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 |
* “Smear” means the microscopic examination of sputum.
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.