Beginning October 29, 2025, clustered cases of lower-limb cutaneous ulcers were reported in the Kayassie community, Safroko Limba Chiefdom, Bombali District, Sierra Leone. The outbreak predominantly affected schoolchildren and displayed sustained transmission: 266 cases by December 24, 2025; 386 cases by January 13, 2026; and approximately 403 cases by February 10, 2026. Lesions were most commonly localized to the lower limbs (over the knee, below the knee, lateral leg, and ankle) and typically presented as single, irregular-bordered ulcers with a mostly dry, crusted base and limited purulent exudate. Some patients exhibited localized edema. Case management and enhanced surveillance were implemented; cases recovered gradually, and no fatalities were reported.
Because anthrax was an early concern, the first seven skin swab samples underwent quantitative PCR targeting rpoB, pagA (pXO1), and capC (pXO2), which excluded Bacillus anthracis. Metagenomic sequencing of those initial swabs using the MinION platform revealed sequences mapping to Haemophilus ducreyi in 4 of 7 samples and did not identify other relevant pathogens. Real-time PCR performed to confirm the sequencing results returned positive H. ducreyi detection in all seven initial samples, supporting a strong association between H. ducreyi and the outbreak.
As the investigation progressed, an additional 149 swab samples were collected and tested by PCR, for a total of 156 samples analyzed. Of these, 96 samples (61.5%) were PCR-positive for H. ducreyi. Quantitative PCR assays detected no DNA evidence of Treponema pallidum subspecies—including subsp. pertenue, the agent of yaws—in any of the 156 samples tested. These findings suggest H. ducreyi was the predominant identifiable bacterial agent in sampled lesions during this outbreak.
To further characterize the microbial content of lesions, investigators sequenced genomic DNA from 22 swab samples (12 H. ducreyi–positive and 10 H. ducreyi–negative) on the DNBSEQ-G99 platform. Metagenomic analyses of these samples found no evidence of T. pallidum subsp. pertenue, consistent with PCR results. The most abundant bacterial species in those samples included Staphylococcus aureus and Klebsiella pneumoniae. H. ducreyi was among the most suspected causative agents based on abundance and targeted PCR results. The report provides a heatmap of species abundance for these samples.
Field culture attempts were performed on 61 swab samples using Columbia blood agar supplemented with yeast extract, vancomycin, and rabbit blood under microaerophilic conditions at 33°C. After 96 hours and subsequent subcultures, grayish-white pinpoint colonies consistent with H. ducreyi were obtained and confirmed by PCR from 9 samples. Investigators noted that ambient transport temperature and absence of CO2 during transport likely reduced culture yield. The nine culture-confirmed isolates underwent whole-genome sequencing on an Illumina platform. Phylogenetic analysis placed these isolates in a cluster with strains previously reported from Ghana and distributed them into two clades, indicating regional relatedness. Sequence read data for 22 swabs and the 9 isolates were submitted to the National Center for Biotechnology Information Sequence Read Archive (accession PRJNA1450830).
To explore potential nonhuman reservoirs or vectors, investigators tested environmental samples by quantitative PCR, including 60 saline-soaked flies, 8 water samples from nearby ponds, and tissue from two goats that died during the outbreak period. None of these environmental or animal samples were positive for H. ducreyi. The source and precise transmission pathways for the outbreak therefore remain unclear based on the tests performed.
This investigation confirmed H. ducreyi as the causative bacterial agent associated with a protracted outbreak of pediatric cutaneous ulcers in Bombali District during late 2025 and early 2026. The outbreak was characterized as low-severity, with progressive ulcerations that resolved gradually under enhanced surveillance and clinical management; the source was not identified. The report underscores that in yaws-endemic countries such as Sierra Leone, nongenital cutaneous ulcers in children may be caused by H. ducreyi as well as by Treponema pallidum subspecies pertenue, and that clinicians and public health programs should include H. ducreyi in differential diagnoses and laboratory testing algorithms.
Limitations and notes from the source: The article notes reduced culture recovery possibly related to transport conditions and reports that specific treatment regimens were not detailed in the source. Data were derived from routine public health programmatic activities; sample collection was done with consent and the study was administratively approved by the National Public Health Agency of Sierra Leone.