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21. November 2002 - Press release: New diagnostic test shown to be highly effective in tuberculosis outbreak in Denmark
For more than 70 years doctors have been using a skin test for diagnosing tuberculosis (TB). New results from a TB outbreak in Thisted, Denmark show that a new blood test is more effective than the skin test.
An 18-year-old high school student from Thisted coughed for six months before he was diagnosed with active lung tuberculosis in October. In that period he took care of his daily business at home, in school and in the local church choir.
Initially, 100 people close to the 18 year old were tested for TB with a traditional skin test, which showed that 25 people were infected with the bacteria. Therefore the medical officer of health chose to skin test the other 600 students at Thisted High School, and the number of infected raised to 37.
However, there was still uncertainty about adults who were BCG vaccinated and thus not suitable for the skin test.
New test based on blood samples is more sensitive
"For a long time we have been aware of the limitations of the skin test. The test cannot differentiate between a BCG vaccinated person and a person infected with TB. The result is positive in both cases, and therefore we do not have a tool to check these people", tells Peter Andersen, Head of Department of Infectious Disease Immunology at Statens Serum Institut (SSI).
A new test based on a blood sample is, after many years of work, on the way to the clinics. That is why SSI in October sent a team of laboratory technicians to Thisted where they took blood samples from 112 people from the 18-year-old student’s circle of acquaintances. The blood samples were tested in the new and more sensitive diagnostic system in the laboratory at SSI.
The test showed that 6 of the BCG vaccinated were infected with TB. Further, four more who were negative in the first round of skin tests were also positive in the new blood test. The skin test had not been sufficiently sensitive for these four people. These two groups of infected people are now undertaking preventive treatment. A third group of five people had a marginal reaction in the blood test. They will be offered a new blood test. If their result is raised from the first test, it means that they have been infected with TB.
The new test from Statens Serum Institut:
SSI and their partner, the Australian company Cellestis, are concluding the development of a new test for diagnosing TB. A combination of Cellestis’ QuantiFERON technology and proteins from SSI form the starting point.
It is possible from a single blood sample to test if the patient’s immune system (the white blood cell) reacts when it is stimulated with TB proteins. If the immune system has been exposed to TB, it will very quickly begin to produce a signal protein called interferon gamma. QuantiFERON measures the presence of the signal protein. If the cells make interferon gamma after stimulation with TB proteins the patient is infected with TB. The test therefore reveals TB infected people (also BCG-vaccinated), before they develop the disease.
Out of the 25 people who tested positive with the skin test, 24 were positive with the blood test.
Of the skin test negative people 4 were positive with the blood test.
Of the BCG vaccinated people 6 were positive with the blood test.
Which means that the new test:
I. Has confirmed the positive skin test results and
II. Has identified 10 new cases of TB infected people.
For further information:
Peter Andersen, Director of Vaccine Research and Development, Head of Department of Infectious Disease Immunology at Statens Serum Institut (SSI).
Phone: 32 68 34 62
Email: [email protected]
Flemming Stenz, The medical officer of health in Viborg County
Phone: 86 62 33 27
Email: [email protected]
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