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Table 3 The impact of new diagnostic tools for TB on the public health system

From: Rapid diagnostics of tuberculosis and drug resistance in the industrialized world: clinical and public health benefits and barriers to implementation

Initial versus new tool Use Staffing impact/advantage Patient impact/advantage Laboratory advantage Reading Public health impact of second tool
TST versus gamma interferon release Latent TB Qualified nurse to apply and read TST vs phlebotomist Two versus one visit Low versus higher specificity Moderately standardized versus more precise cut-off Fewer referrals due to more specific diagnosis LTBI.
infection (LTBI)
Solid versus liquid culture Active TB Unchanged Improved sensitivity Higher sensitivity for detection (but offset if higher contamination) Non-automated versus automated cut-off Identification of all TB cases reduce transmission
Smear* versus Xpert® MTB/RIF system or LPA Active TB Arguably less trained staff needed Greater sensitivity; but no indicator of infectivity Low versus high sensitivity and specificity Variable versus cut-off Fewer false positive results
Due to inactivation lower risk of staff infection
Smear *versus Xpert® MTB/RIF system or LPA, for example, GenoType® MDRTBPlus Drug resistance Less qualified personnel initially for interpretation Short turnaround time for marker antibiotic No versus one key marker antibiotic (rifampicin) and also isoniazid for LPA Variable versus exact cut-off Immediate availability of marker antibiotic results; poor PPV in low prevalence areas
Phenotypic versus GenoType® MTBDRsl line probe assay (LPA) for FQ, injectable agents Drug resistance Unchanged for qualification of staff, reduced risk for staff infection In areas with high MDR rates shorter turnaround for XDR-TB detection Earlier XDR-TB screen and set-up of other drug testing for treatment Simpler cut-off; limited drug range Immediate preliminary screening for MDR- and XDR-TB and aid planning contact investigation
  1. * “Smear” means the microscopic examination of sputum.
  2. LPA, line prove assay; PPV, positive predictive value; MDR-TB, Multidrug-resistant tuberculosis; TST, tuberculin skin testing; XDR-TB, extensively drug-resistant TB; LTBI, Latent TB infection.