A Big Diel.

As Rog has already reported, the results of the long awaited longitudinal study by Diel has finally been formally published. Whilst I have discussed the findings from this study previously here and here its importance is such that it is well worth discussing again.

Firstly (and we will see this in the following), this study gives the Company some really solid, incontrovertible evidence of the efficacy of QuantiFERON TB that they will no doubt be able to use to complement their already extensive marketing. My understanding is that whilst the results of this study have been available for several months the Company is prevented from using them until it has been officially published in print in a peer reviewed journal. That now appears to have been done by the American Journal of Respiratory and Critical Care Medicine, here.

This report is actually an update of Diel's longitudinal study that was published back in 2008. It was that study that enabled me to understand that "It's all about Progression". If you are suitably enthused you might want to click on that link.

Longitudinal studies (the longer the better) are very important in convincing the medical community of the true effectiveness in the real world of treatments, interventions, diagnostics etc. It takes no mental giant to work out why that is. Furthermore longitudinal studies are expensive both in time and resources. They are therefore "worth their weight in gold" (as long as they support the original contention, of course). The other attribute of a study that adds weight to it's value is the size of patient group.

This study has followed 954 close contacts of active Tb patients over a mean period of 3.5 years.

I believe that the results from such a study would be hard to deny.

You can read the results for yourself but in summary the results are:

QFT did not miss a single contact that subsequently progressed to active TB. Let me say that another way - of the 756 patients that QFT identified as not having latent TB, not a single one went on to develop active TB.

In comparison, the TST skin test, even at the very tight 5mm cutoff, missed 11% (2) of the contacts that subsequently went on to develop active TB. At the commonly used 10mm cutoff the TST missed a massive 47% (9) of the contacts that subsequently went on to progress to active TB.

Now, the scientists can apply all sorts of fancy statistics to that but to me it is summarised with the statement that using the TST would have resulted in either 2 or 9 people being turned out into the community to later develop active TB and potentially spread it to others. On the other hand, QFT allowed nobody that later progressed to active TB to be turned out to spread TB further.

As a side note, this statistic alone, destroys the value of the "use TST then retest the positives with QFT" proposal that has been suggested in some jurisdictions. Under such a program those 2 or 9 people would never have been tested with QFT.

But it gets better, a lot better.

On the other side of the coin the TST would have resulted in either 555 or 207 people (depending upon which cutoff was used) to be treated for latent TB. QFT on the other hand would have determined that only 147 needed to be treated.

Using the TST you actually end up with an unenviable choice. Use a 5mm cutoff, treat a massive 555 people for latent TB and still miss 2 people that later progress to active TB or; use a 10mm cutoff, reducing the number of people to treat to 207 but miss 9 people that later progress to active TB.

Surely it makes sense to use QFT, treat only 147 people and miss not a single progression.

So, a huge saving in costs, a huge reduction in people subjected to antibiotic treatment and not a single progression missed.

I believe it will be very hard for anybody, when faced with these results, to deny the superiority of QFT based TB Control program over a TST based system. I look forward to these results permeating throughout the TB Control Community. I would imagine that there are many TB Controllers who have been waiting for such ammunition.