Laboratory diagnosis of Haemophilus ducreyi infection

Genital ulcer disease (GUD) is a well documented risk factor for heterosexual transmission of the human immunodeficiency virus (HIV). In Africa, chancroid is the major GUD. The epidemiology for chancroid and Haemophilus ducreyi infection is still poorly understood, mainly because diagnostic tests for chancroid and H. ducreyi infection are not well established. Yet, culture of H. ducreyi remains the method of choice for confirming clinical diagnosis inspite of an unsatisfactory isolation rate. Various non-culture tests for detection of H. ducreyi were developed. As for other diseases, the polymerase chain reaction (PCR) test is proving its usefulness for diagnosing chancroid. However, sample handling should be optimized and criteria allowing the classification of culture negative/PCR positive patients should be established. Several simple and inexpensive diagnostic tests for use in low-resource settings are in progress. Direct microscopy of Gram-stained clinical specimens is an obvious candidate, but variations in sensitivity still limit the usefulness of this test for confirmation of clinical diagnosis. An enzyme immunoassay using a specific polyclonal antiserum, and immunofluorescence microscopy using a specific monoclonal antibody may be useful for the detection of H. ducreyi antigen. As for PCR, criteria should be established to classify patients with discordant test results. Yet, serological tests are useful only for epidemiology. Specific and sensitive antigens were identified, but their usefulness in diagnostic tests remains to be established.