TB/HIV 2 sides of the same coin Dr. Shamma Shetye, MD Microbiology Metropolis Healthcare, Mumbai
Global- Tb new cases
Diagnosis-Microscopy ZN,Flourescent microscopy(fm) Rapid, inexpensive test Specificity>95% FM Increased sensitivity by 10% At least 2 sputum samples Sputum,not saliva RNTCP grading for reporting EP samples are generally paucibacillary. Speciation,dead bacilli Quality assurance and competency
WHO recommendations At least 2 deep sputum samples Same day approach 1 st AFB smear 80-82 % 2 nd AFB smear 90-94 % 3 rd AFB smear 95-98% FM Increased sensitivity by 10% LED microscopy recommended
Nucleic Acid AmplificationTest Gen probe AMTD (TMA-rRNA) Roche Taqman High specificity and PPV Sensitivity lowered in EP and smear negative samples. Not to be used in follow-up patients. Site specific sample important No swabs, blood not indicated for active pulmonary TB
In-house(Home brew) PCR results are highly variable. False positivity/lack of reproducibility is a concern
Xpert (Cepheid) Automated Hemi-nested PCR. Results in 2 hours Simultaneously Detects TB and RIF resistance.
Summary of updated Cochrane review Used as an initial test(dst),xpert detected 95% of Rifampicin resistant cases, with a specificity of 98%. Overall, Xpert detected 88% of TB cases, with specificity of 98%,as compared to culture. Steingart KR et al
Extra- pulmonary specimens Systematic reviews(20+ studies) Xpert: Good sensitivity vs. culture Lymph node aspirates Gastric fluid CSF Tissue biopsy Other body fluids-low to moderate sensitivity
TB Culture: solid/liquid Solid Liquid (MGIT 960)
Diagnosis -Culture Gold standard and most specific for a definitive diagnosis of active TB. Isolate for Identification of Mycobacteria species (M.tuberculosis complex /NTM) Phenotypic (& genotypic) susceptibility Ideal in EPTB and smear negatives. Culture always recommended along with molecular assays.
Rapid Culture Solid culture-lj Liquid culture Bactec, MGIT 960,Versatrek,BacTalert Faster time to detection 7-10 days (upto 6 weeks) Improved positivity rates Recommended : Solid + liquid culture (Contamination,Mixed,Backup)
Rapid liquid culture & DST BSL3 facility with negative pressure Decontamination of specimens Stringent quality assurance RNTCP/CAP/EQA Proficiency testing Quality indicators Contamination rates Positivity rates
Identification Culture Report: M. Tuberculosis complex OR Mycobacteria other than M. Tuberculosis complex Mycobacteria species is unacceptable MPT64 Ag based(from culture) Molecular LPA for definitive identification
Phenotypic susceptibility Proportion method Automated liquid culture DST-1-3 weeks 1 st line DST 2 nd line: more complex Automated liquid DST is gold standard Laboratory Quality assurance-proficiency testing, accreditation Critical concentrations
Drug Susceptibility Testing What to treat with- What not to use- Mono resistance, MDR,XDR,XXDR Treatment history is very important for the laboratory for result correlation.. Low and high level concentrations may be tested.. Isoniazid, Ethionamide.
Drug-Resistant TB: Definitions Mono-resistant: resistance to a single drug Poly-resistant: resistance to more than one drug, but not to the combination of isoniazid and rifampicin Multidrug-resistant (MDR): resistance to at least isoniazid and rifampicin Extensively drug-resistant (XDR): MDR plus resistance to fluoroquinolones and at least 1 of the 3 injectable drugs (amikacin, kanamycin, capreomycin)
3.7% MDR ( new cases)& 20% (previously treated) By March 2013-84 countries have reported atleast one XDR case. 0.5 million cases of MDR (2011) 60% in BRICS 48% of MDR cases successfully treated 2011-2015-One million MDR cases for detection.
Rapid molecular TB detection & RIF resistance Xpert system(m.tb detection & RIF resistance) Strongly recommended to be used as the initial diagnostic test in individuals suspected of having MDR-TB or HIV associated TB. May also be used as a follow-on test to microscopy esp. smear negatives.
MDR screen by Line Probe Assays Genotype MTB DR plus assay(hain Lifesciences): Isoniazid and Rifampicin as markers for MDR. rpo B mutations-rifampicin resistance inh A-low level Isoniazid resistance kat G high level isoniazid resistance
Each strip consists of 27 reaction zones (bands), including six controls (conjugate, amplification, M. tuberculosis complex, rpob, katg and inha controls), eight rpob wild-type (WT) and four mutant (MUT) probes, one katg wild-type and 2 mutant probes, and two inha wild-type(wt) and four mutant (MUT)probes. Result interpretation: Presence of mutation (MUT) and absence of wild type (WT) indicates resistance.
MDR
Use of Xpert and LPA provides rapid and reliable MDR detection XDR screening by LPA can be helpful when resistant.
Specimen Waste in, waste out Test results are as good as the specimen Appropriate specimen: Site specific Appropriately collected specimen Blood is strongly discouraged, unless blood culture is indicated in c/o disseminated or miliary TB. Dry swabs are not useful
Specimen Site and purpose Specimen of choice Comments Active, pulmonary TB Sputum Deep cough,not saliva Induced sputum,bal,gastric lavage acceptable Active,extrapulmonary TB TB lymphadenitis LN aspirate, biopsy Microscopy,Liq.culture,Xpert and NAAT, TB meningitis CSF Liq.culture,Xpert and NAAT, Other body sites Body fluids-ascites,pleural fluid and biopsy. Microscopy,Liq.culture,NAAT, And Xpert,if positive Bone & Joint Tissue,biopsy Liq.culture,NAAT if positive Genitourinary Urine,tissue Endometrial tissue,24 hrs. urine is not acceptable
Why phenotypic culture/susceptibility EP specimens: For diagnosis, a combination of tests including molecular PCR,culture,histopathology will be useful. For diagnosed MDR, phenotypic culture and DST is important to decide 2 nd line drugs, To rule out XDR. For a MDR negative case, to determine individual drug susceptibility and treatment modifications if required(mono resistance). For definitive diagnosis of NTM species, and treatment if indicated.
GOI ban on serodiagnostic tests for active TB.
TB/HIV the deadly duo PLHV -21-34 times more likely to develop active TB. 1.1 million new TB cases in PLHV TB is the most common presenting illness, even in patients on treatment. Leading cause of death High risk of MDR and XDR
Concerns in diagnosis Sensitivity of smear microscopy is low in HIV positive patients. Delay in detection & initiation of treatment. Xpert is sensitive and specific for diagnosis Xpert improved case detection by 45%.
NTM Nontuberculous mycobacteria (NTM/MOTT) MAC complex Rapid growers (M.fortuitum,M.chelonae,M.abscessus) Species identification critical to ascertain clinical significance and guide susceptibility. Line probe assay Definitive molecular identification of almost 30+clinically significant species
Non-tuberculous mycobacteria - a 2 year Metropolis experience-cidscon 2013 Mycobacteria species distribution, Metropolis ltd. MAC complex M.abscessus M.fortuitum M.chelonae M.tb The MAC complex was the predominant group identified (24.8%), and among the rapid growers, 20.7% were identified as M.abscessus, 14. 9% as M.fortuitum and 5.4% as M.chelonae. Other Mycobacteria Species
NTM susceptibility For clinically relevant species, susceptibility by Micro broth dilution shows good in vivo correlation. Indicated for MAC,M.kansasii and Rapid grower pulmonary and extra-pulmonary isolates.
Summary TB diagnosis: Same size does not fit all Selection of appropriate tests/combination along with site specific samples is important. Newer molecular tests are rapid and reliable for Diagnosis and DR detection and need to be integrated into the management algorithm. Gold standard liquid culture and phenotypic DST will still be required. Rapid PCR tests such as Xpert are crucial in PLHV.
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