DNA sequencing tracks source of MRSA in hospital infection
14 November 2012
DNA sequencing has been used for the first time to confirm and
track the source of an outbreak of MRSA and enable the hospital to
quickly prevent further infection.
Researchers from the Wellcome Trust Sanger Institute, the
University of Cambridge and Cambridge University Hospitals used
advanced DNA sequencing technologies to confirm the presence of an
ongoing outbreak of methicillin-resistant Staphylococcus aureus
(MRSA) in a Special Care Baby Unit at Addenbrooke's Hospital,
Cambridge, in real time. This assisted in stopping the outbreak
earlier, saving possible harm to patients. This approach is much
more accurate than current methods used to detect hospital
Using this technology, the team revealed that the outbreak had
extended into the wider community, a conclusion that could not be
reached with available methods. They also used sequencing to link
the outbreak to an unsuspecting carrier, who was treated to
"We are always seeking ways to improve our patient care and
wanted to explore the role that the latest sequencing technologies
could play in the control of infections in hospitals," says Dr Nick
Brown, author, consultant microbiologist at the Health Protection
Agency and infection control doctor at Addenbrooke's Hospital,
Cambridge. "Our aim is to prevent outbreaks, and in the event that
they occur to identify these rapidly and accurately and bring them
"What we have glimpsed through this pioneering study is a future
in which new sequencing methods will help us to identify, manage and
stop hospital outbreaks and deliver even better patient care."
Identifying the source
Over a six-month period, the hospital infection control team used
standard protocols to identify 12 patients who were carrying MRSA.
However, this standard approach alone could not give enough
information to confirm or refute whether or not an ongoing outbreak
was actually taking place.
In this study, the researchers analysed MRSA isolates from these
12 patients with DNA sequencing technology and demonstrated clearly
that all the MRSA bacteria were closely related and that this was an
outbreak. They also revealed that the outbreak was more extensive
than previously realised, finding that over twice as many people
were carrying or were infected with the same outbreak strain. Many
of these additional cases were people who had recent links to the
hospital but were otherwise healthy and living in the community when
they developed a MRSA infection.
While this sequencing study was underway, the infection control
team identified a new case of MRSA carriage in the Special Care Baby
Unit, which occurred 64 days after the last MRSA-positive patient
had left the same unit. The team used advanced DNA sequencing to
show in real time that this strain was also part of the outbreak,
despite the lack of apparent links between this case and previous
patients. This raised the possibility that an individual was
unknowingly carrying and transmitting the outbreak MRSA strain.
The infection control team screened 154 healthcare workers for
MRSA and found that one staff member was carrying MRSA. Using DNA
sequencing, they confirmed that this MRSA strain was linked to the
outbreak. This healthcare worker was quickly treated to eradicate
their MRSA carriage and thus remove the risk of further spread.
Power of gene sequencing
"Our study highlights the power of advanced DNA sequencing used
in real time to directly influence infection control procedures,"
says Dr Julian Parkhill, lead author from the Wellcome Trust Sanger
Institute. "There is a real health and cost burden from hospital
outbreaks and significant benefits to be gained from their
prevention and swift containment. This technology holds great
promise for the quick and accurate identification of bacterial
transmissions in our hospitals and could lead to a paradigm shift in
how we manage infection control and practice."
In this instance, DNA sequencing was a key step in bringing the
outbreak to a close, saving possible harm to patients and
potentially saving the hospital money.
"Our study indicates the considerable potential of sequencing for
the rapid identification of MRSA outbreaks," says Professor Sharon
Peacock, lead author from the University of Cambridge and clinical
specialist at the Health Protection Agency. "What we need before
this can be introduced into routine care is automated tools that
interpret sequence data and provide readily understandable
information to healthcare workers. We are currently working on such
"If we have a robust system of this type in operation when the
outbreaks occur, we predict that we will be able to stop them after
the first few cases, as we will rapidly find clear connections."
In their next step, the team will study all MRSA carriers and
infected patients over the next year in Addenbrooke's Hospital and
surrounding hospitals and the community to understand transmission
events with the aim of improving infection management.
Sir Mark Walport, Director of the Wellcome Trust, says: "This is
a dramatic demonstration that medical genomics is no longer a
technology of the future — it is a technology of the here and now.
By collaborating with NHS doctors, geneticists have shown that
sequencing can have extremely important applications in healthcare
today, halting an outbreak of a potentially deadly disease."
The study is published in: Simon R. Harris, et al. Using
whole genome sequencing to dissect the cause and effect of a
methicillin-resistant Staphylococcus aureus outbreak: a
descriptive study? Lancet Infectious Diseases 2012. DOI: