The goal of this study is

1. to improve the accuracy of chlamydia multi-site testing in men who have sex with men (MSM) and trans-women, whilst saving diagnostic costs, by comparing two new pooling methods with the 3-samples tested separately
2. to assess the diagnostic accuracy of pooled specimens for lymphogranuloma venereum detection (LGV) - a type of chlamydia infection

Chlamydia and gonorrhoea testing for MSM and trans-women usually involves 3 samples from the throat, bum and wee-pipe. The tests can be combined into a single sample pot (pooled sample) which reduces costs, but in a previous study this reduced the accuracy for finding chlamydia.

The main question for this study is:

Can the accuracy of chlamydia testing in a pooled sample be improved by reducing the amount of urine added to minimise dilution, or by using a meatal sample instead of a urine sample?

Participants will be asked to complete two sets of their own throat and bum samples, and then combine these into two pooled samples with 1)a meatal swab and 2)a smaller amount of first catch urine. The order of these samples will be randomised. These samples will be compared against separate samples taken at the same visit, to see how accurate the pooled samples are at diagnosing chlamydia and gonorrhoea with the different sampling techniques.

Testing for chlamydia and gonorrhoea in men who have sex with men (MSM) and trans-women is recommended every three months for those taking HIV Pre-Exposure Prophylaxis (PrEP). Testing requires throat and bottom samples, and samples from the urethra (wee-pipe), usually a urine sample. However, many sexual health services struggle to afford the costs of these 3-samples, four-times per year, which may restrict numbers given PrEP.

The investigators' previous research has shown that the 3-samples (throat, bottom, urine) can be combined into one pooled specimen to accurately find gonorrhoea and reduce laboratory costs. However, the chlamydia results of pooled samples were not as good, finding only 92 out of 100 infections compared with 99 out of 100 with 3 separate samples. The investigators' past research showed no difference in diagnostic accuracy between clinician and self-taken rectum and pharynx swabs for NG and CT detection. People prefer to take their own swabs and self-taken swabs were more cost effective than clinician taken. Self-taken swabs are now used routinely in clinical practice and are available as on-line ordered commercial kits.

This study aims to improve the accuracy of chlamydia results by comparing two new pooling methods with the 3-samples tested separately.

MSM, and trans-women, aged 18 years or over, attending a large UK city sexual health service for chlamydia and gonorrhoea testing will be invited to take part in the study.

The pooling methods will be: 1) pooling with a smaller amount of urine to reduce the dilution of the other samples; and 2) pooling with a swab sample from the outside of the tip of the penis (meatal swab) instead of urine. Meatal swabs are taken by the person themselves. The swab does not go inside the penis so is easy to do and not painful. Studies suggest meatal swabs may be better at finding chlamydia than urine samples.

To ensure an accurate comparison, the order of taking the two pooling method samples, and the 3-samples tested separately, will be randomised.

The study will recruit 1250 participants. This is a large enough number to show if either of the pooling methods can detect more chlamydia than 92 out of 100 infections.

If a pooling technique was developed for MSM and trans-women that did not reduce diagnostic sensitivity, this would likely be implemented. A sensitive, low-cost, method of triple-site STI testing, available on-line, or using minimal in-house staff, would enable increased testing. The investigators believe this study will identify such a method by using meatal swabs or a reduced urine volume. The reduced diagnostic costs of almost two-thirds would enable sexual health clinics to provide PrEP to more people, and/or utilise the money saved elsewhere in their service.

Inclusion Criteria:

• 18 years and over. Willing to perform self-taken swabs in addition to any clinician required swabs. Able to provide informed consent

Exclusion Criteria:

- Antibiotics taken in the past 14 days (excluding metronidazole). Previous participation in this trial

Males who have sex with males, and trans-females with a penis

Laboratory staff will be masked and will not be able to link pooled samples (sent under a unique study number) to comparator standard care separate samples (sent under a unique patient identifier).