Combat tuberculosis

28 April 2023

In order to assist the World Health Organisation’s ‘End TB Strategy’ with the goal of reducing the global incidence of tuberculosis by 80% in 2030, detecting latent TB infection is key. From the province of Reggio Emilia, Italy, Dr Edoardo Carretto discusses the role of Oxford Immunotec’s T-SPOT.TB test in tackling cases of LTBI to help eradicate TB in the province.

The epidemiology of tuberculosis (TB) in Reggio Emilia has shifted over time. For many years, native Italians accounted for the majority of infections, but today, TB infection is significantly more prevalent in foreign-born citizens. To achieve the ambitious goal of eliminating TB nationwide by 2030, the key step is to move from treating active cases of TB to preventing outbreaks by screening for latent TB infection (LTBI).

Dr Edoardo Carretto is the director of Clinical Microbiology at the Santa Maria Nuova Hospital in Reggio Emilia and is an active part of the committee, which lead the local TB prevention and control programme. As a part of this programme, the screening of migrant workers and immunosuppressed patients has a pivotal role.

“Similarly to the rest of our country, TB cases in Reggio Emilia decreased progressively in the past century and were very low. However, with improvements in global migration, there is now a large number of migrants in the province, many of whom have moved from countries with a high TB burden, such as Bangladesh, India and Pakistan, among others. These are the populations, along with the immunosuppressed, that fit the criteria for screening.”

“The T-SPOT.TB test has revolutionised our TB testing workfl ow and allowed maximum effi ciency in our Reggio Emilia lab.”

Focus on LTBI

Key to achieving TB-free status will be the detection and treatment of latent TB infection (LTBI). Dr Carretto explains, “many people who are infected with TB will go on to develop LTBI, and among them 5–10% will develop active TB. Since this course of the pathology can be prevented, it is quite important to have tools that facilitate the diagnosis of TB.

“In those vaccinated with Bacille Calmette-Guérin (BCG) vaccine and the immunosuppressed, false positive and negative results are common with the Tuberculin Skin Test (TST),” Dr Carretto continues. “When we set up our screening programme in 2011, we considered adopting the ELISPOT technique. After careful consideration of advantages and disadvantages, we decided not to use ELISPOT, due to the large amount of skilled hands-on time required and the issue of sample stability. Since the samples could not be stabilised, the assay had to be performed in a short period of time following sample collection. This would have created a need for daily sessions for performing the tests, and this was not possible for our laboratory setup. However, these complications have been reduced since adopting the World Health Organisation-approved T-SPOT.TB test, an IFN-gamma release assay (IGRA).”

The T-SPOT.TB test is a sensitive blood test that can detect LTBI within 24 hours. Unlike alternative IGRA’s, in the T-SPOT.TB test, cells are washed, counted, and normalised, increasing the reliability of patients’ results, as Dr Carretto notes. “Prior to using the T-SPOT.TB test, some of our results were equivocal mainly in immunosuppressed populations. With the normalisation of T cells in the T-SPOT.TB test, more than 80% of patients with previously “indetermined results are now detected”.

Commenting on the choice of the T-SPOT.TB test, Dr Carretto says: “The T-SPOT.TB test has revolutionised our TB testing workflow and allowed maximum efficiency in our Reggio Emilia lab. The main advantages come with the automated workflow steps, which make previously labour-intensive tasks, like cell isolation or spot counting, both easy and rapid. Now that the TB testing workflow is more technician friendly, we have been able to process far more samples, and identify LTBI with greater accuracy and reliability.”

Looking ahead

Having been actively engaged in the battle against TB in Italy, Dr Edoardo Carretto is optimistic about the future. Before the Covid-19 outbreak, in 2019, the TB rate in Italy was down to 5.5 per 100,000 population. With an increased number of testing regimes like that of Reggio Emilia, and simplifications of the transformative T-SPOT.TB workflow, the WHO’s target of 80% reduction in new TB cases by 2030 could be achieved.

The T-SPOT.TB test detects the presence of activated T cells producing gamma interferon in blood samples.

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