MRSA from community may catch clinicians flat-footed

But will overuse of vancomycin result?

Emerging methicillin-resistant Staphylococcus aureus in communities may blindside unsuspecting clinicians, leading to the kind of ineffective initial antibiotic regimens that likely contributed to some of the recently reported fatal MRSA infections in the upper Midwest, public health investigators advise.

Beta-lactam antibiotics, including cephalospor ins, are widely used as empiric therapy for various infections, including typical drug-susceptible staph strains circulating in a community. However, those antibiotics are uniformly ineffective in treating MRSA infections. All four of the fatal MRSA cases (see case reports, p. 127) were initially treated with a cephalosporin antibiotic, leading the CDC to conclude that delayed use of antibiotics to which the strains were susceptible may have contributed to the fatal outcomes.¹

"In all likelihood, these [community MRSA] strains are no more virulent than regular staph strains, but the problem with a resistant organism is that it does create a higher probability that the initial antibiotic chosen by the physicians at the bedside might be ineffective," says Timothy Naimi, MD, lead investigator in the case and a CDC epidemic intelligence service officer at the Minnesota Department of Health in Minneapolis.

"By the time the culture comes back in two or three days, the infection might have progressed. In at least two of the four cases, that is the very likely scenario. These patients were treated very appropriately for what is the common bacteria and pathogens that one would suspect, but by the time they realized what had happened, the infection had progressed," he says.

In light of the cases, clinicians should consider MRSA a potential pathogen in severe pediatric pneumonia or sepsis syndromes in areas where community MRSA infections have been reported, the CDC notes. In addition, in critically ill patients with invasive infections, empiric treatment with vancomycin (in addition to a third-generation cephalosporin) pending culture results may be necessary to treat cephalosporin-resistant Streptococcus pneumoniae or MRSA, the CDC notes.

Indeed, some hospitals in communities where MRSA is circulating are starting to use vancomycin empirically, notes William Schaffner, MD, chairman of the department of preventive medicine at Vanderbilt University School of Medicine in Nashville. "Certainly, those parts of the country that seem to be encountering community-acquired MRSA could get more bad results unless judicious use of vancomycin for empiric initial therapy is utilized," he says. "[In this case] they didn’t suspect they had MRSA; they hadn’t had this prior experience in their community. So understandably, by the time the laboratory gave them that information, they were behind the eight ball by 48 hours. The use of vancomycin for empiric therapy in pediatric practice is virtually unheard of."

If such strategies are employed, it is important to switch to another drug as soon as the susceptibility pattern of the pathogen is known, he emphasizes. In addition to vancomycin, the MRSA strains in the cases were susceptible to several other antibiotics, making it critical to rapidly obtain cultures of infected sites and discern susceptibility patterns. "Our main point is to be aware that cephalosporins — which are the usual first-line treatment — might not work," Naimi says. "In 99% of these [infections], which are not severe clinical syndromes, vancomycin should not need to be used."

Indeed, public health officials are concerned that physicians will now overprescribe vancomycin — a last-line drug with fading efficacy in some staph strains — to cover for community MRSA. "[Physi cians] may now say, I’d better cover for this,’" says Michael Osterholm, CEO of the Infection Control Advisory Network, Inc., in Eden Prairie, MN.

"The last thing they want to have is one of their patients who is four years old suddenly coming back two days later in the emergency room crashing and dying because they didn’t treat [the patient] with a higher-powered staphylococcal drug. That is a real concern. [Because] if they do that, how fast are we going to lose our last remaining drugs for Staph aureus?"

Reference

1. Centers for Disease Control and Prevention. Four pediatric deaths from community-acquired methicillin-resistant Staphylococcus aureus — Minnesota and North Dakota, 1997-1999. MMWR 1999; 48:707-710.