Andrew D. Kerkhoff

Diagnostic accuracy of a low-cost, urine antigen, point-of-care screening assay for HIV-associated pulmonary tuberculosis before antiretroviral therapy: a descriptive study.

Summary Background The diagnostic accuracy of sputum smear microscopy and routine chest radiology for HIV-associated tuberculosis is poor, and culture-based diagnosis is slow, expensive, and is unavailable in most resource-limited settings. We assessed the diagnostic accuracy of a urine antigen test Determine TB-LAM Ag (Determine TB-LAM; Alere, Waltham, MA, USA) for screening for HIV-associated pulmonary tuberculosis before antiretroviral therapy (ART). Methods In this descriptive study, consecutive adults referred to a community-based ART clinic in Gugulethu township, South Africa, were all screened for tuberculosis by obtaining sputum samples for fluorescence microscopy, automated liquid culture (gold-standard test), and Xpert MTB/RIF assays (Cepheid, Sunnyvale, CA, USA) and urine samples for the Clearview TB-ELISA (TB-ELISA; Alere, Waltham, MA, USA) and Determine TB-LAM test. Patients with Mycobacterium tuberculosis cultured from one or more sputum samples were defined as cases of tuberculosis. The diagnostic accuracy of Determine TB-LAM used alone or combined with sputum smear microscopy was compared with that of sputum culture and the Xpert MTB/RIF assay for all patients and subgroups of patients stratified by CD4 cell count. Findings Patients were recruited between March 12, 2010, and April 20, 2011. Of 602 patients enrolled, 542 were able to provide one or more sputum samples, and 94 had culture-positive tuberculosis (prevalence 17·4%, 95% CI 14·2–20·8). Complete results from all tests were available for 516 patients (median CD4 count, 169·5 cells per μL; IQR 100–233), including 85 culture-positive tuberculosis, 24 of whom (28·2%, 95% CI 19·0–39·0) had sputum smear-positive disease. Determine TB-LAM test strips provided results within 30 min. Agreement was very high between two independent readers of the test strips (κ=0·97) and between the test strips and TB-ELISA (κ=0·84). Determine TB-LAM had highest sensitivity at low CD4 cell counts: 66·7% (95% CI 41·0–86·7) at <50 cells per μL, 51·7% (32·5–70·6) at <100 cells per μL, and 39·0% (26·5–52·6) at <200 cells per μL; specificity was greater than 98% for all strata. When combined with smear microscopy (either test positive), sensitivity was 72·2% (95% CI 46·5–90·3) at CD4 counts less than 50 cells per μL, 65·5% (45·7–82·1) at less than 100 cells per μL, and 52·5% (39·1–65·7) at less than 200 cells per μL, which did not differ statistically from the sensitivities obtained by testing a single sputum sample with the Xpert MTB/RIF assay. Interpretation Determine TB-LAM is a simple, low-cost, alternative to existing diagnostic assays for tuberculosis screening in HIV-infected patients with very low CD4 cell counts and provides important incremental yield when combined with sputum smear microscopy. Funding Wellcome Trust.

Characteristics and Early Outcomes of Patients With Xpert MTB/RIF-Negative Pulmonary Tuberculosis Diagnosed During Screening Before Antiretroviral Therapy

Comparison of the characteristics of HIV-infected patients with Xpert-positive and Xpert-negative tuberculosis and relationship of Xpert status with subsequent clinical and programmatic outcomes.

Determine TB-LAM lateral flow urine antigen assay for HIV-associated tuberculosis: recommendations on the design and reporting of clinical studies.

Detection of the Mycobacterium tuberculosis cell wall antigen lipoarabinomannan (LAM) in urine permits diagnoses of tuberculosis (TB) to be made in HIV-infected patients with advanced immunodeficiency. This can be achieved at the point-of-care within just 30 minutes using the Determine TB-LAM, which is a commercially available, lateral-flow urine ‘strip test’ assay. The assay has been shown to have useful diagnostic accuracy in patients enrolling in antiretroviral treatment services or in HIV-infected patients requiring admission to hospital medical wards in sub-Saharan Africa. Such patients have high mortality risk and have most to gain from rapid diagnosis of TB and immediate initiation of treatment. However, few studies using this assay have yet been reported and many questions remain concerning the correct use of the assay, interpretation of results, the role of the assay as an add-on test within existing diagnostic algorithms and the types of further studies needed. In this paper we address a series of questions with the aim of informing the design, conduct and interpretation of future studies. Specifically, we clarify which clinical populations are most likely to derive benefit from use of this assay and how patients enrolled in such studies might best be characterised. We describe the importance of employing a rigorous microbiological diagnostic reference standard in studies of diagnostic accuracy and discuss issues surrounding the specificity of the assay in different geographical areas and potential cross-reactivity with non-tuberculous mycobacteria and other organisms. We highlight the importance of careful procedures for urine collection and storage and the critical issue of how to read and interpret the test strips. Finally, we consider how the assay could be used in combination with other assays and outline the types of studies that are required to build the evidence base concerning its use.

Clinical significance of lipoarabinomannan detection in urine using a low-cost point-of-care diagnostic assay for HIV-associated tuberculosis.

Objective:A low-cost point-of-care urine assay for lipoarabinomannan (LAM) used for screening patients prior to antiretroviral therapy (ART) rapidly diagnoses a proportion of tuberculosis (TB) cases. We determined the characteristics and outcomes of such patients. Methods:Adults enrolling in a South African township ART clinic were systematically screened for pulmonary TB by testing paired sputum samples using microscopy, liquid culture and Xpert MTB/RIF in a centralized laboratory. Stored urine samples were retrospectively tested for LAM using the Determine TB-LAM assay, but results did not inform treatment. Patients were followed up in the routine ART service and early (90-day) programmatic outcomes were determined. Analysis was restricted to those with CD4 cell counts below 200 cells/&mgr;l. Results:Of patients with CD4 cell counts below 200 cells/&mgr;l and complete results (n = 325), 59 (18.2%) had culture-positive TB. Of these, 23 (39%) patients tested urine LAM-positive and 36 (61%) urine LAM-negative. Patients with LAM-positive TB had much lower CD4 cell counts, higher plasma viral loads, lower haemoglobin concentrations and lower BMIs compared to those with LAM-negative TB. They also had evidence of higher mycobacterial load, more frequently testing sputum smear-positive, Xpert-positive (sputum and urine) and having a shorter time to sputum culture positivity. Of five (8.5%) patients who died, four did so before TB treatment was started. All five retrospectively tested LAM-positive. Conclusions:A low-cost point-of-care urine test for LAM rapidly diagnoses a sub-group of cases with advanced HIV-associated TB and poor prognosis. If used in combination with laboratory-based diagnostics, treatment delays would decrease and survival might be improved.

High diagnostic yield of tuberculosis from screening urine samples from HIV-infected patients with advanced immunodeficiency using the Xpert MTB/RIF assay.

Abstract:We determined the diagnostic yield of the Xpert MTB/RIF assay for tuberculosis (TB) when testing small volumes of urine from ambulatory HIV-infected patients before starting antiretroviral therapy in South Africa. Compared with a gold standard of sputum culture, the sensitivity of urine Xpert among those with CD4 cell counts of <50, 50–100, and >100 cells per microliter were 44.4%, 25.0%, and 2.7% (P = 0.001), respectively. Urine Xpert testing provides a means of rapid TB diagnosis in patients with advanced immunodeficiency and poor prognosis. These data are indicative of high rates of TB dissemination and renal involvement in this clinical population.

HIV-associated tuberculosis: relationship between disease severity and the sensitivity of new sputum-based and urine-based diagnostic assays

BackgroundReducing mortality from HIV-associated tuberculosis (TB) requires diagnostic tools that are rapid and have high sensitivity among patients with poor prognosis. We determined the relationship between disease severity and the sensitivity of new sputum-based and urine-based diagnostic assays.MethodsConsecutive ambulatory patients enrolling for antiretroviral treatment in South Africa were screened for TB regardless of symptoms using diagnostic assays prospectively applied to sputum (fluorescence smear microscopy, Xpert MTB/RIF and liquid culture (reference standard)) and retrospectively applied to stored urine samples (Determine TB-LAM and Xpert MTB/RIF). Assay sensitivities were calculated stratified according to pre-defined indices of disease severity: CD4 count, symptom intensity, serum C-reactive protein (CRP), hemoglobin concentration and vital status at 90 days.ResultsSputum culture-positive TB was diagnosed in 15% (89/602) of patients screened and data from 86 patients were analyzed (median CD4 count, 131 cells/μL) including 6 (7%) who died. The sensitivity of sputum microscopy was 26.7% overall and varied relatively little with disease severity. In marked contrast, the sensitivities of urine-based and sputum-based diagnosis using Determine TB-LAM and Xpert MTB/RIF assays were substantially greater in sub-groups with poorer prognosis. Rapid diagnosis from sputum and/or urine samples was possible in >80% of patients in sub-groups with poor prognosis as defined by either CD4 counts <100 cells/μL, advanced symptoms, CRP concentrations >200 mg/L or hemoglobin <8.0 g/dl. Retrospective testing of urine samples with Determine TB-LAM correctly identified all those with TB who died.ConclusionsThe sensitivities of Xpert MTB/RIF and Determine TB-LAM for HIV-associated TB were highest among HIV-infected patients with the most advanced disease and poorest prognostic characteristics. These data provide strong justification for large-scale intervention studies that assess the impact on survival of screening using these new sputum-based and urine-based diagnostic approaches.

Diagnostic and prognostic value of serum C-reactive protein for screening for HIV-associated tuberculosis.

BACKGROUND Rapid means of ruling in or ruling out tuberculosis (TB) would permit more efficient management of patients starting antiretroviral treatment (ART). OBJECTIVE To assess the diagnostic and prognostic utility of C-reactive protein (CRP) among patients being screened for TB before ART in a South African ART clinic. DESIGN Patients were microbiologically screened for TB regardless of symptoms; serum CRP was measured, and mortality at 3 months was assessed. RESULTS Among 496 patients (median CD4 count 171 cells/l), culture-positive TB was diagnosed in 81 (16.3%). CRP concentrations were much higher among TB cases (median 57.8 mg/l, IQR 20.0202.7) than in those without TB (6.4 mg/l, IQR 2.121.8, P < 0.001). Very low (<1.5 mg/l) CRP concentrations excluded TB (100% negative predictive value), whereas very high concentrations (>400 mg/l) were strongly predictive of TB (100% positive predictive value). However, these thresholds encompassed only 14.3% and 2.0%, respectively, of all patients screened and identified only 12.3% of TB cases. CRP concentrations ≥50 mg/l were associated with poor prognostic characteristics, higher mycobacterial load, disseminated disease and greater mortality risk. CONCLUSION CRP concentrations identified groups of patients with very high or very low TB risk, but only in an unacceptably small minority of patients screened. However, in those with confirmed TB, CRP concentrations had useful prognostic value.

Rapid microbiological screening for tuberculosis in HIV-positive patients on the first day of acute hospital admission by systematic testing of urine samples using Xpert MTB/RIF: a prospective cohort in South Africa

BackgroundAutopsy studies of HIV/AIDS-related hospital deaths in sub-Saharan Africa reveal frequent failure of pre-mortem diagnosis of tuberculosis (TB), which is found in 34–64 % of adult cadavers. We determined the overall prevalence and predictors of TB among consecutive unselected HIV-positive adults requiring acute hospital admission and the comparative diagnostic yield obtained by screening urine and sputum samples obtained on day 1 of admission with Xpert MTB/RIF (Xpert).MethodsTo determine overall TB prevalence accurately, comprehensive clinical sampling (sputum, urine, blood plus other relevant samples) was done and TB was defined by detection of Mycobacterium tuberculosis in any sample using Xpert and/or mycobacterial liquid culture. To evaluate a rapid screening strategy, we compared the diagnostic yield of Xpert testing sputum samples and urine samples obtained with assistance from a respiratory study nurse in the first 24 h of admission.ResultsUnselected HIV-positive acute adult new medical admissions (n = 427) who were not receiving TB treatment were enrolled irrespective of clinical presentation or symptom profile. From 2,391 cultures and Xpert tests done (mean, 5.6 tests/patient) on 1,745 samples (mean, 4.1 samples/patient), TB was diagnosed in 139 patients (median CD4 cell count, 80 cells/μL). TB prevalence was very high (32.6 %; 95 % CI, 28.1–37.2 %; 139/427). However, patient symptoms and risk factors were poorly predictive for TB. Overall, ≥1 non-respiratory sample(s) tested positive in 115/139 (83 %) of all TB cases, including positive blood cultures in 41/139 (29.5 %) of TB cases. In the first 24 h of admission, sputum (spot and/or induced samples) and urine were obtainable from 37.0 % and 99.5 % of patients, respectively (P <0.001). From these, the proportions of total TB cases (n = 139) that were diagnosed by Xpert testing sputum, urine or both sputum and urine combined within the first 24 h were 39/139 (28.1 %), 89/139 (64.0 %) and 108/139 (77.7 %) cases, respectively (P <0.001).ConclusionsThe very high prevalence of active TB and its non-specific presentation strongly suggest the need for routine microbiological screening for TB in all HIV-positive medical admissions in high-burden settings. The incremental diagnostic yield from Xpert testing urine was very high and this strategy might be used to rapidly screen new admissions, especially if sputum is difficult to obtain.

HIV-Related Medical Admissions to a South African District Hospital Remain Frequent Despite Effective Antiretroviral Therapy Scale-Up.

AbstractThe public sector scale-up of antiretroviral therapy (ART) in South Africa commenced in 2004. We aimed to describe the hospital-level disease burden and factors contributing to morbidity and mortality among hospitalized HIV-positive patients in the era of widespread ART availability.Between June 2012 and October 2013, unselected patients admitted to medical wards at a public sector district hospital in Cape Town were enrolled in this cross-sectional study with prospective follow-up. HIV testing was systematically offered and HIV-infected patients were systematically screened for TB. The spectrum of admission diagnoses among HIV-positive patients was documented, vital status at 90 and 180 days ascertained and factors independently associated with death determined.Among 1018 medical admissions, HIV status was ascertained in 99.5%: 60.1% (n = 609) were HIV-positive and 96.1% (n = 585) were enrolled. Of these, 84.4% were aware of their HIV-positive status before admission. ART status was naive in 35.7%, current in 45.0%, and interrupted in 19.3%. The most frequent primary clinical diagnoses were newly diagnosed TB (n = 196, 33.5%), other bacterial infection (n = 100, 17.1%), and acquired immunodeficiency syndrome (AIDS)-defining illnesses other than TB (n = 64, 10.9%). By 90 days follow-up, 175 (29.9%) required readmission and 78 (13.3%) died. Commonest causes of death were TB (37.2%) and other AIDS-defining illnesses (24.4%). Independent predictors of mortality were AIDS-defining illnesses other than TB, low hemoglobin, and impaired renal function.HIV still accounts for nearly two-thirds of medical admissions in this South African hospital and is associated with high mortality. Strategies to improve linkage to care, ART adherence/retention and TB prevention are key to reducing HIV-related hospitalizations in this setting.

Predictive value of anemia for tuberculosis in HIV-infected patients in sub-Saharan Africa: An indication for routine microbiological investigation using new rapid assays

Background:The relationship between anemia and undiagnosed tuberculosis (TB) in patients living with HIV in sub-Saharan Africa is incompletely defined. We assessed the prevalence of TB among those with HIV-related anemia and evaluated new means of rapid TB diagnosis. Methods:Blood hemoglobin levels were measured in unselected antiretroviral treatment–naive patients in Cape Town, South Africa, and anemia was classified according to World Health Organization criteria. All patients were screened for TB by testing paired sputum samples using liquid culture (reference standard), fluorescence microscopy, and Xpert MTB/RIF. Urine samples were tested for lipoarabinomannan (LAM) using the Determine TB-LAM diagnostic assay. Results:Of 602 adults screened, 485 had complete results. Normal hemoglobin levels were found in 44.5% (n = 216) of patients, and mild, moderate, or severe anemia were present in 24.9% (n = 121), 25.4% (n = 123) and 5.2% (n = 25) of patients, respectively. Culture-confirmed pulmonary TB was diagnosed in 8.8% (19/216) of those without anemia compared with 16.5% (20/121), 26.0% (32/123), and 40.0% (10/25) among those with mild, moderate, or severe anemia, respectively (P < 0.001). Anemia was a strong independent predictor of TB. The sensitivities of diagnostic assays were much higher among those with moderate/severe anemia compared with those with no/mild anemia using sputum microscopy (42.9% vs 15.4%), urine LAM (54.8% vs 0%), sputum microscopy plus urine LAM (71.4% vs 15.4%), and sputum Xpert (73.8% vs 41.0%) (P < 0.01 for all). Conclusions:A very high prevalence of undiagnosed TB was found in patients with moderate or severe anemia. Such patients should be prioritized for routine microbiological investigation using rapid diagnostic assays.