Boston ? An infectious-disease nightmare is unfolding: Bacteria that have been made resistant to nearly all antibiotics by an alarming new gene have sickened people in three states and are popping up all over the world, health officials reported Monday.

The U.S. cases and two others in Canada all involve people who had recently received medical care in India, where the problem is widespread. A British medical journal revealed the risk last month in an article describing dozens of cases in Britain in people who had gone to India for medical procedures.

How many deaths the gene may have caused is unknown; there is no central tracking of such cases. So far, the gene has mostly been found in bacteria that cause gut or urinary infections.

Scientists have long feared this — a very adaptable gene that hitches onto many types of common germs and confers broad drug resistance, creating dangerous “superbugs.”

What can people do?

Don’t add to the drug resistance problem, experts say. Don’t pressure your doctors for antibiotics if they say they aren’t needed, use the ones you are given properly, and try to avoid infections by washing your hands. The gene is carried by bacteria that can spread hand-to-mouth, which makes good hygiene very important.

The U.S. cases occurred this year in people from California, Massachusetts and Illinois.