Work package 6: cost-effectiveness analysis

The latent tuberculosis infection screening and VOT intervention demonstrated clear clinical effectiveness and are, hence, considered for this analysis. This section includes separate reporting of the cost-effectiveness analyses for these two interventions.

Latent tuberculosis infection screening in the homeless: transmission dynamic and health economic analysis

Introduction

We analysed the cost-effectiveness of adding screening and treatment for latent tuberculosis infection to screening and treatment for active tuberculosis in people experiencing homelessness in London, using an integrated transmission dynamic and health economic model.108 It is an individual-based model in which individuals are ‘followed’ while they are homeless and after re-entering the general population to capture the long-term health consequences of tuberculosis infection, case finding and treatment while homeless; infection acquired while homeless can result in active tuberculosis disease after re-entering the general population (which causes QALY loss and incurs treatment cost), and treatment of latent tuberculosis infection while homeless may avert this.

Analysis

In the model, each individual is in one of a number of health states: uninfected (naive), uninfected (recovered), latently infected (fast progressing or slow progressing), with active tuberculosis disease (sputum smear negative or positive), on treatment for latent tuberculosis infection, or on treatment for active tuberculosis (see Appendix 1, Figure 7). Uninfected individuals who become infected move into the latent infection state. Individuals with tuberculosis infection history (recovered) are assumed to have partial immunity and, therefore, have a reduced probability of (re-)acquiring tuberculosis infection compared with naive individuals. Individuals in the latent state can progress to active tuberculosis disease, which is infectious and can be diagnosed through active or passive case finding, resulting in individuals being placed on tuberculosis treatment. Active case finding for active tuberculosis takes place through chest radiography in the mobile radiographic unit, with cases of abnormal radiology being referred to hospital for tuberculosis diagnosis. Passive case finding for active tuberculosis takes place through individuals presenting for care. In scenarios where latent tuberculosis infection screening occurs, a proportion of diagnosed individuals are treated. Patients who are successfully treated for latent tuberculosis infection or active tuberculosis enter the recovered state. Patients who are not successfully treated return to their former state of latent tuberculosis infection or active tuberculosis disease. Individuals whose IGRA test was false positive remain in the naive or recovered state regardless of whether they are treated or not, but costs are incurred for those who are treated. Active tuberculosis disease causes QALY loss through morbidity (which is reduced by treatment) and mortality.

Economic analysis

The economic analysis is from an NHS perspective. In the baseline (current practice) scenario, a mobile radiographic unit provides screening for active tuberculosis to people experiencing homelessness; individuals with abnormal radiographs are referred to hospital for diagnosis and those with tuberculosis are treated. Individuals with active tuberculosis can also be found passively, when they present for care.

We compared the baseline scenario with intervention scenarios in which people experiencing homelessness are offered testing for latent tuberculosis infection by IGRA, and offered treatment if they test positive. As treatment was not offered in the empirical study, there is uncertainty regarding the proportion of IGRA-positive patients who would accept and complete latent tuberculosis infection treatment, so we compared scenarios in which this proportion varied (i.e. 25%, 50% and 75%). The intervention is applied for 10 years, and the model considers the lifetime of the population cohort. Analysis was from the perspective of the NHS. The total net costs incurred (including staff time, drugs and diagnostic tests) and QALYs accrued by the patient cohort are calculated. Cost-effectiveness of different options is compared using incremental cost-effectiveness ratios (ICERs) relative to current practice. Each scenario (baseline and interventions) was run 1000 times. Costs and health utilities are discounted at 3.5% per annum. Parameter values were obtained primarily from sources used to inform NICE guidance11,33 or this study, as appropriate (see Appendix 1, Tables 13 and 14).

Results

In our analysis, screening for and treating latent tuberculosis infection had a net cost, as the intervention cost was greater than the averted costs of active tuberculosis disease; however, the intervention was beneficial to health, with a QALY gain.

Whether or not the intervention would be considered cost-effective depends on the value of 1 QALY and the proportion of IGRA-positive individuals who are treated for latent tuberculosis infection (see Figures 8 and 9, and Appendix 1). The higher the value of 1 QALY, and the greater the proportion of IGRA-positive patients who are treated for latent tuberculosis infection, the more likely it is that the intervention would be considered to be cost-effective.

In the three scenarios that we considered regarding the proportion of IGRA-positive patients who are treated for latent tuberculosis infection, we find that if this proportion was 25% then introducing latent tuberculosis infection screening and treatment would be cost-effective when 1 QALY was valued at £30,000 (see Appendix 1, Figure 8). If the proportion was 50% or 75%, then introducing latent tuberculosis infection screening and treatment would be cost-effective if 1 QALY was valued at £20,000; however, there is substantial uncertainty about the cost-effectiveness (see Appendix 1, Table 15).

Discussion

Successful treatment of latent tuberculosis infection prevents progression to infectious active tuberculosis disease and thereby averts transmission, which benefits population health and averts future costs of treatment in others, as well as benefiting the individual patient. However, not all patients with latent tuberculosis infection would progress to active tuberculosis disease without treatment and, therefore, several patients with latent tuberculosis infection have to be treated to avert a case of active tuberculosis disease. We find that the cost-effectiveness of adding screening and treatment for latent tuberculosis infection to screening and treatment for active tuberculosis in people experiencing homelessness depends on the proportion of IGRA-positive patients who accept and complete latent tuberculosis infection treatment, and that the greater this proportion the more likely it is that the intervention would be considered cost-effective. As treatment for latent tuberculosis infection was not recommended at the time of the study, it was not offered to patients, and, therefore, we do not know what proportion of patients would accept and complete treatment. As this is a key determinant of cost-effectiveness, further empirical study is required to determine if this intervention should be recommended.

The probability that latent tuberculosis infection screening is cost-effective would be increased if the cost of latent tuberculosis infection testing were lower than in our analysis. With latent tuberculosis infection screening and treatment for immigrants from high-burden countries now recommended, bulk procurement of test kits may enable cost savings that would make latent tuberculosis infection screening and treatment of people experiencing homelessness more likely to be cost-effective.

Economic analysis of video-observed treatment versus directly observed treatment

Parts of this section have been reproduced or adapted from Story et al.86 © 2019 Published by Elsevier Ltd. This is an Open Access article under the CC BY 4.0 license. See: http://creativecommons.org/licenses/by/4.0/. The text includes minor additions and formatting changes to the original text.

Introduction

The trial showed that VOT has superior outcomes to DOT. Here, we present a comparison of costs of VOT versus costs of DOT.

Analysis

Taking the perspective of the NHS, DOT involving observations three times weekly costs £570 per patient per month based on costs calculated by White et al.109 and inflated to 2015–16 prices using the Hospital and Community Health Service index.109 Observation five times weekly costs £950 per patient per month. All of the costs of DOT are unit costs and, therefore, the cost of DOT per patient is determined only by the duration of treatment.

Costs of VOT are summarised in Table 11. For VOT, there is an initial information technology infrastructure set-up cost of £2000 and a monthly cost of cloud data storage, software licences and system maintenance of £3270. Providing VOT requires a band 7 nurse to lead the service, conduct face-to-face training with patients and liaise with tuberculosis clinics. The monthly (combined) cost of a 100% full-time equivalent band 5 and band 7 nurse in inner London is £4425.

Observation of videos and patient support is provided by band 5 nurses. A patient creates seven videos per week. With 20% of videos being checked for quality assurance, each patient requires 8.4 observations per week. A nurse can observe 65 videos per day (based on this study), which is 325 videos per week, and, therefore, each full-time equivalent nurse can manage 38 patients at once (i.e. each patient requires 2.6% of a full-time equivalent nurse). The monthly cost of a 100% full-time equivalent band 5 nurse in inner London is £3045, of which 2.6% is £79.

Results

The monthly cost per patient of DOT depends on the frequency of observation, but the minimum of three observations per week costs £2850 per patient for 5 months of treatment, £3420 for 6 months of treatment and £3990 for 7 months of treatment. The per-patient cost is not affected by the number of patients.

In contrast, the per-patient cost of VOT depends on the number of patients, owing to the fixed costs of setting up the service and the fixed monthly cost of a band 7 nurse to manage the service. If only 10 patients were managed by VOT then the cost per patient would be higher than if DOT were used three times per week, although it would still be cheaper than DOT five times per week (except for the longest treatment durations) and VOT provides seven observations per week. If 25 patients were managed by the VOT service then it would be cheaper than DOT three times per week, and with greater numbers of patients the cost per patient of VOT falls substantially (Table 12).

Conclusion

Video-observed treatment is cheaper than DOT except if small numbers of patients are managed. In settings with sufficient demand for tuberculosis treatment support, VOT is, therefore, cheaper for the NHS than DOT and has superior outcomes, so VOT dominates DOT. VOT has the additional benefits of being cheaper for patients and more convenient than DOT, as there are fewer appointments to be attended in person. The economies of scale offered by VOT are particularly beneficial in the context of tuberculosis control, where, historically, the distribution of resources has often not reflected the distribution of need.110

Deviation from the protocol

The protocol specified economic analyses of effective interventions identified in the programme. Prior economic analysis of radiographic and latent tuberculosis infection screening had already been conducted for NICE Public Health Guidance 3712 so were not undertaken.