Community-Associated MRSA Infections on the Rise: Can Changes in Your Practice Be Far Behind?

Stories about community-associated infections with methicillin-resistant Staphylococcus aureus (MRSA) have been making headlines in recent months in both the medical and popular press. A familiar problem in hospitals and nursing homes for decades, growing numbers of MRSA infections have been documented over the past few years in prison inmates, soldiers, athletes, Pacific Islanders, Alaska Natives, Native Americans, and men who have sex with men.

Most recently, 2 studies in the April 7, 2005, issue of the New England Journal of Medicine showed that even beyond such specific populations, community-associated MRSA (CA-MRSA) infections are becoming more widespread in the United States.^1,2 Moreover, CA-MRSA has been associated with an increased number of cases of necrotizing fasciitis. Although the recent flurry of reports on CA-MRSA by local newspapers and broadcasters may have been sparked more by the New England Journal articles (and another recent high-profile article in Sports Illustrated³) than by any sudden increase in the number of cases, the growing prevalence of these serious infections is still cause for concern.

JUST HOW PREVALENT, HOW VIRULENT IS CA-MRSA?

The CDC collected data on MRSA infections from 3 states that were participating in the Emerging Infections Program to determine the incidence, epidemiology, and nature of CA-MRSA infections. The results of this surveillance study were reported in the issue of the New England Journal mentioned above.¹ The percentage of MRSA infections classified as community-associated ranged from 8% to 20%. Of the 1647 patients with CA-MRSA infection, nearly a quarter (23%) required hospitalization.

A sister study underscored the potential for greater-than-normal virulence of at least some strains of CA-MRSA.² Physicians from a Los Angeles hospital identified 14 patients (of 843 whose wound cultures grew MRSA) from the community in whom necrotizing fasciitis or necrotizing myositis attributable to MRSA developed.² Four (29%) of those 14 patients had no serious coexisting conditions or risk factors.

WHEN TO SUSPECT CA-MRSA: CLUES FROM THE HISTORY

Although clusters of CA-MRSA infections have been identified in certain populations, consideration of the pathogen should not be limited to these groups. Factors such as close skin-to-skin contact, openings in the skin (cuts or abrasions), exposure to contaminated items or surfaces, crowded living conditions, and poor hygiene have been associated with the spread of MRSA. Also, the CDC researchers found that the incidence of CA-MRSA was significantly higher in infants younger than 2 years than in other age groups.¹

Among adult patients included in the CDC study, about half had at least one comorbidity or underlying condition (eg, smoking, diabetes, asthma, HIV infection). However, about half the adult patients and more than three quarters of those younger than 18 years had no comorbidity.¹

WHEN TO SUSPECT CA-MRSA: CLUES FROM THE CLINICAL PRESENTATION

CA-MRSA most often presents as a skin or soft tissue infection (abscess, cellulitis, furuncle, folliculitis) (Figure).¹ The site of infection is often red, swollen, and painful, and it may produce pus or other purulent discharge; the patient may recall a spider bite. However, CA-MRSA can also cause invasive infection. In addition to necrotizing fasciitis and myositis, bacteremia, septic arthritis, osteomyelitis, and pneumonia have been associated with CA-MRSA.

THE IMPORTANCE OF CULTURE

No epidemiologic or clinical features decisively distinguish CA-MRSA infections from those caused by other staphylococcal strains. Therefore, consider CA-MRSA a possible pathogen in any patient with suspected S aureus infection in the community. Culture is required for definitive diagnosis. Although no official guideline revisions have been issued, experts recommend a much lower threshold for obtaining cultures, along with follow-up on results of susceptibility testing for all staphylococcal isolates. Cultures are especially important for patients in whom empiric antibiotic therapy has failed and in those who present with advanced or aggressive infection.

The diagnosis of CA-MRSA infection is established when a culture is positive for MRSA and criteria for community association are met (Table).

DO YOU NEED TO REPORT CA-MRSA?

MRSA infection is considered a reportable disease in some states. Check with your local health department to find out the reporting requirements where you live. Even if CA-MRSA is not officially reportable in your locale, you may want to consider alerting the appropriate authorities if you believe that an infection may be associated with conditions or practices at a local athletic facility.

It is recommended that the family members and close contacts of a patient with documented MRSA infection be evaluated and counseled about precautions to help halt the spread of infection.

SHOULD EMPIRIC TREATMENT OF STAPH INFECTIONS CHANGE?

Despite the rising incidence of CA-MRSA infections, updated protocols for empiric therapy have not yet been published. Some experts have recommended that first-generation cephalosporins no longer be used empirically in areas with a high prevalence of CA-MRSA.4 Others recommend empiric therapy with an antibiotic active against MRSA for seriously ill inpatients who have suspected S aureus infection. In particular, Miller and colleagues2 suggest that empiric therapy for MRSA infection not be withheld from patients with suspected necrotizing fasciitis, even if they have no clinical risk factors.

Of note, CDC investigators found that patients with CA-MRSA skin or soft tissue infections whose initial treatment included antibiotics to which the bacteria were resistant had outcomes similar to those who received agents to which the bacteria were susceptible in vitro.¹

TREATMENT OF CONFIRMED CA-MRSA INFECTIONS

Treat skin infections such as abscesses or furuncles with incision and drainage, depending on severity. Some experts stress the importance of surgical drainage in the management of more serious CA-MRSA infections.1,5

More studies are needed to determine whether the addition of active systemic therapy results in better outcomes than surgical drainage or topical agents alone. When antibiotic treatment is indicated for a skin or soft tissue infection caused by CA-MRSA, select an agent based on the susceptibility profile of the pathogen. Vancomycin remains the preferred antibiotic for empiric and definitive therapy.⁵ Several other antimicrobials are effective against CA-MRSA--at least in vitro. These include trimethoprim-sulfamethoxazole, clindamycin, rifampin, and doxycycline. Note, however, that some agents are associated with in vitro susceptibility but have little evidence of clinical effectiveness.¹ Linezolid has been approved by the FDA for the treatment of MRSA infections but is very expensive. *

References:

REFERENCES:

1.

Fridkin SK, Hageman JC, Morrison M, et al; Active Bacterial Core Surveillance Program of the Emerging Infections Program Network. Methicillin-resistant Staphylococcus aureus disease in three communities. N Engl J Med. 2005; 352:1436-1444.

2.

Miller LG, Perdreau-Remington F, Rieg G, et al. Necrotizing fasciitis caused by community-associated methicillin-resistant Staphylococcus aureus in Los Angeles. N Engl J Med. 2005;352:1445-1453.

3.

Taylor P. Special report: a menace in the locker room. Sports Illustrated. February 23, 2005.

4.

Moran GJ, Talan DA. Community-associated methicillin-resistant Staphylococcus

aureus:

is it in your community and should it change practice? Ann Emerg Med. 2005;45:321-322.

5.

Chambers HF. Community-associated MRSA--resistance and virulence converge. N Engl J Med. 2005;352:1485-1487.