Pseudomonas aeruginosa liver abscess: Rare case of community-acquired infection

INTRODUCTION

Liver abscess is an inflammatory space-occupying lesion caused by a range of infectious agents, including bacteria, parasites, fungi, mycobacteria, and other atypical organisms. In India, amoebic liver abscesses account for more than 60% of all cases while pyogenic liver abscesses constitute approximately 10% of presentations.^[1] Among pyogenic abscesses, Escherichia coli, Klebsiella, Proteus, and Streptococcus species are most frequently isolated.^[2] In contrast, Pseudomonas aeruginosa is a relatively uncommon pathogen and is typically associated with infections in immunocompromised hosts.

Here, we report an unusual case of a community-acquired P. aeruginosa liver abscess (PALA) occurring in a previously healthy young woman with no identifiable comorbidities or predisposing factors.

CASE REPORT

A 24-year-old woman presented to the emergency department with a 2-month history of dull aching pain in the right hypochondrium and intermittent low-grade fever for 15 days. She denied having diarrhea, vomiting, hematochezia, urinary symptoms, or respiratory complaints. There was no history suggestive of an immunocompromised state, chronic illness, long-term medication use, or high-risk behavior.

On examination, she was alert and oriented. Her vital signs were stable with a blood pressure of 106/78 mmHg, pulse rate of 82/min, oxygen saturation of 97% on room air, and random blood glucose of 116 mg/dL. Abdominal examination revealed right hypochondrial tenderness, while cardiovascular, respiratory, and neurological examination was unremarkable.

Ultrasonography demonstrated hepatomegaly (16.8 cm) with a single 370-cc predominantly liquefied hypoechoic subcapsular lesion in segments V and VII of the right lobe, accompanied by a right-sided pleural effusion (maximum separation 11 mm) likely reactive. These findings were consistent with liver abscess. Blood cultures were obtained and empirical intravenous metronidazole and ciprofloxacin were initiated on the day of admission.

Admission laboratory findings showed hemoglobin 10.6 g/dL; total leukocyte count 7,700/cumm; platelet count 266,000/cumm; sodium 132 mmol/L; potassium 4.5 mmol/L; creatinine 0.4 mg/dL; blood urea 17 mg/dL; total bilirubin 0.4 mg/dL; aspartate aminotransferase 27 U/L; alanine aminotransferase 10 U/L; alkaline phosphatase 153 U/L; and international normalized ratio 1.42. Viral serology for human immunodeficiency virus, hepatitis B surface antigen, and hepatitis C virus was negative.

Blood cultures received on day 3^rd of admission subsequently grew P. aeruginosa, sensitive to quinolones and cephalosporins. Based on these results, ciprofloxacin was continued and metronidazole was discontinued. Despite antibiotic therapy, the patient continued to experience fever spikes, prompting percutaneous drainage through pigtail catheter insertion.

Following the drainage, fever persisted on day 4 of admission, necessitating escalation of antibiotics from ciprofloxacin to piperacillin–tazobactam as per sensitivity results. The patient showed clinical improvement within a day of antibiotic modification, becoming afebrile by day 5 of admission. Repeat ultrasonography revealed a residual 180-cc organized abscess in segments V and VII. A repeat blood culture on day 7 of admission showed no growth. She completed the antibiotic regimen and was discharged on day 14 of admission after removal of the pigtail catheter.

DISCUSSION

Liver abscess constitutes the most common form of visceral abscess. While most are amebic or pyogenic in origin, pyogenic liver abscess commonly presents with fever, abdominal pain, anorexia, and vomiting. Less typical manifestations include unexplained anemia, respiratory symptoms, pyrexia of unknown origin, and occasionally sepsis or septic shock.^[3]

Community-acquired P. aeruginosa infection leading to liver abscess in immunocompetent adults is exceedingly uncommon. The incidence of PALA is around 2–6%.^[4] Mortality associated with PALA is reported to be nearly 4 times higher than that observed in liver abscess caused by other pathogens.^[5] Most cases occur in individuals with an underlying predisposition such as immunosuppression due to medications or systemic illness.^[6] Consequently, PALA occurring in a healthy adult without risk factors, as demonstrated in this case, is exceptionally rare.

Our case is peculiar in the way that Pseudomonas growth was in the blood culture but not in the aspirated pus culture. The various possibilities for this peculiar finding may be described by the death of bacteria by host white blood cells as a natural response to infection in addition to antibiotics given which may suppress bacterial growth in pus but may fail to eradicate infection in the blood. Another reason can be due to the peculiar nature of Pseudomonas having “Biofilm formation” at the tissue level or medical devices (in this case, pigtail catheter insertion may influence this), making it difficult to grow in standard cultures despite having bacteria in the bloodstream and contributing to its “dormant phenotype” nomenclature. Moreover, the sampling time variability may also contribute to the finding by potentially having blood culture drawn during transient bacteremia spike while the pus sample may not catch viable, live bacteria.

Imaging modalities such as ultrasonography and computed tomography have greatly enhanced early diagnosis, with ultrasonography often preferred as the initial investigation due to its availability and cost-effectiveness.^[7] Microbiological culture remains the cornerstone of identifying the etiological agent in pyogenic liver abscess.

Management typically involves a combination of targeted antibiotic therapy and percutaneous drainage when indicated. Standard treatment duration includes approximately 2 weeks of intravenous antibiotics.^[8] Improvements in diagnostic tools, drainage techniques, and antibiotic therapy have reduced mortality from liver abscess in India from 24% to 1–3% in recent years.^[1,2]

CONCLUSION

Culture-guided antimicrobial therapy is vital for optimal management of liver abscesses. Although uncommon, clinicians should recognize that P. aeruginosa may present in this manner, and prompt diagnosis with early targeted treatment can markedly improve outcomes.