What is trich, and why isn’t it in a standard STI screen?

If you’ve had a full STI check and noticed “trich” wasn’t on the list, you might wonder whether something was missed. It wasn’t. Trichomoniasis (“trich”) is the world’s most common curable STI, yet in most of Australia it’s deliberately left off the routine screen — for reasons that are quite different from the other infections. Here’s what it is, and when a test actually makes sense.

What is trich?

Trich is short for trichomoniasis, an infection caused by Trichomonas vaginalis — not a bacterium or a virus, but a tiny single-celled parasite. That makes it a little different from most of the STIs people know. It infects the vagina and urethra in women, and the urethra in men, and it’s passed on through sex. Globally it’s the most common curable STI, with millions of new cases each year, and the good news is that it’s straightforward to cure once it’s found.

What’s unusual about trich in Australia is how unevenly it’s spread. In most urban settings it’s an uncommon cause of vaginal discharge or urethritis. But it’s considerably more common in older people, in regional and remote communities — particularly among Aboriginal and Torres Strait Islander people — and among some sex workers. Where you live and your age can matter as much as anything else, and that uneven pattern is central to why testing is targeted rather than universal.

How do you get trich?

Trich is passed on through unprotected vaginal sex, and through genital-to-genital contact. Unlike some STIs, it’s not typically spread through oral or anal sex, because the parasite lives in the genital tract rather than the throat or rectum. As with other STIs, condoms reduce the risk, and it’s more likely with a new partner or multiple partners. It can also pass back and forth between partners, which is why treating everyone involved at the same time matters.

What are the symptoms of trich?

Trich is another infection that often stays silent, which is a big part of how it keeps circulating. Up to half of women with trich have no symptoms at all, and most men have none.

When women do get symptoms, they can include:

• a profuse, frothy vaginal discharge, often yellow-green
• an unpleasant or “fishy” odour
• vulval itching, soreness or redness
• discomfort or burning when passing urine
• pain during sex.

Men are usually symptom-free, but occasionally trich causes:

• discharge from the penis
• irritation or burning in the urethra
• discomfort passing urine.

Because these symptoms overlap so heavily with other causes of discharge — including chlamydia and gonorrhoea, and non-STI conditions like bacterial vaginosis and thrush — symptoms alone can’t tell you what you have. That takes a test.

Why isn’t trich in a standard STI screen?

This is the part that surprises people, and it comes down to one idea: prevalence. A standard asymptomatic screen in Australia looks for chlamydia, gonorrhoea, syphilis, HIV and hepatitis B — the infections common enough, and serious enough if missed, that testing everyone clearly pays off. Trich doesn’t sit in that group for most of the population.

It’s uncommon in the general population

In most urban Australian settings, trich is genuinely rare. When an infection is uncommon, testing everyone who has no symptoms turns up very few true cases and a relatively higher share of false alarms — results that then need repeating and can cause needless worry. Screening is most useful when there’s a reasonable chance of actually finding the infection, and for trich that chance is low across the general population.

So testing is targeted, not universal

Rather than screen everyone, the guidelines focus trich testing where it’s far more likely to be found or to matter: people with symptoms, and people in higher-prevalence groups — including some regional and remote communities. It’s the same principle behind the whole screen: test for what you’re realistically likely to find, so the results mean something. This is different from an infection like Mgen, which is left off mainly because of antibiotic-resistance concerns; with trich, it’s chiefly about how uncommon it is in most of the country.

The practical upshot: if you have no symptoms and no particular risk factors, not being tested for trich is the right call, and your standard screen hasn’t missed anything. If you do have symptoms, that changes the picture entirely.

When should you be tested for trich?

Testing for trich makes sense when there’s a real chance of finding it, including if you:

• have symptoms such as an unusual or frothy discharge, odour, genital itch or soreness, or discomfort passing urine
• are the sexual partner of someone diagnosed with trich
• are pregnant and have symptoms, given the risks to pregnancy
• live in or have partners from a community where trich is known to be more common.

If any of those apply, a Specialist GP can arrange the right test alongside a broader check if needed. If you simply want a routine check-up and have no symptoms, a standard STI screen remains the appropriate choice. If you’re unsure, our trich test page explains how testing works.

How is trich tested for?

The test is simple and private. In women it’s usually a self-collected vaginal swab; in men, a first-pass urine sample (the first part of the stream). The laboratory uses a NAAT — a sensitive DNA-based test — which has largely replaced older methods like looking at a sample under the microscope, because it detects far more infections, including in people without symptoms. If trich is found, it’s worth checking for other STIs at the same time, since having one raises the chance of another.

Treatment

Trich is reliably curable with antibiotics, and treatment is well established. It’s treated with metronidazole, either as a short course of tablets over about a week or, in some cases, a single larger dose. A few practical points matter:

• avoid alcohol during treatment and for at least 24 hours afterwards, because the combination can cause unpleasant nausea and flushing
• avoid sex until you and your partner(s) have finished treatment, to stop it bouncing back and forth
• partners should be treated at the same time, even if they have no symptoms — this is often done without waiting for their own test result
• if symptoms persist after treatment, see your doctor, as a further course may be needed.

Because reinfection from an untreated partner is the most common reason trich comes back, treating everyone involved together is the single most important step.

Complications if left untreated

Trich is usually more of a nuisance than a danger, but it isn’t entirely harmless if ignored. Ongoing infection can cause persistent irritation and discomfort, and it can make passing the infection to partners more likely. Importantly, trich is associated with a higher risk of acquiring and transmitting HIV, because the inflammation it causes makes the genital tract more vulnerable.

In pregnancy it deserves particular care: untreated trich is linked to premature rupture of the membranes, preterm delivery and low birth weight. That’s why testing and treatment are recommended for pregnant women who have symptoms.

The bottom line: trich isn’t missing from the standard screen by mistake. For most people with no symptoms, it’s simply too uncommon for routine testing to be worthwhile. But if you have symptoms, a partner has been diagnosed, or you’re in a higher-risk group, it’s well worth testing — and it’s one of the most straightforward STIs to cure once it’s found.