(CNN) - An illness caused by eating fish or seafood is on the rise.
The condition, anisakiasis, results from a contamination by parasites.
That increase is notable in western countries where eating sushi and other raw or uncooked fish is becoming more popular.
The report from BMJ Case Reports highlights a case study. It is about a previously healthy man in his 30s who developed severe upper gut pain.
A week later he was in the hospital, and an upper gastrointestinal endoscopy revealed a parasitic worm penetrating his stomach.
The man said he had recently eaten sushi.
The study's lead author says Japan typically sees the most cases of the parasitic herring worm disease.
But new estimates suggest there are several thousand cases now in Spain.
The Centers for Disease Control says cases are showing up in the United States, South America, Europe and elsewhere.
Scholars on the topic suggest the illness in general is underestimated and under-diagnosed.
Copyright 2017 CNN. All rights reserved.