A blood test used to detect tuberculosis in adults can predict the onset of the disease in young children, researchers from the South African Tuberculosis Vaccine Initiative at UCT, Stanford, Oxford and the London School of Hygiene and Tropical Medicine have found.
The QuantiFERON test is commonly used in adults, particularly in developed countries, and conversion from a negative to positive test indicates recent infection with tuberculosis, often triggering drug treatment to prevent the disease.
The researchers analysed QuantiFERON results from a large tuberculosis vaccine trial conducted by the initiative in more than 2 700 children in Worcester, Western Cape.
Until now there has been scant evidence to suggest that the QuantiFERON test could or should be used in young children from TB endemic countries as an indication for preventive treatment.
The new findings, published in The Lancet journal today, show that young South African children with very high QuantiFERON results, more than 10 times the recommended adult cut-off value for a positive test, had more than 40 times greater risk of developing TB than children with a negative test.
By contrast, children with a positive test at the usual adult cut-off value were likely to change back to negative when next tested.
The director of the initiative, Professor Mark Hatherill, said the results showed that the QuantiFERON test works very differently in young children than in adults. And for the first time, researchers had an idea of how the test might be used to identify those infected children who are most at risk of developing TB, and most in need of investigation for TB and/or preventive therapy for the disease.
“The QuantiFERON test is usually used in adults as an indicator of infection with the bacterium that causes TB - Mycobacterium tuberculosis.
"Most people who are infected remain healthy, but some, particularly those who have recently become infected, progress to TB disease,” Hatherill explained.
“For this reason, some countries, mostly low TB burden, developed countries, provide preventive therapy to adults who have a positive QuantiFERON test.
"World Health Organisation and South African national guidelines do not recommend the test be used for this purpose in young children because there is very little data on whether/how the test works in young children.
"The results would need to be replicated in other studies. But if the findings hold true, it could lead to revision of international and national guidelines for how we test children for Mycobacterium tuberculosis infection.
"And particularly for how we identify those children who are most at risk of progressing from infection to disease, and who would most benefit from investigation and preventive treatment," Hatherill said.