Clustering of leprosy beyond the household level in a highly endemic setting on the Comoros, an observational study

Nimer Ortuno-Gutierrez, Abdallah Baco, Sofie Braet, Assoumani Younoussa, Aboubacar Mzembaba, Zahara Salim, Mohamed Amidy, Saverio Grillone, Bouke de Jong, Jan Hendrik Richardus, Epco Hasker

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The island of Anjouan (Comoros) is highly endemic for leprosy with an annual incidence of 5-10/10,000. In May/June, 2015 single-dose Rifampicin post-exposure prophylaxis (SDR-PEP) was administered to 269 close contacts of 70 leprosy-patients in four villages as a pilot programmatic intervention. Two years later we revisited the villages for follow-up investigations. The main aim of our study was to quantify spatial associations between reported leprosy cases before and after PEP implementation. A secondary aim was to assess the effect of this single round of SDR-PEP at the individual level.


We conducted door-to-door leprosy screening in all four villages in August/September, 2017. We screened all consenting individuals for leprosy and recorded geographic coordinates of their household. We also recorded whether they had received SDR-PEP and whether they had been diagnosed with leprosy, before or after the 2015 intervention. We fitted a Poisson model with leprosy as outcome and distance to the nearest pre-intervention case and SDR-PEP as predictors.


During the survey we found 114 new cases among 5760 contacts screened (2.0% prevalence), in addition to the 39 cases detected in the two preceding years. We found statistically significant associations of incident leprosy with physical distance to index cases ranging from 2.4 (95% confidence interval (95% CI) 1.5-3.6) for household contacts to 1.8 (95% CI 1.3-2.5) for those living at 1-25m, compared to individuals living at 75m.The effect of SDR-PEP appeared protective but did not reach statistical significance due to the low numbers, with an incidence rate ratio (IRR) of 0.6 (95% CI 0.3-1.2) overall, and 0.5 (95% CI 0.2-1.3) when considering only household contacts.


This pilot demonstrated an increased risk of leprosy in contacts beyond the household, therefore a wider circle should be considered for chemoprophylaxis. Baseline surveys and extended contact definitions are essential for improving SDR-PEP effectiveness.

Original languageEnglish
Article number501
JournalBMC Infectious Diseases
Issue number1
Number of pages7
Publication statusPublished - 2019


  • Antibiotics, Antitubercular/therapeutic use
  • Cluster Analysis
  • Comoros/epidemiology
  • Humans
  • Leprosy/diagnosis
  • Post-Exposure Prophylaxis
  • Prevalence
  • Rifampin/therapeutic use


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