Prevalence, risk factors, and genetic diversity of Bartonella henselae infections in pet cats in four regions of the United States.

Blood was collected from a convenience sample of 271 pet cats aged 3 months to 2 years (mean age, 8 months, median and mode, 6 months) between May 1997 and September 1998 in four areas of the United States (southern California, Florida, metropolitan Chicago, and metropolitan Washington, D.C.). Sixty-five (24%) cats had Bartonella henselae bacteremia, and 138 (51%) cats were seropositive for B. henselae. Regional prevalences for bacteremia and seropositivity were highest in Florida (33% and 67%, respectively) and California (28% and 62%, respectively) and lowest in the Washington, D.C. (12% and 28%, respectively) and Chicago (6% and 12%, respectively) areas. No cats bacteremic with B. clarridgeiae were found. The 16S rRNA type was determined for 49 B. henselae isolates. Fourteen of 49 cats (28.6%) were infected with 16S rRNA type I, 32 (65.3%) with 16S rRNA type II, and three (6.1%) were coinfected with 16S rRNA types I and II. Flea infestation was a significant risk factor for B. henselae bacteremia (odds ratio = 2.82, 95% confidence interval, 1.1 to 7.3). Cats >or=13 months old were significantly less likely to be bacteremic than cats <or=6 months old (odds ratio = 0.18, 95% confidence interval, 0.05 to 0.61). Flea infestation, adoption from a shelter or as a stray cat, hunting, and being from Florida or California were significant risk factors for B. henselae seropositivity. DNA fingerprint was significantly associated with region (P = 0.03) and indoor/outdoor status of cats (P = 0.03).