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