A Rare Case of Salmonella Gastroenteritis Presenting as Aspiration Pneumonia With Pleural Empyema in an Immunocompetent Patient

Non-typhoidal salmonella (NTS) can cause infections ranging from self-limited chronic carriers to gastroenteritis, bacteremia, and extraintestinal infections. Pulmonary involvement, particularly empyema, is quite rare and generally found in immunosuppressed individuals. We present a case of salmonellosis in an immunocompetent patient with rare pulmonary complications of empyema. The patient, with no underlying immunocompromised illness, presented with a one-day history of worsening generalized weakness, fever, shortness of breath, and productive cough after having gastroenteritis symptoms of five days duration, which stopped two days prior to admission. On further investigation, imaging revealed right lower lobe pneumonia with empyema. The patient was managed with intravenous antibiotics and chest tube placement with good clinical response. Pleural fluid analysis showed exudative fluid and grew Salmonella enteritidis with negative blood and sputum cultures. The patient, in stable condition, was discharged on four weeks of amoxicillin/clavulanic acid after consulting the infectious disease specialist for presumed aspiration pneumonia complicated with empyema in the setting of multiple episodes of vomiting due to gastroenteritis. The lung is an atypical site for salmonellosis. Pulmonary infections in immunocompetent hosts are rare in the medical literature. Early recognition and timely management of pulmonary complications can lead to better outcomes.


Introduction
Salmonellae are gram-negative rods belonging to the Enterobacteriaceae family. It can cause infections ranging from self-limited chronic carrier to gastroenteritis, bacteremia, and extraintestinal infections such as osteomyelitis, meningitis, urinary tract infection (UTI), and endocarditis. The involvement of lungs, particularly empyema, is quite rare [1] and often reported in immunosuppressed patients with comorbidities such as human immunodeficiency virus (HIV), diabetes mellitus, malignancy, long-term use of steroids, or chemotherapy.
This article was previously presented as a meeting abstract/poster presentation at the 2019 American College of Gastroenterology (ACG) meeting on October 26, 2019.

Case Presentation
A 76-year-old male with a past medical history of ischemic cardiomyopathy with 30% ejection fraction (EF) status post-defibrillator, chronic kidney disease stage 3, and previous stroke with residual mild left-sided weakness presented to the emergency room (ER) with a one-day history of worsening generalized weakness, fever, shortness of breath, and productive cough. The patient had been suffering from five days of nausea, multiple episodes of vomiting, and non-bloody diarrhea, which stopped two days prior to admission. Physical examination showed oxygen saturation of 80% on room air with a breathing rate of 24 breaths/minute, fever of 101.1°F, blood pressure of 110/75 mmHg, and pulse rate of 70 beats/minute. He was appearing toxic and acutely ill with lethargy, and his mucus membranes were dry. The belly was soft without tenderness or distention. Breath sounds were decreased at the bases. Laboratory results revealed a white cell count of 14K/uL, blood urea nitrogen (BUN) of 47 mg/dL, and creatinine of 2 with the regular hepatic panel. Chest X-ray revealed small bilateral pleural effusions (the right side greater than the left side) and bibasilar infiltrates/atelectasis.
The patient was started on intravenous broad-spectrum antibiotics for suspected right-sided pneumonia. While on antibiotics, the patient continued to have low-grade fevers for the next 1-2 days, along with worsening hypoxia and rapid heart rate greater than 100 beats/minute. The second chest X-ray revealed worsening right pleural effusion ( Figure 1). Computed tomography (CT) scan of the chest was obtained, which showed right lower lobe pneumonia with loculated right pleural effusion along with a small left-sided effusion ( Figure 2). A chest tube was placed, and antithrombotic therapy was injected to break loculations. Pleural fluid was found exudative and grew Salmonella enteritidis. Blood and sputum cultures were negative. In getting further details, recent intake of dairy products was confirmed by the patient, which was likely the source of gastroenteritis. The patient improved clinically, and after consultation with infectious disease, the patient was sent home on four weeks of oral antibiotics (amoxicillin/clavulanic acid) for presumed aspiration pneumonia due to salmonella complicated with empyema.

Discussion
Salmonella is a facultative intracellular gram-negative bacillus. It is mainly transmitted by the ingestion of contaminated or undercooked food and contact with animal wastes. It is estimated that 1.2 million cases of salmonellosis occurred in the United States, with 23,000 cases of hospitalizations and 450 deaths per annum [2]. Non-typhoidal salmonella (NTS), including S. enteritidis, S. typhimurium, and S. heidelberg usually cause self-limiting gastroenteritis. Among NTS, S. enteritidis has been reported as the most frequent cause of lung disease, although geographical distribution plays a role in its prevalence [3,4].
The pathogenesis of salmonella infection is affected by gastric acidity and gastric surgery. Patients using proton pump inhibitors (PPIs) and those with gastric surgery have increased chances of infection. This could be explained by the susceptibility of salmonella to gastric acid [5]. The intensity and risk of translocation are calculated on the basis of the virulence of the isolate and the immunity of the host. In serious cases, patients are at greater risk of death if prompt treatment with antimicrobials is not provided. Elderly, infants, and immunocompromised individuals are at greater risk of severe illness.
In our case, the patient developed gastroenteritis symptoms, including multiple episodes of vomiting followed by pulmonary infection. It was presumed that, most likely, the patient aspirated, resulting in pneumonia, which was complicated further by empyema. No significant underlying etiology was found for salmonella gastroenteritis other than possible exposure to contaminated food as one of his family members also developed similar self-limiting gastrointestinal (GI) tract symptoms.
The lung is an atypical site for salmonellosis, and pulmonary infections in immunocompetent hosts are rare in the medical literature. Only five cases have been reported so far after doing PubMed/MEDLINE search (1966-2019) limited to humans and the English language by using the keywords Salmonella enteritidis AND pneumonia AND/OR immunocompetent ( Table 1).

Conclusions
Non-typhoidal salmonella causing pneumonia and empyema in immunocompetent patients is very rare but can result in increased morbidity and mortality. We presented the sixth case of its kind, which emphasized the importance of considering non-typhoidal salmonella as a cause of pulmonary infections in appropriate clinical settings. Early recognition and timely management of pulmonary complications can lead to better outcomes.

Additional Information Disclosures
Human subjects: Consent was obtained or waived by all participants in this study. Conflicts of interest: In compliance with the ICMJE uniform disclosure form, all authors declare the following: Payment/services info: All authors have declared that no financial support was received from any organization for the submitted work. Financial relationships: All authors have declared that they have no financial relationships at present or within the previous three years with any organizations that might have an interest in the submitted work. Other relationships: All authors have declared that there are no other relationships or activities that could appear to have influenced the submitted work.