What are the limitations of Covid-19 tests? Elizabeth Tracey reports

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Can you trust Covid-19 tests you take at home, whether they are positive or negative? Infectious disease expert Stuart Ray at Johns Hopkins says it’s important to remember that all tests have limitations.

Ray: The humbling thing about our diagnostics is that we only see the surface, so it’s more like an iceberg. So when we see the virus become undetectable with any of our tests, it’s not gone. Thinking about HIV or hepatitis C, we have about 15 liters of extracellular fluid in our body, so that when we say that there’s less than this many per ml, you still have hundreds of thousands of viruses, possibly, in your bloodstream at that moment. With this virus because we’re sampling the nose, we’re not even sampling the internal organs, and so we don’t know how much virus the person may be harboring.  :33

Ray notes that it’s also true that some people may never test positive even though they know they’ve been exposed and may have symptoms, for the same reason. At Johns Hopkins, I’m Elizabeth Tracey.