A "nightmare" drug resistant bacteria that's linked to contaminated medical instruments has infected scores of people in the US.

An outbreak of deadly, drug-resistant bacteria that has infected scores of people in the US is linked to contaminated medical instruments.

The US Food and Drug Administration issued the warning after Ronald Reagan Medical Centre at the University of California Los Angeles announced that 179 patients may have been exposed to the drug-resistant CRE bacteria through contaminated scopes used in a widespread hospital procedure.

Seven have been confirmed infected, and two have died.

An additional 135 people were infected at other US hospitals in 2013 and 2014, the FDA said, in cases that may also be linked to contaminated scopes.

CRE is short for carbapenem-resistant Enterobacteriaceae, but the US Centre for Disease Control calls it a "nightmare bacteria".

Related to the better-known E coli, it kills up to half of infected patients because it is resistant to last-resort carbapenem antibiotics and can spread unchecked.

The bacteria spreads through direct contact, such as that between an improperly disinfected medical instrument and bodily tissue.

The bug was discovered in one US hospital in 2001, and by 2013 had spread to hospitals in 46 of 50 US states.

The scope in question is inserted down the gastrointestinal tract in a procedure to examine and treat pancreatic disease.

About half a million Americans undergo the procedure each year, according to the FDA.

In a statement, UCLA said it had disinfected the scopes according to manufacturer instructions, but since the infections were discovered had instituted new, more stringent procedures.

Bacteria develop resistance to antibiotics through continued exposure, a phenomenon public health experts blame on misuse of the drugs, including doctors who prescribe unnecessary antibiotics and patients who take them improperly.

In a 2014 report on antimicrobial resistance, the World Health Organisation said carbapenem antibiotic resistance has spread to all areas of the world.

The organisation warned without immediate coordinated action, "the world is heading toward a post-antibiotic era, in which common infections and minor injuries which have been treatable for decades, can once again kill".