Lymphogranuloma venereum

If you test positive for chlamydia, the result usually stops there. It rarely tells you which strain you have, and that distinction matters more than most people realize.

Most chlamydia is a mild surface infection cleared in a week. A small share is an invasive form that burrows into deeper tissue and can need up to three times the antibiotics to fully clear. This test looks for that invasive form in a urine sample.

What Makes This Strain Different

LGV (lymphogranuloma venereum) is caused by three specific types of the chlamydia bacterium, labeled L1, L2, and L3. Ordinary chlamydia stays on the surface lining of the genitals or rectum and often causes mild or no symptoms. These L-type strains are different: they can invade the lymphatic tissue underneath, drive intense inflammation, and produce whole-body symptoms.

The lab confirms which strain is present by reading a small stretch of the bacterium's genetic code, a step called genotyping. In current outbreaks the L2 group of strains dominates, though the exact variant differs by place and time. The L2b variant has been the hallmark of the epidemic among men who have sex with men in most settings, while one Lisbon series found that roughly two-thirds of its cases were a different L2 variant, L2/434. This is a bacterial infection you can clear, not a fixed feature of your body.

Why a Urine Test Misses Most Cases

Here is the part that trips people up: a negative urine test does not rule out this infection. In current outbreaks the infection is overwhelmingly anorectal, not urethral, so urine is often the wrong place to look.

In a large Amsterdam clinic study of men who have sex with men, the invasive strain turned up in about 0.06% of urine samples versus about 0.9% of rectal samples, roughly 15 times lower in urine. An early Dutch outbreak report found the infection by rectal testing while every urine sample came back negative. A urine result reflects only the urethral site, so a clean urine test can coexist with an active rectal infection.

This is not a contradiction, just a matter of geography. Urethral infection with these strains is genuinely uncommon but still occurs, and it appears to contribute to transmission. Concurrent urethral infection was found in about 2% of men who already had anorectal disease and in nearly 7% of their partners, which is why urine testing has value even though it cannot stand alone.

The HIV and Coinfection Connection

This infection runs in tight sexual networks, and it overlaps heavily with HIV and other sexually transmitted infections. In one Amsterdam case-control study, people with the invasive strain were about 5.7 times as likely to be HIV positive as those with ordinary chlamydia, and about 9.3 times as likely as those with no chlamydia at all.

A pooled analysis across studies found a similarly strong link, with an odds ratio of 8.19 for HIV among cases. Coinfection with syphilis, gonorrhea, and hepatitis C is also common. A positive result is therefore a prompt to check for these other infections at the same time, not an isolated finding.

The old assumption that this is only an HIV-positive problem no longer holds. Recent surveillance in England, the Netherlands, and Canada shows a rising share of cases among HIV-negative men, particularly those taking HIV prevention medication (pre-exposure prophylaxis). It has also emerged among transgender women who have sex with men.

What Happens If It Goes Untreated

The reason this strain earns its own test is the damage it can do when missed. Because it invades deeper tissue rather than staying on the surface, an untreated infection can progress through stages, from an early ulcer or sore, to swollen, tender lymph nodes that break down (buboes), and later scarring.

In the rectum, that late scarring can produce strictures, abnormal channels between organs (fistulas), and abscesses that permanently distort the anal and rectal structures. These late complications are largely irreversible, which is the whole argument for catching and treating the infection early. When the infection is anorectal, the most common presentation is inflammation of the rectum (proctitis) with discharge, pain, and bleeding.

A Rising Share of Silent Infections

You cannot rely on symptoms to tell you whether you carry this strain. Across surveillance programs, the proportion of cases with no symptoms at all has climbed, ranging from roughly 27% in UK clinics to over 50% in more recent cohorts.

When clinics switched from testing only symptomatic patients to testing every positive rectal chlamydia sample, they uncovered a large hidden pool. In one Melbourne program, universal testing meant that about 34% of the invasive-strain cases it found were asymptomatic and would have been missed under a symptom-based approach. That silent fraction is exactly what thorough, repeat testing is designed to catch.

Why One Test Is Not Enough

For an infection like this, a single reading answers less than a pattern of testing does. A negative urine result reflects only one site on one day, so if you have ongoing exposure or symptoms elsewhere, retesting at the relevant site matters more than trusting one clean urine sample.

Timing also affects follow-up after treatment. Studies of rectal infection found that the bacterium's genetic material can linger for up to about 16 days after starting antibiotics, so a test-of-cure done too early can mislead. If you are treated, retest after the full course has finished and enough time has passed, and screen again after any new exposure rather than assuming past clearance protects you.

What to Do With an Unexpected Result

A positive urine result means an invasive-strain infection was detected at the urethra, and it changes your treatment. Ordinary chlamydia is cleared with about a week of doxycycline. Symptomatic infection with this strain is treated for 21 days, though current guidelines note that asymptomatic or mild infection may be adequately treated with a shorter 7-day course. Confirm with your clinician that the sample was actually genotyped for the L-type strains, since some labs report only generic chlamydia.

A positive result should also trigger a wider workup: testing at the rectal and throat sites, plus HIV, syphilis, and hepatitis C screening, because coinfection is common. Partner testing and treatment matter too. A sexual health clinician or infectious disease specialist can coordinate this.

If your urine test is negative but you have rectal symptoms such as pain, discharge, or bleeding, do not treat that as reassurance. Ask specifically for rectal chlamydia testing with reflex genotyping, since that is where this infection usually hides.

When a Urine Result Can Mislead You

The most important limitation is site, not chemistry. A urine sample captures only the urethra, so it can be genuinely negative while an infection is present in the rectum, which is the dominant site in current outbreaks.

• Wrong specimen site: urine reflects urethral infection only, and this strain is far more often anorectal, so a negative urine test cannot clear you if your exposure was rectal.
• No automatic strain typing: a routine urine chlamydia test detects the bacterium but usually cannot say whether it is the invasive L-type, which requires a separate genotyping step many labs do not run.
• Antibody-based screens are less specific: older serum antibody tests can be positive in people without active infection, and one modern antibody assay correctly identified only about 75% of true cases, which is why direct molecular testing is preferred.
• Sample inhibitors: substances in a specimen can occasionally interfere with the genetic amplification method and blunt detection, so a borderline or invalid result may need to be repeated.