Pasteurella multocida Bacteremia: Concern Remains Even in the Absence of Direct Animal Contact

Pasteurella are pleiomorphic, facultatively anaerobic, gram-negative bacteria commonly isolated as commensals in the oral flora of a variety of wild and domesticated animals. In dog and cat bite wounds, Pasteurella species, in particular P. multocida, are isolated in 50% to 70% of the cases. Although direct inoculation of the skin through animal bite or scratch is the most common route of human disease, infection has been documented even in the absence of direct animal contact. Upper respiratory colonization and infections including pneumonia, sinusitis, pharyngitis, even otitis media are believed to be transmitted from atraumatic exposure. Bacteremia, although uncommon, is also associated with more severe manifestations including sepsis, disseminated intravascular coagulation, and even endocarditis, even in healthy individuals. In this issue of the Journal, Ebright et al reported their experience with Pasteurella infections from 1987 to 2007 at a single institution. Of 179 patients with documented Pasteurella infections, 14 (7.8%) of these presented as bacteremia. The most common clinical manifestations were fever, sepsis, and cellulitis. All of the patients had chronic medical conditions, mostly cardiac disease, hypertension, or diabetes. Four of the patients had malignancies (acquired immunodeficiency syndrome with Kaposi sarcoma, lung cancer, breast cancer, and myelodysplastic syndrome). In contrast to a previous study that reported cirrhosis as a major risk factor, present in up to 34% of Pasteurella bacteremia (n = 95), none of the patients in this cohort had chronic liver disease. Only 1 person died from sepsis, and this was a patient who received peripheral blood stem cell transplantation for myelodysplastic syndrome. The rest recovered without significant complications. Again, this is in contrast to earlier studies that have estimated mortality from Pasteurella bacteremia ranging from 20% to 30%. They posited that improved blood culture techniques and earlier treatment might have contributed to better outcomes. Another interesting result was that 7 of the 14 patients reported no animal exposure at all. The article by Prakash presents an uncommon manifestation of epiglottitis and bacteremia in a patient with chronic lymphocytic leukemia. The patient’s only risk factor was transient contact with a neighborhood cat. Presumably, the patient may have been colonized in his upper respiratory tract from droplet inhalation, leading to epiglottitis and sepsis. He recovered after 14 days of intravenous antibiotics. Another case reported a renal transplant patient who developed sinusitis from close contact with a pet dog and ultimately requiring sinus surgery and 6 weeks of antibiotics to control the infection. These cases highlight the risk of potentially severe zoonotic infection encountered by immunosuppressed individuals, even those who do not have pets of their own. One cannot emphasize enough exercising prudent measures to refrain from close contact with animals. Once infection is present, prompt therapy should be administered, and choice of antibiotics should be guided by susceptibility testing. Pasteurella species have A-lactamases, and resistance to ampicillin has been reported. Clindamycin, a common agent used for skin and soft tissue infections, has demonstrated poor activity to the bacteria. What remains controversial is whether prophylaxis with antibiotics after animal bites should be encouraged in special populations at high risk for invasive disease. More studies defining the specific risk factors and complications of Pasteurella infections in the immunosuppressed patient should address these concerns. REFERENCES