Updated

The Food and Drug Administration is ordering stronger warnings on four medications used to treat rheumatoid arthritis.

The drugs — Humira, Cimzia, Enbrel and Remicade — work by suppressing the immune system, and the FDA says that can expose some patients to serious, even fatal, fungal infections. The agency said Thursday it has received 240 reports of one such type of infection, called histoplasmosis. In at least 21 of the cases, doctors didn't initially recognize the problem, and 12 of the patients died.

The fungus that causes the infection is common in the Mississippi and Ohio river valleys. Patients should stop taking their medication and call the doctor if they develop persistent fever, cough, shortness of breath and fatigue.