Blastocystis hominis associated acute urticaria.

Acute urticaria has many causative factors, which may include infections, medications (nonsteroidal anti-inflammatory drugs, antibiotics, contraceptives and others), insect bites, physical stimuli, allergens or underlying systemic disorders. Blastocystis spp, although ubiquitous in developing countries, is rarely implicated in causing disease in the developed world. The authors present a case of acute urticaria caused by Blastocystis hominis (protozoon parasite) in an elderly farmer in rural United States. This case vignette emphasizes the importance of checking stool for ova and parasites to look for Blastocystis species in patients with urticaria under appropriate clinical settings when other common causative factors of the same have been ruled out.