Out of respect for our prior interactions, I will attempt to answer the "why PCR, with its known false positives" question, which is a serious one.
Start here:
Good general overview
13 cases out of 650, particular PCR test - recommendations to improve testing (2006)
Suggestion:
The best test (virus isolation) is expensive, time consuming, and limited both by facilities capable of doing the testing, and resources for conducting the tests - a backlog is inevitable in the case of wide area (such as multi-state) testing. Due to the lethality of HPAI, delays in diagnosis have real world consequences on the spread of the disease (and one can easily imagine a suspect flock dying from HPAI
LONG before VI testing is complete). In the interim, such a suspect flock would need to be kept under strict quarantine, not only to prevent its spread thru routine business, but also to isolate from wild carriers of the disease (waterfowl, starlings, etc).
PCR testing is fast, cheap, and easily conducted by a large number of public and private labs. False negatives from the test are of greater concern (due to viral mutations) than false positives, though false positives are known to occur (see study linked above).
The costs of a false positive - from the Gov't point of view, is quite minor. A back yard flock or small scale poultry operation has negligible effect on the trade, whether in shell eggs, poultry for human consumption, or sale of live birds. Compensation may be available to the owner by the State, or by private insurance, but in any event is a small number - my own flock of birds is valued at less than $1,000, for instance. In the event of a large producer (such as the several million+ cullings), while this has some short term impact on industry, the cost remains small. Business Insurance is expected to cover the loss, most modern facilities can be shut down, sterilized, tented/closed, and subjected to high heat for an extended period, then begin new operations within a 10 - 14 day period. Against the total US poultry business, even a few million birds is a very small number.
The cost of a false negative, on the other hand, potentially allows exposure to a far greater number of birds than are present at a single facility, due to the chokepoints in the supply chain associated with processing prior to wholesale.
Thus, as a matter of risk management, a low false positive rate at a breeder or keeper facility is more acceptable than waiting on a more accurate test which requires more resources to manage (such as by establishing and maintaining a quarantine) while awaiting results, and ultimately provides no particular benefit on the national scale.
Finally, remember that it it the policy of the Gov't as declared by APHIS/USDA to
destroy all tested cases of Influenza A H5Nx or H7Nx, whether they are HPAI H5N1 or otherwise - and has been for more than a decade.