First Report of Digital Skin Ulcer with Stenotrophomonas maltophilia Infection in an Immunocompetent Patient

Discussion

S. maltophilia is an ubiquitous bacterium which has been isolated from water, soil, plants and medical devices. It is an opportunistic nosocomial pathogen acquired from an independent source, possibly even before hospitalization, and selected from the commensal flora during anti-microbial exposure. The most important risk factors for developing S. maltophilia infection are associated with a severely-compromised health status and various medical treatments, i.e. intravascular catheter positioning, mechanical ventilation and exposure to broad-spectrum anti-microbials. Hematological malignancy is the most common risk factor for developing S. maltophilia infection, as reported in the literature (5, 6). Moreover, some series suggest the existence of an altered microenvironment in neoplastic tissue favorable for the multiplication of S. maltophilia. Therefore, in the presence of such infection, malignancy should be ruled out and the presence of latent disorders resulting in neutropenia should be excluded (7).

Despite the fact that S. maltophilia has been considered to be a nosocomial-acquired pathogen, community-acquired infection with this bacterium may occur more frequently than previously recognized (8-11). However, unlike recent reports, in our case the onset is not ascribable to a trauma nor to concomitant disease. The patient is a bricklayer who occasionally looks after cattle, so perhaps the cause of the infection is related to his job.

Cutaneous infections are very rare, and infection of intact skin is even more rare (12).

The most frequently described skin and soft tissue manifestations due to S. maltophilia infection are subcutaneous nodules and primary or metastatic cellulitis, which may manifest as ecthyma gangrenosum (6, 12, 13).

S. maltophilia is a bacillus with low virulence that usually causes infection in immunocompromised patients, while in our case, the patient was immunocompetent and S. maltophilia proved to have a particular clinical severity. The superficial swabs were not useful for the diagnosis. Only the deep tissue biopsy allowed isolation of the bacterium and selection of the targeted therapy.

Treatment of S. maltophilia infections is challenging because this organism is intrinsically resistant to most antibiotics and disinfectants, grows slowly, and has a high rate of mutation, which can confer antibiotic resistance. Resistance to β-lactams, carbapenems, aminoglycosides, and chinolones is well-known (14). Recommendations for therapy rely on in vitro susceptibility testing.

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Figure 1.

A: Infected digital ulcer of the second and third fingers of the right hand. B: Postoperative image showing the outcomes of the amputation of the distal phalanges and their reconstruction with Atasoy flap. C: Detailed postoperative image.

In summary, S. maltophilia is emerging as an important cause of skin infection in immunoresponsive patients. Several community-acquired infections have been recently reported, however, our case appears to represent the first report of a digital wound of intact skin, i.e. without history of trauma, caused by community-acquired S. maltophilia infection in an immunocompetent patient.