Genomic Surveillance of MRSA can Detect Unsuspected Outbreaks


Genomic surveillance has revealed the first complete picture of MRSA spread across the east of England. Researchers from the Wellcome Trust Sanger Institute and the London School of Hygiene & Tropical Medicine tracked MRSA-positive people and were able to describe the complete picture of MRSA transmission within and between hospitals, and in GPs surgeries and communities.

The study, reported in Science Translational Medicine, has important implications for infection control. It shows that sequencing of MRSA (methicillin-resistant Staphylococcus aureus) whenever someone is detected with the strain, and combining this with information on when and where transmission may have occurred, could link cases and detect outbreaks much sooner. This would help to prevent further transmission and reduce the number of people involved.

Patients may be screened for MRSA after they are admitted to the hospital, where infection control measures are used to monitor and try to reduce the spread of MRSA. When new MRSA carriers are detected, this is investigated to confirm whether an outbreak is underway, looking for links between patients in time and place.

However, this current approach is not very sensitive, especially given the speed with which patients can move around different parts of the hospital or even between hospitals during their care. This approach can also miss MRSA transmission between people in hospitals and the community, and outbreaks in family or community groups can be difficult to detect.

The study reported by Dr. Francesc Coll et al. tracked everyone who had an MRSA-positive sample in the east of England over one year. They sequenced the DNA of at least one MRSA strain from 1465 people, based on routine samples submitted to a microbiology laboratory that served three hospitals and 75 GP surgeries. They detected 173 different outbreaks, most of which had not been previously spotted, and discovered MRSA outbreaks in hospitals, in the community, GP surgeries, homes and in between these places.

Dr. Julian Parkhill, from the Wellcome Trust Sanger Institute, said: "Using whole-genome sequencing we have been able to see the full picture of MRSA transmission within hospitals and the community for the first time. We found that sequencing MRSA from all affected patients detected many more outbreaks than standard infection control approaches. This method could also exclude suspected outbreaks, allowing health authorities to rationalize resources."

Dr. Jonathan Pearce, head of infections and immunity at the MRC, said: "Antibiotic resistance poses a global challenge to healthcare. To tackle it we need to prevent infections, preserve existing antibiotics and promote the development of new therapies and interventions. This study sheds light on MRSA transmission within and between hospitals and the community, which could help strengthen infection prevention and control measures.

Professor Sharon Peacock, the study lead, said: "Our study has shown that sequencing all MRSA samples as soon as they are isolated can rapidly pinpoint where MRSA transmission is occurring. If implemented in clinical practice this would provide numerous opportunities to catch outbreaks early and target these to bring them to a close. We have the technology in place to do this, and it could have a positive impact on public health and patient outcomes."