Study details staph's broadening reach

Researchers hope to use these data to create interventions that will stop its spread.

By Victoria Stagg Elliott — Posted Jan. 30, 2006

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Nearly 90 million people, or about one-third of the country, carry Staphylococcus aureus in their noses. At least 2 million of them, or almost 1%, are colonized with the methicillin-resistant version, according to a study by Centers for Disease Control and Prevention researchers published in the Jan. 15 issue of the Journal of Infectious Diseases.

"MRSA is still relatively unusual," said Matthew J. Kuehnert, MD, lead author and a medical epidemiologist at the CDC's National Center for Infectious Diseases. "These data are giving us the baseline. Now we need to watch and see what's happening."

These numbers are the result of the analysis of samples collected from nearly 10,000 participants in the 2001-2002 National Health and Nutrition Examination Survey. And study authors say that although it is a cause for concern, because colonization tends to precede infection, it does not indicate a need to screen widely for MRSA in those who otherwise are healthy. Instead, they hope that this information eventually will lead to new strategies that might interrupt the bug's spread.

"I wouldn't recommend blindly swabbing individuals. There is a lot about staph colonization that we don't know," Dr. Kuehnert said. "We need to learn more in order to allow design of new, more effective interventions for the isolates that cause disease."

The study found significant differences in colonization by race and gender. But it is not known exactly what the true implications of these racial and gender differences are or what should be done for those who are MRSA carriers.

For instance, children ages 6 to 11 were most likely to harbor all variants of the bacteria, and women were most likely to carry a drug-resistant type. Those who were young and black were most likely to harbor a variant of the MRSA bug that puts them at the greatest risk for illness.

"There are not good data yet to decide what to do with the patient who is colonized," said Buddy Creech, MD, lead author on the accompanying editorial and a fellow in pediatric infectious diseases at Vanderbilt University School of Medicine in Nashville, Tenn. "More investigation is needed to understand what this really means."

Experts widely praised the study for providing national prevalence information for something that has been a problem in the health care setting for decades and only in recent years emerged in the general population.

"It's an important study and shows us how prevalent MRSA generally is in the community," said Timothy Dellit, MD, director of the antibiotic management program and infectious disease clinic at Harborview Medical Center in Seattle.

Critics charge, though, that while the findings are valuable, they also could underestimate what is going on at the present time. The samples were taken in 2002, before community-acquired MRSA had emerged with full force. Many suspect that a similar study at a later date might present a more ominous picture.

"The trends are changing. It's probably higher now," said John Francis, MD, PhD, who is an infectious disease fellow at Johns Hopkins University in Baltimore.

Reinforces public health messages

But although this study will not immediately lead to changes that may control MRSA's spread, some say it reinforces the need for steps physicians should be taking anyway and for infection control efforts they should be recommending to their patients -- specifically, regular hand washing and judicious antibiotic use.

Many experts suspect that children may have higher rates of staph because of hygiene issues, and women may have higher rates of MRSA because of they tend to have more exposure to the health care system than men, although this link is far from proven.

"The message is that hand hygiene is very important. Judicious use of antibiotics is very important," Dr. Kuehnert said.

Raising awareness about these topics has long been the focus of efforts by public health and medical societies, including the American Medical Association.

In a related study, also by CDC researchers, it appears that community-acquired MRSA may be making inroads in the hospital setting. This study, appearing in a February issue of Clinical Infectious Diseases, found that the variants of MRSA most common in the community might now be appearing in hospital intensive care units. The rate of infections resistant to antibiotics in this setting increased from 36% in 1992 to 64% in 2003.

An increasing number, however, appeared to be the community-acquired strain that is far less resistant to as many antibiotics as the usual one acquired in the hospital but is far more likely to cause significant illness.

"Unlike traditional MRSA, the community strain is very fit," said Monina Klevens, DDS, MPH, a medical epidemiologist at the CDC's Division of Healthcare Quality Promotion. "When it is introduced into a hospital where ill patients are more vulnerable to infection, it has the potential to cause significant morbidity and mortality."

Experts said both of these studies also reinforced the need to better track MRSA. To address this issue, numerous states and municipalities have made it a reportable disease. In January, the Allegheny County (Pa.) Health Dept. became the latest to ask physicians to contact them about cases.

"We'd like to get a better handle on the true extent of MRSA in the community so we can attempt to prevent the occurrence," said Guillermo Cole, a department spokesman.

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How common is MRSA?

Objective: Determine the prevalence of colonization with various types of Staphylococcus aureus.

Methods: Nasal samples collected from nearly 10,000 participants in the National Health and Nutrition Examination Survey 2001-2002 were tested for the presence of the bacteria. The samples that tested positive were then assessed for antibiotic susceptibility.

Results: About 32% were colonized with the bug, and just shy of 1% of those colonized carried a drug-resistant strain. This finding can be extrapolated to mean that approximately 90 million people are carriers and just over 2 million play host to a variant that has at least some drug resistance. Colonization with all types of staph was most common in children ages 6 to 11. Those who were colonized with a drug-resistant version were more likely to be female and older than 60. The more virulent drug-resistant strains were more likely to make their home in the noses of those who were young and black.

Conclusions: Many are colonized, but rates differ among various demographic groups.

Source: Journal of Infectious Diseases, Jan. 15

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External links

"Combating Antibiotic Resistance Via Physician Action and Education: AMA Activities," AMA Council on Scientific Affairs report, June 2000 (link)

For "Prevalence of Staphylococcus aureus Nasal Colonization in the United States, 2001-2002," abstract, Journal of Infectious Diseases, Jan. 15; and "Community-Associated Methicillin-Resistant Staphylococcus aureus: The Way to the Wound Is through the Nose," Journal of Infectious Diseases, Jan. 15 (link)

For "Changes in the Epidemiology of Methicillin-Resistant Staphylococcus aureus in Intensive Care Units in U.S. Hospitals, 1992-2003," abstract, Clinical Infectious Diseases, Feb. 1 (link)

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