FINAL DIAGNOSIS: Pasteurella multocida peritonitis
More than 24,000 people in the United States are on peritoneal dialysis (PD). Peritonitis is a common cause of morbidity and the most common cause of peritoneal dialysis failure. PD-associated peritonitis is usually monomicrobial in contrast to the polymicrobial nature of other forms of peritonitis. Gram-positive cocci from the skin are the most common organisms followed by gram-negative organisms. If bowel perforation is involved, the peritonitis will most likely be polymicrobial with gram-negative organisms and anaerobes. No organisms may grow in up to 30% of cases possibly due to early empiric antibiotic treatment.
Organisms in the genus Pasteurella are primarily animal pathogens but can cause disease in humans. Pasteurella multocida is the species most commonly encountered in human hosts. Human disease usually manifests as local infection resulting from an animal bite (usually cats). Patients may present with cellulitis, abscess, or osteomyelitis. Pasteurella infection may also present as a respiratory tract infection with pneumonia, empyema, or lung abscess. Colonization of the bronchial tree in patients with chronic pulmonary disease is not uncommon. Finally, systemic infection such as peritonitis, meningitis, bacteremia, or endocarditis may occur.
Pasteurella multocida are aerobic, non-motile, ovoid or rod-shaped gram-negative cocco-bacilli with bipolar staining. They can be very pleomorphic on smears of exudates suggesting mixtures of Haemophilus and Neisseria species. A capsule may be evident. Specific virulence factors in humans have not been identified. They grow best on media containing blood and form small, non-hemolytic, gray colonies. The organism cannot grow on MacConkey agar. Media containing vancomycin, clindamycin, and/or amikacin have been used for selective growth. There are five capsular serogroups and sixteen O antigen serotypes known.
PD-associated peritonitis with Pasteurella multocida is quite uncommon with less than twenty cases reported in the literature. It appears to be more common in patients on continuous cycling peritoneal dialysis. In half of the reported cases, gram stain of the peritoneal fluid was not revealing. Cats were the suspected source in 100% of the cases. A domestic cat had punctured the dialysis tubing with evidence of leaking in 69% of the cases. Close contact with cats was noted in 25% of the cases, and in only one case the presence of a cat in the house was the only association. Cats have also been associated with peritonitis caused by other organisms such as Neisseria pharynges, Staphylococcus hominis, and Capnocytophaga canimorsus. Pasteurella multocida peritonitis may be much more prevalent than currently reported. When considering the frequent administration of empiric antibiotics and the fact that approximately 60% of American homes have at least one domestic pet, it is possible that many of the culture negative cases of PD-associated peritonitis could be caused by Pasteurella multocida. Patients on peritoneal dialysis should be educated about the risk of acquiring an infection from their pets and should be advised to keep pets away from peritoneal dialysis equipment. Frequent hand washing, especially after handling pets, should be emphasized.
Contributed by James T Edinger, MD and A William Pasculle, ScD