Skin and Soft Tissue Infections (Patera Foot) in Immigrants, Spain

An unusual skin and soft tissue infection of the lower limbs has been observed in immigrants from sub-Saharan Africa who cross the Atlantic Ocean crowded on small fishing boats (pateras). Response to conventional treatment is usually poor. Extreme extrinsic factors (including new pathogens) may contribute to the etiology of the infection and its pathogenesis.

Among the varied medical problems affecting these young, previously healthy immigrants are unexpectedly high numbers of severe skin and soft tissue infections (SS-TIs), especially those involving the feet and legs. Clinical characteristics of these SSTIs were unfamiliar to our department, even though our unit collaborates directly with vascular surgeons, endocrinologists, and dermatologists to manage diabetes-related foot infections. The clinical picture comprises a painful cellulitis with minimal or imperceptible port of entry, deep abscesses, and tissue necrosis. Response to surgical debridement and broad-spectrum antimicrobial drugs is frequently poor, making amputation necessary in many cases. Here we describe the epidemiology, clinical features, microbiology, treatment, and outcome of 7 patients affected with severe SSTIs of the foot and leg and discuss the pathogenic role of Shewanella algae as an etiologic agent in this syndrome.

The Study
The 7 patients were treated at our Unit of Infectious Diseases and Tropical Medicine at the Hospital Universitario Insular of Las Palmas (Gran Canaria Island, Canary Islands, Spain). We defi ned the condition we call "patera foot" as all of the following: 1) acute SSTI involving the feet or legs, 2) direct relation of the infection to sea journey by overcrowded patera under extreme conditions, and 3) good health status before travel. For this report, we excluded patients with diabetes, chronic arterial or venous leg disease, edema, or any other predisposing conditions.
We performed the following basic interventions for all patients: registry of epidemiologic data; complete clinical history and physical examination; blood extraction for routine tests; blood cultures (if fever); cleaning and debridement of the affected area (if indicated by the vascular surgery team); and acquisition of cultures from the affected area by syringe (if abscess), skin punch (if cellulitis only), or deep infected tissue (if surgical debridement). Plastic surgery was performed when indicated. Amputation was carried out only after every effort was made to preserve the affected foot or leg.
All 7 patients whose conditions met the classifi cation criteria were young, black, sub-Saharan men (Table). In all patients, we ruled out a defi ned immunodefi ciency, specifi cally HIV infection; use of immunosuppressive agents; and indirect data suggesting primary immunodefi ciency (lymphopenia or immunoglobulin defi ciency). Organisms isolated from local specimens were gram-negative bacteria in all microbiologically positive cases. Four patients underwent amputation, including 1 transtibial and 1 transmetatarsal. Patient 7, a 21-year-old man, was admitted to the intensive care unit because of shock secondary to severe SSTI and intense dehydration with acute renal failure and rhab- domyolysis. Bilateral painful enlargement of his lower extremities was evident, with disseminated round ulcers and serohemorrhagic, confl uent blisters. The ulcers were covered with a fi brinoid, purulent exudate ( Figure, panel A).
After blood and skin samples were collected for culture, the patient began taking meropenem and linezolid . Skin samples grew gram-negative rods, initially identifi ed as S. putrefaciens by using the API 20E system (bioMérieux, Marcy l'Etoile, France). By using experimental work (3)(4)(5) that allows differentiation between Shewanella species, we identifi ed the organism as S. algae on the basis of its capacity to grow at 42ºC in 6.5% NaCl and to produce betahemolysis. The organism displayed in vitro susceptibility to ceftazidime, meropenem, piperacilin/tazobactam, ciprofl oxacin, aminoglycosides, trimethoprim/sulfamethoxazole and aztreonam but resistance to amoxicilin/clavulamate, cefotaxime, and, notably, to imipenem (because S. algae is sensitive to other carbapenems i.e., meropenem). Four days after the patient was admitted to our unit, a large fl uctuant area appeared on the dorsum of his left foot; drainage from the area consisted of a grossly purulent, foul-smelling material. Extensive debridement was necessary to control infection ( Figure, panel B); 1 month later, a skin allograft was implanted ( Figure, panel C). The patient was discharged, asymptomatic, after 70 days of hospitalization.

Conclusions
During sea crossing by patera, immigrants are exposed to extreme extrinsic conditions, such as cold weather and defi cient hygienic conditions. Intrinsic factors, such as limited skin compliance related to young age and possibly race, may play additional roles in the pathogenesis of this syndrome. Black race may be an intrinsic factor because, to our knowledge, immigrants of other ethnic origin (Magreb countries) have not developed this syndrome.
The presence of gram-negative bacteria in all casepatients, especially S. algae in 1, instead of gram-positive cocci, indicates a source of infection related to water and illustrates the specifi c pathogenesis of this syndrome. Shewanella spp. are ubiquitous gram-negative bacteria; possible reservoirs include all types of water, oil emulsions, petroleum brines, protein-rich foods, and soil (5-7). Two Shewanella species, S. algae and S. putrefaciens, have been found in clinical specimens. Because automated systems are unable to distinguish between the 2 species, a number of infections attributed to S. putrefaciens probably correspond to S. algae (4). S. algae is considered a rare opportunistic pathogen for humans, frequently involving immunocompromised hosts (6,8,9), and are usually part of a polymicrobial infection (6,10,11), which may mask its clinical importance. The presence of chronic leg ulcers in the context of peripheral vascular disease occurs commonly in adults with S. algae SSTI (6,10,12,13), and the affi nity of S. algae for necrotic or ischemic tissues has been well described (12,14,15).
The following sequence may explain why these young, previously healthy men developed such aggressive SSTIs. We speculate that specifi c etiologic agents (mainly GNB, including S. algae) present in densely contaminated water enter through macerated skin, then reach deep tissues that   have been submitted to subacute ischemia from overpressure and defi cient venous drainage, both related to forced, prolonged sitting. The ensuing inner infl ammation, expanding against a young skin with limited compliance, further aggravates the ischemia and leads to necrosis, probably by a compartmental-like mechanism. These cases appear to represent a new syndrome, with specifi c etiology, pathogenesis, clinical features, and response to treatment. GNB, including S. algae, are involved, and an ischemic mechanism may be crucial in the development of these destructive infections. The initial election of empirical therapy, always covering those pathogens, and early surgical evaluation are crucial in preventing major disability in these young people.