Order of authorship in the original publication: Chomel, Kasten, Floyd-Hawkins.... Chomel and colleagues studied 47 cattery cats from a private home for 12 months. They found that such cats typically are bacteremic. Since fleas feed on the cats' blood they studied the fleas that were biting the cats (132 fleas) and found that 34% of those fleas were positive for the bacterium. This explained why people who were not actually scratched by a cat, but were instead bitten by a flea that had bitten an infected cat, could catch cat scratch fever.

(Thanks to Juan Weiss for this reference and its interpretation.)