Lack of rapid and reliable laboratory tests make diagnosis and treatment decisions based on microbiologic findings difficult. Available laboratory tests involve acquiring a sample of ulcer exudate and include: Gram stain, culture, and multiplex PCR (M-PCR).

• Ulcer exudate can stained to typically reveal Gram-negative coccobacilli organized in a chain, so-called a “school of fish.”^[1]
• Sensitivity of Gram stain is poor and cannot be used for definitive diagnosis.

• Definitive diagnosis of chancroid requires culturing Haemophilus ducreyi from ulcer exudate.
• H. ducreyi is a fastidious bacterium and is therefore difficult to culture. Most facilities do no have the required media or experience to culture the bacterium.^[2]

• A multiplex PCR (M-PCR) technique has been developed to amplify DNA from ulcer exudate and identify H. ducreyi.^[3]
• PCR tests have not yet been approved by the FDA.
• PCR may not be practical due to the high cost of testing and slow availability of results.

Human Immunodeficiency Virus (HIV) testing is recommended due to the high occurrence of coinfection with H. ducreyi.

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  Direct smear microscopic exam revealed the presence of Haemophilus ducreyi indicative of a chancroid infection. From Public Health Image Library (PHIL). ^[4]
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  Photomicrograph of a rabbit blood culture showing Haemophilus ducreyi bacteria using Gram-stain technique. From Public Health Image Library (PHIL). ^[4]
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  Gram-negative Haemophilus ducreyi bacteria, which had been extracted from a culture. From Public Health Image Library (PHIL). ^[4]
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  Gram-negative Haemophilus ducreyi bacteria, which had been extracted from a culture. From Public Health Image Library (PHIL). ^[4]
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  Gram-negative Haemophilus ducreyi bacteria. From Public Health Image Library (PHIL). ^[4]
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  Gram-negative Haemophilus ducreyi bacteria (1200x mag). From Public Health Image Library (PHIL). ^[4]
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  Gram-negative Haemophilus ducreyi bacteria. From Public Health Image Library (PHIL). ^[4]
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  Gram-negative Haemophilus ducreyi bacteria. From Public Health Image Library (PHIL). ^[4]
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  Gram-negative Haemophilus ducreyi bacteria arranged in parallel rows. From Public Health Image Library (PHIL). ^[4]
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  Gram-negative Haemophilus ducreyi bacteria arranged in parallel rows. From Public Health Image Library (PHIL). ^[4]

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