Distinguishing Complicated from Uncomplicated Bacteremia Caused by Staphylococcus aureus: The Value of "New" and "Old" Serological Tests

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Abstract
Antibody responses to staphylococcal a-toxin, cell wall teichoic acid, and cell wall peptidoglycan were measured in 259 serum samples from 74 consecutive patients with Staphylococcusaureus bacteremia. All patients with complicated bacteremia were seropositive in at least one of three tests, and 18 (72%) of 25 were positive in two or three assays; six (75%) of eight patients with endocarditis were positive for all three tests. In contrast, 15 (75%) of 20 patients with uncomplicated bacteremia were positive in only one or none of the tests. These differences in antibody response patterns were statistically significant (χ2 = 18.33, P < .001). Patients with complicated bacteremia had peak antibody titers that were significantly higher than those of patients with uncomplicated bacteremia. The assay for antibody to a-toxin was as sensitive as the assays for antibody to cell wall antigens but had less specificity for complicated bacteremia. The clinical severity of the bacteremia did not correlate with a complicated vs. uncomplicated nature of the infection but was predictive of early death due to staphylococcemia. The calculated predictive values suggest that the serology of S. aureus bacteremia may be clinically valuable when multiple tests are performed in paired serum samples.