There have been 30 reported cases of infection caused by a bacterium called Mycobacterium marinum, according to the city Health Department.
Symptoms include red, tender lumps and swelling under the skin of the hands or arms. Those infected sometimes also develop swelling or pain in their hands or arms and have difficulty moving their fingers. Anyone who is infected should be treated with antibiotics, the department said.
All the victims said they had handled live or raw seafood from fish markets in one of the city's three large Chinese enclaves, the department said. Those are in downtown Manhattan's Chinatown, Brooklyn's Sunset Park and Flushing, Queens.
The Health Department is urging people to wear waterproof gloves when handling raw fish that came from markets in one of the three areas.
There is no risk associated with eating the fish.
Patrick Kwan, a spokesman for the Chinatown Partnership, a business group, said people should wear gloves and wash their hands if they are handling live or raw fish from any neighborhood, not just Chinatown.