Cyclospora is easy for doctors to miss. The US made it even harder to spot | Robert B Shpiner

Last year the federal government downgraded active surveillance for this parasite. Now thousands are sick

A patient arrives after two weeks of relentless watery diarrhea, sometimes 20 episodes a day. She has lost weight and cannot keep fluids down. Her stool tests come back negative. Unless someone thinks to order an assay that includes Cyclospora cayetanensis, she may leave without a diagnosis and stay ill for weeks longer.

Cyclospora is easy to miss in a clinic. Many routine stool tests do not include it, so a clinician must consider the parasite before the laboratory will look for it. You find it on purpose, or you do not find it.

Robert B Shpiner is a clinical professor of medicine in pulmonary and critical care at the David Geffen School of Medicine at UCLA