Do you really think a battery of tests weren’t run for any toxin with an acceptable symptom profile? Ciguatoxin is hardly undetectable, along with virtually all of the pharmaceuticals, heavy metals, and toxins listed.
"In the absence of a human biomarker to confirm CFP, the diagnosis of CFP is based on the clinical scenario and the patient’s recent fish-eating history. CFP is associated with gastrointestinal (GI), cardiovascular, neurological and neuropsychiatric symptoms and signs."
...Unless you’re a nation state that really wants to figure it out. If you’re willing to put people through hell just to diagnose them, it’s probably doable.