A few years ago I spent a month camping in the Scottish Highlands, a Lyme endemic area. I found an embedded tick on my back on the plane on the way home, had a few weeks of fever, malaise, joint aches, and developed a classic bulls-eye rash around the site of the tick bite. My initial Elisa test was positive, and I took the course of antibiotics, but my follow up Western Blot was negative. Clearly I had Lyme, but the US test only tests for one strain, not the European one as it turns out, and even then it is often wrong, and the full pattern of antibodies, or bands, take months to develop, I got my test a bare 3 weeks after my tick bite. Yet, technically, according to the CDC without a positive Western Blot I never had Lyme. Even with the antibiotics it took me at least 6 months to feel normal again. I now carry doxycycline in my camping first aid kit, and do tick checks every night of a trip. If I find an embedded tick I will immediately start the antibiotics, it's just not worth the risk. Luckily the Minnesota (another endemic area) recommendations are to aggressively treat all Erythema Migrans with 14 days of antibiotics.