The article literally says that all tests for infection came back negative. It is not said explicitly, but this heavily implies that she had negative cultures (not uncommon for leptospirosis) and did not present with things like elevated white counts (also not uncommon for this pathogen - especially for superficial infections). The article also clearly says they (mis-)diagnosed it as autoimmune disease and treated with steroids, which is pretty much the worst thing you can do in that case. Leptospirosis goes away most of the time without any treatment if you have a working immune system. So if you really need a contrarian takeaway from this editorial, it's that doctors are still sometimes more dangerous than diseases (which used to be true in general up until about 100 or so years ago).