The people: We want tests! Labs: <argh>
Here is a quick explainer: to test a patient you need a swab. There is a global shortage of swabs. The swab goes to a lab.

The lab extracts the viral RNA from the swab. There is a global shortage of viral RNA kits, a shortage of plastics and a shortage of RNA extraction systems that can process 96 samples at a time.

96 samples is not a random number. It is 8 x 12; labware is standardised along that format for ease of use. We can then employ robots to do all the tedious moving of tiny amounts of liquid quickly.

The viral RNA is then tested using an approved kit. There is a shortage of approved kits. Why do we need such an approval?

We cannot have false negatives. Ever. That is where someone has symptoms and you test and the test says: no presence of virus. That person, told they are negative, then goes on to infect lots of others.

The test is usually run on a lightcycler which can deal with 1 plate of 96 every 1hr 30m. You need controls to tell you if the test has worked, so 92 patients every 1hr 30. So: 1472 samples per 24 hours.

Or you can use high throughput robotic lines to do it non stop 24/7, 2000-10,000 samples a day.

The people: now you're talking! Do it. Now.

These machines are extremely expensive and not a lot of places have them and kits to run on them are fewer still. You guessed. A global shortage.

People: But South Korea and Germany are doing lots of testing? They are. They are like the people who bought the 10 packs of loo roll and left the shelves bare. And the US are trying to buy the shop and keep everyone else out.

Also. All these tests will only show up active infections. It will not show if people had it last week. For that you need antibody tests and they are still very much in development.