T-Spot.™ TB Test More Accurate in Contact Tracing

A recent study undertaken by Jean-Pierre Zellweger, who is recognised worldwide as an expert in TB control supports the outcome of previous work undertaken by Jean-Paul Janssens, presented at the European Respiratory Society congress, Copenhagen in September 2005, and concludes that Oxford Immunotec’s T-SPOT.™ TB test is superior to the traditional Tuberculin Skin Test ('TST') in identifying individuals who should be treated for latent TB infection.

T-SPOT.TB is an in vitro T cell measurement assay used for diagnosing TB disease and latent TB infection and the first product from Oxford Immunotec using the T-SPOT technology. The product is extremely robust in that it gives a result every time and offers unrivalled and maintained sensitivity in high risk and immunocompromised patient groups.

The Zellweger study assessed 91 people who had previously been in contact with a person infected with TB, using both the traditional TST and T-SPOT.TB. The aim of the study was to evaluate how well the results of each of the tests correlated with exposure to the infected individual. The results for T-SPOT.TB were statistically significant with a positive T-SPOT.TB result correlating strongly with prior exposure to the infected patient. The results for the TST did not correlate with exposure.

Of the cases tested, T-SPOT.TB correctly identified 14 positive infections (15% of those tested) whilst the TST identified 40 (44% of those tested) as positive. The TST identified 29 false positives, which were not confirmed by T-SPOT.TB, resulting from previous vaccination with the BCG vaccine. This finding confirms the large existing body of published data showing that the TST is confounded by prior vaccination with BCG.

Of the 11 cases identified as positive by both tests, 6 cases were identified by the TST when first performed. The remaining 5 cases were only confirmed by the TST after a second test, performed one month later.

Taking the T-SPOT.TB results as a true measure of infection, the study concluded that up to 65% of patients could have received incorrect treatment if decisions were based on the outcome of the TST.

This has economic as well as health care implications. T-SPOT TM.TB is approved for sale in Europe and
is designed to replace the 115 year old tuberculin skin test.


Reference:
Zellweger et al - Contact Tracing using a new T-cell based test, International Journal for Tuberculosis and Lung Disease 9(11):1242-1247 2005