JAIDS, Aug 2009 Infectious Disease Journal Club 17 September 2007 Dr Preneshni Naicker

Introduction TB is the leading cause of death among HIV-infected patients 50% of TB patients are HIV co-infected Sputum smear microscopy detects less than half of HIV-infected TB cases Priority = simple, accurate, inexpensive test for TB case detection in HIV-positive individuals Strategy = Detection of mycobacterium tuberculosis ANTIGENS

TB is the leading cause of death among HIV-infected patients

50% of TB patients are HIV co-infected

Sputum smear microscopy detects less than half of HIV-infected TB cases

Priority = simple, accurate, inexpensive test for TB case detection in HIV-positive individuals

Strategy = Detection of mycobacterium tuberculosis ANTIGENS

LAM (Lipoarabinomannan) 17.5 kD glycolipid component of the cell wall of mycobacteria

17.5 kD glycolipid component of the cell wall of mycobacteria

Attractive diagnostic target Theoretical potential to discriminate active TB from latent TB (independent of immune responses) Heat stable Cleared by kidney Detectable in urine Facilitates TB diagnosis if sputum unhelpful Lacks infection control risks associated with sputum production or blood collection Amenable to simple, inexpensive, point-of-care platform

Attractive diagnostic target

Theoretical potential to discriminate active TB from latent TB (independent of immune responses)

Heat stable

Cleared by kidney

Detectable in urine

Facilitates TB diagnosis if sputum unhelpful

Lacks infection control risks associated with sputum production or blood collection

Amenable to simple, inexpensive, point-of-care platform

Aim Evaluated the accuracy of U-LAM test for the diagnosis of active TB in patients admitted to 3 hospitals in South Africa with a presumptive diagnosis of TB

Evaluated the accuracy of U-LAM test for the diagnosis of active TB in patients admitted to 3 hospitals in South Africa with a presumptive diagnosis of TB

Materials and Methods Nested in a prospective multicenter cohort study Chris Hani Baragwanath Hospital (tertiary hospital) Selby hospital (private hospital) Tshepong Hospital (provincial hospital) Participants were identified by review of admission intake log by study personnel Chart reviews and clinical interviews were utilised to determine study eligbility Eligibility criteria were kept broad to capture pulmonary and extrapulmonary TB cases Study interview at 2 months after enrollment to assess clinical status

Nested in a prospective multicenter cohort study

Chris Hani Baragwanath Hospital (tertiary hospital)

Selby hospital (private hospital)

Tshepong Hospital (provincial hospital)

Participants were identified by review of admission intake log by study personnel

Chart reviews and clinical interviews were utilised to determine study eligbility

Eligibility criteria were kept broad to capture pulmonary and extrapulmonary TB cases

Study interview at 2 months after enrollment to assess clinical status

Inclusion criteria ≥ 18 years Signs and/or symptoms compatible with TB Urine sample available for testing Informed consent Exclusion Prior hospitalization within 2 weeks TB therapy for >2 months

Inclusion criteria

≥ 18 years

Signs and/or symptoms compatible with TB

Urine sample available for testing

Informed consent

Exclusion

Prior hospitalization within 2 weeks

TB therapy for >2 months

Study directed testing 1 sputum for AFB smear microscopy and culture 1 mycobacterial blood culture HIV antibody testing (CD4 for HIV +) Spot urine sample Additional diagnostic tests : TB Culture (CSF, pleural fluid, LN biopsies, other resp samples) All treatment provided at the discretion of the treating clinician Study results (except U-LAM) were available to the treating clinician

Study directed testing

1 sputum for AFB smear microscopy and culture

1 mycobacterial blood culture

HIV antibody testing (CD4 for HIV +)

Spot urine sample

Additional diagnostic tests :

TB Culture (CSF, pleural fluid, LN biopsies, other resp samples)

All treatment provided at the discretion of the treating clinician

Study results (except U-LAM) were available to the treating clinician

Laboratory testing Clearview TB ELISA Direct antigen sandwich immunoassay (96-well plate format) Rabbit anti-LAM antibody conjugated to horseradish peroxidase Substrate= tetramethylbenzidine Duplicate samples with average OD  0.1 greater than the negative control = POSITIVE

Clearview TB ELISA

Direct antigen sandwich immunoassay (96-well plate format)

Rabbit anti-LAM antibody conjugated to horseradish peroxidase

Substrate= tetramethylbenzidine

Duplicate samples with average OD  0.1 greater than the negative control = POSITIVE

TB diagnostic categories Confirmed TB —M. tuberculosis cultured from any site, or microscopical examination of any specimen revealing AFB or granuloma(s) in the absence of a culture positive for any Mycobacteria. Possible TB —no culture positive for M. tuberculosis, and presence of clinical response to empiric TB treatment as defined by subjective report of improvement in cough, weight loss, and/or fever at 2-month follow-up. Not TB —cultures negative for M. tuberculosis, and  1 of the following: (a) alternative definitive microbiological diagnosis, (b) clinical improvement in the absence of TB treatment, and (c) failure to respond to empiric TB treatment. Indeterminate —failure to meet criteria for any of the above diagnostic categories

Results

Disease categorizations

LAM test performance

LAM performance by HIV status

All participants PPV for confirmed TB = 73% NPV = 34% HIV + PPV for confirmed TB = 75% NPV = 30%

All participants

PPV for confirmed TB = 73%

NPV = 34%

HIV +

PPV for confirmed TB = 75%

NPV = 30%

HIV Positive with confirmed TB - LAM test sensitivity differed by CD4 category (p < 0.001) 71% 50-100 85% < 50 56% 100-150 14% 150-200 55% > 200 LAM sensitivity CD4 Count

HIV Positive with confirmed TB - LAM test sensitivity differed by CD4 category (p < 0.001)

Factors associated with a positive LAM HIV Infection Positive TB blood culture Positive sputum smear Independently associated with + LAM in confirmed TB patients

HIV Infection

Positive TB blood culture

Positive sputum smear

Independently associated with + LAM in confirmed TB patients

U-LAM compared with Sputum Smear Microscopy

Discussion For the diagnosis of active TB in a setting of high HIV prevalence, the LAM test had a sensitivity of 59% in confirmed TB cases and a specificity of 96% in ‘not TB’ patients LAM sensitivity higher in HIV-positive TB patients than HIV-negative LAM sensitivity highest in subgroup of HIV-positive TB patients with CD4 < 50 Able to detect over half of confirmed TB cases not detected by smear microscopy Combination of sputum smear + LAM identified 75% of confirmed TB cases.

For the diagnosis of active TB in a setting of high HIV prevalence, the LAM test had a sensitivity of 59% in confirmed TB cases and a specificity of 96% in ‘not TB’ patients

LAM sensitivity higher in HIV-positive TB patients than HIV-negative

LAM sensitivity highest in subgroup of HIV-positive TB patients with CD4 < 50

Able to detect over half of confirmed TB cases not detected by smear microscopy

Combination of sputum smear + LAM identified 75% of confirmed TB cases.

Comparison of LAM test performance 100% 38% (All) 67% (CD4 <50) Lawn 2009 Cape Town - 52% HIV + TBcul + Corbett 2003 Harare Unaffected by HIV status 99% 80.3% Boehme 2005 Tanzania Specificity Sensitivity

Limitations Unable to establish definite diagnosis (indeterminate group) Unable to assess if LAM detects NTM

Unable to establish definite diagnosis (indeterminate group)

Unable to assess if LAM detects NTM

Conclusions Combination of LAM and smear microscopy attractive in the setting of high HIV burden Further studies needed to determine if LAM testing results in improved clinical outcomes.

Combination of LAM and smear microscopy attractive in the setting of high HIV burden

Further studies needed to determine if LAM testing results in improved clinical outcomes.