Whole genome sequencing used to track outbreak

19 November 2012

A proof-of-principle study has been published showing how molecular techniques were used to track and stop the spread of a meticillin-resistant Staphylococcus aureus (MRSA) outbreak first detected in an infant ward in Cambridge.

The outbreak was suspected by the infection control team in the hospital after 12 infants were identified as having MRSA during a 6 month period in 2011. However, standard culture based techniques could not establish if the infections were related. Whole genome sequencing (WGS) and analysis of the bacterial isolates from the infants showed that they were from a single outbreak. Although the outbreak seemed to stop after cleaning the ward, a case was detected two months later.

As the outbreak continued in a protracted fashion, the team attempted to identify the route of transmission and source of the infection by molecular characterisation of other MRSA isolates. They were able to show that subsequent cases that occurred in the hospital were also due to the same strain and that transmission was occurring through a network of infants and mothers, and they hypothesised that a healthcare worker may be the source of the outbreak. Following testing of a number of staff members they were able to identify an individual as the source and treat them, thereby stopping the outbreak.

New technologies such as WGS together with epidemiological methods are having an increasing impact on public health, especially in outbreak investigation (see previous news). Rapid mapping of outbreaks allows control measures to be put in place more quickly, thereby reducing subsequent infections and their adverse effects and allowing cost savings to be made. However, as highlighted by the authors, routine use in clinical microbiology will require several practical developments such as a central database for comparison of sequence data with previous local, national, and global isolates as well as an automated system to interpret sequence information.

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