Friday, December 23, 2016 Written by Dr. Al Story, Clinical Lead for Find and Treat & Dr. Rob Shorten, Royal Free Hospital and University College London

Innovative Mobile X-Ray Unit and Xpert® MTB/RIF

The mobile x-ray unit (MXU) has been operating in London since 2005. It is staffed by TB nurse specialists, reporting radiographers, social workers and outreach workers. Its role is to identify hard-to-reach patients with suspected TB using digital chest radiograph. These patients, including individuals who are homeless or have substance abuse issues, are then linked into local healthcare provision via A&E or community TB programmes.

In December 2011 the service was augmented with Cepheid’s Xpert MTB/RIF molecular diagnostic test, which was used as near-patient test in the mobile unit for the molecular detection of Mycobacterium tuberculosis in sputum.
The incidence of TB in the UK has been rising since 1988. Data from the Health Protection Agency(1) shows that the majority of these cases are concentrated in urban areas, with almost 40% being in London (3,300 in 2010).

Additionally, one or more of the following risk factors were present in 10% of cases; history of problem drug use, alcohol misuse/abuse, homelessness or imprisonment. Indeed, the growing problem of TB in these hard-to-reach groups has led to specific NICE guidance(2).

Prior to the implementation of Xpert MTB/RIF, if a digital chest radiograph indicated active pulmonary TB, then the patient underwent immediate referral to the nearest hospital with a TB service. This involved a TB nurse specialist or outreach worker accompanying the patient to an A&E department for assessment, conventional microbiological investigation and possible admission.

The MXU screens between 8,000 – 10,000 patients annually. Approximately 1% of these patients have an abnormal chest x-ray. However, approximately 75% of these patients who are referred are subsequently not diagnosed with TB.

The resource implications of these referrals, including staff time during the accompanied visit, administrative, nursing and clinician time during assessment in A&E, and urgent pathology samples being sent to the laboratories is very significant. Additionally, the inconvenience to the patient is considerable.

The Cepheid Xpert MTB/RIF molecular diagnostic test identifies MTB and rifampicin resistance directly from sputum samples and in less than 2 hrs. The Xpert MTB/RIF assay had already been in use within the microbiology department of the Royal Free Hospital for two years and its performance compared well with gold-standard culture methods. Indeed, the technology is endorsed by the World Health Organisation Foundation for Innovative New Diagnostics (WHO FIND) and is in use globally, outside
of the U.S., for rapid TB diagnosis.

The simplicity of the test, minimal hands-on time and the level of automation of the GeneXpert® instrument made it feasible to implement near-patient testing in the MXU. For additional safety, a container with a rubber septum in the lid allows the MXU staff to safely process sputum samples without the need for containment facilities or a microbiological safety cabinet.

In November 2011, the GeneXpert System was installed in the Find and Treat MXU. The MXU staff were comprehensively trained and assessed for competence during November 2011 and on-board testing went live in the centers across London for Crisis Christmas week.

None of the staff had any laboratory or analytical experience prior to the implementation of this assay.

Now patients with suspect chest x-rays are tested with Xpert MTB/RIF* in real time in the MXU. If positive, they are accompanied to the nearest hospital with TB service. If negative, they are referred to community follow-up.

The new pathway has been in place since December 2011. It is well received by patients, particularly as a negative result prevents a referral to hospital, and the simplicity and safe use of the assay has been well adopted by the MXU staff.

Other MXUs exist in the UK and Europe, but we believe that this is the first example of a molecular diagnostic test being used near to patients anywhere in Europe.

We have demonstrated the potential of this technology in focussing resources on the most appropriate individuals and therefore improving the quality of care in this vulnerable group of patients.

In the first few days we used the Xpert MTB/RIF to test two people with suspicious chest x-rays and got the results while we were still at the shelter. Without the test we would have had to escort these individuals to the nearest hospital where they could have a sample taken for testing. Then we would have had to try to follow up their pathology results a few weeks later and if positive, try to find them again then initiate management through the local TB service. With this test we can avoid time-consuming processes and delays in getting results, and importantly, avoid the high possibility of losing the individuals. Treatment and case management can begin straight away…this will transform our service.

Phil Windish
Find and Treat

*CE-IVD not available in the USA.


1. Health Protection Agency — Tuberculosis in the UK: 2011 report
2. NICE Guidance — Tuberculosis — hard to reach groups (March 2012)
3. Dedicated outreach service for hard-to-reach patients with tuberculosis in London: observational study and economic evaluation. Jit et al., BMJ 2011 343.