Using DNA sequencing scientists have been able to reveal an outbreak of MRSA in a special care unit at Rosie Hospital in Cambridge and identify the carrier.

MRSA (methicillin resistant Staphylococcus aureus) is an antibiotic resistant form of bacteria, the spread of which is not common in the UK, but may cause potentially deadly wound infections in hospitals.

A case of MRSA was found to be spreading among babies at Rosie Hospital. Normally the hospital cannot easily tell whether such cases are simply a string of unrelated infections, or a case of an MRSA outbreak. "The original investigation was inconclusive, we couldn't say whether it was an outbreak or not", says co-author of the study, Julian Parkhill. Because most people have the same type of MRSA, the commonly used test results are usually not able to identify whether or not individuals transmitted the bug to each another.

However, with the new technique, scientists were able to break the structure of the bug down and provide a more detailed picture of where the bacteria came from. In the case of the Rosie Hospital, 13 earlier cases were analysed to reveal that 8 of them were caused by a strain of MRSA similar to that found in new cases. Four days after the deep clean, another baby was diagnosed with MRSA, and using the new technique, doctors found that this was linked to the previous cases. Overall, 14 people were found to be part of the MRSA outbreak, which involved a previously unknown strain of the bacteria.

When hospital staff was screened using genome sequence, one person was revealed to be carrying the same MRSA strain as the already diagnosed cases. This gave the hospital a unique chance to intervene. Without this technology, the superbug would probably have spread much more before doctors could identify its character or the carrier.

The cost of the MRSA outbreak was estimated at £10, 000, which is double of the cost of the DNA sequencing, according to the research team. Moreover, the costs could fall to only "a few pounds" per sample in the future, says Parkhill. He also states that the technology may become routinely available "maybe in the next few years".

There is still work to be done however before this technique can be introduced widespread, with researchers now developing the technology so it can be used by staff who are not genetics experts. Moreover, a comprehensive database of bacterial genomes will have to be established, before the technique can be introduced into common medical practice.