Non-zoonotic Pasteurella multocida Infection as a Cause of Septic Shock in a Patient with Liver Cirrhosis: A Case Report and Review of the Literature.

Pasteurella multocida is a Gram-negative organism characterized morphologically as coccobacillus. It is the commonest organism infecting pet bites. However, severe infections may occur in the absence of animal bites or scratches. Pasteurella multocida serves as an opportunistic pathogen in humans, especially in patients with depressed immune system. Few cases in the literature identify Pasteurella multocida as the causative agent of septic shock, especially in cirrhotic patients. We report a patient who presented with septic shock as a result of Pasteurella multocida bacteremia, without prior history of animal exposure.

INTRODUCTION

Pasteurellosis is a zoonosis with a world-wide distribution that occurs sporadically. Pasteurella multocida was first described by Revolee in 1877 and further characterized by Pasteur in 1880.[1] Pasteurella species usually have low virulence in humans, but serious manifestations sometimes occur and can lead to bacteremia. We present a patient who developed septic shock as a result of P. multocida bacteremia, presumptively from an intra-abdominal infection.

CASE REPORT

A 52-year-old African American female was brought to the emergency department for generalized abdominal discomfort, altered mental status, diarrhea, fevers and chills for 4-5 days. Her past medical history was significant for alcohol abuse and alcohol-related liver cirrhosis. In the emergency department, vital signs were as follows: Blood pressure of 74/42 mmHg, heart rate of 112 beats/min, respiratory rate of 20 breaths/min and temperature of 98.6 F. Remarkable findings on physical examination included jaundice as well as abdominal distention and tenderness to palpation, especially in the right upper quadrant. There was no rash or ulcers. As per family, she did not have recent travels or exposure to sick people. They denied having domestic animals at home or any contact to the patient with pets. She was placed on mechanical ventilation and admitted to the medical intensive care unit. Admission diagnosis was systemic inflammatory response syndrome with sepsis and septic shock with multi-organic dysfunction syndrome, presumptively secondary to community-acquired pneumonia, possible biliary tract infection (ascending cholangitis), probable spontaneous bacterial peritonitis (SBP) and alcoholic hepatitis. Aggressive intravenous fluids resuscitation with crystalloids along with vasopressors was initiated. Blood, urine, respiratory cultures and Legionella urine antigen were obtained. Empiric intravenous antimicrobial therapy, composed by piperacillin/tazobactam (2.25 g every 8 h) and azithromycin (500 mg every 24 h), was initiated.

Laboratory results on admission were: A complete blood cell count of 21,000/mm3(90% neutrophils), a platelet count of 51,000/mm3, a sodium level of 127 mEq/L, a potassium level of 5.3 mEq/L, a bicarbonate level of 15 mEq/L and a creatinine level of 6.3 mg/dl. Aspartate aminotransferase and alanine aminotransferase levels were 121 and 65 IU/L, respectively. Alkaline phosphatase level was 290 IU/L, gamma-glutamyl transpeptidase level was 290 U/L and lactate dehydrogenase level was 482 U/L. Total bilirubin level was 14.5 mg/dl, with a direct bilirubin level of 10.1 mg/dl. Lactic acid level was 6.4 mg/dl. Prothrombine time was 25.2 s, with an INR of 2.29. Serum alcohol level was within the normal limits. Arterial blood gases showed a pH of 7.15, a pCO2 of 23, and a pO2 of 132 while the patient was receiving mechanical ventilation with FIO2 of 60%. Chest X-ray showed left lung infiltrate with pleural effusion.

After 24 h of admission, patient remained in critical condition and requiring maximum doses of vasopressors, despite of what it seems to be the appropriate empiric antimicrobial therapy. Blood cultures drawn of admission grew P. multocida. Blood culture system Bact-Alert 3D® was used for the recovery of the organism. No polymerase chain reaction analysis was performed. Isolate was tested sensitive to piperacillin/tazobactam and azithromycin. No minimal inhibitory concentrations for these antimicrobials were reported. In spite of all medical efforts, general medical condition deteriorated and patient expired on day 3 of admission.

DISCUSSION

P. multocida is a small Gram-negative non-spore forming facultative anaerobe organism that is a natural inhabitant of the normal gastrointestinal flora and the upper respiratory tract of wild and domestic animals, especially cats and dogs. It is easily overgrowing by other flora in the sputum and might be regularly missed, as it resembles Haemophilus influenzae, Francisella tularensis and Yersinia pestis. The five species that cause the majority of pasteurellosis are: Multocida, septica, canis, stomatis, and dagmatis.[2] Human P. multocida infections have been reported to occur with and without animal exposure, the former mostly associated with the domestic cat and dog bites or scratches. Most of the infections involve the skin and soft-tissues and they can be complicated by abscess formation, osteomyelitis or septic arthritis.[34] The respiratory tract is the second most common site of infection with a wide spectrum of diseases that includes rhinosinusitis, tracheobronchitis, epiglottitis, pneumonia, empyema and lung abscesses. The majority of P. multocida pneumonia cases occur in elderly patients with underlying chronic pulmonary disease. Bacteremia has been reported in up to 55% of patients with pneumonia.[35] Invasive forms of P. multocida infection usually occur in immunocompromised patients, such as those with advanced age, chronic renal failure, solid tumors, hematological malignancies, diabetes mellitus or liver cirrhosis.[367] P. multocida causes a wide variety of disease, including abdominal and pelvic infections, endocarditis, meningitis and endophtalmitis.[3] Von Graevenitz et al. reviewed 21 proven cases of P. multocida bacteremia. A remarkable number of those cases involved patients with liver diseases, including liver cirrhosis of any etiology, hepatitis and infiltrating tumors.[8] Impaired function of the reticuloendothelial system and the presence of portosystemic shunts in patients with liver disease seem to play a major role in the development of bacteremia.[910] This case seems peculiar in that no direct contact with a domestic animal could be documented. Our patient had a history of alcohol-induced liver cirrhosis, which predisposed her to the development of bacteremia. However, retrospectively, it is difficult to establish the primary source of infection in this case. The findings of the abdominal examination may suggest that the primary source was the intra-abdominal cavity. Unfortunately, the medical team was not able to performed paracentesis to obtain ascitic fluid for cytology and cultures due to patient’s medical condition. No abdominal imaging was available. On the other hand, the chest radiography findings of infiltrate and pleural effusion may point the respiratory tract as the primary source of infection. We believed that, given the history of symptoms on admission and the presence of underlying liver disease, the intra-abdominal cavity was the most likely primary source of infection in this patient. Respiratory and intra-abdominal infections have been associated with inhalation of the organism. Nasopharyngeal colonization with P. multocida with transient bacteremia and seeding of the peritoneal cavity in immunosupressed cat owners could play an important role in the development of SBP.[1112] SBP caused by P. multocida is rare. Tamaskar et al. reviewed 13 patients with P. multocida SBP. Ten of these patients were exposed to animals, nine had positive blood cultures and four patients died.[13]

The treatment of choice of P. multocida infections is penicillin. However, penicillin-resistant strains in human infections have been described. In these cases, 2nd and 3rd generation cephalosporins, macrolides, fluoroquinolones, tetracyclines, and trimethoprim-sulfamethoxazole are recommended as an alternative therapy.[21415]

Mortality rate ranges from 15% to 30% among bacteremic patients. Outcome is associated with severity of the infection, the extent of the underlying disease and the early initiation of appropriate therapy.[3616]

CONCLUSION

Although cases of bacteremic P. multocida infections has been infrequently reported in the literature, clinicians should considered this organism as an important and potentially lethal pathogen in humans, where it can cause life-threatening infections. P. multocida should be included in the microbiologic differential diagnosis in patients with underlying chronic liver diseases who presents with possible intra-abdominal infection, even without history of exposure to domestic animals.