differences were found in OR when comparing QFT-IT positive and negative patients. OR: Odds Ratio. CI: Confidence interval. BMI: Body Mass Index. Age of 33 years and lymphocyte count of 1640 cells/µl represents medians for all patients. 3+ AFB by sputum smear microscopy: More than 10 acid fast bacilli (AFB) per field.</p

QuantiFERON-TB® Gold In-tube results for all study participants and according to HIV status.

<p>QFT-IT: QuantiFERON-TB® Gold In-tube test.</p>*<p>p-value for difference between HIV-negative and HIV–positive patients.</p

Antigen dependent and mitogen induced absolute IFN-γ levels by QuantiFERON-TB® Gold In-tube test result in HIV-negative and HIV-positive patients respectively.

<p>Horisontal lines represent medians. Dotted lines represent the applied cut-off values as recommended by the manufacturer: 0.35 IU/ml for antigen (ESAT-6, CFP-10, TB7.7) dependent IFN-γ production and 0.50 IU/ml for mitogen (PHA) induced IFN-γ production respectively. The assay is not able to quantify values above 10 IU/ml why values above this limit were assigned the value 10 IU/ml. No significant differences in median levels between HIV-positive and HIV-negative were observed.</p

Influence of CD4 cell count on performance of the QuantiFERON-TB® Gold In-tube test in HIV-positive patients.

<p>For HIV-positive patients the % of indeterminate and positive test responders respectively was grouped by the individual number of CD4 cells/µl. P-values are for Cochrane-Armitage test for trend. A similar relationship was not found in HIV-negative patients. The number of patients in each CD4 cell group was: 0–99: 5, 100–199: 17, 200–299: 20, 300–399∶6, 400–499∶6, >500∶14. QFT-IT: QuantiFERON-TB® Gold In-tube test.</p

Antigen dependent and mitogen induced absolute IFN-γ levels by HIV-status and CD4 cell count group.

<p>Horisontal lines represent medians with interquartile range. Dotted lines represent the applied cut-off values as recommended by the manufacturer: 0.35 IU/ml for antigen (ESAT-6, CFP-10, TB7.7) dependent IFN-γ production and 0.50 IU/ml for mitogen (PHA) induced IFN-γ production respectively. The assay is not able to quantify values above 10 IU/ml why values above this limit were assigned the value 10 IU/ml.</p