"Epidemiologists say mass testing for SARS-CoV-2 — requiring millions of tests per country per week — is the most practical way out of the current crisis. It allows officials to isolate those who test positive, limit the spread of disease and help to determine when it is safe to relax restrictions. But countries are struggling to ramp up testing. One reason is that the standard test to detect SARS-CoV-2 — based on a mainstay lab technique called the reverse-transcription polymerase chain reaction, or RT-PCR — requires trained personnel, specific chemical supplies and expensive instruments that take hours to provide results and are often available only in labs that provide routine, centralized services. This limits the number of tests that can be done, especially in developing countries. Even in wealthy regions such as the United States, providers have reported a severe shortage of test kits and required materials — from nose swabs to chemical reagents — because of supply-chain problems. Scaling up reliable tests quickly has proved challenging, too: early RT-PCR tests developed by the US Centers for Disease Control and Prevention malfunctioned, for example, leading to a series of delays."