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Feature Article

Study sheds light on threat from new 'super bug'

The bacterium Staphylococcus aureus (S. aureus) has become a major problem in many countries, resulting in significant morbidity, mortality, and health care costs. Infections caused by S. aureus range from mild, requiring no treatment, to severe and potentially fatal.

In November 2011, a team of researchers led by Zhi Li, PhD, of the Boise, Idaho, VA Medical Center published a paper in the journal PloS ONE on their analysis of an unusual strain of S. aureus. It was found in a 14-year old who died of a disease called necrotizing pneumonia soon after complaining of sore throat and fever. i

Their research, funded by VA and St. Luke's Mountain States Tumor and Medical Research Institute, raised the specter that this potentially deadly strain of bacteria not only caused difficult-to-treat infections in humans, but could possibly spread throughout the world.

Bacterium found in the patient produced not one, but two toxins often associated with severe S. aureus infections: Panton-Valentine Leukocidin (PVL), which often causes necrotizing pneumonia; and Toxic Shock Syndrome 1 (TSST-1), which is one of the causes of toxic shock syndrome, a potentially fatal illness. (Toxins are poisonous substances produced within living cells or organisms.) Historically, these two toxins have very rarely been found in a single strain of S. aureus.

The team looked at the genetic makeup of the S. aureus bacterium found on the patient, which they described as being hypervirulent, or extremely poisonous. They learned that the bacterium they looked at was fully capable of producing both PVL and TSST-1 toxins, and that co-production of the two toxins was probably the reason for the patient's rapid death. Both toxins are also mobilizable, meaning they can be transferred into other S. aureus strains and therefore spread to other people.

Their paper cited recent reports that this patient is not the only one to have acquired this unusual form of S. aureus bacteria. S. aureus bacteria with both PVL and TSST-1 toxins are beginning to appear in patients worldwide. Because of this, according to Li, "The strain we studied may be the next form of 'superbug' with which doctors and researchers will need to contend."

She and her team are now investigating whether other bacteria have the same features as the one the team studied.

S. aureus is one of 30 different types of a group of bacteria (staphylococcus) that can infect humans, but it is by far the most frequent cause of infection among that group. It's normally found in the nose and on the skin of about 25 to 30 percent of healthy adults. In the majority of cases, the bacteria do not cause disease. Anyone can develop a S. aureus infection, but certain people are at greater risk, including newborn infants, breastfeeding women, and people with chronic conditions such as diabetes, cancer, vascular disease, and lung disease.

Those who inject drugs, have skin injuries or disorders, are using intravenous catheters, have recently had surgical incisions, or have a weakened immune system also have an increased risk of developing S. aureus infections.

Methicillin-resistant Staphylococcus aureus (MRSA) is a type of S. aureus that is resistant to the usual treatments for such infections: the antibiotic methicillin and other drugs of the same kind, including penicillin, amoxicillin, and oxicillin. MRSA infections are usually mild superficial infections of the skin that can be treated successfully with proper skin care and antibiotic. MRSA can be difficult to treat, however, and can progress to life-threatening infections, because there are fewer effective antibiotics available for treatment.

All VA hospitals have tough screening requirements for MRSA in place. Nasal swabs and cultures are done on most incoming patients to determine whether the bacteria is present; VA is committed to strict hospital hygiene procedures, such as hand-washing; infected patients are isolated; and VA has emphasized to all of its health care employees the importance of the threat and the need to make infection prevention a routine component of care during each patient encounter every day.

A study published in the April 14, 2011, issue of the New England Journal of Medicineii looked at whether these requirements, called the "MRSA bundle," actually reduced MRSA infection rates. The study team found that between October 2007, when the bundle was fully implemented at all VA Health Care facilities, and June 2010, MRSA infections in VA intensive care units decreased by 62 percent. In VA's non-intensive care units, infection rates decreased by 45 percent over the same period of time.

The department believes its ability to reduce the number of cases of MRSA infection saves lives and enhances its ability to provide Veterans with quality health care. New bacterial threats such as those described by Li and her team demonstrates the importance of remaining vigilant in this area.

i Z Li, DL Stevens, SM Hamilton, T Parimon, Y Ma, AM Kearns, RW Ellis, AE Bryant. Fatal S. aureus Hemorrhagic Pneumonia: Genetic Analysis of a Unique Clinical Isolate Producing both PVL and TSST-1, PloS ONE, 6(11): e27246. doi:10.1371/journal.pone.0027246 ii R Jain, SM Kralovic, ME Evans, M Ambrose, LA Simbarti, DS Obroski, ML Render, RW Freyberg, JA Jernigan, RR Mider, LJ Miller, GA Roselle. Veterans Affairs Initiative to prevent methicillin-resistant Staphylococcus aureus infection, N Engl J Med, 2011 Apr 14; 364(15):1419-30.

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