Chancroid and Genital Ulcer Testing in Bangkok: Working Out What Caused the Ulcer

Sexual health testing guide · 2026

Genital ulcers are one of the few sexual health presentations where getting the diagnosis right quickly genuinely changes the outcome.

By MedEx · Updated September 2026 · Approx. 7-minute read

Quick answer

Chancroid, caused by Haemophilus ducreyi, produces a painful genital ulcer with ragged edges, often with tender, swollen lymph nodes that can suppurate. It has become uncommon globally following syndromic management programmes, but still occurs. Because it cannot be reliably distinguished from herpes or syphilis by appearance alone, the practical approach to any genital ulcer is a multiplex PCR from the ulcer covering HSV-1, HSV-2, Treponema pallidum and H. ducreyi, plus syphilis serology and an HIV test. More than one cause can be present at the same time.

In this guide

1. The realistic differential for a genital ulcer
2. How the ulcer should be tested
3. Chancroid: course and treatment
4. Why HIV testing is not optional here

The realistic differential for a genital ulcer

Studies of clinical diagnosis against laboratory confirmation consistently show that appearance alone performs poorly. Testing is not a formality — it changes treatment.

How the ulcer should be tested

Swab the ulcer early. Sensitivity falls as the lesion heals, so the day you notice it is the best day to be seen. A swab from the base of the ulcer, or fluid from an intact blister, gives the highest yield.

A complete workup for a genital ulcer includes:

• Multiplex ulcer PCR for HSV-1, HSV-2, T. pallidum and, where available, H. ducreyi.
• Syphilis serology (treponemal and non-treponemal), since serology may be negative very early — repeat testing may be needed.
• HIV testing, because genital ulceration substantially increases both HIV acquisition and transmission risk, and because ulcers may be more severe in HIV.
• Chlamydia and gonorrhoea testing from relevant sites, since co-infection is common.

Same-day assessment is available through the MedEx STI service or the 24/7 doctor on call.

Chancroid: course and treatment

After an incubation of roughly 3 to 10 days, a tender papule appears and rapidly becomes a painful ulcer with a soft base and ragged, undermined edges. Around half of cases develop tender inguinal lymphadenopathy, which can form a fluctuant abscess (a bubo) that may need drainage.

Chancroid responds well to antibiotics, and there are several effective options; a clinician selects based on local resistance patterns, allergy and pregnancy status. Ulcers usually improve within days and lymph node resolution takes longer.

Partners should be examined and treated if they had contact within the 10 days before symptoms began, whether or not they have symptoms. Follow-up is important: failure to improve should prompt reconsideration of the diagnosis, including co-infection and HIV.

Why HIV testing is not optional here

Genital ulceration disrupts the mucosal barrier and increases HIV transmission risk in both directions. The association is strong enough that every genital ulcer should trigger an HIV test, and repeat testing after the window period.

Two further points. Ulcerative disease may be more extensive and slower to heal in people with HIV, and treatment response should be monitored more closely. And if the exposure that caused the ulcer was recent and carried HIV risk, post-exposure prophylaxis is time-critical — within 72 hours — and should be discussed immediately rather than after test results return. See MedEx PEP and PrEP services.

For the window periods that determine when a negative HIV test can be trusted, see the STI window periods guide.

Frequently asked questions

How can I tell chancroid from herpes or syphilis?

You often cannot from appearance alone, and clinical diagnosis performs poorly against laboratory testing. A multiplex PCR from the ulcer covering HSV-1, HSV-2, Treponema pallidum and H. ducreyi, plus syphilis serology and HIV testing, is the practical approach.

Is a painful ulcer more likely to be chancroid?

Pain makes primary syphilis less likely, since the classic syphilitic chancre is painless. But herpes ulcers are also painful and far more common, so testing is still needed.

How soon should a genital ulcer be swabbed?

As early as possible. Sensitivity falls as the lesion heals, so the day you notice it is the best day to be seen.

Do I need an HIV test if I have a genital ulcer?

Yes. Genital ulceration substantially increases HIV transmission risk in both directions, and repeat testing after the window period is also advised.

Do partners need treatment for chancroid?

Yes. Partners who had contact within the 10 days before symptoms began should be examined and treated regardless of whether they have symptoms.

Is chancroid still common?

It has become uncommon globally following syndromic management programmes, but it still occurs and should not be excluded on the basis of rarity alone.

Sources and further reading

1. CDC Sexually Transmitted Infections Treatment Guidelines: Genital Ulcers
2. WHO guidelines for the management of symptomatic sexually transmitted infections
3. MedEx STD and STI testing service

Medical disclaimer: This article is general health information and does not replace medical advice, diagnosis or treatment. Laboratory reference ranges differ between laboratories and results must be interpreted alongside your symptoms, medicines and medical history. Speak with a qualified clinician before starting, stopping or changing any treatment. Service details, inclusions and prices can change — confirm them with MedEx before booking.