Serologic testing for cat-scratch disease
Cat-scratch disease (CSD) may lead to prolonged lymphadenopathy, which sometimes is accompanied by fever and malaise that may raise concerns about an occult malignancy. Some patients with CSD have atypical features, such as eye involvement, encephalitis, endocarditis, hepatitis, or osteomyelitis. Recent advances in serologic testing have improved the ability to reliably diagnose this often clinically vague infection. Metzkor-Cotter and colleagues describe the use of an enzyme immunoassay (EIA) technique for diagnosis of CSD.
The most widely used diagnostic test for CSD at present is an immunofluorescent antibody assay, but it is technically difficult to perform and prone to interobserver variability regarding the interpretation of immunofluorescence. Because the EIA described in this study is numeric, there is no need for subjective interpretation. The authors enrolled 98 patients with clinical and serologic evidence of CSD in their study. About 95 percent of the subjects had regional lymphadenopathy (most commonly axillary, inguinal, or cervical), and about one half reported fever and malaise. The most common atypical manifestation was eye involvement (oculoglandular syndrome or neuroretinitis), which was noted in about 10 percent of subjects.
Anti-Bartonella henselae IgM titers were positive in 53 percent of patients, while 92 percent had positive anti-B. henselae IgG levels. The first serologic sample was obtained three weeks after the infection began, on average, and patients were followed for a median duration of 35 weeks. Both IgM and IgG titers declined over time. Within three months, 92 percent of patients with initially positive IgM levels became seronegative. IgG titers persisted for more than two years in some patients. All patients with positive IgG titers measured at a level of 1.0 optical density or more were within the first 12 months of CSD infection. Neither the initial antibody titers nor their decline over time correlated with disease severity or duration.
The authors conclude that the presence of anti-B. henselae IgM by EIA indicates an acute onset of infection within the previous three months, but it is present in only one half of CSD patients. The slow decline in IgG levels prevents any use of acute and convalescent titers to identify the onset of infection, and the lack of correlation between antibody titers and CSD course precludes its use as a monitor of disease activity.
Metzkor-Cotter E, et al. Long-term serological analysis and clinical follow-up of patients with cat scratch disease. Clin Infect Dis November 1, 2003;37:1149-54.
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