The sorts of lab methodology I’ve described earlier, involving PCR to screen for recognizable fragments of DNA or RNA, combined with molecular assays to detect antibodies or antigens, are useful only in searching for what’s familiar—or, at least, for what closely resembles something familiar. Such tests essentially give you a positive, negative, or approximated answer in response to a specific question: Is it this? Finding an entirely new pathogen is more difficult. You can’t detect a microbe by its molecular signature until you know roughly what that signature is. So the lab scientist must
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