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Update on cost-effectiveness of a 12-dose regimen for latent tuberculous infection at new rifapentine prices. An editorial in the December 2013 issue of this.
CORRESPONDENCE

INT J TUBERC LUNG DIS 18(6):751–753 Q 2014 The Union

Correspondence Update on cost-effectiveness of a 12-dose regimen for latent tuberculous infection at new rifapentine prices An editorial in the December 2013 issue of this Journal1 addressed our recent cost-effectiveness analysis2 of a 12-dose regimen of weekly isoniazid plus rifapentine (3HP) for the treatment of latent tuberculous infection (LTBI). The editorial accurately notes that the assumptions underlying the costeffectiveness analysis are conservative with respect to the cost-effectiveness of the 3HP regimen, particularly as 3HP becomes more widely used for the treatment of LTBI. Our base case in the cost-effectiveness analysis comparing 3HP to the standard 9-month regimen of daily isoniazid (INH) assumed the then-current price of $12.31 per 900 mg dose of rifapentine (RFP) vs. $0.05 per individual dose of INH. The manufacturer of RFP, Sanofi US, announced that in January 2014 the price of rifapentine (Priftinw) for tuberculosis (TB) programs in the United States would be lowered to $6.00 per 900 mg dose. We recalculated the costeffectiveness of 3HP vs. 9H using the updated price of RFP. We found that, over a 20-year period, the cost to the health system per TB case prevented by 3HP compared to 9H decreases to US$8861 (from US$21525 at the former RFP price), while the cost to the health system per quality-adjusted life year (QALY) gained by 3HP compared to 9H decreases to US$1879 (from US$4565 at the former RFP price). From the societal perspective, which includes costs to the health system as well as direct costs to patients and the economic value of lost patient productivity, 3HP is cost-saving compared to 9H at the new RFP price. Our cost-effectiveness analysis assumed that 3HP was administered by directly observed therapy (DOT), adding substantially to the cost of the 12dose regimen as compared to self-administered 9H. Current US guidelines recommend that 3HP be given by DOT.3 The results of a study being conducted by the Tuberculosis Trials Consortium to assess the adherence to the 3HP regimen given by self-administered therapy are expected to be available in late 2014. If adherence to self-administered 3HP is maintained at levels achieved by DOT, then 3HP would be cost-saving compared to 9H from both a health system and a societal perspective. Under these conditions, over a 20-year period, US TB programs would save US$141 per individual treated by switching from 9H to 3HP (including the cost of

treatment and prevention of future cases of TB for each regimen). From the societal perspective, these savings would rise to US$231 per individual treated. Finally, as program costs can vary widely depending on location, we feel it is important to make the computational tool we developed in conducting our cost-effectiveness analysis publicly available. This tool allows users to input costs and change key variables to fit local conditions. The software can be freely downloaded at http://www.mtholyoke.edu/ ~dshepard/LTBI/LTBI-cost-effectiveness.zip. DYLAN SHEPARDSON, PHD* WILLIAM R. MAC KENZIE, MD† *Mount Holyoke College South Hadley, Massachusetts †Centers for Disease Control and Prevention Atlanta, Georgia USA e-mail: [email protected] http://dx.doi.org/10.5588/ijtld.14.0052

References 1 Diel R, Loddenkemper R, Sotgiu G, et al. Cost-effectiveness of treating latent tuberculous infection: a step towards elimination? Int J Tuberc Lung Dis 2013; 17: 1515. 2 Shepardson D, Marks S M, Chesson H, et al. Cost-effectiveness of a 12-dose regimen for treating latent tuberculous infection in the United States. Int J Tuberc Lung Dis 2013; 17: 1531–1537. 3 Centers for Disease Control and Prevention. Recommendations for use of an isoniazid-rifapentine regimen with direct observation to treat latent Mycobacterium tuberculosis infection. MMWR Morb Mortal Wkly Rep 2011; 60: 1650–1653.

Effect of smear-negative pulmonary tuberculosis on transmission The study by Cruz-Ferro et al. in a recent issue of the Journal showed that tuberculosis (TB) incidence in Galicia, Spain, fell from 72.9 cases per 100 000 population in 1996 to 24.6/100 000 in 2011.1 The median patient and health care system diagnostic delay was respectively 21 and 15 days. The diagnostic delay in pulmonary tuberculosis (PTB) and smearpositive PTB cases was 59 and 63 days, respectively, causing 37 outbreaks of TB. The authors concluded that the long diagnostic delay may have contributed to the high TB incidence rate in children. Estimates for patients with smear-negative, culturepositive pulmonary disease were not shown, but according to the satisfactory results reported in Table 3 they can be obtained by the difference between culture-positive and smear-positive PTB cases. For

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example, there were 172 smear-negative patients (792 culture-positive minus 620 smear-positive) in 1996, corresponding to 22% of pulmonary cases with satisfactory results. This estimate increased to 32% in 2003 (635 minus 430 ¼ 205 cases) and to 36% in 2010 (368 minus 236 ¼ 132), indicating that smearnegative cases make an important contribution to the disease burden in Galicia. Hence, an estimation of patient and health care system diagnostic delay in patients with smear-negative, culture-positive pulmonary disease would also have been important in this study to establish whether a long diagnostic delay is a problem in this patient group as well as in smearpositive patients. The evaluation of contacts of smear-positive patients with pulmonary disease has likely helped to reduce TB incidence in Galicia. It is a priority in all national TB programmes to find and treat contacts with active TB or latent tuberculous infection (LTBI) to interrupt transmission. As patients with smearnegative, culture-positive pulmonary disease can also transmit the disease, contact tracing for this group is also important and should be implemented in regions/countries that can afford it. This could partially help towards TB elimination. Contact tracing is particularly important in children, as they represent future cases and sources of infection. We and others2–5 have shown that 10–20% of TB cases acquire the disease from smear-negative index cases. Our estimate in children from British Columbia was 10%.3 ˜ EDUARDO HERNA´NDEZ-GARDUNO MD, MHSC Unidad de Investigacion, Pretelini ´ Hospital Monica ´ Sa´enz Instituto de Salud del Estado de Mexico ´ Colonia Universidad Toluca, Estado de Mexico, Mexico ´ ´ e-mail: [email protected]

http://dx.doi.org/10.5588/ijtld.14.0084

References 1 Cruz-Ferro E, Ursua-D´ ıaz M I, Taboada-Rodr´ıguez J A, et al; ´ Galician Tuberculosis Prevention and Control Programme Working Group. Epidemiology of tuberculosis in Galicia, Spain, 16 years after the launch of the Galician tuberculosis programme. Int J Tuberc Lung Dis 2014; 18: 134–140. 2 Herna´ndez-Garduno ˜ E, Cook V, Kunimoto D, et al. Transmission of tuberculosis from smear-negative patients: a molecular epidemiology study. Thorax 2004; 59: 286–290. 3 Elwood R K, Cook V J, Herna´ndez-Garduno ˜ E. Risk of tuberculosis in children from smear-negative source cases. Int J Tuberc Lung Dis 2005; 9: 49–55. 4 Tostmann A, Kik S V, Kalisvaart N A, et al. Tuberculosis transmission by patients with smear-negative pulmonary tuberculosis in a large cohort in the Netherlands. Clin Infect Dis 2008; 47: 1135–1142. 5 Behr M A, Warren S A, Salamon H, et al. Transmission of Mycobacterium tuberculosis from patients smear-negative for acid-fast bacilli. Lancet 1999; 353: 444–449.

In reply In response to Dr Herna´ndez-Garduno’s comments, ˜ we would like to provide the data he refers to. The median patient and health care system diagnostic delay and total diagnostic delay in 2011 are shown in the Table. As patients with smear-negative tuberculosis (TB) are not diagnosed in a timely manner, disease may develop further, initiation of treatment may be delayed and further TB transmission may occur. The percentage of smear-negative, culture-positive pulmonary tuberculosis (PTB) cases in the period 1996–2011 amounted to 19.4%. Since 2009 the Galician Tuberculosis Prevention and Control Programme (GTPCP) has therefore recommended conducting contact investigations for such cases.1 This recommendation was reinforced in 2012 with the publication of the GTPCP update, which emphasises contact screening to further improve TB control in our region.2 In Galicia, a considerable number of smear-negative, culture-positive PTB contacts are studied every year. In the period 1996–2011, 3822 smear-negative, culture-positive PTB cases were recorded, of which 2038 (53.3%) had been identified in contact tracing (of 15 855 contacts screened). The result of this study was 129 (0.8%) cases of TB and 4777 (30.1%) of latent tuberculous infection (LTBI). The same information for smear-positive, culture-positive PTB is 6314 smear-positive, culture-positive PTB cases, 4847 (76.8%) recorded contacts, 90 696 contacts screened, 1119 (1.2%) TB cases and 30 279 (33.4%) cases of LTBI. Dividing the 129 smear-negative transmission events that occurred in the 3822 smear-negative TB patients by the 1119 smear-positive transmission events that occurred in the 6314 smear-positive TB patients resulted in a relative transmission rate of 0.19. This means that smear-negative PTB patients were only 0.19 times as likely to spread TB as those with smear-positive PTB. We have assumed that the first patient in a cluster is the index patient of that cluster. This may not always be true, as the real source patient of that cluster could have been diagnosed before the start of the study period. Exposure to an unidentified or unrecognised smear-positive source case thus remains an inherent limitation of any study of TB transmission. Our results suggest that transmission of Mycobacterium tuberculosis from smear-negative, culturepositive PTB patients contributes to the incidence of the disease in Galicia, although we should analyse other variables or use molecular biology to verify this. We therefore agree with Dr Herna´ndez-Garduno. ˜ Patients who are smear-negative clearly excrete fewer

Correspondence

Table

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Median patient and health care system diagnostic delay and total diagnostic delay in 2011 Median patient diagnostic delay days

Median health care system diagnostic delay days

Median total diagnostic delay days

21 25 28 32 22

15 11 10 6 24

56 59 62 63 55

Total TB cases* PTB (culture positive and negative) PTB culture-positive Smear-positive, culture-positive PTB Smear-negative, culture-positive PTB

* Pulmonary and extra-pulmonary, culture-positive and -negative. TB ¼ tuberculosis; PTB ¼ pulmonary tuberculosis.

organisms than those who are smear-positive. However, their relative transmission rate suggests that other characteristics, such as delayed treatment and lack of isolation, contribute to their infectivity, so for greater progress in the control of TB in our region, we must insist on contact screening for all culturepositive PTB cases, both smear-positive and smearnegative. E. CRUZ-FERRO* ´ -D IAZ ´ * M. I. URSUA ´ J. A. TABOADA-RODRIGUEZ * X. HERVADA-VIDAL* L. ANIBARRO† ‡ ˜ V. T U´ NEZ GALICIAN TUBERCULOSIS PREVENTION AND CONTROL PROGRAMME WORKING GROUP *Galician Tuberculosis Prevention and Control Programme, Direccion ´ General de Innovacion ´ y Gestion ´ de la Salud Publica, Xunta de Galicia, Santiago de Compostela ´ †Tuberculosis Unit, Department of Internal Medicine, Complexo Hospitalario de Pontevedra, Pontevedra

‡Tuberculosis

Unit, Department of Preventive Medicine, Complexo Hospitalario Universitario de Santiago, Santiago de Compostela, Spain e-mail: [email protected] [email protected] http://dx.doi.org/10.5588/ijtld.14.0084-2

References 1 Direccion y Planificacion. ´ General de Salud Publica ´ Infeccion ´ ´ tuberculosa y estudios de contactos. Santiago de Compostela, Spain: Direccion y Planificacion, ´ General de Salud Publica ´ ´ Conseller´ıa de Sanidad, Xunta de Galicia, 2009. http:// www.sergas.es/cas/DocumentacionTecnica/docs/SaudePublica/ Tuberculose/Infeccion%20tuberculosa%20y%20estudio%20de %20contactos.pdf 2 Direccion ´ General de Innovacion ´ y Gestion ´ de la Salud Publica. ´ Programa Gallego de Prevencion ´ y Control de la Tuberculosis 2012–2015. Santiago de Compostela, Spain: Direccion ´ General de Innovacion Conseller´ıa de ´ y Gestion ´ de la Salud Publica, ´ Sanidad, Xunta de Galicia, 2012. http://www.sergas.es/cas/ documentacionTecnica/docs/SaudePublica/Tuberculose/Programa %20Gallego%20de%20Prevencion%20y%20Control%20de %20la%20Tuberculosis.%202012-2015.pdf Accessed March 2014