A study led by professionals from the Microbiology Department and the ITS Drassanes Unit of the Infectious Diseases Department at Vall d’Hebron University Hospital has described nine cases of dermatophilosis diagnosed in Barcelona between December 2025 and March 2026. The clinical, epidemiological, and genomic findings point to a possible person-to-person transmission in the context of intimate or sexual contact. The study has been published in the journal Emerging Infectious Diseases.

Dermatophilosis is an uncommon skin infection in humans caused by bacteria of the genus Dermatophilus. Until now, the human cases described in the scientific literature had mainly been associated with individuals in contact with animals, particularly livestock, horses, or other mammals.

In this study, nine cases detected in Barcelona were analysed. The patients were men who have sex with men and who presented with mild cutaneous lesions, such as rashes, papules, or nodules, predominantly located in the genital area, groin, thighs, or beard region. All patients showed a favourable clinical course and responded well to antibiotic treatment, without complications.

Microbiological and genomic analysis of the samples indicated that the identified microorganisms were highly similar to one another, reinforcing the hypothesis of a recent common source. “The findings point to a possible shift in the transmission pattern of this bacterium, which until now had primarily been associated with animal exposure. In addition, the genomic data show that the bacteria form a distinct lineage within Dermatophilus, raising the possibility that they may correspond to a previously undescribed bacterial species with epidemiological characteristics different from those known to date”, explains Dr. Juan José González, specialist in the Microbiology Department at Vall d’Hebron University Hospital and head of the Microbiology Group at the Vall d’Hebron Research Institute (VHIR). “Nevertheless, this remains an uncommon infection and the observed cases presented with mild clinical manifestations.”

The authors note that the clinical manifestations may be non-specific. For this reason, Dr. Vicente Descalzo, physician at the Infectious Diseases Department at Vall d’Hebron University Hospital and researcher at the Infectious Diseases group at VHIR, highlights that “it is important for healthcare professionals to consider this infection in the differential diagnosis of certain cutaneous presentations in order to facilitate diagnosis and treatment.”

In this context, the Study Group on Sexually Transmitted Infections of the Spanish Society of Infectious Diseases and Clinical Microbiology has also circulated an informational document among its members describing these cases and another similar cluster detected simultaneously in Lyon and Paris. The document indicates that the disease may be emerging as a transmissible bacterial dermatosis within sexual networks with high levels of exposure. Following this communication, researchers became aware of additional compatible cases in other cities across Spain and Europe, suggesting that this is not a strictly local phenomenon and that we may be facing an emerging skin infection that is likely underdiagnosed.

Although additional studies are needed to accurately determine the extent and mechanisms of transmission involved, the authors underline the importance of increasing clinical awareness in the presence of compatible skin lesions, promoting microbiological sampling, and strengthening coordinated surveillance among sexually transmitted infection units, microbiology departments, and public health services.