Leprosy Mailing List – August 7, 2026
Ref.: (LML) Long-lasting adverse impact of chemoprophylaxis & what actually works
From: Claudio Guedes Salgado, Marituba, Brazil
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Dear Pieter,
I have followed with great interest the recent exchange initiated by Joel Almeida, followed by the thoughtful comments from Benedict Quao and Ben Naafs about the “(LML) Long-lasting adverse impact of chemoprophylaxis & what actually works”.
Rather than focusing exclusively on the proposed biological mechanism, I believe the discussion has now reached a broader and perhaps more important scientific question: what level of evidence is required before a preventive intervention is considered sufficiently safe for widespread implementation?
Joel Almeida proposes a biological hypothesis that seeks to explain the epidemiological observations reported in a recent publication. Benedict Quao rightly reminds us that ecological associations should not be interpreted as proof of causality and that mechanistic hypotheses must remain clearly distinguished from experimental evidence. Ben Naafs, in turn, accepts several of Benedict's methodological criticisms while simultaneously reminding us that the available evidence is also insufficient to conclude that SDR-PEP is free from important long-term adverse consequences.
To me, this is the central point.
Regardless of whether Joel's proposed mechanism ultimately proves correct, the current discussion highlights an important limitation of the existing evidence base. Most SDR studies were designed to evaluate reductions in case detection, operational feasibility, implementation, or acceptability. They were not specifically designed to investigate delayed clinical outcomes such as multibacillary disease, nerve function impairment, immunological reactions, or grade 2 disability.
This distinction is important.
Operational feasibility is not equivalent to long-term clinical safety.
Likewise, high acceptance of a single tablet should not be interpreted as evidence supporting the intervention itself. In communities where Hansen's disease remains a feared condition, acceptance of a simple preventive intervention is naturally expected. Acceptance tells us that implementation is possible; it does not tell us whether the intervention is the optimal strategy or whether all clinically relevant risks have been adequately evaluated.
Another aspect deserves attention. The pivotal COLEP trial demonstrated a protective effect primarily during the first two years of follow-up. Thereafter, this advantage was no longer statistically demonstrable. Subsequent multicountry studies have contributed valuable information regarding implementation and feasibility, but relatively few, if any, have been specifically designed to determine whether SDR provides sustained protection or whether it influences clinically relevant long-term outcomes.
Another issue that deserves far greater attention is the quality of contact examination itself.
The effectiveness and safety of any chemoprophylaxis programme depend fundamentally on correctly identifying who truly does not have Hansen's disease before SDR is administered. This requires experienced clinical evaluation. Unfortunately, global expertise in clinical leprosy has declined considerably since the WHO declaration of leprosy elimination as a public health problem in 2000. In many endemic countries, relatively few health professionals have extensive experience in recognizing early, subtle, oligosymptomatic or predominantly neural forms of the disease.
Our own experience strongly supports this concern. Following the structured training of 55 physicians as leprologists in the Brazilian state of Mato Grosso, case detection increased substantially, particularly in the municipalities where these specialists are now practicing (de Medeiros Junior NF, Salgado CG, Andrade VLG, Maluf GA. Hanseníase no Brasil: Mato Grosso em foco. Cuiabá: Tribunal de Contas do Estado de Mato Grosso; 2024). This observation suggests that one limiting factor in Hansen's disease control is not simply transmission itself, but the capacity to recognize disease early and accurately.
This naturally raises an important question for current SDR programmes: who is examining contacts before they receive chemoprophylaxis, and what level of expertise is required to confidently exclude early Hansen's disease?
An equally important question concerns diagnostic support. In the settings where SDR trials are being conducted, or where SDR has already been incorporated into control programmes, are complementary diagnostic tools routinely available? Are serological assays such as anti-PGL-I IgM, molecular methods such as RLEP qPCR, or high-resolution peripheral nerve ultrasonography being systematically used to improve the detection of oligosymptomatic or subclinical disease before chemoprophylaxis is offered?
If the answer is no, then an unavoidable concern remains: individuals with early or unrecognized Hansen's disease may be incorrectly classified as healthy contacts and consequently receive a single dose of rifampicin instead of prompt multidrug therapy followed by appropriate neurological monitoring.
Several additional questions therefore remain unanswered.
Could administration of SDR to contacts with unrecognized subclinical disease delay diagnosis rather than prevent disease?
Could this contribute to later multibacillary presentations or increased disability?
Has nerve function impairment been systematically monitored after SDR administration with the same rigor routinely recommended during multidrug therapy?
Have studies been adequately powered and specifically designed to detect delayed neurological or immunological outcomes?
Has the possibility of altered transmission dynamics, rather than simply altered case detection, been sufficiently explored?
Has the potential selection of rifampicin-resistant organisms, whether in Mycobacterium leprae or other bacteria exposed within the community, been adequately investigated under conditions of large-scale administration?
Finally, could widespread confidence in chemoprophylaxis inadvertently reduce the emphasis placed on what remains the cornerstone of Hansen's disease control: careful clinical examination, experienced assessment of contacts, early diagnosis, and longitudinal follow-up?
None of these questions demonstrates that SDR-PEP is harmful.
Equally, however, none has yet been answered sufficiently to conclude that SDR-PEP is unequivocally safe under routine programmatic conditions.
In science, absence of evidence of harm should never be confused with evidence of absence of harm.
The present discussion should therefore not be viewed as being for or against SDR. Rather, it should encourage the Hansen's disease community to generate the level of evidence that such a globally promoted intervention deserves. Future studies should move beyond operational feasibility and short-term case detection to include rigorous clinical assessment by experienced leprologists, systematic evaluation of nerve function, disability, multibacillary disease, reactions, molecular diagnosis, antimicrobial resistance, and prolonged follow-up.
Perhaps the first question should not be "Should SDR be given to this contact?" Rather, it should be "How certain are we that this individual truly does not already have Hansen's disease?" Until we can answer that question with confidence, caution remains both scientifically justified and clinically prudent.
Kind regards,
Claudio Salgado
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Claudio Guedes Salgado, MD, PhD
Full Professor
Institute of Biological Sciences
Federal University of Pará
Coordinator of the Biological Sciences II Area at CAPES, Brazil
Former President of Brazil Hansen's Disease Society (SBH), 2018-2023
International Relations Advisor for the SBH
Elected Councillor for the Americas 2025–2028 International Leprosy Association (ILA)
Dermato-Immunology Lab
Av. João Paulo II, 113
Bairro: Dom Aristides
Marituba - Pará - Brasil
CEP: 67200-000
Phone: +55-91-3201-7033
Cell phone: +55-91-991465641
E-mails: csalgado@ufpa.br and claudioguedessalgado@gmail.com
Lattes CV (Brazil format): http://lattes.cnpq.br/2310734509396125
ORCID ID: https://orcid.org/0000-0003-3961-7764
LinkedIn: https://www.linkedin.com/in/claudio-guedes-salgado/
Instagram: https://www.instagram.com/claudiosalgado/
Facebook: https://www.facebook.com/claudioguedessalgado
Map to the Lab: https://goo.gl/maps/7omyd54wy7z
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LML - S Deepak, B Naafs, S Noto and P Schreuder
LML blog link: http://leprosymailinglist.blogspot.it/
Contact: Dr Pieter Schreuder << edit...@gmail.com
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