A multidrug-resistant superbug infection that can cause life-threatening illness in people with cystic fibrosis (CF) has spread globally and is becoming increasingly virulent, British researchers said on Thursday.

In a study published in the journal Science, the researchers said the bug, a species of multidrug-resistant bacteria called Mycobacterium abscessus (M. abscessus), can cause severe pneumonia and is particularly dangerous for patients with CF and other lung diseases.

"The bug initially seems to have entered the patient population from the environment, but we think it has recently evolved to become capable of jumping from patient to patient, getting more virulent as it does so," said Andres Floto, a Cambridge University professor who co-led the study.

Cystic fibrosis is a relatively rare genetic disorder that affects the respiratory, digestive and reproductive systems. It causes patients' lungs to become clogged up with thick, sticky mucus and makes them vulnerable to respiratory infections.

In this study, researchers from Cambridge and the Wellcome Trust Sanger Institute sequenced the genomes of more than 1,000 samples of mycobacteria from 517 CF patients at specialist clinics in Europe, the United States and Australia.

They found that the majority of patients had picked up transmissible forms of M. abscessus that had spread globally.

Further analysis suggested the infection may be transmitted within hospitals via contaminated surfaces and through the air, the researchers said - presenting a serious challenge to infection control practices in hospitals.

Because the superbug has already become resistant to many antibiotics, it is also extremely difficult to treat successfully, Floto said. Patients infected with it need 18 months or more of treatment with a combination of powerful antibiotics, and fewer than one in three cases is cured.

Julian Parkhill of the Sanger Institute, who worked on this study, said that while its findings were alarming for CF patients, they did also provide a degree of hope.

"Now that we know the extent of the problem and are beginning to understand how the infection spreads, we can start to respond," he said.

The sequencing data has thrown up potential new drug targets, he explained, and the researchers now plan to focus on seeking to develop new medicines to beat the bug.