Isoniazid or rifampicin preventive therapy with and without screening for subclinical TB: a modeling analysis

Modeling the impact of universal tuberculosis molecular testing and timing of tuberculosis preventive treatment during antiretroviral therapy initiation in South Africa

OBJECTIVES

Targeted universal tuberculosis (TB) testing can improve TB detection among people with HIV. This approach is being scaled up in South Africa through Xpert MTB/RIF Ultra testing for individuals starting antiretroviral therapy and annually thereafter. Clarity is needed on how Universal Xpert testing may affect TB preventive treatment (TPT) provision, and on whether TPT should be delayed until TB is ruled out.

DESIGN

State-transition microsimulation.

METHODS

We simulated a cohort of South African patients being screened for TB while entering HIV care. We compared clinical and cost outcomes between four TB screening algorithms: symptom-based, C-reactive protein-based, and Universal Xpert testing with either simultaneous or delayed TPT initiation.

RESULTS

Prompt TB treatment initiation among simulated patients with TB increased from 26% (24-28%) under symptom screening to 53% (50-56%) with Universal Xpert testing. Universal Xpert testing led to increased TPT uptake when TPT initiation was simultaneous, but to approximately 50% lower TPT uptake if TPT was delayed. Universal Xpert with simultaneous TPT prevented incident TB compared to either symptom screening (median 17 cases averted per 5000 patients) or Universal Xpert with delayed TPT (median 23 averted). Universal Xpert with Simultaneous TPT cost approximately $39 per incremental TPT course compared to Universal Xpert with delayed TPT.

CONCLUSIONS

Universal Xpert testing can promote timely treatment for newly diagnosed people with HIV who have active TB. Pairing universal testing with immediate TPT will improve the promptness, uptake, and preventive effects of TPT. Simultaneous improvements to TB care cascades are needed to maximize impact.

The identification of key metabolites and mechanisms during isoniazid/rifampicin-induced neurotoxicity and hepatotoxicity in a mouse model by HPLC-TOF/MS-based untargeted urine metabolomics

The co-administration of isoniazid (INH) and rifampicin (RIF) is associated with hepatotoxicity and neurotoxicity. To systematically investigate the mechanisms of hepatotoxicity and neurotoxicity induced by INH/RIF, we used high performance liquid chromatography-time of flight mass spectrometry (HPLC-TOF/MS)-based untargeted metabolomics to analyze urine from a mouse model and screened a range of urinary biomarkers. Mice were orally co-administered with INH (120 mg/kg) and RIF (240 mg/kg) and urine samples were collected on days 0, 7, 14 and 21. Hepatotoxicity and neurotoxicity were assessed by samples of liver, brain and kidney tissue which were harvested for histological analysis. Toxicity analysis revealed that INH/RIF caused hepatotoxicity and neurotoxicity in a time-dependent manner; compared with day 0, the levels of 35, 82 and 86 urinary metabolites were significantly different on days 7, 14 and 21, respectively. Analysis showed that by day 21, exposure to INH+RIF had caused disruption in vitamin B6 metabolism; the biosynthesis of unsaturated fatty acids; tyrosine, taurine, hypotaurine metabolism; the synthesis of ubiquinone and other terpenoid-quinones; and the metabolism of tryptophan, nicotinate and nicotinamide. Nicotinic acid, nicotinuric acid and kynurenic acid were identified as sensitive urinary biomarkers that may be useful for the diagnosis and evaluation of toxicity.

Limitations of Chest Radiography in Diagnosing Subclinical Pulmonary Tuberculosis in Canada

Subclinical pulmonary tuberculosis (PTB) is defined as "…a state of disease due to viable Mycobacterium tuberculosis that does not cause TB-related symptoms but does cause other abnormalities that can be detected using existing radiologic and mycobacteriologic assays." In high-income countries, subclinical PTB is usually diagnosed during active case finding, is acid-fast bacilli smear negative, and associated with minimal or no lung parenchymal abnormality on chest radiograph. In the absence of symptoms, the epidemiologic risk of TB and chest radiograph are critical to making the diagnosis. In a cohort of 327 patients with subclinical PTB, we address the question-how well field radiologists perform at identifying features important to the diagnosis of PTB, the presence or absence of which have been established by a panel of expert radiologists? Although not performing badly compared with this "gold standard," field readers were nevertheless susceptible to overread or underread films and miss key diagnostic features, such as the presence of a lung parenchymal abnormality, typical pattern, or cavitation. In the context of active case finding during which most patients with subclinical PTB are discovered, limitations of the chest radiograph need to be recognized, and sputum, ideally induced, should be submitted regardless of the radiographic findings.

The Global Expansion of LTBI Screening and Treatment Programs: Exploring Gaps in the Supporting Economic Evidence

The global burden of latent TB infection (LTBI) and the progression of LTBI to active TB disease are important drivers of ongoing TB incidence. Addressing LTBI through screening and TB preventive treatment (TPT) is critical in order to end the TB epidemic by 2035. Given the limited resources available to health ministries around the world in the fight against TB, we must consider economic evidence for LTBI screening and treatment strategies to ensure that limited resources are used to achieve the biggest health impact. In this narrative review, we explore key economic evidence around LTBI screening and TPT strategies in different populations to summarize our current understanding and highlight gaps in existing knowledge. When considering economic evidence supporting LTBI screening or evaluating different testing approaches, a disproportionate number of economic studies have been conducted in high-income countries (HICs), despite the vast majority of TB burden being borne in low- and middle-income countries (LMICs). Recent years have seen a temporal shift, with increasing data from low- and middle-income countries (LMICs), particularly with regard to targeting high-risk groups for TB prevention. While LTBI screening and prevention programs can come with extensive costs, targeting LTBI screening among high-risk populations, such as people living with HIV (PLHIV), children, household contacts (HHC) and immigrants from high-TB-burden countries, has been shown to consistently improve the cost effectiveness of screening programs. Further, the cost effectiveness of different LTBI screening algorithms and diagnostic approaches varies widely across settings, leading to different national TB screening policies. Novel shortened regimens for TPT have also consistently been shown to be cost effective across a range of settings. These economic evaluations highlight key implementation considerations such as the critical nature of ensuring high rates of adherence and completion, despite the costs associated with adherence programs not being routinely assessed and included. Digital and other adherence support approaches are now being assessed for their utility and cost effectiveness in conjunction with novel shortened TPT regimens, but more economic evidence is needed to understand the potential cost savings, particularly in settings where directly observed preventive therapy (DOPT) is routinely conducted. Despite the growth of the economic evidence base for LTBI screening and TPT recently, there are still significant gaps in the economic evidence around the scale-up and implementation of expanded LTBI screening and treatment programs, particularly among traditionally hard-to-reach populations.

Preventive Treatment for Household Contacts of Drug-Susceptible Tuberculosis Patients

People who live in the household of someone with infectious pulmonary tuberculosis are at a high risk of tuberculosis infection and subsequent progression to tuberculosis disease. These individuals are prioritized for contact investigation and tuberculosis preventive treatment (TPT). The treatment of TB infection is critical to prevent the progression of infection to disease and is prioritized in household contacts. Despite the availability of TPT, uptake in household contacts is poor. Multiple barriers prevent the optimal implementation of these policies. This manuscript lays out potential next steps for closing the policy-to-implementation gap in household contacts of all ages.