---
title: "Haemophilus ducreyi Identified as Cause of Cutaneous Ulcer Outbreak in Sierra Leone Children, 2025"
id: "cdc-emerging-infectious-diseases-journal-2-haemophilus-ducreyi-bacteria-causing-cutaneous-ulcer-outbreak-in-children"
canonical_url: "https://medichelpline.com/clinical-feed/cdc-emerging-infectious-diseases-journal-2-haemophilus-ducreyi-bacteria-causing-cutaneous-ulcer-outbreak-in-children"
content_type: "clinical_feed_article"
specialty: "Infectious Disease"
source_name: "CDC Emerging Infectious Diseases Journal"
source_url: "https://wwwnc.cdc.gov/eid/article/32/10/26-0727_article"
published_at: "2026-09-21T04:00:00.000Z"
evidence_level: "Agency Feed"
license: "CC-BY-NC-4.0 / Informational Use"
---
# Haemophilus ducreyi Identified as Cause of Cutaneous Ulcer Outbreak in Sierra Leone Children, 2025
## Provenance & Clinical Metadata
- **Canonical URL:** https://medichelpline.com/clinical-feed/cdc-emerging-infectious-diseases-journal-2-haemophilus-ducreyi-bacteria-causing-cutaneous-ulcer-outbreak-in-children
- **Specialty:** [Infectious Disease](https://medichelpline.com/clinical-feed/infectious-disease.md)
- **Primary Source:** CDC Emerging Infectious Diseases Journal
- **Source URL:** [Original Journal Publication](https://wwwnc.cdc.gov/eid/article/32/10/26-0727_article)
- **Published At:** 2026-09-21T04:00:00.000Z
- **Evidence Rating:** Agency Feed
## Executive GIST (TL;DR)
- An outbreak of **cutaneous ulcers** began October 29, 2025, in Kayassie community, Bombali District, Sierra Leone, primarily affecting schoolchildren and culminating in ≈403 reported cases by February 10, 2026. - Initial differential included **Bacillus anthracis**, but rapid PCR screening of the first 7 swabs excluded B. anthracis. - Metagenomic sequencing (MinION) and confirmatory real-time PCR found **Haemophilus ducreyi** sequences in the first 7 swabs and all 7 were PCR-positive for H. ducreyi. - Across 156 total skin swab samples collected during the outbreak, 96 (61.5%) were PCR-positive for H. ducreyi; no DNA evidence of Treponema pallidum subspecies (including pertenue) was detected. - Metagenomic analysis of 22 swabs (12 PCR-positive, 10 PCR-negative) on the DNBSEQ-G99 platform showed no T. pallidum pertenue and identified Staphylococcus aureus and Klebsiella pneumoniae among the most abundant species; H. ducreyi was a leading suspect pathogen. - Field culture of 61 swabs onto supplemented Columbia blood agar yielded H. ducreyi isolates from 9 samples after microaerophilic incubation and subculture; ambient transport conditions may have reduced culture success. - Whole-genome sequencing of 9 isolates placed them in a cluster with strains from Ghana, distributed into two clades, suggesting regional relatedness. Sequence data were submitted to NCBI SRA (accession PRJNA1450830). - Environmental testing (60 flies, 8 pond water samples, tissues from 2 goats) by quantitative PCR did not detect H. ducreyi, leaving the outbreak source unresolved. - The outbreak was protracted but low-severity, produced no fatalities, and cases showed gradual recovery under enhanced surveillance and case management; specific treatment details were not reported in the source. - The investigation highlights that **H. ducreyi** can be a primary cause of nongenital cutaneous ulcers in yaws-endemic settings and should be considered by clinicians and public health programs in such regions.
## Clinical Analysis & Structured Key Points
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[EID Journal](https://wwwnc.cdc.gov/eid/) 2. [Volume 32](https://wwwnc.cdc.gov/eid/early-release) 3. [Early Release](https://wwwnc.cdc.gov/eid/early-release#issue-1346) 4. [Main Article](https://wwwnc.cdc.gov/eid/article/32/10/26-0727_article) * [Facebook](https://www.facebook.com/sharer/sharer.php?u=%2Feid%2Farticle%2F32%2F10%2F26-0727_article "Share to Facebook") * [Twitter](http://twitter.com/share?url=%2Feid%2Farticle%2F32%2F10%2F26-0727_article&text= "Share to Twitter") * [LinkedIn](https://www.linkedin.com/shareArticle?url=%2Feid%2Farticle%2F32%2F10%2F26-0727_article&title= "Share to LinkedIn") * [Syndicate](https://tools.cdc.gov/medialibrary/index.aspx#/sharecontent//eid/article/32/10/26-0727_article "Embed this Page") [ Emerging Infectious Disease journal ISSN: 1080-6059 ](https://wwwnc.cdc.gov/eid/) _Disclaimer: Early release articles are not considered as final versions. Any changes will be reflected in the online version in the month the article is officially released._ #### Volume 32, Number 10—October 2026 ##### _Research Letter_ ### _Haemophilus ducreyi_ Bacteria Causing Cutaneous Ulcer Outbreak in Children, Sierra Leone, December 2025 On This Page [Research Letter](https://wwwnc.cdc.gov/eid/article/32/10/26-0727_article) * * * [Suggested Citation](https://wwwnc.cdc.gov/eid/article/32/10/26-0727_article) Figures [Figure 1](https://wwwnc.cdc.gov/eid/article/32/10/26-0727-f1) * * * [Figure 2](https://wwwnc.cdc.gov/eid/article/32/10/26-0727-f2) Downloads [Appendix ](https://wwwnc.cdc.gov/eid/article/32/10/26-0727-app1.pdf) * * * [RIS [TXT - 2 KB] ](https://wwwnc.cdc.gov/eid/article/32/10/26-0727.ris) Article Metrics [Metric Details](https://wwwnc.cdc.gov/eid/article/32/10/26-0727_article) Jianxu Zhang[1](https://wwwnc.cdc.gov/eid/article/32/10/26-0727_article#fn1), Peng Lv[1](https://wwwnc.cdc.gov/eid/article/32/10/26-0727_article#fn1), Teng Zhao, Hanji Jiang, James S. Squire, Martin S. Yonnie, Zikan Koroma, Ibrahim F. Kamara, Abdulai A. Jalloh, Guangqian Pei, Yunfei Wang, Hongling Liu, Mohamed B. Jalloh[![Comments to Author](https://wwwnc.cdc.gov/eid/content/images/icon/email.gif)](https://wwwnc.cdc.gov/eid/article/32/10/26-0727_article#comment) , and Zhiqiang Mi[![Comments to Author](https://wwwnc.cdc.gov/eid/content/images/icon/email.gif)](https://wwwnc.cdc.gov/eid/article/32/10/26-0727_article#comment) Author affiliation: Changchun Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Changchun, China (J. Zhang); National Key Laboratory of Advanced Biotechnology, Academy of Military Medical Sciences, Beijing, China (P. Lv); State Key Laboratory of Pathogen and Biosecurity, Academy of Military Medical Sciences, Beijing (T. Zhao, H. Jiang, G. Pei, Y. Wang, Z. Mi); University of Sierra Leone, Freetown, Sierra Leone (J.S. Squire); National Public Health Agency, Freetown (J.S. Squire, Z. Koroma, A.A. Jalloh, M.B. Jalloh); Ministry of Health, Bombali DHMT, Makeni, Sierra Leone (M.S. Yonnie); World Health Organization, Health Systems and Services Cluster, Freetown (I.F. Kamara); The Fifth Medical Center of Chinese PLA General Hospital, Beijing (H. Liu); College of Medicine and Allied Health Sciences, University of Sierra Leone, Freetown (M.B. Jalloh) [Suggested citation for this article](https://wwwnc.cdc.gov/eid/article/32/10/26-0727_article#suggestedcitation) ### Abstract We report a cutaneous ulcer outbreak in Sierra Leone in 2025 that predominantly affected ≈403 schoolchildren. The causative agent was confirmed as _Haemophilus ducreyi_ , a bacterium traditionally associated with the sexually transmitted infection chancroid but more recently recognized as an emerging cause of lower limb cutaneous ulcers in tropical regions. Nongenital cutaneous ulcers as a public health problem commonly affect children in many tropical regions, especially in West and Central Africa, the South Pacific, and South Asia ([_1_](https://wwwnc.cdc.gov/eid/article/32/10/26-0727_article#r1 "1")). Yaws, which is caused by _Treponema pallidum_ subspecies _pertenue_ , has historically been considered the primary causative agent of such ulcers ([_2_](https://wwwnc.cdc.gov/eid/article/32/10/26-0727_article#r2 "2")). In recent years, however, several studies have demonstrated that _Haemophilus ducreyi_ is a leading bacterial cause of cutaneous ulcers (lower leg lesions in the absence of genital lesions) in yaws-endemic regions ([_3_](https://wwwnc.cdc.gov/eid/article/32/10/26-0727_article#r3 "3")–[ _5_](https://wwwnc.cdc.gov/eid/article/32/10/26-0727_article#r5 "5")). Figure 1 ![Irregular appearance of cutaneous ulcer lesions from patients in study of Haemophilus ducreyi bacteria causing cutaneous ulcer outbreak in children, Sierra Leone, December 2025. A\) Lesions over the knee. B\) Lesions below the knee. C\) Lesions on the mid-lateral aspect of the leg. D\) Lesions at the ankle.](https://wwwnc.cdc.gov/eid/images/26-0727-F1-tn.jpg) [Figure 1](https://wwwnc.cdc.gov/eid/article/32/10/26-0727-f1 "Figure 1"). Irregular appearance of cutaneous ulcer lesions from patients in study of _Haemophilus ducreyi_ bacteria causing cutaneous ulcer outbreak in children, Sierra Leone, December 2025. A) Lesions over the knee.... Beginning on October 29, 2025, several clustered cases of lower limb cutaneous ulcers predominantly affecting schoolchildren in the Kayassie community, Safroko Limba Chiefdom, Bombali District, Sierra Leone, were reported to the National Public Health Agency of Sierra Leone. The infections were originally suspected to be _Bacillus anthracis_ infection. Restriction of close student-to-student contact was advised for school management, while immediate laboratory testing for pathogen identification was launched. The outbreak showed sustained transmission: 266 cases by December 24, 2025; 386 cases by January 13, 2026; and 403 cases by February 10, 2026. Patients showed progressive skin ulcerations, sometimes associated with localized edema. The ulcers predominantly occurred on the lower limbs, where opportunistic skin injuries could easily develop, and commonly manifested as a localized lesion with an irregular border. The base of the ulcer was mostly composed of dry and crusted tissue without a purulent exudate ([Figure 1](https://wwwnc.cdc.gov/eid/article/32/10/26-0727-f1)). Recovery progressed steadily after case treatment and management ([Appendix](https://wwwnc.cdc.gov/eid/article/32/10/26-0727-app1.pdf)). Skin swab sample collection was conducted with consent from all participants or their parents or guardians, and the study was conducted using deidentified data derived from routine public health programmatic activities and interventions. The study was also reviewed and approved administratively by the National Public Health Agency of Sierra Leone. _B. anthracis_ infection was immediately excluded in the first 7 skin swab samples by using quantitative PCR targeting _rpoB_ , _pagA_(pXO1), and _capC_(pXO2) (BioPerfectus Technologies, [External Link](https://www.biosearchtech.com)). Analysis of metagenomic sequence data produced from MinION (Oxford Nanopore Technologies, [External Link](https://nanoporetech.com)) ([Appendix](https://wwwnc.cdc.gov/eid/article/32/10/26-0727-app1.pdf)) revealed that _H. ducreyi_ sequences were present in 4 of the 7 swab samples; no other relevant pathogens were identified ([Appendix](https://wwwnc.cdc.gov/eid/article/32/10/26-0727-app1.pdf) Figure 1). To confirm sequencing results, we performed real-time PCR according to a previous report ([_6_](https://wwwnc.cdc.gov/eid/article/32/10/26-0727_article#r6 "6")). All of the first 7 samples tested positive for _H. ducreyi_ Those preliminary results demonstrated that _H. ducreyi_ was highly associated with this cutaneous ulcer outbreak. As the outbreak progressed, another 149 swab samples were collected and shipped to the laboratory for PCR testing. Of the 156 total samples, 96 (61.5%) tested positive for _H. ducreyi_. No DNA evidence of _T. pallidum_ subsp. _pertenue_ , subsp. _pallidum_ , or subsp. _endemicum_ bacteria was detected by quantitative PCR in any of the 156 samples ([_7_](https://wwwnc.cdc.gov/eid/article/32/10/26-0727_article#r7 "7")). Figure 2 ![Heatmap of bacterial species investigated from study of Haemophilus ducreyi bacteria causing cutaneous ulcer outbreak in children, Sierra Leone, December 2025. Values are shown as log10\(abundance + 0.01\)%. Metagenomic analysis based on the DNBSEQ-G99 sequencing platform \(MGI Tech, https://www.mgi-tech.com\). The heatmap revealed that H. ducreyi, the third most abundant bacterium, was the most suspected causative agent through 22 skin swab samples. The samples were designated as follows: FS, samples collected on November 18, 2025; S, samples collected on December 12, 2025; AS and BS, samples collected on December 18, 2025.](https://wwwnc.cdc.gov/eid/images/26-0727-F2-tn.jpg) [Figure 2](https://wwwnc.cdc.gov/eid/article/32/10/26-0727-f2 "Figure 2"). Heatmap of bacterial species investigated from study of _Haemophilus ducreyi_ bacteria causing cutaneous ulcer outbreak in children, Sierra Leone, December 2025. Values are shown as log10(abundance... To further determine the etiologic agent causing this outbreak, we sequenced genomic DNA from 22 swab samples (12 _H. ducreyi_ –positive and 10 _H. ducreyi_ –negative) on the DNBSEQ-G99 platform (MGI Tech, [External Link](https://www.mgi-tech.com)) ([Appendix](https://wwwnc.cdc.gov/eid/article/32/10/26-0727-app1.pdf)). Metagenomic analysis indicated no evidence of _T. pallidum_ subsp. _pertenue_ in the 22 samples, which is consistent with the PCR result. We identified no other etiologic pathogen associated with cutaneous ulcers in the 22 samples. The most abundant bacterial species were _Staphylococcus aureus_ and _Klebsiella pneumoniae_ ([Figure 2](https://wwwnc.cdc.gov/eid/article/32/10/26-0727-f2)). To isolate _H. ducreyi_ , we immediately inoculated 61 swab samples in the field onto Columbia blood agar base (Thermo Fisher Scientific, [External Link](https://www.thermofisher.com)), supplemented with 2.5% fresh yeast extract, 3 µg/mL of vancomycin, and 30% rabbit blood ([_8_](https://wwwnc.cdc.gov/eid/article/32/10/26-0727_article#r8 "8")). After 96 hours of microaerophilic culture at 33°C, grayish-white pinpoint-sized colonies were picked up ([_9_](https://wwwnc.cdc.gov/eid/article/32/10/26-0727_article#r9 "9")). After 3 consecutive subcultures, we confirmed PCR-positive colonies to be _H. ducreyi_ ([Appendix](https://wwwnc.cdc.gov/eid/article/32/10/26-0727-app1.pdf) Figure 2). Among the 61 inoculated samples, _H. ducreyi_ grew from 9 samples. Ambient transport temperature and lack of CO2 might have reduced isolation. We sequenced the complete genomes of 9 _H. ducreyi_ strains on an Illumina platform ( [External Link](https://www.illumina.com)) ([Appendix](https://wwwnc.cdc.gov/eid/article/32/10/26-0727-app1.pdf)). Phylogenetic analysis demonstrated that the 9 isolates recovered in Sierra Leone formed a cluster with strains from Ghana and were distributed into 2 separate clades ([Appendix](https://wwwnc.cdc.gov/eid/article/32/10/26-0727-app1.pdf) Figure 3). We submitted short reads for 22 skin swab samples and 9 strains of _H. ducreyi_ bacteria to the National Center for Biotechnology Information Sequence Read Archive ( [External Link](https://www.ncbi.nlm.nih.gov/sra); accession no. PRJNA1450830). To try to determine a source for the outbreak, we tested 60 saline-soaked fly samples, 8 water samples from neighboring ponds, and tissue samples from 2 goats that died during the outbreak by quantitative PCR. No samples were positive for _H. ducreyi_. This investigation confirmed that _H. ducreyi_ was the causative bacterial agent of the cutaneous ulcer outbreak among children in Bombali District, Sierra Leone, in 2025. Sierra Leone is historically classified as a yaws-endemic country ([_10_](https://wwwnc.cdc.gov/eid/article/32/10/26-0727_article#r10 "10")), and national eradication campaigns have been conducted in past decades. This outbreak, in essence, was a protracted, low-severity outbreak of cutaneous _H. ducreyi_ infection, yielding no fatalities and leading to gradual resolution under enhanced surveillance and case management. However, the source of _H. ducreyi_ in this outbreak remains unclear. Clinicians should be aware of the possibility of cutaneous _H. ducreyi_ infection in yaws-endemic regions. Dr. Zhang works at the Chinese Academy of Agricultural Sciences, the Changchun Veterinary Research Institute, Changchun, China. His primary research interest is detection, prevention, and control of bacterial pathogens causing zoonotic diseases. [TopExternal Link](javascript:void\(0\)) ### Acknowledgment We thank all study participants and their parents or legal guardians for their time, the field team from the National Public Health Emergency Operations Centre, the Bombali District Health Management Team, and the World Health Organization Country Office for Sierra Leone. We also thank Shiyang Cao for her constructive s
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