Cat scratch disease in Connecticut. Epidemiology, risk factors, and evaluation of a new diagnostic test.

BACKGROUND: Although cat scratch disease is commonly diagnosed in patients who have unexplained regional lymphadenopathy after encounters with cats, its epidemiology and the risk factors for disease are not clearly defined, and there is no generally accepted diagnostic test.

METHODS: We conducted a physician survey to identify cases of cat scratch disease occurring over a 13-month period in cat owners in Connecticut. We interviewed both the patients (or their parents) and controls matched for age who owned cats. Serum from the patients was tested for antibodies to Rochalimaea henselae with a new, indirect fluorescent-antibody test.

RESULTS: We identified 60 patients with cat scratch disease and 56 age-matched subjects. Patients were more likely than controls to have at least one pet kitten 12 months old or younger (odds ratio, 15), to have been scratched or bitten by a kitten (odds ratio, 27), and to have had at least one kitten with fleas (odds ratio, 29). A conditional logistic-regression analysis found that in kitten-owning households, patients were more likely than controls to have been scratched or bitten by a cat or kitten (odds ratio, 12.4; 95 percent confidence interval, 1.0 to 150). Of 45 patients, 38 had serum samples with titers of 1:64 or higher for antibody to R. henselae, as compared with 4 of 112 samples from controls (P < 0.001). The positive predictive value of the serologic test was 91 percent. Of 48 serum samples from patients' cats, 39 were positive for antibodies to R. henselae, as compared with positive samples from 11 of 29 control cats (P < 0.001).

CONCLUSIONS: Cat scratch disease is strongly associated with owning a kitten, and fleas may be involved in its transmission. The serologic test for rochalimaea may be useful diagnostically, and our results suggest an etiologic role for this genus.