Traditional Diagnostic Methods

Clinical diagnosis with in vitro culture of H. ducreyi currently remains the main tool for the diagnosis of chancroid. Laboratory culture technique has been used as the "reference standard" for evaluating new methods of diagnosis for many years. On the other hand, direct microscopic examination of clinical material by Gram stain can be misleading due to the polymicrobial flora that are often present in most genital ulcers. Direct microscopy is, therefore, not recommended to be used as a routine diagnostic tool for chancroid (Albritton, 1989). H. ducreyi grows relatively slowly with small-sized colonies, rendering it easily overlooked on culture plates. This is especially so with respect to specimens taken from sites with mixed bacterial flora. Selective agents and/or special incubation procedure have been advocated to solve this problem, such as incubation at 33°C with 5-10% CO2 on Mueller-Hinton agar supplement with 5% chocolatized horse blood, 1% IsoVitaleX, and 3 mg of vancomycin per liter (MH-HB) (Dangor et al., 1992). Antigen detection assays have also been made available for diagnostic use. These assays use a monoclonal antibody raised against outer membrane protein (OMP) or lipo-oligosaccharide (LOS) in H. ducreyi for immunofluorescence detection of H. ducreyi (Hansen et al., 1995; Patterson et al., 2002). These methods have been shown to be more sensitive than culture in detecting H. ducreyi in genital ulcer smears. Serological tests for H. ducreyi include enzyme immunoassays (EIAs), dot immunobinding, agglutination, complement fixation, and precipitation (Schalla et al., 1986; Museyi et al., 1988; Alfa et al., 1992; Totten et al., 2000). Sensitivity of serological approach to diagnose chancroid is rather low for the detection of circulating antibodies to H. ducreyi in individual symptomatic patients, although they may still be useful tools for epidemiological studies in at-risk communities.

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