Musk told his Twitter followers he is just feeling cold-like symptoms.
Although the Tesla CEO suspects there is “something extremely bogus” with fast tests, that’s not the case. Fast tests help isolate a person that may have COVID-19 before they infect others. They are one of the main strategies governments have to try to keep the disease under control, even if they are not the most accurate ones. If someone gets a positive result in a fast test, more precise testing is usually performed.
That’s the case for Elon Musk, who has also taken a polymerase chain reaction (PCR) test. As a Nature article explains, it is almost 100 percent effective because it detects viral RNA. The downside is that it is way more complex and demands “trained personnel, specific reagents, and expensive machines that take hours to provide results.”
The truth is that fast tests confirm if a person has been exposed to COVID-19 because it detects antigens on the virus's surface. Musk’s PCR test is just to confirm the infection. If he were not sick with COVID-19, all four tests would probably be negative.