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CA-MRSA: An Epidemic of MILD DISEASE

Scheck, Anne

doi: 10.1097/01.EEM.0000343553.70566.29
Special Report

She was a typical patient on a typical day with a typical complaint: an infected insect bite. There, on the tip of a young woman's nose, sat a knob of swollen tissue. A spider had gotten the best of her, she said, and the tiny nip on her proboscis was wreaking havoc in a most unsightly way.

But a culture pinned the blame on an entirely different bug—methicillin-resistant Staphylococcus aureus (MRSA). The information prompted the woman to joke that no matter the creature responsible, it certainly had turned her into Rudolph in time for Christmas.

Dr. Greg Moran

Dr. Greg Moran

But to the medical community, this bacterial bug is no laughing matter. “MRSA is now endemic, and the most common cause of skin and soft-tissue infections through the ED in the United States,” said David Talan, MD, the chairman of emergency medicine at the University of California, Los Angeles.

And this is a new kind of MRSA, different from the strains that occurred only a few years ago. It's acquired in the community, and is causing infections of epidemic proportion. The outbreaks have ignited a debate over whether this MRSA is becoming a source of increased morbidity, such as pneumonia, or whether this is just another emerging infection, generally speaking, with a fairly simple cure.

Results of a recent study using data from the National Hospital Ambulatory Medical Care Survey indicate that this form of MRSA is now responsible for adding two million patient visits to emergency departments annually, and that this increase largely stems from the community-acquired variant. In fact, the study indicates that community-acquired MRSA (CA-MRSA) accounts for a 200 percent rise in ED treatment for soft-tissue infections. (Ann Emerg Med 2008;51[3]:291.)

The findings of this study and others have prompted some dire advisories by organizations in the medical community. This past June, for example, the American College of Emergency Physicians warned that CA-MRSA was linked to pneumonia, and that a high number of those cases caused death in young and otherwise healthy people. This fall, a report presented at a conference of the Infectious Diseases Society of America implicated MRSA in a cluster of refractory cases in Spain, a cluster so resistant to standard treatment that one news account labeled it an attack of the “superbug of superbugs.”

Some emergency physicians, including Dr. Talan, are more worried about the likelihood of public hysteria over news about MRSA than the bacterial invasion itself. “There are rare and dramatic cases that have caught the public's and medical community's attention coincident with the emergence of this new strain as a common cause of general infection, but still most cases are minor and easily treated,” Dr. Talan said.

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Simply following guidelines from the federal Centers for Disease Control and Prevention for MRSA infection is adequate most of the time, noted Daniel Pallin, MD, MPH, the senior author of the CA-MRSA study utilizing the NHAMCS data and an assistant professor of medicine and pediatrics at Harvard Medical School in Boston. There is indeed an epidemic, Dr. Pallin affirmed, “but an epidemic of mild disease.”

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Prevalence of CA-MRSA

At a time when MRSA has been linked to flesh-eating bacteria and the tragic strike of pneumonia-related death among young adults, the views of these emergency physicians are in stark contrast to some others in the public health profession. The growing prevalence of CA-MRSA has prompted calls for increases in reporting protocols and more intense investigation into therapeutic options.

In an editorial in the Annals of Emergency Medicine that appeared in the same issue as the NHAMCS study by Dr. Pallin, Dr. Talan flatly dismisses the idea of a CA-MRSA as a superbug. “Community-associated MRSA is not a deadly superbug. It is more like an aggressive type of standard honeybee than the Africanized variety, more apt to sting, usually causing a mild and sometimes uncomfortable lesion that is infrequently more serious but only rarely fatal,” he wrote. “Although community-associated MRSA appears to be more efficient at causing infection in healthy individuals than methicillin-susceptible S. aureus, particularly among groups with frequent skin-to-skin contact, most infections are uncomplicated skin and soft tissue infections.

“Patients with community-associated MRSA skin and soft tissue infections should be reassured that they have a good prognosis and many antibiotic treatment options, including several inexpensive oral drugs,” he asserted.

There is a single strain of MRSA (USA 300) that has certain toxic genes that make it a more aggressive organism and more prone to causing skin infections, said Dr. Pallin. Nonetheless, “the mainstay of treatment continues to be surgical incision and drainage,” he said.

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Gregory Moran, MD, a professor of emergency medicine at UCLA and a frequent collaborator with Dr. Talan, noted that there are increasing reports of invasive infections. “Fortunately, most of these are minor skin infections that we can treat effectively with drainage and maybe a few days of oral antibiotics,” he said.

In addition, “there are a number of cheap, generic antibiotics that still work against these community MRSA strains, including trimethoprim-sulfamethoxazole, clindamycin, and doxycycline,” Dr. Moran added.

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Routine Culture?

In fact, the New England Journal of Medicine, which has begun an online poll on common controversial subjects in clinical practice, reported that readers from around the world responded to the question of how to manage skin and soft-tissue infections fairly overwhelmingly, and most favored a standard two-prong approach of incision and drainage along with an oral microbial agent for MRSA. (www.nejm.org)

Dr. David Talan

Dr. David Talan

There is no mention of routine culture by the online poll or in any of the emergency medicine studies so far, but that added step has been suggested in public health discussions. “Whether you obtain cultures depends on the likelihood the results will change your actions,” Dr. Talan said. A suspected outbreak, particularly with strains suspected of causing severe or refractory infection, would certainly justify more routine cultures, he said.

“These also could be justified in patients who are more ill or more at risk of becoming ill, like those who are immunocompromised, those who failed initial treatment, or those with antibiotic intolerances,” he said, adding that “another reason to do cultures for admitted patients is to guide infection control precautions.”

A new, rapid test based on polymerase chain reaction has a one-hour turnaround, he pointed out. “Antibiotics are probably not needed, but if there is substantial surrounding cellulitis or other complication, Bactrim should be considered first-line,” Dr. Pallin said.

How did CA-MRSA increase so quickly over the past several years? Research shows that increased transmission occurs mainly in “close contacts,” like families, which also can perpetuate recurrent infections among individuals. CA-MRSA resulted from “the introduction of nosocomial strains into the community and the de novo emergence of novel strains of pathogenic MRSA,” according to public health investigators who have tracked it. Community strains now are penetrating the medical settings, expanding the reservoir. (Public Health Rep 2008;123[1]:21.)

Striking changes in MRSA surveillance have captured public attention as well. In a study of 11 geographically varied EDs across the United States, Dr. Moran and colleagues from the emergency medicine surveillance network, EMERGEncy ID NET, found that MRSA caused 59 percent of skin and soft-tissue infections in more than 400 adults, and almost all were CA-MRSA in origin. (N Engl J Med 2006;355[7]:666.)

The study basically served as a snapshot to see how many skin infections in the United States are caused by MRSA, Dr. Moran explained. “We found that it has now emerged as the most common cause of skin infections in most U.S. cities,” he said. “Most physicians were already aware that we were seeing a huge number of these cases, but our study gave numbers to back up this impression.”

Dr. Daniel Pallin

Dr. Daniel Pallin

The results show there are some differences in how and where CA-MRSA is likely to occur, but even so, the results failed to show a strong association. For example, African-American race was one factor that was statistically associated with a higher probability of MRSA, but it was not a particularly robust one. “I don't think it truly represents a significantly higher risk,” Dr. Moran said. “It may just be that the hospitals in the cities with higher prevalence of MRSA—more in the South—had higher populations of African-Americans.”

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The results of the study also indicated that other factors had statistical associations with MRSA, “but none of them were strong predictors,” he added. “The bottom line is that now anyone with skin is at risk of MRSA.”

Now that CA-MRSA has been tied to such increases in skin infections, will it be implicated more in cellulitis? It is a question that Dr. Pallin and his colleagues expect to address, in part because cellulitis has a much murkier etiology. Dr. Pallin and his team are conducting a randomized trial to investigate if MRSA underlies cellulitis more commonly than previously thought. The clinical trial is the first to try to determine definitively whether such a link exists.

“There isn't good evidence—so far, anyway—that community-associated MRSA is a cause,” he said. Lab results often are inconclusive, and “the absence of evidence is not evidence of absence,” he pointed out. “For now, standard treatment with cephalexin or amoxicillin-clavulanic acid should be sufficient.”

Recent reports of MRSA as a complication of influenza have prompted some infectious disease programs, including a few at Southern hospitals, to heighten efforts at early detection. But Dr. Pallin sees no reason for worry. If CA-MRSA pneumonia is suspected as a complication of influenza, treatment with vancomycin should be considered. “Of all the patients who get the flu, MRSA is fairly uncommon,” he said.

Dr. Talan concurred. “I do not see the utility of a national epidemic warning system of the typical MRSA infections, like for influenza,” he said.

© 2009 Lippincott Williams & Wilkins, Inc.