You can still do this kind of audit, but you need to test a statistically significant number of samples in your "spot check" such that you know you some of them will be infected. The number will vary depending on the incidence of a particular type of infection present, but this is data that should be available.
I agree that sending control samples can also be effective, though. But if you need to send the whole organ to the test lab (and not just a small tissue sample), you probably don't want to be wasting healthy organs by infecting them. Better to just wait until you have an organ that's known to be infected already.
> But if you need to send the whole organ to the test lab
Why would you need to do that? Realistically the sample needed here is a small vial of blood from the organ donor’s body.
> You can still do this kind of audit, but you need to test a statistically significant number of samples in your "spot check" such that you know you some of them will be infected.
Nah. It really doesn’t work. The problem is that HIV is very rare. (HIV incidence per 1000 population adults 15-49 in Brazil is between 0.34 - 0.45[1])
Let’s be ultra conservative and set the “spot check” rate at 100%. That is you are sending samples from every single body to two labs. Because of the low incidence rates you would still expect hundreds and hundreds of those samples to return as negative from both labs. This might work if you would somehow have a “gold standard” lab you trust and an other “less trusted lab”. But in reality there is no such a thing as a “gold standard” lab you can trust without QA. (And if there would be you would just use them, instead of the other lab.) Even with that ridiculously high “spot check ratio” you wouldn’t know if you are getting negative results because they are in fact negative, or because both of your labs are falling for some reason and giving you constant false negatives.
In conclusion spot checking the results with a second lab simply doesn’t work. Even if you spot check every single organ donor you would be still blind for even the most basic error cases for unacceptably long times.
On the other hand if you intermingle a control sample into every single batch that changes the game. Lets say they run the tests on batches of 10 and you make sure that a random one of those is always known to be positive. Now if something goes wrong and they don’t detect the sample you can straight away reject the whole batch of tests as faulty. And it only costs you an 11% extra over not doing any QA.
So with the “spot checking” test you can pay as much as 100% extra and still not know if the tests are having the most elementary kind of fault for hundreds and hundreds of organ donors. Or you can go with the “control sample” strategy and have a reasonably high confidence for every batch right away at much less of a cost. Yeah you can do the “spot check” audits but it is ridiculously bad at catching issues even if you spend a lot of money on it.
I agree that sending control samples can also be effective, though. But if you need to send the whole organ to the test lab (and not just a small tissue sample), you probably don't want to be wasting healthy organs by infecting them. Better to just wait until you have an organ that's known to be infected already.