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Strains of potentially deadly, antibiotic-resistant
Staphylococcus aureus bacteria show seasonal
infection preferences, putting children at greater
risk in summer and seniors at greater risk in winter,
according to results of a new nationwide study led
by a Johns Hopkins researcher.
It's unclear why these seasonal and age preferences
for infection with methicillin-resistant Staph
aureus (MRSA) occur, says Eili Klein, Ph.D., lead
author on the study and a researcher at the Johns
Hopkins Center for Advanced Modeling in the Social,
Behavioral and Health Sciences.
But he says that increased use of antibiotics in the
winter may be one of the reasons. The winter strain
that infects seniors at a greater rate is generally
acquired in the hospital and resistant to more
antibiotics. On the other hand, the summer strain of
MRSA, which is seen with growing frequency in
children, is largely a community-transmitted strain
that is resistant to fewer antibiotics.
"Overprescribing antibiotics is not harmless," Klein
notes. "Inappropriate use of these drugs to treat
influenza and other respiratory infections is
driving resistance throughout the community,
increasing the probability that children will
contract untreatable infections."
In fact, the study found that while MRSA strains
exhibit a seasonal pattern, overall MRSA infections
have not decreased over the last five years, despite
efforts to control their spread.
A report on the study, which used sophisticated
statistical models to analyze national data for
2005-2009, appears today in the online issue of the
American Journal of Epidemiology.
As the researchers report, hospitalizations from
infections tied to MRSA doubled in the United States
between 1999 and 2005. The ballooning infection
numbers were propelled by MRSA acquired in community
settings, not hospital or other health care settings,
as had been the case prior to 1999.
Specifically, the study found that a strain of MRSA
typically seen in community settings is more likely
to cause infection during the summer months, peaking
around July/August. The authors' data analysis
showed children were most at risk of becoming
infected with this strain, typically from a skin or
soft tissue wound or ailment.
In fact, in examining data for one year — 2008 — the
research team found that 74 percent of those under
the age of 20 who developed an infection with MRSA
had a community-associated MRSA infection.
Meanwhile, the health care-associated MRSA strain,
which is typically seen in hospitals, nursing homes
and other health care settings, was found to be most
prevalent in the winter months, peaking in February/March.
Patients aged 65 or older are more likely to acquire
a MRSA infection from this strain.
Other authors on the paper include Ramanan
Laxminarayan of the Center for Disease Dynamics,
Economics & Policy in Washington, D.C., and David L.
Smith of the Johns Hopkins Bloomberg School of
Public Health.
For more information
http://aje.oxfordjournals.org/content/early/2013/02/28/aje.kws273.abstract
Johns Hopkins Medicine
(MDN)
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