Serratia marcescens Endocarditis

Abstract

Severe infections due to Serratia marcescens have been documented with increasing frequency in persons who inject drugs and are frequently associated with nosocomial outbreaks. S marcescens endocarditis is rare, and there are very few, if any, reported cases secondary to an infected wound acquired at home. We present such a case in an immunocompetent 50-year-old man with paraplegia for 30 years and chronic decubitus ulcers who likely contracted the rare opportunistic Serratia following sacral wound contact with unclean surfaces in his hotel room bathroom. While it is also possible that the organism was obtained during a hospital admission 2 months before the positive blood cultures, he was found sitting with his ulcer in direct contact with red-pigmented accumulations on the shower floor. Therefore, it is more likely that he acquired the infection outside of the hospital setting. Early and effective management with advanced cardiac techniques and appropriate antibiotic coverage resulted in a positive outcome.

Introduction

Infective endocarditis (IE) is an infection of one or more heart valves secondary to microorganisms that have entered the circulatory system from a distant primary focus or due to nonsterile injections or procedures. Management can be complex, especially in patients with comorbidities. Most cases of IE are due to gram-positive organisms, such as Staphylococcus and Streptococcus species; infections due to gram-negative organisms are extremely rare and can carry a high mortality rate.^1,2 Infective endocarditis due to either gram-negative or gram-positive organisms has similar risk factors, including intravenous drug use (IVDU), indwelling venous catheters, and the immunocompromised state. ³ Here, we present the exceedingly rare IE due to Serratia, which appears to have been acquired at home, probably via an infected sacral decubitus ulcer that came into contact with a contaminated surface.

Case Presentation

A 50-year-old man with paraplegia for 30 years secondary to a gunshot wound and chronic decubitus ulcers called Emergency Medical Services because of chest pain. He was found in a local hotel room on the floor in squalid conditions, where he had been living for quite some time with no assistance. Notably, the shower floor was covered in patchy, red, pigmented residue. Hospitalization history was significant for admission 4 months prior for infected sacral decubiti and osteomyelitis. Blood cultures from the arm at that time were positive for extended-spectrum beta-lactamase (ESBL) Klebsiella pneumoniae, which was treated with ertapenem for 2 weeks. Two months later, he was admitted for left arm numbness and septic shock, and 2 vials of blood cultures obtained from the arm were positive for Serratia marcescens. He completed another 2 weeks of ertapenem and was discharged again, only to be re-admitted 2 weeks later for the current admission. Secondary to paraplegia, he also presents with a neurogenic bladder and chronic condom catheter. He has a history of smoking an unknown number of cigarettes daily and drinks 1 to 2 beers monthly, with no recent travel and no recreational or IV drug use. His only regular medication is acetaminophen-hydrocodone for chronic pain. On arrival to the emergency department, his temperature was 38°C, heart rate 120 beats per minute, respirations 24 breaths per minute, oxygen saturation 99% on room air, and blood pressure 82/64 mm Hg. Physical examination demonstrated paraplegia and multiple purulent stage IV sacral decubitus ulcers.

Hematologic laboratory studies were significant for 18 000 white blood cells (WBCs) per milliliter with 74% segmented neutrophils; hemoglobin, 8.1 grams per deciliter; platelets, 85 000 per milliliter; sodium, 125 milliequivalents per liter; chloride, 90 milliequivalents per liter; bicarbonate 22.3 milliequivalents per liter; albumin, 2.5 milliequivalents per liter, representing an albumin-corrected high anion gap metabolic acidosis at 16.4 milliequivalents per liter; potassium, 2.8 milliequivalents per liter; and blood glucose, 518 milligrams per deciliter. Urinalysis demonstrated WBC levels that were too numerous to count.

He was given IV fluids and started on IV cefepime and vancomycin after blood cultures were drawn from a vein in the right arm. He required intubation, vasopressors, and wound debridement. A computed tomography (CT) scan of the pelvis showed subcutaneous gas and erosive bone changes consistent with osteomyelitis of the sacrum (Figure 1). Computed tomography scan of the chest showed multiple cavitary nodules consistent with septic pulmonary emboli (Figure 2). Inferior thoracic CT slices also revealed left lower lobe pneumonia and a bullet fragment in a vertebral body from the gunshot wound that caused his paraplegia (Figure 3). Within 24 hours, blood cultures were positive for S marcescens, susceptible to cefepime. Thus, vancomycin was discontinued. A transthoracic echocardiogram (TTE) was ordered due to sustained positive blood cultures. The TTE revealed a 21 mm × 24 mm tricuspid valve vegetation with a left ventricular ejection fraction of 40% (Figure 4). One week later, he underwent vacuum cannula removal of the tricuspid vegetation, which was also culture-positive for S marcescens. He was eventually stabilized, and blood cultures were cleared 10 days after admission. He was discharged to a rehabilitation facility with 1 additional week of oral ciprofloxacin to complete a 6-week total course of antimicrobial therapy.

Figure 1.

Pelvic X-ray demonstrating osteomyelitis of the sacrum and femur bilaterally.

Figure 2.

Computed tomography of the thorax showing gas in soft tissue with cavitating ground glass nodules suspicious for septic emboli.

Figure 3.

Computed tomography of the thorax demonstrating left lower lobe pneumonia and the bullet fragment.

Figure 4.

Transthoracic echocardiogram demonstrating a large tricuspid vegetation.

Discussion

Presentation, Workup, and Treatment

Infective endocarditis is a rare but serious disease, with an estimated global incidence of 2 to 10 cases per 100,000 people. ² Healthy cardiac tissue is usually resistant to bacteria introduced by activities of daily living. ⁴ However, cardiac disease states such as valvular sclerosis, valvulitis, or prior bacterial activity can damage the endothelium, which subsequently initiates a localized inflammation cascades to provide a platelet-fibrin thrombus that enables bacterial adherence and biofilm formation. ⁵ Subsequent bacterial deposition, colonization, and activity propagate further endothelial injury and thrombus formation, eventually forming an infectious vegetation resistant to antibiotic activity secondary to bacterial biofilm formation. ⁶

Patients usually present with generalized constitutional symptoms, such as fever, chills, or fatigue, with occasional potential damage to other organs due to septic emboli released from the cardiac vegetation. Right-sided IE will release emboli primarily to the lungs, while left-sided vegetations will release septic emboli systemically through the body, affecting any end organ. On physical examination, some patients may develop a new heart murmur or a change in a preexisting murmur if the vegetation alters valvular functionality or grows large enough to disrupt flow. Furthermore, deep or perivalvular thrombi can cause arrhythmias. ⁷

All patients with suspected bacteremia and IE should have at least 2 sets of blood cultures from different sites. If possible, empiric antibiotic therapy should be initiated immediately after blood cultures have been drawn. Once results are obtained, targeted antibiotic treatment should follow culture results and in vitro susceptibilities. Initial laboratory tests will likely demonstrate leukocytosis with a left shift, increased inflammatory markers, and possibly urinalysis with multiple abnormalities, including glomerulonephritis. ⁸ Physicians often apply the modified Duke criteria, which uses specific major and minor criteria to determine the diagnostic likelihood of IE. Notably, negative blood cultures do not absolutely rule out IE. ⁹ Complications due to IE should be treated appropriately. Transthoracic echocardiography is indicated to assess for a valvular lesion, abnormal heart valves, and cardiac tissue functionality. ⁶

The indication for surgical removal of a vegetation is determined through multidisciplinary discussion between cardiology, cardiothoracic surgery, and infectious disease services, along with specialties involved with extra-cardiac emboli, such as neurosurgery in cases of intracranial infections. ⁸ A surgical consult is indicated in cases of prosthetic valve endocarditis, uncontrolled infection, perivalvular complications, vegetation presentations larger than 10 mm or visibly mobile on TTE, and other indications as determined by the interdisciplinary team. ¹⁰

Epidemiology

Rheumatic heart disease continues to serve as the major risk factor in developing countries for streptococcal IE. Risk factors in developed countries have shifted to favor opportunistic infections associated with degenerative valve disease, prosthetic valves, intravenous lines, and implantable electronic devices. ¹¹ Staphylococcus aureus is the most common cause of acute IE in developed countries, likely due to its ability to colonize healthy valves. Right-sided infections are frequently seen in IVDU populations and patients with central lines due to complicated bacteremia. ¹²

Together, gram-positive cocci, including S aureus, Streptococcus spp., and Enterococcus species, account for 80% to 90% of IE globally, with HACEK organisms (Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, and Kingella) cited as the major gram-negative culprits.^6,13 As of 2021, HACEK organisms cause 1.5% to 2% of IE with an associated 2% mortality, while non-HACEK gram-negative IE accounts for 2.5% to 3% of all IE cases with a 20% to 30% mortality. ¹ Most of these gram-negative cases reported in recent history have been associated with preceding cardiac surgery, the presence of prosthetic material, or IVDU. ³

The rapid systemic sequelae in this case demonstrate the morbidity of gram-negative opportunistic bacteremia and the importance of swift, efficient management.

Serratia marcescens, an opportunistic gram-negative rod of the Enterobacteriaceae family, has been observed with increasing frequency in persons who inject drugs ¹⁴ and hospitalized patients^14,15 and maintains a higher mortality rate in patients with associated comorbidities.^3,15 However, Serratia is still an extremely rare cause of IE. In the International Collaboration on Endocarditis (ICE) prospective cohort, 4 (0.14%) of the total 2781 cases of IE were due to Serratia.^3,16 Serratia is found in natural environments, such as water, soil, plants, and animals, and is known to cause a variety of infectious presentations in humans when given access. The predilection for water could account for bloodstream infections from the municipal water used in needles used for IV drug use, ³ as well as cases of ventilator-associated pneumonia ¹⁷ and urinary tract infections. ¹⁸ It can quickly colonize wet surfaces, forming the characteristic red pigmentation. This distinct color is due to the production of prodigiosin, a chemical compound that aids in ATP production and aerobic energy generation. ¹⁹ S marcescens endocarditis was first reported in 1951, ²⁰ with rare reports worldwide since then. ³ Our review of the literature, combined with efforts made by Phadke and Jacob in 2017, show that Serratia continues to act opportunistically in humans, with most cases citing open wound access with or without chronic illness or an immunocompromised state. Moreover, most wound infections were acquired in the hospital setting, occasionally postoperatively or via infected lines. ³ This case is unique in that the patient was chronically ill with sacral ulcers, did not use IV drugs, and was not HIV-positive. His history is notable for a hospitalization for Klebsiella bacteremia treated with ertapenem 2 months before presenting with Serratia bacteremia. It is possible that Serratia was acquired from the prior hospital admission, although it is also possible that he acquired the organism from the bathroom or shower floor, given that he was found sitting on a surface contaminated with red-pigmented accumulations.

Conclusion

The patient described herein presented with S marcescens endocarditis with multiple pulmonary septic emboli. Besides its rarity, this case is unique in that it demonstrates the opportunistic nature of Serratia in an otherwise immunocompetent individual if given adequate access in an ideal environment. Swift, efficient management and effective communication between the medicine, infectious disease, and surgery departments led to a positive outcome in this case.