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In a difficult flu season, another bug is a big worry

Potent MRSA clones may take advantage of higher flu rates and cause more cases of necrotizing pneumonia

From the December ACP Observer, copyright 2004 by the American College of Physicians.

By Christine Bahls

With half the nation's flu vaccine supply quarantined for the entire season, public health officials are on high alert, watching for flu outbreaks across the country to make sure patients get treated quickly with antivirals.

But infectious diseases specialist Merle A. Sande, MACP, is worried about another bad bug this year: community-acquired methicillin-resistant staphylococcus aureus (MRSA).

And for good reason. Reports presented at a September meeting of the Infectious Diseases Society of America (IDSA) found that cases of community-acquired MRSA are on the rise, which in itself is bad news.

Even worse, patients who catch the flu are especially susceptible to these potent, opportunistic bacteria that can cause necrotizing pneumonia if untreated. Dr. Sande is afraid that fewer flu vaccinations due to scarce vaccine could translate into spiking numbers of community-acquired MRSA cases this year.

During last year's flu season, the Centers for Disease Control and Prevention (CDC) reported 17 cases of necrotizing pneumonia, virtually all of which occurred among unvaccinated patients.

Normally, necrotizing pneumonia attacks only the sick and the old. But according to the CDC, last year's cases were healthy patients who had an average age of 21.

Internists need to be aware that this MRSA clone contains the toxin-encoding panton valentine leukocidin (PVL) gene that causes necrotizing pneumonia, said Dr. Sande, an ACP Regent and program director of the department of internal medicine at the University of Utah Medical Center in Salt Lake City.

"Community-acquired MRSA spreads easily, it has the PVL gene, it attacks young people and it's virulent," he said.

Telltale signs?

The prevalence of community-acquired MRSA has jumped dramatically over the past several years, he added. One study presented at the IDSA meeting found that one children's hospital in Corpus Christi, Texas, treated nine cases in 1999—and 459 in 2003.

As many as 70% of all staph infections among prisoners are probably caused by MRSA, Dr. Sande pointed out. Community-acquired MRSA is spread from person to person, with bacteria carried in hair follicles; the sentinel location is the nose. It can also be spread among people who share a towel, making it a threat for families and students who play sports.

To detect community-acquired MRSA, it's important to keep in touch with local public health officials. "It behooves internists to know if it is circulating in their own neighborhoods," said Dr. Sande.

When patients come to the office to be treated for flu, physicians should look for signs of community-acquired MRSA, keeping in mind that symptoms are not always apparent. In addition to the characteristic boils of staph infections, other symptoms can be mistaken for the flu itself, such as high fever and shaking chills.

There are other symptoms as well. If a patient has had influenza and boils, and then develops pleurisy and a productive cough, "you've got to worry about this now being a secondary bacterial pneumonia following influenza that could well be caused by community-acquired MRSA," Dr. Sande said.

Treating MRSA

Treating the bug is not particularly difficult, he said, as there are a number of drug classes that are effective. At the same time, of course, there are a few that aren't.

"Internists have to do cultures with sensitivity testing" to see how local MRSA strains respond, he said. At the top of the can-do list is vancomycin, which Dr. Sande considers the best drug to start with.

Two other highly effective new drugs are linezolid and daptomycin. Community-acquired MRSA may also be sensitive to trimethaprim/sulfamethazole, and, in some cases, to the quinolones including levofloxacin, as well as clindamycin. Sensitivity testing with these strains will enable physicians to appropriately plan an extended course of therapy, Dr. Sande said.

However, the bacteria do not respond to penicillins, including nafcillin or oxacillin, nor to cephalosporins such as cefataxine, cefazolin, cefalexin or ceftriaxone.

"Up until now, patients that came in from the community could be treated with these drugs, but these [emerging] clones can't be treated in the same way," Dr. Sande explained. "The scene is changing out there, and we really need to be vigilant."

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