Research and analysis

MARS protocol

Updated 24 February 2026

Applies to England

Background

Mycoplasma genitalium (M. genitalium) is a sexually transmitted infection (STI) that can manifest as non-gonococcal urethritis, cervicitis and pelvic inflammatory disease. However, most infections are asymptomatic and spontaneous clearance can occur. Evidence on the long-term clinical consequences of untreated asymptomatic M. genitalium infection remains limited, which constrains the rationale for population-level screening.

Treatment options for M. genitalium are suboptimal and have contributed to the emergence and spread of antimicrobial resistance (AMR), with resistance to first-line azithromycin (a macrolide) reported in approximately 63.6% of infections and resistance to second-line moxifloxacin (a fluoroquinolone) in 16.7% of infections in England in 2024. Doxycycline has limited efficacy against M. genitalium, achieving microbiological cure in only 30 to 40% of infections, and is therefore primarily used as part of sequential or resistance-guided treatment regimens.

To monitor trends in AMR in M. genitalium in England, the Mycoplasma genitalium Antimicrobial Resistance Surveillance (MARS) programme was established. Following 2 pilot collections conducted in 2019 and 2020, MARS was implemented as an annual national surveillance programme at a larger scale in 2023 by the UK Health Security Agency (UKHSA).

Objectives

The MARS sentinel surveillance programme aims to:

• estimate the prevalence of genotypic macrolide and fluoroquinolone resistance in M. genitalium infections in individuals attending sentinel sexual health services (SHSs) in England
• determine the demographic, behavioural and clinical factors associated with resistance

As of MARS 2025, this additional aim is no longer included; however, in the 2023 and 2024 cycles, the MARS programme also aimed to assess the treatment outcomes of individuals diagnosed with M. genitalium and relate them to the presence of markers of resistance.

Methods

MARS is a collaboration between the:

• Blood Safety, Hepatitis, STIs and HIV (BSHSH) division, part of the Public Health Programmes directorate at UKHSA
• Sexually Transmitted Infections Reference Laboratory (STIRL), part of the Public Health Microbiology Directorate at UKHSA
• SHSs across England and the associated primary diagnostic laboratories

Sentinel site overview

Analyses from the MARS sentinel surveillance system are based on:

• antimicrobial susceptibility data from specimens from individuals with an M. genitalium diagnosis at a sentinel SHS during the collection period
• demographic, clinical and behavioural information sourced from GUMCAD for these individuals

All laboratory methods for identification and genotypic determination of antimicrobial susceptibility of MARS specimens are accredited to ISO 15189:2022 by the United Kingdom Accreditation Service.

Laboratory collection, handling and shipping of specimens

Prior to the start of the collection period, MARS scientists estimate the number of specimens expected from collaborating laboratories on the basis of previous years’ submissions.

Collection packs are sent to participating laboratories in advance of the collection period starting, comprising:

• laboratory protocol and MARS SHS list
• 2 ml screw-cap tubes
• MARS ID labels
• archive boxes

Aliquots of consecutive M. genitalium-positive clinical specimens (in nucleic acid amplification test buffer) are stored at -20 degrees Celsius in the provided tubes labelled with a unique MARS ID at the participating laboratories. Collection packs and courier shipments are provided and organised by UKHSA.

In addition to the collection packs, primary laboratories are sent an electronic laboratory line list that includes the MARS ID, laboratory specimen number, Genitourinary Medicine (GUM) patient ID, clinic name, clinic ID, age, gender, and date of specimen collection. This data is required to link the laboratory specimen to the GUMCAD data.

For laboratories that refer to UKHSA for M. genitalium diagnostic and/or susceptibility testing, the primary laboratory is not required to send any additional specimens. To facilitate processing, during the collection period, laboratory referral forms associated with possible MARS specimens from participating SHSs (laboratories may provide services for multiple clinics, including non-MARS clinics) should include the GUM patient ID and indicate it as a ‘MARS specimen’.

Receipt of isolates

After the end of the collection period, specimens are transported from collaborating laboratories to STIRL via courier. On receipt, the specimens are stored at -20 degrees Celsius prior to testing.

Participating laboratories also submit an accompanying electronic laboratory line list which details the aforementioned information for each specimen. The electronic line list is uploaded to the HIV and STI Data Exchange (access is restricted to registered users) by the collaborating laboratory via the ‘Upload MARS Lab Data’ function under ‘Data Upload’ at the end of the collection period.

The laboratory electronic line list is quality checked and cleaned according to MARS inclusion criteria (for example, excluding specimens outside of the collection period or from non-MARS SHSs).

Confirmatory testing

Prior to susceptibility testing, specimens received from participating MARS SHSs are confirmed as M. genitalium-positive using the STIRL in-house reference RT-PCR targeting 2 intrinsic M. genitalium genes, MgPa and gap. Only specimens confirmed as M. genitalium-positive using the STIRL in-house reference assay will proceed to antimicrobial susceptibility testing (AST).

Antimicrobial susceptibility testing

Molecular AST is applied to ascertain the genotypic antibiogram for macrolides and fluoroquinolones for all confirmed M. genitalium-positive specimens in MARS. UKHSA has developed molecular assays that amplify and sequence:

• for macrolide resistance: Region V of the 23S rRNA gene
• for fluoroquinolone resistance: the quinolone resistance-determining region of the Topoisomerase IV subunit C (parC) and Gyrase Subunit A (gyrA) genes (the gyrA gene is only amplified in specimens found to have a non-wild type parC sequence)

Archive isolates

Residual aliquots of clinical specimens are stored long-term at -20 degrees Celsius in the STIRL. Extracted DNA is stored in 96-well plates at -20 degrees Celsius in the STIRL and stored according to local retention policies.

Patient data

MARS demographic, clinical and behavioural data are extracted from the GUMCAD STI Surveillance System, UKHSA’s mandatory national STI surveillance dataset. MARS laboratory specimens are linked by GUM patient ID and clinic ID to an M. genitalium diagnosis reported to GUMCAD.

From MARS 2025, the following fields are sourced from GUMCAD:

• GUM patient ID
• attendance date
• gender identity
• age
• sexual orientation
• ethnicity
• country of birth
• concurrent STIs
• previous STIs (last 12 months)
• HIV status and HIV pre-exposure prophylaxis use
• number of sexual partners in the past 3 months
• site of specimen
• symptomatic status
• doxycycline post-exposure prophylaxis use

In MARS 2023 and 2024, clinical staff at MARS SHSs provided enhanced demographic, clinical and behavioural data obtained from patient medical records:

• date of diagnosis
• reason for M. genitalium test (for example, M. genitalium symptoms)
• STI prophylaxis
• sexual partners whilst abroad (number of partners and country)
• symptom status at treatment
• doxycycline pre-treatment
• up to 5 courses of treatment
• up to 5 test-of-cure results

Ethical statement relating to the processing of patient data

MARS is a routine public health surveillance activity, and no specific consent is required from the patients. The MARS programme has been reviewed by the UKHSA Caldicott Panel, in relation to Regulation 3 of the Health Service (Control of Patient Information) Regulations 2002, which makes provision for the processing of patient information for the recognition, control and prevention of communicable disease and other risks to public health.

UKHSA have published a Sexual Health and HIV privacy notice that explains the information on STIs and HIV that we collect and use for public health purposes.

Data reporting

There are several outputs related to the reporting of findings from MARS. These include:

• the annual MARS report, produced within the year following the collection period
• the annual MARS collaborators’ meeting, which features presentations and discussions of the latest data on AMR in M. genitalium
• a section in the ‘AMR in specialist areas’ chapter in the English surveillance programme for antimicrobial utilisation and resistance (ESPAUR) report
• peer-reviewed articles; anticipated that articles will be produced for dissemination in peer-reviewed journals
• oral and poster presentations of MARS findings to end-users at appropriate fora

Use of MARS specimens and data

The MARS data set draws data from GUMCAD. Therefore, UKHSA staff seeking access to MARS data must complete a GUMCAD data request form detailing the purpose of the request and the data that is required. Typically, a new form is required for each new analysis planned. Once completed, the form should be sent to grasp.enquiries@ukhsa.gov.uk for review.

If the requestor is not a member of UKHSA staff, then:

• an honorary contract must be set up for an employee of another organisation who is coming to complete work or a project with UKHSA
• a visiting worker’s agreement must be set up if the requestor does not have a principal employer (for example, an MSc student)