Introduction
Edwardsiella tarda, a gram-negative bacillus, is a member of the Enterobacteriaceae family, which was first described by Bockemühl et al. [1]. This bacterium has been isolated from a wide range of animals in aquatic environments (including reptiles as well as saltwater and freshwater fishes), and rarely causes disease in humans. E. tarda causes mild digestive disease as well as gastroenteritis in most cases (80%) [2]. The remaining 20% of human E. tarda infections are extraintestinal diseases. Systemic and extraintestinal manifestations, including myonecrosis, meningitis, septic peritonitis, bacteremia, etc., have been reported in a few cases of patients (especially in patients with underlying disorders such as immunodeficiency disease, i.e. malignancy), which are potentially life-threatening conditions [2, 3]. Risk factors for E. tarda infections include exposure to aquatic animals, dietary habits (e.g. raw fish ingestion), pre-existing hepatobiliary diseases, hematological disorders, and malignancy [4].
Here, we report a rare case caused by E. tarda infection in a young patient with unknown previous underlying or immunodeficiency diseases.
Although systemic and extraintestinal E. tarda infections typically occur in patients with pre-existing risk factors and underlying diseases, we recommend that doctors consider this potentially fatal foodborne infection even in patients with a healthy immune system and no underlying conditions.

Case Presentation
The patient was a 25-year-old Iranian woman who was hospitalized in Shafayahyaeian Hospital, Tehran, Iran, on March 11, 2024, with right shoulder pain 24 days earlier. After taking x-ray photographs, the diagnosis of fracture of the greater tuberosity of the right humerus was raised. The patient underwent fracture fixation with a deltopectoral approach with ETHIBOND EXCEL™ suture. In a one-month follow-up, the patient was recovering and reported no problems. However, she gradually developed pain and restricted movement. In serial radiographs, the greater tuberosity of the humerus was absorbed.
After 3 months, the patient was admitted to the hospital due to pain, restricted movement, and fever with a diagnosis of infection. On June 15, 2024, the sutures were removed. In the second operation, the large tuberosity was completely absorbed, and the patient’s symptoms improved.
A tissue culture sample was obtained, which was reported to be E. tarda. Before the preparation of culture results, the patient was treated with vancomycin 1 g, twice a day, accompanied by ceftazidime 1 g, thrice a day. With preparation of culture results and consultation with the infectious disease service, the antibiotic treatment regimen of the patient was switched to ciprofloxacin 500 mg, twice a day, as well as clindamycin 300 mg, thrice a day.
In this way, the patient had an uneventful recovery. She was examined for immune and genetic studies, and no immune deficiency-related problems were reported. Past medical history of the patient, except for the computed tomography coronary angiography (CTCA) in the previous month, was unremarkable. She also had no familial history, allergy history, or drug history.
It should be noted that this case report has been written using the CARE (CAse REport) reporting guidelines [5]. Moreover, the verbal and written informed consent were obtained from the patient.

Discussion
E. tarda is a motile anaerobic bacterium of the Enterobacteriaceae family, which is isolated from various animals living in aquatic environments (e.g. reptiles, amphibians, and fish). E. tarda is not a part of the normal human flora and rarely causes illness in humans. E. tarda infection is regarded as a foodborne infection and is transmitted to humans by eating contaminated food such as raw seafood [6]. The risk factors of E. tarda infection include being injured in aquatic environments, certain dietary habits (sushi, fish, and raw meat), immunodeficiency, and chronic diseases such as liver cirrhosis or diabetes [3, 7].
E. tarda bacterial infection in humans can be classified into two types, namely gastrointestinal diseases (80%) and extraintestinal or systemic infections (20%) [3, 7]. Gastrointestinal diseases are among the most common manifestations of this bacterium. Fortunately, the bacterium is sensitive to most antibiotics [6]; nevertheless, severe extraintestinal infections have also been reported, including bacteremia, liver abscess, wound infection, necrotizing fasciitis, osteomyelitis, cholecystitis, endocarditis, and brain abscess, which are potentially life-threatening conditions. The mortality rate of E. tarda infection in the case of sepsis reaches 50% [3, 7].
Here we report a case of extraintestinal infection with E. tarda in a young patient with unknown underlying or immunodeficiency diseases. This issue demonstrates that E. tarda can also cause extraintestinal infection even in immunocompetent patients. This infection is most common in the elderly, with an average age of 61 years [6, 8]. In contrast, our patient was a 25-year-old woman with E. tarda infection.
Based on the available studies, E. tarda infections have been more common in East Asia, Australia, and North America [6]. However, our patient is one of the few reported cases of extraintestinal infections with this bacterium in Iran. Considering that aquatic animals transmit this pathogen, there is a possibility of more cases of human diseases in Iran [8].
E. tarda bacterium can produce beta-lactamase enzyme, but it is usually sensitive to β-lactam antibiotics [9]. According to previous studies, antibiotics with activity against gram-negative bacilli (aminoglycosides, tetracyclines, fluoroquinolones, etc.) are usually effective on almost all strains of this bacterium [8, 10]. Our patient underwent treatment with vancomycin, accompanied by ceftazidime, before the results of the culture were determined. Afterwards, based on the results of culture and consultation with an infectious diseases specialist, the patient’s antibiotic treatment regimen was changed to ciprofloxacin and clindamycin, which led to the improvement of the patient’s symptoms.

Conclusions
E. tarda, although infrequently encountered as a human pathogen, can cause severe extraintestinal infections with varied clinical presentations. Our investigation reveals that E. tarda can affect immunocompetent patients, thereby suggesting that E. tarda should be regarded as a potentially significant pathogen, particularly in immunocompromised individuals without underlying diseases.

Ethical Considerations

Compliance with ethical guidelines
Verbal and written informed consent were obtained from the patient to write and publish this report.

Funding
This study was performed with the support of Iran University of Medical Sciences, Tehran, Iran.

Authors' contributions
Conceptualization: Morteza Nakhaei Amroodi, Babak Roshanravan, Saeedreza Amiri, and Pouria Tabrizian; Methodology: Morteza Nakhaei Amroodi, Mojtaba Baniasadi, Amir Sobhani, Saeedreza Amiri, and Pouria Tabrizian; Formal analysis and investigation: Morteza Nakhaei Amroodi, Babak Roshanravan, Amir Sobhani, and Mojtaba Baniasadi; Writing the original draft: Morteza Nakhaei Amroodi, Babak Roshanravan, and Mojtaba Baniasadi; Review and editing: All authors; Supervision: Saeedreza Amiri and Pouria Tabrizian.

Conflict of interest
The authors declared no conflict of interest.

Acknowledgments
The authors appreciate the support of Iran University of Medical Sciences, Tehran, Iran. The authors also thank the patient for her consent to release information and clinical photographs for the writing of this article.





References