Role of contact tracing and prevention strategies in the interruption of leprosy transmission

W. Cairns S. Smith; Ann Aerts

doi:10.47276/lr.85.1.2

The global prevalence of leprosy has declined from 5.2 million in the 1980s to 200,000 today.1 However, the new case detection rate remains high: over the last 8 years, around 220,000–250,000 people have been diagnosed with leprosy each year. In June 2013, an international meeting was organised by the Novartis Foundation for Sustainable Development in Geneva, Switzerland,2 with the objective of discussing the feasibility of interrupting the transmission of leprosy. The group of physicians, epidemiologists and public health professionals concluded that a successful programme would require early diagnosis and prompt multidrug therapy (MDT) for all patients, tracing and post-exposure prophylaxis (PEP) for contacts of patients newly diagnosed with leprosy, improvements in diagnostic tools, as well as strict epidemiological surveillance and response systems to monitor progress.

As a follow-up, a second expert group meeting was convened by the Novartis Foundation in January 2014 in Zurich, Switzerland, with the objective of reviewing the evidence for chemoprophylaxis in contacts and high-risk communities. The meeting also considered the definitions of ‘contacts’ and ‘contact tracing’, discussed alternative prophylaxis regimens, preliminary findings of operational pilot projects on PEP in Indonesia, as well as the development of diagnostic tools, and identified the priority questions for operational research in leprosy transmission.

The meeting outlined how contact tracing and chemoprophylaxis programmes can be implemented to interrupt leprosy transmission. The expert panel reached the following conclusions:

Chemoprophylaxis with single-dose rifampicin (SDR) is efficacious in reducing the risk of developing leprosy, although the protective effect appears to be smaller in contacts closer to the index patient than in more distant contacts.3 SDR can be targeted to contacts or implemented as community mass prophylaxis in certain circumstances; the preferred approach depends on local factors, such as the case detection rate, the level of community stigma against leprosy, and the degree of access to healthcare for patients and contacts. Alternative prophylaxis regimens and the role of post-exposure immunoprophylaxis need to be further investigated.

Contact tracing combined with PEP across very diverse settings offers protection rates similar to those reported in controlled trials. For high-incidence pockets (‘hotspots’) or remote or confined high-incidence populations (‘hotpops’), blanket administration of PEP may be a better option.

Implementation of contact-tracing programmes is feasible and cost-effective, particularly in high-risk groups, but it should be integrated into local healthcare services to ensure their long-term sustainability. Funding and support must be maintained after an initial pilot has finished. New programmes for contact tracing need effective surveillance systems to enable appropriate follow-up and outcome evaluation.

The Novartis Foundation and Netherlands Leprosy Relief (NLR) are currently developing and implementing a large international programme to demonstrate the feasibility, acceptability, cost-effectiveness and real-world efficacy of PEP as a strategy to interrupt leprosy transmission, in six pilot projects in Asia, Africa and South America. These new pilot projects will be developed together with the local health authorities, healthcare workers, communities and patients, in order to create local ownership from the outset. The pilots should aim to be scalable and sustainable, and should therefore include an objective outcome assessment. Local ownership ensures that locally appropriate language and definitions of contacts are used in each of the pilots.

A test to identify subclinical disease and distinguish M. leprae exposure from infection would facilitate early and appropriate therapy (with PEP or MDT). The identification and validation of new, sensitive biomarkers for M. leprae infection and exposure may allow better targeting of PEP to those contacts at highest risk of developing leprosy.

Research priorities

The expert panel considered a number of research priorities regarding contact tracing and prophylactic treatment of contacts of patients newly diagnosed with leprosy:

Does contact tracing combined with PEP with SDR reduce the incidence of leprosy in the general population, and, as such, interrupt transmission of the disease?

What is the efficacy of alternative PEP regimens?

When should PEP be used as a blanket approach, and when should it be targeted to contacts of newly diagnosed patients? Can a prevalence/case detection rate threshold be defined, above which mass administration of SDR would be preferable?

Do different types of contact require different PEP regimens or interventions (e.g. higher or repeated dosing of rifampicin, longer-acting rifapentine, or a multidrug therapy for prevention in close contacts)?

What would be an effective follow-up and management plan after PEP?

Can specific biomarkers be identified that differentiate infected (asymptomatic) contacts from non-infected contacts?

Can biomarkers be identified that predict progression to disease in infected individuals?

Based on such biomarkers, can robust and reliable field-friendly diagnostic tests be developed to facilitate early diagnosis and appropriate targeting of treatment?

Will immunoprophylaxis work synergistically with SDR in PEP?

What are the limitations in sensitivity and specificity of seroconversion tests based on antigens such as PGL-I and LID-1? What is the ability of these tests to detect infection or predict the emergence of clinical symptoms?

Do index patients, contacts and other stakeholders accept PEP with SDR, particularly in areas with a high level of leprosy-related stigma?

Does the introduction of PEP affect the perception of leprosy in the community?