Vertebral discitis caused by Salmonella enterica serovar Montevideo infection

Abstract

Salmonellosis is a common cause of foodborne illness worldwide, manifesting as non-invasive non-typhoidal salmonellosis, invasive non-typhoidal salmonellosis, and typhoid fever. It also rarely presents as Salmonella osteomyelitis in children with hemoglobinopathies and immunocompromised adults and even rarer osteomyelitis in an immunocompetent host without significant risk factors. Our case is of a 38-year-old immunocompetent male without significant risk factors presented with biopsy proven Salmonella vertebral discitis due to exposure to contaminated and undercooked poultry. It illustrates the importance of thorough and complete history taking even in immunocompetent patients and early recognition with prompt targeted treatment of Salmonella osteomyelitis/discitis to prevent unfavorable outcomes.

Introduction

Salmonella is a genus of gram negative bacillus comprising two species, S. bongori and S. enterica. Most of the human pathogenic salmonellae are serovars (or serotypes) of one of the S. enterica subspecies. S. enterica subspecies enterica including S. enterica serovar Typhi (the cause of typhoid fever) and many of the non-typhoid salmonellae including Typhimurium, Enteritidis and Montevideo. These are differentiated based on their specific O (somatic) and H (flagellar) antigens. Salmonellosis is a common cause of foodborne illness worldwide and outbreaks in the US and has been associated with meat, poultry, fruits, and vegetables. Salmonella infections manifest as three syndromes – non-invasive non-typhoidal salmonellosis, invasive non-typhoidal salmonellosis, and typhoid fever.

S. enterica serovars typically cause self-limited gastroenteritis but, can be invasive causing bacteremia and extraintestinal infection rarely appearing as an infectious osteomyelitis or discitis [3], [4], [5], [10], [11]. Salmonella osteomyelitis is reported in only 0.45% of all osteomyelitis cases and comprises 0.8% of all Salmonella infections [1], [2], [3], [11]. This manifestation predominantly appears in children with hemoglobinopathies and adults with immunosuppressive disorders [10], [11]. There have also been a few reported cases of Salmonella species causing osteomyelitis in immunocompetent hosts without significant risk factors. These cases occur most probably due to hematogenous seeding of bone or joints after a transient bacteremia [7], [8], [9], [10].

Case presentation

A 38-year-old male with a history of hypertension and well controlled non-insulin dependent diabetes mellitus type 2 presented to an outside facility for a complaint of worsening sharp mid-thoracic back pain for three weeks. He denied other systemic symptoms including fevers or chills or loss of bowel or bladder incontinence. At the outside facility, a CT angiogram ruled out pulmonary embolism, however, was notable for T10–11 region cortical changes and paraspinal inflammation, concerning vertebral osteomyelitis. He subsequently completed an outpatient MRI thoracic spine with and without intravenous contrast which confirmed T10–11 discitis/osteomyelitis. He was admitted to our facility for evaluation by orthopedic surgery, who proceeded with a CT-guided vertebral bone biopsy with neuroradiology and started the patient on gabapentin 300 mg three times per day.

Infectious disease service was consulted on hospital day three after bone biopsy culture grew 1 + Salmonella species, ultimately identified as S. enterica serovar Montevideo. Further history obtained from the patient was notable for initial sharp mid-thoracic back pain starting three months prior with no significant trauma. The patient admitted to working with heavy machinery (bulldozers), performing heavy lifting activities daily, and a prior T10–11 vertebral disc herniation. He denied any interactions with amphibians or reptiles at home or as part of his job. Shortly after the onset of pain, he reported a flu-like illness with blistering rash along T10 dermatome. He was evaluated by a primary care provider who diagnosed shingles at T10 dermatome and prescribed a 14-day course of oral antiviral therapy and prednisone per the patient. He had complete resolution of his rash; however, external prescription history noted a 10-day course of oral amoxicillin-clavulanate and Medrol dose pack at that time rather than the mentioned "antiviral medication." Outside records were unable to be obtained to confirm diagnosis from the primary care provider. He reported his current pain was in the same distribution as the previously reported rash. He also stated during this timeframe he was eating fresh eggs multiple days per week from his pet hens. The patient and wife developed symptoms of nausea and non-bloody diarrhea lasting for 24–48 h after each time they consumed eggs. He stated he ate these eggs with a "runny yolk" for one to two months before getting rid of the chickens, this coincided with resolution of his aforementioned nausea and diarrhea.

His Salmonella discitis was presumed to be secondary to undercooked farm egg consumption causing Salmonella colonization of his gastrointestinal tract and transient bacteremia which subsequently infected the thoracic spine after an acute varicella zoster virus reactivation. He was discharged on a six week course of intravenous ceftriaxone 2 g every 24 h. He reported resolution of back pain upon outpatient follow-up after completion of antimicrobial therapy.

Discussion

This case highlights an unusual serotype (S. enterica serovar Montevideo) of an already rare agent (S. enterica) as the cause of vertebral discitis. Salmonella vertebral discitis/osteomyelitis is clinically and radiologically indistinguishable from spinal infections caused by other organisms. The three most common Salmonella serovars linked to osteomyelitis are S. Typhi and S. enterica serovars Typhimurium and Enteritidis. Predisposing factors for invasive Salmonellosis include sickle cell disease, HIV infection, diabetes mellitus, malignancy, and rheumatologic disease. A less frequently reported serotype, S. enterica serovar Montevideo (SM) has been linked to foodborne illnesses in humans and isolated from chickens. In 2008, a chicken-related outbreak in Arizona associated with a restaurant chain identified 21 people infected with SM in Arizona using PulseNet (a national molecular subtyping networking for foodborne disease surveillance) [6].

Our patient had a history of well controlled diabetes mellitus on metformin and prior consumption of undercooked eggs coinciding with acute gastroenteritis. He was an immunocompetent adult except for well controlled diabetes mellitus and recent acute varicella zoster virus reactivation with no other significant risk factors for vertebral discitis. Typical complications of herpes zoster include secondary bacterial infection, postherpetic neuralgia and nerve palsy. His raw egg consumption led to the development of chronic Salmonella carriage in his immune system. The persistent asymptomatic shedding of Salmonella puts our patient at risk for progression to an invasive non-typhoidal Salmonella infection (Salmonella discitis). In addition, his reduced immunity from prior varicella inoculation with concurrent steroid use could potentially explain the development of an invasive Salmonella spinal infection as an immunocompetent adult. His bone biopsy confirmed a Salmonella infection, specifically due to SM. Treatment for Salmonella discitis consists of systemic fluoroquinolones or third generation cephalosporins for several weeks based on expert opinion. Third generation cephalosporins are generally preferred due to increasing antimicrobial resistance. Our patient’s antimicrobials were tailored to the susceptibilities of his bone biopsy cultures and he completed a six week course of intravenous ceftriaxone.

Salmonella discitis should be suspected in immunocompetent patients with exposure to contaminated and undercooked poultry. Furthermore, to reduce the incidence of Salmonellosis, public health interventions are necessary at poultry farms, processing plants, and all restaurants. Earlier recognition and prompt treatment of Salmonella spinal infections can prevent residual neurological deficits and unfavorable outcomes.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or non-for-profit sectors.

Ethical approval

N/A.

Consent

A consent was obtainedfrom the patient to publish case report.

Credit Authorship Contribution Statement

Maithri P. Reddy: Conceptualization, Writing – original draft. Zoheb Irshad Sulaiman: Conceptualization, Writing – original draft. Gina Askar: Supervision, Writing – review & editing.

Declaration of Competing Interest

The authors whose names are listed on this publication certify that they have no affiliations or involvement in any organization or entity with any financial interest or non-financial interest in the subject matter or materials discussed in this manuscript. They also certify all information presented is their own opinion and not of their employers.