Another study reported that in a mostly BCG-vaccinated Korean control population, 51% of the subjects were TST+ and only 4% were QFT-IT positive, while the expected prevalence of M. tuberculosis infection was 33%It wasnt quite like that, the referred Korean study (published 4 years ago) came from a population with an intermediate TB burden and substantial BCG vaccination in which the selected group was divided up into 4 categories according to their risk of infection;
#1, no identifiable risk of M tuberculosis infection (n = 99);
#2, recent casual contacts (n = 72);
#3, recent close contacts (n = 48);
#4, bacteriologically or pathologically confirmed TB patients (n = 54)
When using QFT-GIT the results for these groups were;
#1, 4%;
#2, 10%;
#3, 44%;
#4, 81%
whereas for the skin test
#1, 51%;
#2, 60%;
#3, 71%,
#4, 78%
The Korean researchers had no problem finding that
IFN-gamma assay is a better indicator of the risk of M tuberculosis infection than TSTThe Italian study focussed on 106 healthy TST+ individuals with suspected LTBI (recent contact of smear-positive TB and homeless). They felt that the TST response was valid because of 2 reasons;
1. they had high risk factors
2. they had a great TST response
however the results of the QFT-GIT caused them to pause and reflect
the observation that almost 34% of the these TST+ individuals had negative results by QFT-IT may reflect, at least in part, a less than perfect sensitivity to this test for detecting LTBI.Of course it is one thing to fiddle around the edges of the results and another to actually gain results that are meaningful
the amount of the refusal rate among the homeless [refusal rate was 4.3% (13/300) at recruitment, 10.1% (29/287) for the TST reading, and 11.8% (7/59) to undergo further investigation for those resulted TST+] that may have accounted for a selection of the subjects tested.Why are these researchers still ploughing the same old fields?
