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Infectious Diseases in Clinical Practice:
doi: 10.1097/01.idc.0000217664.73871.96
IDC Snapshots

Snapshots for March 2006

Rice, Louis B. MD

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SNAPSHOTS FROM THE ICAAC: COMMUNITY-ACQUIRED METHICILLIN-RESISTANT STAPHYLOCOCCUS AUREUS AND OTHER STAPHYLOCOCCUS STORIES

Usha Stiefel, MD and Louis B. Rice, MD

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Presentation L-143: A Pyoderma Cluster Caused by a New Community-Acquired MRSA (CA-MRSA) Strain in a Family of Egyptian Origin. N.V. Rau, G. Gindi, T. Du, D. Spreitzer, and M. Mulvey

These authors discuss the epidemiology of a novel "foreign" strain of Community-Acquired Methicillin-Resistant Staphylococcus aureus (CA-MRSA).

CA-MRSA outbreaks are relatively rare in Western Canada. Rau et al report a cluster of CA-MRSA involving an otherwise healthy family without health care contact or injection drug use. The index case was a 38-year-old man who emigrated from Egypt in September 2003. In December 2003, he developed and was treated for an abscess of the elbow. The pathogen was CA-MRSA. In November 2004, one of the index case's twin baby daughters (born in Canada in July 2004) developed a chest wall abscess with CA-MRSA. The 2 strains were identical by pulsed-field gel electrophoresis and were positive by polymerase chain reaction for the mecA and Panton-Valentine leukocidin genes. In December 2004, a visiting grandmother who had been providing childcare developed a CA-MRSA chest wall abscess, and the index case's spouse also developed a thigh abscess with CA-MRSA. Interestingly, pulsed-field gel electrophoresis indicated that the strains were distinct from any previously identified Canadian MRSA types. The authors conclude that recent immigration from a developing country could be a risk factor for CA-MRSA and that importation of novel virulent CA-MRSA strains with high transmission rates may occur.

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Presentation C2-284: Introduction of Community-Associated Methicillin-Resistant Staphylococcus aureus (CA-MRSA) into Hospital Settings: Impact on MRSA Antimicrobial Susceptibility. C.M. Cheung, J.L. Watt, M. Amjad, and W.J. Brown

These authors report the incorporation of CA-MRSA into the tertiary care hospital setting.

Changes in S. aureus (SA) susceptibility to fluoroquinolones (FQs) over an 11-year period in an urban trauma teaching hospital were investigated. These results were compared with SCCmec typing. More than 16,000 isolates from 1993 to 2004 were examined, and a representative sample was chosen for genetic testing. Staphylococcus aureus susceptibilities to FQs were as shown in Table 1. Interestingly, as 2002 to 2003 was when CA-MRSA began to appear in their community, the authors hypothesized that the increase in FQ susceptibility seen in 2003 represented the introduction of CA-MRSA into the hospital setting. This finding was confirmed by genotyping the isolates for the presence of the type IV SCCmec. SCCmec type IV percentages are shown in Table 2. The percentage of SA possessing the SCCmec type IV genotype increased to 55% in the 2002 to 2004 period, confirming the entry of CA-MRSA into the hospital setting. Finally, the authors looked specifically at SCCmec type IV isolates, comparing nosocomially acquired strains (>72 hours into hospitalization) with community-acquired strains. They found that only 57% of the nosocomial strains were FQ-susceptible, compared with 89% of the community-acquired strains. The implications of this study are that (1) SCCmec type IV strains of MRSA (historically called CA-MRSA) are currently the most common MRSA currently in some hospital settings and (2) CA-MRSA quickly develops further antimicrobial resistance in the hospital setting.

Table 1
Table 1
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Table 2
Table 2
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Our comment: CA-MRSA, as evidenced by its toxin profile, is already a virulent pathogen. Luckily, it has thus far not been an extremely antibiotic-resistant one (except for β-lactams). The suggestion that CA-MRSA is rapidly developing resistance to commonly used antibiotics is therefore highly concerning.

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Presentation K-426a: Daptomycin Versus Standard Therapy for Staphylococcus aureus Bacteremia (SAB) and Infective Endocarditis (SAIE). V. Fowler, S. Cosgrove, E. Abrutyn, H. Boucher, H. Chambers, G. Corey, I Demeyer, S. Filler, D. Levien, A. Link, M. Rupp, and A. Karchmer

These authors compare the use of daptomycin with other agents commonly used for S. aureus bacteremia.

This multicenter, international, randomized, open-label trial was a late-breaker talk at the ICAAC. The authors compared the use of daptomycin (6 mg/kg per day) to vancomycin or a semisynthetic antistaphylococcal penicillin for S. aureus bacteremia (SAB) or right-sided endocarditis. Two hundred thirty-five patients were enrolled. The end points were tests of cure in the intention-to-treat and per-protocol analyses. Results are depicted in the accompanying table and showed equivalence of daptomycin to standard therapy for the end points studied. Adverse event rates were similar in the 2 groups. The authors concluded that daptomycin is as effective as standard therapy for SAB and S. aureus infective endocarditis, irrespective of methicillin susceptibility, and is well tolerated.

Our comment: the applicability of these data to left-sided infectious endocarditis, which may be a different disease entity, is presently unclear.

MSSA indicates methicillin-susceptible S. aureus.

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Presentation K-424: Clinical Outcomes in Hemodialysis-Dependent Patients With Methicillin-Susceptible Staphylococcus aureus (MSSA) Bacteremia Treated With Vancomycin or First-Generation Cephalosporins. M. Stryjewski, L. Szczech, D. Benjamin, J. Inrig, Z. Kanafani, J. Engemann, V. Chu, L. Reller, R. Corey, and V. Fowler

These authors report the superiority of β-lactam antibiotics to vancomycin in treating patients with methicillin-susceptible S. aureus bacteremia.

To compare treatment with vancomycin with treatment with β-lactam antibiotics, 123 hemodialysis patients with methicillin-susceptible S. aureus (MSSA) bacteremia were prospectively identified. For the purposes of multivariate analysis, the combined end point of death and recurrent infection was used. In patients with MSSA bacteremia who continued to receive vancomycin after sensitivities were known, the end point of death plus recurrent infection was more common at 12 weeks (31.2% vs 13%. P = 0.024). On multivariate analysis, prolonged vancomycin use and failure to remove the dialysis catheter were independently associated with death and recurrent infection (odds ratios, 3.53 and 4.99, respectively). The authors conclude that, in most patients undergoing chronic hemodialysis with MSSA bacteremia, dialysis catheters should be removed if possible, and vancomycin should be discontinued once susceptibility results are available.

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Presentation K-423: Prevalence of Infective Endocarditis (IE) Among Patients With Healthcare-Related (HCR) Staphylococcus aureus Bacteremia (SAB). R. Finkelstein, I. Oren, E. Kasssis, E. Braun, S. Edelstein, I. Mogilewsky, F. Nakhul, H. Sprecher, A. Raz, Y. Agmon, and S. Reissner

These authors attempt to answer the age-old question: which hospitalized patients with S. aureus bacteremia (SAB) have underlying endocarditis?

To determine the frequency of endocarditis in patients with health care-associated SAB, consecutive patients at a tertiary care hospital with more than 1 positive blood culture for S. aureus were prospectively enrolled in this study. During the 24-month period of the study, there were 140 episodes of SAB, of which 83.6% were health care-related. In addition, 54.7% were catheter-related. Definite infective endocarditis (IE) (by modified Duke criteria) was diagnosed in 8.5% of health care-related SABs. Patient characteristics associated with health care-related endocarditis included more positive blood cultures, infection due to MRSA, and the presence of predisposing conditions for IE. On multivariate analysis, persistent bacteremia of more than 4 days and the presence of predisposing conditions for IE remained significantly associated with health care-related IE.

Our comment: although it is remarked that this prevalence of underlying IE is lower than that reported in previous studies, the rate is still significant enough to warrant ruling out endocarditis in most patients with SAB.

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Presentation K-553: Efficacy of Intranasal Mupirocin on Nasal Carriage to Prevent Subsequent Staphylococcus aureus Infections. K. Becker, G. Lubritz, G. Gosheger, G. Silling, M. Deiwick, G. Knichwitz, N. Damerau, A.W. Friedrich, F. Kipp, G. Peters, and C. Von Eiff

These authors discuss the effects of decolonization on subsequent staphylococcal infection.

Correlation between S. aureus (SA) strains colonizing the anterior nares and those recovered from blood suggests that many staphylococcal infections are of endogenous origin. In this study, patients admitted to selected wards were screened for nasal carriage weekly and randomized to intranasal mupirocin for 5 days (197 patients) or to no treatment (206 patients). Within a 6-week period, SA infections developed in 0.5% of the mupirocin group and 3.4% of the untreated group (p = 0.038). Patients were followed up further, however, and by 18 months, 5 patients in the mupirocin arm and 8 patients in the untreated arm had developed SA infections. In the mupirocin-treated arm, only one patient developed an infection with a previously colonizing strain, in contrast to 5 of 8 patients in the untreated arm. The authors concluded that mupirocin decolonization of the nares resulted in significantly fewer SA infections when compared with patients who were not decolonized. It appears that this protective effect was lost with longer follow-up.

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Presentation E-815: Prevalence of Mupirocin Resistance in Clinical Isolates of Methicillin-Resistant Staphylococcus aureus (MRSA) in German Intensive Care Units (ICUs). U.K. Frank, D.R. Jahn, and F. D. Daschner

These authors report an increased nosocomial prevalence of mupirocin-resistant MRSA.

Six hundred fifty-one isolates of MRSA were prospectively recovered from intensive care unit (ICU) patients in Germany (35 ICUs) from 2001 to 2003. Isolates were tested by the disk diffusion and E-test methods for mupirocin resistance. Mupirocin resistance was detected in 6% to 7% of MRSA in German ICUs. The authors conclude that current patterns of mupirocin consumption should be reviewed and the use of the antibiotic rationalized to attempt to preserve the efficacy of this antibiotic.

Our comment: these findings present a disturbing contrast to information presented at last year's ICAAC [now published-Infect Control Hosp Epidemiol July 2005;26(7):662-667], where surveillance over 4 years in a surgical hospital that routinely uses 5 days of perioperative mupirocin prophylaxis revealed no MRSA isolates with high-level mupirocin resistance.

© 2006 Lippincott Williams & Wilkins, Inc.