Comparison of In-House and Commercial Slides for Detection by Immunofluorescence of Immunoglobulins G and M againstBartonella henselaeandBartonella quintana

Abstract

We compared the sensitivities and specificities of indirect fluorescent antibody tests developed in our laboratory and commercially available from Focus Technologies (FT; formerly MRL Diagnostic) for detection of serum antibodies toBartonellaspp. Serum samples tested were from patients with culture- or PCR-confirmedBartonella quintanaorB. henselaeinfections causing cat scratch disease (CSD), chronic bacteremia, or endocarditis. At a cutoff titer of 64, the FT test had higher sensitivity than our in-house test in detecting anti-B. henselaeimmunoglobulin G (IgG) antibodies in CSD patients (91.2 versus 52.9%;P< 0.001). The specificity in serum samples from 85 control patients was, however, lower with the FT test (87%) than with the in-house test (98.8%) (P= 0.002). A cutoff titer of 128 improves the specificity for the FT test but lowers the sensitivity to 85%. For patients infected withB. henselae, our in-house test, but not the FT test, enabled endocarditis to be detected more reliably. With the in-house test, titers of IgG againstB. henselaeof ≥1,024 were found only in endocarditis patients and not in CSD patients. With the FT test, 19.1% of CSD patients had titers of IgG againstB. henselaeof ≥1,024 (P< 0.001). Our in-house technique also improved detection of anti-B. quintanaantibodies in homeless patients with endocarditis. IgG titers of ≥1,024 were present in 75% of serum samples, but only in 16.7% of serum samples with the FT test (P= 0.004). Since each test has advantages over the other, the serological diagnosis ofBartonellainfections would benefit if both tests were used concurrently.