Pooled SARS-CoV-2 testing has been proposed as a way of processing a high number of samples quickly, but the New York Times writes that the approach isn't useful in much of the US because too many people test positive for the virus.
For instance, it reports that Nebraska's public health lab had to stop pooling its tests — which it had started doing in March — when the positivity rate there exceeded 10 percent in late April. At that point, the Times notes, there's little benefit in pooling tests because of the need to then retest all the samples that were combined. It adds that other places use different cut-off values, with a Mayo Clinic doctor telling it he would question pooling if positivity rates were above 5 percent and perhaps even if they were above 2 percent.
The Times notes that pooled samples are being used in parts of the US like New York where the positivity rate has recently been low, around 1 percent, or for particular social groups like classrooms.