P2.222: Beyond the Usual Suspects: Listeria Monocytogenes Bacteremia in an Immunocompetent Toddler

Introduction: Introduction
Listeria monocytogenes is a facultative anaerobic, non-spore-forming, gram-positive rod that multiplies intracellularly. Listeriosis is an uncommon infection caused by Listeria monocytogenes, presenting as self-limiting gastroenteritis and rarely as invasive disease. Invasive listeriosis typically affects pregnant individuals, newborns, elderly or immunocompromised individuals. We describe a rare case of invasive listeriosis in a healthy child with no known risk factors.

Case Description: Case Description
A previously healthy three-year-old female presented to an outside hospital for a syncopal episode in the setting of one day of fever, abdominal pain, emesis, and severe diarrhea. Her father had similar symptoms. There were no known animal, reptile or food exposures including undercooked meat, deli meat, soft cheese or dairy products. Her WBC was 35.7 (91% neutrophils), hemoglobin 12.2, platelets 365 and bicarbonate 19. She received ceftriaxone before transfer. Her C reactive protein (CRP) was elevated to 139 mg/L, blood and stool cultures were obtained, and aggressive fluid resuscitation was started. She tested positive for influenza B, started on oseltamivir but antibiotics were held until GI PCR resulted. GI PCR was negative and CRP continued to rise so ceftriaxone was restarted, infectious disease was consulted and abdominal ultrasound confirmed enteritis. She continued to be febrile with worsening metabolic acidosis. Blood culture was positive at 19 hours for gram-positive coccobacilli, thought to be diphtheroids, later confirmed as Listeria monocytogenes on a rapid diagnostic polymerase chain reaction panel. Antibiotics were switched to ampicillin and gentamicin. Within 24 hours, she became afebrile, with improved diarrhea and abdominal pain. A basic immunodeficiency workup was negative. She completed 14 days of IV ampicillin and gentamicin.

Discussion: Discussion
Invasive listeriosis is associated with a high mortality, though most literature focuses on high-risk hosts. Few case reports document Listeria bacteremia in healthy pediatric patients outside infancy. Listeriosis accounts for less than 1% of foodborne illnesses in the U.S., typically linked to deli meats, unpasteurized milk or soft cheeses. All cases require public health reporting, and the source of this infection remains under investigation. No controlled trials have established the treatment of choice or duration of therapy; however, current guidelines recommend a 14 day course of ampicillin and gentamicin for invasive listeriosis without CNS involvement. This report highlights a rare case of Listeria bacteremia in an otherwise healthy child. Initial symptoms suggested severe non-bacterial gastroenteritis, but persistent fevers, worsening metabolic acidosis and rising inflammatory markers raised concern for alternative diagnosis. A high index of suspicion is required to identify Listeria monocytogenes.

Conclusion: Conclusion
Invasive listeriosis is rare in healthy children and should be considered in severe gastroenteritis cases unresponsive to initial treatments. Our patient’s symptoms only resolved after starting the appropriate antibiotic regimen, emphasizing the importance of early recognition and treatment.