Advice

Technology overview

Technology overview

This briefing describes the regulated use of the technology for the indication specified, in the setting described, and with any other specific equipment referred to. It is the responsibility of healthcare professionals to check the regulatory status of any intended use of the technology in other indications and settings.

About the technology

CE marking

The Xpert GBS test is classed as an in vitro diagnostic device. The manufacturer, Cepheid, received the first CE mark for the device in March 2006. The most recent renewal was in October 2010.

Description

The Cepheid Xpert GBS test is a qualitative in vitro diagnostic test to detect GBS colonisation in women during childbirth. The test is designed for use at the point of care in labour wards, or in clinical laboratories, and is run on the GeneXpert molecular diagnostic system. The test identifies GBS DNA from combined vaginal and rectal swab specimens, using fully automated real‑time polymerase chain reaction (PCR) with fluorogenic detection of the amplified DNA. Test results are available in 50 minutes or less.

Each test kit comprises a transport container that has 2 swabs attached to the lid of the container. The swabs are used to take 2 identical combined rectal and vaginal samples, which are then processed differently. The 2 swabs are inserted into the woman's vagina, to collect samples of the secretions from the mucosa of the lower third of the vagina. The same swabs are then each inserted approximately 2.5 cm beyond the anal sphincter to collect the rectal samples. The swabs are then returned to the transport container. Only one swab is needed for Xpert GBS testing. The second swab can be used for antimicrobial susceptibility testing for women who are GBS positive but who have a penicillin allergy. The samples should be analysed immediately, and must be refrigerated if not processed within 24 hours.

The Xpert GBS test is run using the Cepheid clinical in vitro diagnostic system, consisting of 3 main components:

  • The GeneXpert molecular diagnostic system. This is available in 4 configurations (I, II, IV or XVI) consisting of 1, 2, 4 or 16 modules, and a larger Infinity version with 16 to 80 modules. Point of care testing is more suited to the smaller 1 or 2 module versions; the larger 4 and 80 module configurations are more suitable for clinical laboratory use. Each module is loaded with 1 Xpert GBS test cartridge per person. Multi‑module versions can run several, independent tests using different test cartridges at any time.

  • A computer system, which is supplied with the GeneXpert system, to run the GeneXpert DX software and store a results database. The software is used to select test definitions, to monitor the automated test process, and to view, print and export the results and generate reports. A cartridge barcode scanner is included to facilitate data entry.

  • The single‑use Xpert GBS cartridge. The Xpert test cartridge is self‑contained and holds pre‑packaged freeze‑dried PCR reagent beads. The cartridge holds the PCR reaction in an integrated reaction tube. There are 3 automated quality control samples in each cartridge: a probe check control, an internal control and a sample processing control.

Each Xpert GBS cartridge consists of several internal processing chambers to hold the original sample, PCR reagents, the processed sample and waste solutions. The Xpert GBS test swab is inserted into the sample chamber of the cartridge and the swab tip is broken off. The cartridge is loaded into a system module, and GBS test processing and analysis starts automatically by closing the module door.

The manufacturer also supplies a range of cartridges for 18 other in vitro diagnostic tests including methicillin‑resistant Staphylococcus aureus (Xpert MRSA), influenza (Xpert Flu) and Chlamydia trachomatis (Xpert CT). These tests are beyond the scope of this briefing.

Additional accessories available for the GeneXpert system include 16 or 32 cartridge trays, a colour laser printer with USB cable and an uninterruptible power supply.

Results are analysed by the GeneXpert software from measured fluorescent signals, using calculation algorithms. Positive results are reported in approximately 35 minutes and negative results confirmed in approximately 50 minutes.

Intended use

The Xpert GBS test is designed for the rapid identification of antepartum and intrapartum GBS colonisation, via clinical laboratory testing or point of care in the labour ward. Antepartum testing is beyond the scope of this briefing.

Setting and intended user

The Xpert GBS test and GeneXpert system can be used in secondary care maternity wards or delivery units. In these settings, the system would be operated by midwives and nursing staff, who would know about GBS risks and have received appropriate training on the Xpert GBS test with the GeneXpert system.

The Xpert GBS test could also be used in clinical laboratories, where it would be used by laboratory staff.

Current NHS options

There is currently no routine testing for GBS colonisation at any stage of pregnancy. Selective testing for GBS colonisation in women who are at high risk of GBS transmission is not recommended in NICE's guidelines on antibiotics for early-onset neonatal infection or on intrapartum care. Diagnosis of GBS infection is typically incidental after detecting an infection from routine urine testing during pregnancy.

At present, a risk‑factor approach is used in the NHS. The RCOG guidelines (2012) recommend that women who are at increased risk for transmission of GBS are given intrapartum antibiotic prophylaxis during labour to prevent colonisation of the baby. These are women who:

  • have previously had a baby with clinical GBS infection

  • have had a vaginal swab for GBS during their current pregnancy when there had been a clinical indication of infection

  • have had GBS bacteriuria during their current pregnancy.

The following indications are also considered for offering broad‑spectrum antibiotics, which should include activity against GBS:

  • intrapartum fever (pyrexia >38°C)

  • intra‑amniotic infection (chorioamnionitis).

For women in these groups, the RCOG (2012) guidelines recommend that 3 g intravenous benzylpenicillin should be given as soon as possible after the onset of labour and then 1.5 g given 4‑hourly until delivery. Women with an allergy to benzylpenicillin should have 900 mg of clindamycin intravenously every 8 hours.

NICE is not aware of other CE marked devices that have a similar function to the Xpert GBS test for the rapid detection of GBS in women during labour.

Costs and use of the technology

The Xpert GBS system consists of several essential components and optional accessories. List prices (excluding VAT) for the essential components are as follows:

  • the GeneXpert molecular diagnostic system (1–16 modules) including computer system costs from £17,602 for a single‑module system to £118,119 for a 16‑module system

  • the Xpert GBS cartridge costs £38.80 per single test

  • sample collection device (transport container with dual swab) costs £37 per pack of 50.

List prices for optional accessories (excluding VAT) are:

  • uninterruptible power supply for GeneXpert: £1,522

  • laser printer with USB cable: £110

  • GeneXpert 16‑cartridge tray: £8

  • GeneXpert 32‑cartridge tray: £12.

Training is given by the manufacturer during installation and is free of charge. This includes training in sample collection, preparing the cartridge(s) and analysing results. Training takes about 30 minutes and additional training materials are provided to staff. Refresher training is available on request and is also free of charge.

The GeneXpert system has an anticipated lifespan of over 10 years. The manufacturer offers annual maintenance contracts ranging from £2,103 to £7,107 depending on the number of modules in the system. The annual service includes preventative maintenance and module calibration, and on‑site and telephone technical support are available.

Likely place in therapy

Although not currently recommended in NICE guidelines, the Xpert GBS test is designed for use at the onset of labour to test for GBS colonisation in women at increased risk of carrying GBS, with the aim of reducing unnecessary intrapartum antibiotic prophylaxis in high‑risk women who are not colonised. This would support current initiatives to improve antibiotic stewardship in the NHS.

Specialist commentator comments

One specialist commentator highlighted that the Xpert GBS test would be of some value to women who are at increased risk for transmission of GBS. Confirmation of a negative result for GBS would avoid both unnecessary venous cannulation and the use of intrapartum antibiotic prophylaxis for these women. Also, it would allow these women a greater choice of options for giving birth, such as labour in water or homebirth. However, this commentator noted that the benefits of testing would be limited. Because babies of women with confirmed GBS colonisation are usually only observed for 12 hours after birth, it was unlikely that testing would shorten the length of hospital stay.

Two specialist commentators indicated that the reduction of intrapartum antibiotic prophylaxis may be limited to 3 of the 5 high-risk groups because women with maternal pyrexia or recognised chorioamnionitis would always be given broad spectrum antibiotics at the onset of labour within 1 hour. Similarly, women who had previously had a baby with a GBS infection would be given antibiotics regardless of the GBS test result. A third commentator further highlighted that regardless of GBS status and the result of testing, a woman considered to be at increased risk of GBS transmission would still receive intrapartum antibiotic prophylaxis.

One commentator indicated that midwives would require full training for adoption of the technology and that it would require significant financial commitment from NHS trusts that do not currently carry out screening. One commentator highlighted that the system would be operated by midwives or nursing staff with additional support from a hospital point‑of‑care team. Appropriate internal quality control and external quality assessment monitoring would be needed.

Equality considerations

NICE is committed to promoting equality and eliminating unlawful discrimination. In producing guidance, NICE aims to comply fully with all legal obligations to:

  • promote race and disability equality and equality of opportunity between men and women

  • eliminate unlawful discrimination on grounds of race, disability, age, sex, gender reassignment, pregnancy and maternity (including women post‑delivery), sexual orientation, and religion or belief (these are protected characteristics under the Equality Act 2010).

The Xpert GBS test is intended for use in pregnant women during labour. Sex and pregnancy are protected characteristics under the Equality Act (2010).

Patient and carer perspective

The patient organisation Group B Streptococcus Support provided the following commentary on a draft version of the briefing:

  • Some babies are at increased risk of GBS infection, including babies of women in preterm labour, and women with prolonged rupture of membranes.

  • A rapid bedside test would potentially enable the GBS status of these women to be identified more quickly than using conventional culture techniques.