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02-04-2013 | General practice | Article

Human-to-human spread of multidrug resistant mycobacteria confirmed


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medwireNews: Findings from an investigation into an outbreak of the non-tuberculosis mycobacterium (NTM) Mycobacterium abscessus in a cystic fibrosis center show that human-to-human transmission of the pathogen can occur.

The team, led by Andres Floto (University of Cambridge, UK), collected and sequenced 168 isolates of multidrug resistant M. abscessus from 31 patients. They found that isolates collected from 11 of the infected patients were near identical (less than 10 base pair difference) M. abscessus subspecies massiliense.

"This variation represents less diversity than that seen within isolates from a single individual, strongly indicating between-patient transmission," a previously suspected but not confirmed process, note the authors.

Floto and colleagues also found that the near identical M. abscessus isolates showed evidence of transmission of mutations acquired during the infection process of one patient to that of another. For example, several patients who had no prior exposure to long-term macrolides or aminoglycosides were infected with M. abscessus showing resistance to amikacin and clarithromycin.

Adding further to the evidence for person-to-person transmission, nothing was found to suggest an environmental source of infection, despite comprehensive testing at the time of the outbreak. However, all the patients had numerous opportunities for within-hospital transmission from other individuals at the center.

NTM infection is a problem in patients with inflammatory lung diseases, such as cystic fibrosis, and chronic obstructive pulmonary disease, and multidrug resistant M. abscessus infection is becoming an increasingly common major respiratory pathogen in these individuals.

"The increased resolution provided by whole genome sequencing over previous typing techniques allowed us to clearly identify the existence, and in some cases the direction, of patient-to-patient transmission, something that would not previously have been possible," said co-author Julian Parkhill, Wellcome Trust Sanger Institute, Hinxton, UK, in a press statement.

Floto added: "Despite our evidence of transmission of M. abscessus subspecies massiliense between patients, the exact mechanism of cross-infection remains to be established. Because of strict infection control policies, we believe that transmission probably occurred indirectly, for example via fomite (eg, hair, clothing, and bedding) contamination or aerosol generating procedures such as lung function testing."

By Helen Albert, Senior medwireNews Reporter

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