CULTURE OR PCR WHAT IS BEST FOR AFRICA? Peter R Mason BRTI
TB IN AFRICA GLOBAL 9 MILLION NEW CASES/YR 1.5 MILLION TB DEATHS AFRICA 95% TB DEATHS IN LMIC 9/22 HIGH BURDEN COUNTRIES IN AFRICA STRONG LINK BETWEEN HIV AND TB
TB OR NOT TB CLASSICAL DIAGNOSTICS SYMPTOMS CHEST X-RAY MICROSCOPY ZN CULTURE? SOLID
WHAT DO WE MEAN BY BEST? RELIABILITY SENSITIVITY SPECIFICITY ACCESSIBILITY POINT OF CARE TIME TO DETECTION COST AFFORDABLE IN SETTING OF HIGH HIV BURDEN POOR INFRASTRUCTURE
RELIABILITY SENSITIVITY DETECT ALL CASES SPECIFICITY DETECTED CASES REALLY ARE TB
WHAT ARE THE CONSEQUENCES? LOW SENSITIVITY CASES REMAIN UNDIAGNOSED INFECTIOUS TO OTHERS HIGH RISK OF MORTALITY LOW SPECIFICITY OVERUSE OF TB DRUGS IN COMMUNITY INCREASED RISK OF EMERGENCE OF MDR-TB
WHAT IS BEST? HIGH SENSITIVITY RAPID AFFORDABLE ACCESSIBLE DOTS CAN COMPENSATE FOR LOW SPECIFICITY
HOW TO MEASURE AFFORDABILITY? COST OF MATERIALS INCL. COST OF REJECTED/FAILED MEDIA COST OF PERSONNEL SPECIALISED TRAINING COST OF INFRASTRUCTURE LABORATORY EQUIPMENT SAFETY QUALITY COST PER CASE DETECTED WHICH SPECIMEN COST OF COLLECTION COST OF EXAMINATION COST PER PATIENT ON Rx INCLUDING DEFAULTERS
ESTIMATED COSTS (WHO) LABORATORY INFRASTRUCTURE $200,000 CONSUMABLES >$25 PER SPECIMEN FOR CULTURE TRAINING $20,000 PER PERSON EQA $5,000 PER YEAR SALARIES FOR MIN. 2 LAB STAFF
HOW DO WE MEASURE ACCESSIBILITY? MOST TB CASES IN POORER COMMUNITIES ACCESS TO DIAGNOSTIC FACILITY SIMPLER THE BETTER
WHAT ARE OUR OPTIONS? CLINICAL + CXR MICROSCOPY CULTURE MOLECULAR OTHER
HOW GOOD ARE STANDARD DIAGNOSTIC SCREENS? ACTG STUDY 80 (Swindells et al, IJ TB Lung Dis, 2013) 70 60 Symptom-based screening with smear microscopy was insufficiently sensitive. More sensitive diagnostic testing is required for HIVinfected patients. 50 40 30 20 10 0 SOC screen Sensitivity Specifiity
DELAY IN ACCESS TO TREATMENT MEDIAN DAYS DELAY PATIENT 30 (20-60) DIAGNOSTIC 7 (3-28) TREATMENT 3 (1-4) TOTAL 45 (35-70) Asefa A, Teshome W. PLoS ONE 2014
MICROSCOPY ADVANTAGES RAPID TRAINING HIGH SPECIFICITY (85-95%) LOW COST (<$1) ACCESSIBLE DISADVANTAGES LOW SENSITIVITY (35-75%) ESP. PAUCIBACILLARY ESP. IN HIV HIGH OPERATOR VARIANCE LABOUR INTENSIVE LOW THROUGHPUT
HOW CAN WE IMPROVE MICROSCOPY? SPECIMEN AND PROCESSING STAINS READING
SPECIMENS STANDARD SPOT SPUTUM MORNING SPUTUM ALTERNATIVES SPUTUM INDUCTION USING LIQUID CULTURE AS GOLD STANDARD DIAGNOSTIC YIELD OF INDUCTION +0.7% (-7 - +8.5%) AGAINST SPOT +4.7% (-3.2 - +12.5%) AGAINST MORNING Geldenhuys et al. PLoS ONE 2014
STAINS FLUORESCENCE INCR. SENSITIVITY BY UP TO 10% REDUCES TIME TO DETECTION REDUCES WORK LOAD INCREASES THROUGHPUT LED MICROSCOPY BATTERY POWER LONG LIFE USE IN DAYLIGHT COMMUNITY DIAGNOSIS
MICROSCOPY AFFORDABLE ACCESSIBLE RAPID 50 40 Sens (%) BUT LOW SENSITIVITY EVEN WITH MODIFICATIONS, ESP. IN HIV CO-INFECTION (Alfred et al, BMJ Open 2014) 30 20 10 0 Direct ZN Direct Fluor LED
CULTURE STANDARD APPROACH IN BACTERIOLOGY BUT LONG DIVISION TIME (20hrs) SLOW GROWTH SAFETY
STANDARD CULTURE SOLID MEDIA EGG-BASED e.g. LOWENSTEIN JENSEN SENSITIVITY 85-95% SPECIFICITY 93-100% MATERIAL COST $5-12
LJ CULTURE ADVANTAGES HIGH SENSITIVITY IN CLINICAL SPECIMENS (10-100 bacteria/ml) DRUG SENSITIVITY PERMANENT DISADVANTAGES LABOUR INTENSIVE LOW THROUGHPUT SLOW GROWTH 6-8 WEEKS SAFETY ISSUES SPECIAL INFRASTRUCTURE & TRAINING
ALTERNATIVES MGIT MODS
BACTEC MGIT (MYCOBACTERIUM GROWTH INDICATOR TUBE) LIQUID CULTURE (MIDDLEBROOK 7H9 BROTH + ENHANCEMENT + ANTIBIOTIC) FLOURESCENT DETECTION OF BACTERIAL GROWTH AUTOMATED OR MANUAL DETERMINATION OF FLUORESENCE UNDER UV
BACTEC MGIT INCREASED DIAGNOSTIC YIELD LJ 23% MGIT 30% MGIT smear - MGIT-smear + Days (Chihota et al, IJ TB Lung Dis, 2010) LJ DECREASED TIME TO DETECTION 0 10 20 30
MODS (MICROSCOPICALLY OBSERVED DRUG SUSCEPTIBILITY) THIN LAYER SOLID MEDIA GROWTH DETECTED BY MICROSCOPY ADAPTED TO DRUG SUSCEPTIBILITY ASSAY
MODS ZIMBABWE (vs MGIT) SENSITIVITY 85% (69-95%) SPECIFICITY 93% (84-98%) MEDIAN TTD 7 days (MGIT 12d; LJ-28d) Makamure et al. PLoS ONE 2013
MODS IN HIV SETTINGS ALL CULTURES SENSITIVITY 88% (86-90%) SPECIFICITY 100% (95-100%) MEDIAN TTD 8 days SMEAR NEGATIVE SENSITIVITY 88% (86-90%) SPECIFICITY 98% (96-99%) Systematic Review: Wikman-Ingesen (Mozambique) BMC Inf Dis 2014
MODS KITS TTD Specifity Sensitivity 0 50 100
MOLECULAR METHODS IN HOUSE PCR MOSTLY BASED ON IS6110 LARGE INTER-LABORATORY VARIABILITY GENE XPERT MTB/RIF AUTOMATED RAPID SAFE RESISTANCE TO RIFAMPICIN
GENE XPERT MTB/RIF
RELIABILITY 18 STUDIES > 10,000 SPECIMENS >3,000 TB POSITIVE >6,000 SMEAR & CULTURE NEGATIVE 100 80 60 % Average sensitivity for diagnosis of TB: 90.4% Average specificity for diagnosis of TB : 98.4% Chang et al, J Infection 2012 40 20 0 Sensitivity Specificity
IN TERTIARY CARE SETTINGS ZAMBIA COMPARED WITH CULTURE POSITIVE O Grady et al. Clin Inf Dis 2012 100 80 60 40 20 0 % Sensitivity Specificity Sputum -ve
IN PRIMARY CARE SETTINGS MULTI-CENTRE STUDY IN SOUTHERN AFRICA COMPARING MTB/Rif & FM AT PoC 100 80 60 40 20 0 Sensitivity Specificity Theron et al, Lancet, 2014
ADVANTAGE OF PoC TESTING SAME DAY DIAGNOSIS 40 SAME DAY TREATMENT INITIATION 20 MTB/Rif FM Theron et al, Lancet, 2014 0 Same day DX Same day Rx
GENE XPERT MTB/Rif ADVANTAGES RAPID SAME DAY RESULT ACCESSIBLE CAN BE USED AT POINT OF CARE RELIABLE HIGH SENSITIVITY & SPECIFICITY DISADVANTAGES COST ANNUAL MAINTENANCE SHELF LIFE POWER SUPPLY
WHEN TO USE GXP MTB/Rif? SYSTEMATIC REVIEW 27 STUDIES REPLACE ZN ADD ON TO ZN (smear negatives) 100 80 60 40 20 0 Sensitivity Specificity Steingard etal, Cochrane DB Sys Rev 2014
WHO RECOMMENDATION (2011) GXP MTB/Rif DOES NOT PRECLUDE THE NEED FOR OTHER ASSAYS MICROSCOPY & CULTURE HAVE A ROLE TO PLAY GXP MTB/Rif CAN REPLACE MICROSCOPY HIGH RISK OF HIV HIGH RISK OF MDR IN OTHER SITUATIONS ADD ON IS MORE APPROPRIATE
OTHERS NOVEL APPROACHES RATS (CRICETOMYS) IMMUNOLOGICAL APPROACHES INTERFERON GAMMA LIPOARABINOMANNAN NEW ANTIGENS
INTERFERON GAMMA (IGRA) USEFUL FOR DETECTION OF LATENT TB LESS VALUE IN DETECTION OF ACTIVE TB ESP. IN HIV LOWER SPECIFICITY THAN OTHERS
LAM URINARY EXCRETION OF LAM HIGHLY VARIABLE FINDINGS SENSITIVITY 6% TO 81% SENSITIVITY USUALLY HIGHEST IN HIV-INFECTED PATIENTS WITH LOW CD4 COUNTS
NEW ANTIGENS IMMUNODOMINANT PEPTIDE ANTIGENS USING DIFFERENT ANTIGEN COMBINATIONS, SENSITIVITY & SPECIFICITY >90% LATERAL FLOW ASSAYS UNDER DEVELOPMENT Gonzalez et al, PLoS One, 2014
THE FUTURE?