John Berry compares his puzzlement over Art Lee's case with "the Peru case." What is the Peru case to which he refers?

John Berry feels that there is something wrong, something missing in Art Lee's case. He compares what he is feeling now with what he was feeling during a recent experience he calls "the Peru case." In that instance, a patient was visibly sick even though his lab work indicated his condition was not serious. John and the other doctors were puzzled. How could someone who was so sick have such normal lab test results? It turns out his lab work had never been done. After a mix up in the laboratory, the doctors were inadvertently given lab results from another patient. John feels something vital is missing from Art's case, just as something very important was missing from the Peru case.