Listeria Monocytogenes: A Case Series and Clinical Insights from a Tertiary Care Hospital

Abstract

Listeria monocytogenes is a rare but serious illness, especially in the immunocompromised patient. It causes invasive infection, such as bacteremia and meningitis with insidious presentation and high mortality without treatment. A cluster of six Listeria monocytogenes bacteremia was noted within 10 months at a tertiary care referral center. Patients were 27-72 years old; four also had concomitant immunosuppressive diseases, including chronic renal disease, diabetes mellitus, and cancer. All the infections were confirmed on blood culture performed with the VITEK 2 system. The organisms were all gentamicin and ampicillin-sensitive. Five patients improved on intravenous antibiotic therapy, and one died from multiorgan failure. The series reiterates the importance of maintaining listeriosis as a significant concern in febrile patients with predisposing conditions. Early diagnosis and early treatment with appropriate antibiotics have positive outcomes.

INTRODUCTION

Listeria monocytogenes is a Gram-positive, facultatively anaerobic rod with the ability to cause a rare but serious infection referred to as listeriosis. It is predominantly a food-borne pathogen and is the etiology of invasive disease in certain high-risk populations like pregnant women, neonates, elderly, and immunocompromised people.[1] Listeria possesses the unique characteristic of being able to grow at refrigeration temperatures and resist severe environmental conditions, and is thus a hard pathogen to manage in foods. The clinical course of listeriosis ranges from self-resolving febrile gastroenteritis to life-threatening diseases, such as septicemia, meningitis, brain abscess, and maternal-fetal infection. In non-pregnant adults, Listeria typically manifests as bacteremia or meningoencephalitis, particularly in cancer patients, organ transplant recipients, patients with renal failure, diabetes, or those receiving immunosuppressive therapy.[2] Diagnosis is routinely delayed because the symptom presentation is non-specific and the disease is rare, and consequently may be underdiagnosed or misclassified. Blood cultures continue to be the standard of diagnosis, and identification of the organism is possible by using automated culture and identification systems such as the BacT/ALERT and VITEK 2. Early institution of proper antibiotics, such as ampicillin, usually in combination with gentamicin, is essential for the survival of the patient. Resistance to third-generation cephalosporins makes empirical coverage a challenge, particularly in patients where Listeria is not initially suspected.[3] In India, the incidence of invasive listeriosis is likely underreported due to a lack of awareness and limited surveillance data.

However, sporadic cases and small outbreaks continue to be documented, often in tertiary care settings. This article describes a series of six proven instances of Listeria monocytogenes bacteremia, diagnosed over a period of ten months in a tertiary care center. The case series is intended to emphasize clinical presentation, comorbidities encountered, diagnostic difficulty, treatment, and outcome, with a view to raising clinical suspicion and optimizing patient care in such situations.

CASE PRESENTATIONS

Case 1

A 65-year-old man with a history of chronic kidney disease was admitted with high-grade fever, altered sensorium, and vomiting. Physical examination revealed him to be febrile (38.8°C) and disoriented with neck stiffness. Investigations included leukocytosis with neutrophilia and raised C-reactive protein. CSF analysis indicated raised protein and low glucose, consistent with bacterial meningitis. Blood and CSF cultures were sent. The blood culture was positive after 17 hours and was cultured by the VITEK 2 system, which gave Listeria monocytogenes. The isolate was susceptible to ampicillin and gentamicin. The patient received intravenous ampicillin and gentamicin for 14 days. The patient had a good response to treatment and was discharged stable.

Case 2

A 48-year-old female with no significant medical history presented with fever, headache, and drowsiness for 3 days. She had no known comorbidities. Physical examination revealed mild neck rigidity and confusion. Her complete blood count was within normal limits, but inflammatory markers were elevated. Blood cultures were drawn and empiric antibiotics were started. Culture turned positive after 19 hours and grew Listeria monocytogenes, confirmed by VITEK 2. The organism was sensitive to ampicillin and gentamicin. She was treated with intravenous antibiotics and improved clinically over the next few days. She was discharged after 10 days of inpatient care.

Case 3

A 72-year-old male undergoing chemotherapy for carcinoma of the cervix presented with fever and vomiting. He had generalized weakness and an altered mental status. On examination, he was febrile and hypotensive. Laboratory tests showed leukocytosis and elevated CRP. Blood cultures yielded Listeria monocytogenes within 16 hours, identified by VITEK 2. The patient was started on high-dose intravenous ampicillin and gentamicin. Despite intensive care support, the patient deteriorated and succumbed to multiorgan dysfunction syndrome on day 5 of admission.

Case 4

A 35-year-old woman presented with fever, chills, and myalgia. She had no comorbid diseases. Physical examination was normal apart from fever. Laboratory findings were mildly elevated white blood cells and CRP. Blood culture became positive in 15 hours, and Listeria monocytogenes was cultured, confirmed by VITEK 2. The patient was treated with ampicillin for 10 days and recovered completely.

Case 5

A male patient aged 27 years with poorly managed diabetes mellitus presented with fever, pain in the abdomen, and headache. He was febrile and lethargic on examination. Lab investigations were positive for hyperglycemia, leukocytosis, and elevated CRP. Blood culture was positive in 18 hours and isolated Listeria monocytogenes. He was given a combination of ampicillin and gentamicin. He improved and was discharged in 12 days of hospital course.

Case 6

A 43-year-old male on maintenance hemodialysis for chronic kidney disease was evaluated with fever, nausea, and confusion. Physical examination was also positive for hypotension and confusion. Laboratory study was positive for azotemia and inflammatory markers. Blood cultures were positive for Listeria monocytogenes on day 20 using the VITEK 2 system. The organism was sensitive to standard antibiotics. He received intravenous ampicillin and gentamicin for 14 days. The patient gradually improved and was discharged with follow-up instructions.

DISCUSSION

Listeria monocytogenes is a rare but clinically significant organism that has the capability to produce life-threatening infection in susceptible individuals. The case series described here reflects six cases of bacteremia due to Listeria monocytogenes over a period of 10 months in a tertiary care facility, detailing its varied presentations, risk factors, diagnosis, and treatment. The patients in the present series ranged from 27 to 72 years, with a mean of 48.3 years.[4] Four of six patients had existing comorbidities that are well known to cause patients to be predisposed to listeriosis: two had chronic kidney disease, one had chemotherapy for cervical carcinoma, and one had diabetes mellitus, which was uncontrolled. These findings are consistent with the established fact that immunosuppression is an important risk factor for invasive Listeria infection. The most consistent clinical feature, seen in all six patients,[5] was fever. Altered mental status was reported in four, and neck stiffness in one, both of which are signs of central nervous system involvement. Formal lumbar puncture and analysis of CSF were recorded, however, in only one case. Two of the patients also had gastrointestinal manifestations such as abdominal pain and vomiting, which are classic prodromal symptoms in systemic listeriosis. Blood culture was the key to diagnosis in all instances. Time to culture positivity was between 15 and 20 hours. Organism identification was carried out using the VITEK 2 system, which gave consistent speciation and sensitivity profiling. All isolates were evenly sensitive to ampicillin and gentamicin. Resistance to third-generation cephalosporins was to be anticipated and in accordance with established resistance patterns of Listeria monocytogenes.[6] Beta-lactam empirical therapy was successful in five cases. Death occurred in one patient, an elderly man with malignancy, despite use of appropriate antibiotic therapy, probably as a consequence of his immunocompromised state and fulminant progression to multiorgan failure. This points to the extreme case-fatality rate of listeriosis in immunosuppressed patients if it is delayed to make a diagnosis and intervene. Treatment for all surviving cases consisted of a combination of intravenous gentamicin and ampicillin. The course of therapy lasted between 10 and 14 days based on clinical response and occurrence of complications. No relapses or reoccurrence of infections were seen at short-term follow-up. This case series underlines the need to include Listeria monocytogenes in the differential diagnosis of febrile illness, especially in those with immunosuppressive diseases, renal disease, diabetes, or malignancy. Because of its cephalosporin resistance, empirical therapy in high-risk patients with suspected CNS infection or sepsis may need to be amended to address Listeria coverage.[7]

The few reported cases in India can likely not represent the actual incidence but are instead due to underdiagnosis secondary to clinical suspicion and limited peripheral center diagnostic capabilities. Increased vigilance among clinicians and microbiologists, and utilization of high-sophistication identification devices, such as VITEK 2, can enhance detection rates and patient prognosis. Although this series is weakened by its small number of cases and its retrospective design, it highlights important clinical patterns and the success of general antibiotic therapy when diagnosis is prompt.

CONCLUSION

Listeria monocytogenes, although infrequent, can lead to serious invasive infections, especially in immunocompromised individuals. Early clinical suspicion, prompt diagnosis through blood cultures, and early initiation of ampicillin-based treatment are critical for successful outcomes. Augmented awareness and empirical targeted therapy can dramatically minimize related morbidity and mortality.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.