INTRODUCTION
Shewanella algae are heterotrophic facultative anaerobes that are widely distributed in aquatic habitats (Figure 1). Typically, this infection is seen among the immunocompromised population in the setting of open water trauma.1,2 Cases of Shewanella have been reported worldwide but are more common in the tropics and during summer months in temperate zones where people are more often in contact with the water.3 Previously reported cases suggest that S. algae can cause otitis externa, soft tissue infections, bacteremia, and hepatobiliary infections. The organism is often susceptible to third generation cephalosporins, Ī²-lactam/Ī²-lactamase inhibitors, aminoglycosides, and fluroquinolones.4 Specific comorbidities associated with Shewanella infections include chronic liver and kidney disease, severe peripheral vascular disease (PVD), and skin and soft tissue infections (SSTI).1
Shewanella algae morphology and identifiable singular flagella.5 This figure appears in color at www.ajtmh.org.
Citation: The American Journal of Tropical Medicine and Hygiene 106, 1; 10.4269/ajtmh.21-0614
Shewanella algae morphology and identifiable singular flagella.5 This figure appears in color at www.ajtmh.org.
Citation: The American Journal of Tropical Medicine and Hygiene 106, 1; 10.4269/ajtmh.21-0614
Shewanella algae morphology and identifiable singular flagella.5 This figure appears in color at www.ajtmh.org.
Citation: The American Journal of Tropical Medicine and Hygiene 106, 1; 10.4269/ajtmh.21-0614
CASE REPORT
Patient is a 73-year-old Caucasian male, with past medical history significant for asthma, chronic obstructive pulmonary disease (COPD), allergic bronchopulmonary aspergillosis, coronary artery disease (CAD), diabetes mellitus type II, and recent acute cholecystitis complicated by sepsis, and treated with a percutaneous cholecystostomy drain. He is a resident of a long-term care facility who initially presented to the emergency department for acute onset of altered mental status, fever (101.4Ā°F), tachycardia (110 bpm), dyspnea, and hypoxia. Initial laboratory evaluation was notable for leukocytosis (19.4) with neutrophil predominance (89.2%), elevated blood urea nitrogen (31), elevated glucose (228), elevated procalcitonin (0.51), and negative COVID-19 test. Chest X-ray demonstrated a left lower lobe pneumonia with associated pleural effusion and atelectasis (Figure 2). Patient was admitted into the hospital with suspected pneumosepsis and empiric antibiotic therapy was initiated with doxycycline and cefepime (to provide broad coverage for methicillin-resistant Staphylococcus aureus, Pseudomonas and atypical organisms). Blood samples were drawn from the patient and both aerobic cultures resulted in the growth of S. algae. Antibiotic susceptibility was assessed via Kirby Bauer disc diffusion assay. The data is displayed in Table 1. The patient improved clinically and the antibiotic regimen was then narrowed to ceftriaxone based on both infectious disease literature and laboratory antibiotic susceptibilities. After completion of the course of antimicrobials, the patient had resolution of all symptoms and was discharged from the hospital.
Chest X-ray obtained upon initial presentation. Notable for left lower lobar consolidation with associated pleural effusion, and atelectasis.
Citation: The American Journal of Tropical Medicine and Hygiene 106, 1; 10.4269/ajtmh.21-0614
Chest X-ray obtained upon initial presentation. Notable for left lower lobar consolidation with associated pleural effusion, and atelectasis.
Citation: The American Journal of Tropical Medicine and Hygiene 106, 1; 10.4269/ajtmh.21-0614
Chest X-ray obtained upon initial presentation. Notable for left lower lobar consolidation with associated pleural effusion, and atelectasis.
Citation: The American Journal of Tropical Medicine and Hygiene 106, 1; 10.4269/ajtmh.21-0614
Antibiotic sensitivity assessed via Kirby Bauer disc assay*
| Antibiotic used | Zone of inhibition (mm) | Sensitivity |
|---|---|---|
| āCeftazidime | 29 | Sensitive |
| āCiprofloxacin | 27 | Sensitive |
| āGentamicin | 23 | Sensitive |
| āPiperacillin/Tazobactam | 30 | Sensitive |
| āTobramycin | 21 | Sensitive |
| āImipenem | 18 | Sensitive |
| āAmikacin | 20 | Sensitive |
| āAmpicillin | 20 | Sensitive |
| āAmpicillin/Sulbactam | 24 | Sensitive |
| āSulfamethoxazole/Trimethoprim | 24 | Sensitive |
| āCefazolin | 0 | Resistant |
| āCeftriaxone | 26 | Sensitive |
MIC results were unable to be obtained.
DISCUSSION
Shewanella algae infections are most common following traumatic injuries and near drownings in both freshwater and saltwater.6 Tourists, swimmers, fisherman, and sailors with underlying liver disease and immunocompromising conditions are at highest risk of contracting a water-related soft tissue or pulmonary Shewanella infection.7ā9 This patientās exposure to S. algae is not easily identified. One potential avenue of infection would be aspiration of a contaminated water supply at the long-term care facility. However, there are no previous case studies describing incidents of aspiration pneumonia caused by S. algae. Another possible source of infection would be ingestion of raw seafood, though the patient was unable to recall recent ingestion of any such foods.10 Exposure of cutaneous ulcers to seawater is also a well-documented source of infection; however, this patient had no open skin ulcers or seawater exposure in the last 6 months. As such, clinicians should broaden their awareness of this organismās potential routes of inoculation, predisposing factors for infection, and the wide variety of clinical presentations associated with S. algae.
CONCLUSION
This case presentation describes a unique situation in which a patient develops S. algae bacteremia without any identifiable preceding exposures. Though human infection remains rare, the incidence is increasing, and this case highlights the importance of considering Shewanella spp. as the cause of infection in settings where the patient may have been exposed to seawater or raw shellfish. This case also brings to light the question of whether potable water may serve as a source of infection and whether additional testing for contamination is indicated.
ACKNOWLEDGMENTS
We would like to thank Dr. Mary Saleeby (Internal Medicine attending at Tripler Army Medical Center) for reviewing and advising on the preparation of the manuscript.
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