Cat Scratch Disease CSD

CSD most often occurs in young (80 percent less than 21 years of age) immunocompetent hosts.31 The initial site develops a transient erythematous papule or pustule for which the patients do not often seek medical attention. They usually come after the development of persistent regional lymphadenopathy in an area of the body draining lymph from the scratch or bite, usually 7 to 12 days after the injury. Symptomatic lymphadenopathy usually resolves in 2 to 4 months. Systemic complications—with involvement of the central nervous system, eye, liver, spleen, and bone—can be seen in up to 2 percent of cases. It has been estimated that CSD affects about 22,000 individuals annually in the United States (9.3 per 100,000 population) and results in about 2000 hospitalizations. There is a male as well as a fall/winter seasonal predominance.

The precise etiologic agent has been difficult to determine. Most investigations implicate Bartonella henselae, a small gram-negative rod. Diagnosis is made by (1) history of cat exposure, (2) typical lymphadenopathy, (3) no other cause of lymph gland swelling, and (4) a positive serologic test for B. henselae. Serologic assay using the polymerase chain reaction (PCR) is the most accurate method (86 percent sensitive and 96 percent specific) and more sensitive than either the IgG indirect fluorescence assay (IgG IFA) (41 percent sensitive) or the IgM enzyme-linked immunoassay (IgM EIA) (71 to 80 percent sensitive). 32 Serologic testing can be improved by using PCR to assay pus and lymph node specimens, with sensitivities approaching 100 percent. 33

Most patients with CSD are not seriously ill, spontaneous resolution is common, and antibiotic therapy has not been studied in large controlled clinical trials. As a result, most reviews do not recommend antibiotic therapy for uncomplicated cases. A recent controlled study of 29 patients with typical CSD found that a 5-day course of azithromycin led to more rapid resolution in lymph node volume during the first 30 days. 34 After that, there was no difference in rate or degree of resolution.

Antimicrobial susceptibility testing has shown favorable minimum inhibitory concentration (MIC) values to a number of antibiotics, but since the bacterium resides intraceullularly, agents that achieve high concentrations inside human cells would probably be the most effective—rifampin, gentamicin, doxycycline, and the macrolides. Severely ill patients, those with systemic complications, and those who are immunocompromised should be treated with either rifampin or trimethoprim-sulfamethoxazole.

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