An assessment of nucleic acid amplification testing for active mycobacterial infection

Net financial implications to the MBS

The population eligible for NAAT is projected based on the number of patients who accessed mycobacterial MC&S testing (MBS items 69324, 69325, 69327, 69328, 69330 or 69331) each year during 200913 (Table ). As these items are used to monitor the effectiveness of treatment and as this is not a proposed use of NAAT, the number of patients rather than the number of services has been used. This patient pool accounts for the population suspected of TB (who can or cannot have an AFB) and the population suspected of NTM.

Table Number of patients who accessed MC&S services, 2009–13

-	2009	2010	2011	2012	2013
No. patients who accessed at least one MC&S service	28,188	27,853	30,213	32,857	34,302

MC&S = acid-fast bacilli microscopy, culture and sensitivity

A linear regression model fitted to the observed patient numbers (R² = 0.92) was projected to 2019 (Figure and Table ). This approach may overestimate the eligible population for NAAT, as patients tested who are suspected of M. leprae may be included (but would not be eligible for NAAT) and, as these tests are used to monitor treatment effectiveness, patients may receive testing across multiple years for the same infection. Further, as the current MBS items are not restricted to patients with clinical signs and symptoms of a mycobacterial infection, and as HESP member feedback has indicated that testing may be ordered as part of the initial work-up of a chronic obstructive pulmonary disease or some renal diseases, this approach may further overestimate the eligible population. This will be tested in a sensitivity analysis.

Figure Number of patients who accessed MC&S services, observed 2009–13 and projected 2014–19

MC&S = acid-fast bacilli microscopy, culture and sensitivity

Furthermore, it is proposed that use of NAAT may earlier identify TB and MDR-TB, enabling faster treatment and decreasing the number of secondary transmissions. Neither the potential decrease in the rate of increasing cases due to reduced transmissions, nor the potential savings on treatment costs due to decreased transmissions, is captured in the financial estimates.

As the MBS items for MC&S do not distinguish between TB and NTM, and do not distinguish between those who do and do not have an AFB test, these projected patient numbers cannot be separated into the three proposed populations with any degree of confidence. As NAAT costs differ between TB and NTM, the applicant has estimated that approximately 50% of the patients currently tested for mycobacterial infections are suspected of TB, and so 50% are suspected of NTM.

Generally, one NAAT is assumed per eligible patient. However, this approach may underestimate the estimated number of tests (and so costs) in circumstances in which multiple mycobacteria are suspected. For example, TB may be initially suspected with a pulmonary infection (and therefore be tested using TB NAAT), and then may also be tested using NAAT for M. kansasii and/or MAC. It is unclear how often this situation would occur—the applicant has made an estimate of approximately 30% of patients initially suspected of TB. This is used in the estimation of the financial implications associated with NAAT for NTM and will be tested in sensitivity analyses.

NAAT for TB

The cost per TB NAAT is as used in the economic modelling ($130); the financial implications of a range of test costs are presented in Appendix . Over the past 5 years average bulk-billing rates for the current MC&S items ranged from 59% to 62%; the midpoint (60.5%) will be used in the analysis. It is assumed that the provider does not charge above the MBS fee, and so the patient contribution, in those not bulk-billed, is 15% of the proposed NAAT fee.

Of all patients suspected of a mycobacterial infection, it is assumed that 50% are suspected of having TB (based on applicant advice). This estimate is tested in sensitivity analyses. Applying this proportion to the projected eligible population estimates, 18,800 patients are estimated to be eligible for TB NAAT in the first year, increasing to 22,200 in the fifth. The total MBS fees associated with the introduction of NAAT for TB increase from $2.4 million to $2.9 million over the 5-year period, of which $2.1 million in year 1 to $2.5 million in year 5 are paid by the MBS. Safety net effects to the MBS have not been considered in these calculations, as MBS data relating to the proportion of patients eligible for the safety net are not available. Patient contributions are estimated to increase from $145,000 to $171,000 over the 5 years. This may be an overestimate as, due to the contagious nature of TB, state TB services may waive all patient fees associated with the investigation of TB.

Table Number of patients eligible and cost of NAAT for TB

-	2015	2016	2017	2018	2019
Projected no. of patients eligible for NAAT	37,575	39,299	41,022	42,745	44,468
Population suspected of TB	-	-	-	-	-
Proportion of patients suspected of TB	50%	50%	50%	50%	50%
Number of patients suspected of TB	18,788	19,650	20,511	21,373	22,234
Proposed NAAT fee:	$130.00	$130.00	$130.00	$130.00	$130.00
MBS benefit (85%)	$110.50	$110.50	$110.50	$110.50	$110.50
Patient contribution (15%)	$19.50	$19.50	$19.50	$19.50	$19.50
Proportion of patients bulk-billed	61%	61%	61%	61%	61%