Deadlier Strain of MRSA Emerges
'USA600' Strain Is Partly Resistant to Treatment by Another Antibiotic
Nov. 2, 2009 (Philadelphia) -- A newly discovered strain of drug-resistant
staph bacteria is five times more deadly than other strains, a new study
Adding insult to injury, the new superbug appears to have some resistance to
the antibiotic commonly used to treat it, researchers report.
Half of patients infected with the new strain of MRSA (methicillin-resistant
Staphylococcus aureus) died within 30 days, says Carol Moore, PharmD, a
research investigator in infectious diseases at Henry Ford Hospital in
That compares to only about 10% of patients infected with other MRSA
strains, she tells WebMD.
Moore and colleagues studied 16 people infected with the new strain, called
USA600, and 64 people infected with other MRSA strains at their
MRSA strains are typically susceptible to the antibiotic vancomycin, Moore
says. But the USA600 strain was at least party immune to vancomycin, she
Though the new superbug appears to have unique characteristics that make it
deadly, other factors, such as the patients' older age, may have played a role,
Moore says. The average age of patients infected with the USA600 strain in the
study was 64 vs. 51 for patients with other MRSA strains.
The study was presented at the meeting of the Infectious Diseases Society of
While USA600 infections have only been seen in hospitalized patients to
date, a growing number of MRSA infections are being seen in otherwise healthy
people in the community.
"In light of the potential for the spread of this virulent and resistant
strain and its associated mortality, it is essential that more effort be
directed to better understanding this strain to develop measures for managing
it," Moore says.
MRSA Spikes in Summer Months
Other new research presented at the meeting shows a spike in MRSA infections
in summer months -- probably driven, experts says, by the rise in cases outside
the hospital setting in recent years.
Loyola University researchers studied the medical records of more
than 400,000 people admitted to a Chicago hospital from 2000 to 2008. They
identified about 1,300 people who tested positive for MRSA.
The number of infections did not vary by season during the first four years
But from 2004 to 2008, the risk of being infected was about 30% greater in
the summer months than in the winter or spring.
That's likely due to the rise in community-acquired infections, says the
CDC's Fernanda Lessa, MD, who tracks MRSA but was not involved with this
"We know that the skin is a major entry point for the bacteria, so one would
expect more infections in the community in the summer when your wear fewer
clothes and are more prone to skin lesions," she tells WebMD.