Spread of Staphylococcus aureus in hospitals: causes and prevention

Methicillin-resistant Staphylococcus aureus (MRSA) has become a major nosocomial pathogen in many hospitals worldwide. Even more alarming, MRSA strains that are vancomycin intermediate-susceptible are isolated with increasing frequency, making therapy for staphylococcal infections even more difficult and prevention more important than ever. Spread of S. aureus in hospitals and infection control measures are reviewed. The major sources of S. aureus in hospitals are septic lesions and carriage sites of patients and personnel. Carriage often precedes infection. The anterior nares are the most consistent carriage site, followed by the perineal area. Skin contamination and aerial dissemination vary markedly between carriers and are most pronounced for combined nasal and perineal carriers. The principal mode of transmission is via transiently contaminated hands of hospital personnel. Airborne transmission seems important in the acquisition of nasal carriage. Infection control strategies include screening and isolation of newly admitted patients suspected of carrying MRSA or S. aureus with intermediáte resistance to vancomycin, implementation of an infection control program to prevent transmission of resistant strains between patients and hospital personnel, and institution of a proper antibiotic policy to minimize antibiotic resistance development. MRSA carriers should be treated with intranasal antibiotics, e.g. mupirocin, and skin disinfectants to eliminate carriage. Education of hospital personnel is essential. Improved knowledge about the best ways to ensure favourable infection control practices is needed. Active intervention against the spread of MRSA is important.     

New agents for Staphylococcus aureus endocarditis

PURPOSE OF REVIEW: The increasing prevalence of methicillin-resistant Staphylococcus aureus (MRSA) as well as newly discovered S. aureus strains with reduced susceptibility to vancomycin mandates development of new antistaphylococcal agents. This review summarizes currently available and forthcoming antimicrobials for treatment of S. aureus endocarditis. RECENT FINDINGS: No new antimicrobial has been proven superior to antistaphylococcal penicillins for treatment of methicillin-sensitive S. aureus (MSSA) endocarditis. Vancomycin has become standard treatment for MRSA but poor outcomes have been reported, both with susceptible and intermediately resistant S. aureus strains (VISA). Linezolid has successfully treated individual cases of MRSA endocarditis, but limitations include long-term safety. Daptomycin has recently been proven effective and well tolerated for MSSA and MRSA bacteremia, including right-sided endocarditis. New glycopeptides, including dalbavancin and telavancin, as well as the new cephalosporin ceftobiprole, have not yet been studied for treatment of endocarditis but appear active against MRSA and potentially VISA. SUMMARY: Antistaphylococcal penicillins remain the treatment of choice for MSSA. Of the currently available newer agents, daptomycin appears to have the most rapid bactericidal activity and provides a much-needed alternative to vancomycin for treatment of MRSA or MSSA bacteremia and right-sided endocarditis.     

Synercid plus vancomycin for the treatment of severe methicillin-resistant Staphylococcus aureus and coagulase-negative staphylococci infections: evaluation of 5 cases

Synercid (quinupristin/dalfopristin), the first semi-synthetic injectable streptogramin, is a promising alternative to glycopeptides against many Gram-positive multiresistant bacteria. Vancomycin is still considered an effective agent for the treatment of methicillin-resistant Staphylococcus aureus (MRSA) infections but therapeutic failures with glycopeptides have been observed, even for the treatment of infections caused by S. aureus strains sensitive to vancomycin. Synercid, in combination with a glycopeptide, may address this problem without causing significant side effects due to the different toxicity patterns of the 2 antimicrobials. This study reports our experience with the combination of Synercid and vancomycin in 5 patients with severe infection caused by MRSA or methicillin-resistant coagulase-negative Staphylococcus.     

Diagnosis and management of Staphylococcus aureus infections of the skin and soft tissue

Infections involving the skin and soft tissue are common and range from superficial, localized and sometimes self-limiting infections to deep, rapidly spreading and potentially life-threatening infections. Skin infections caused by Staphylococcus aureus include primary pyodermas, while those involving the soft tissues include cellulitis and pyomyositis. Surgical site infections and infections in intravenous drug users are also commonly caused by S. aureus. The severity of the infection determines the choice of treatment. There are few studies that have critically appraised the use of antibiotics in skin and soft tissue infections, and most guidelines are based on expert opinion. The beta-lactam group of antibiotics are the mainstay of treatment for methicillin-susceptible S. aureus infections. For methicillin-resistant S. aureus (MRSA) infections, both with community-acquired and hospital-acquired strains--which are becoming an increasing problem--the antibiotic choice is determined by local susceptibility patterns. Macrolides, clindamycin and cotrimoxazole are options for community-acquired MRSA, while vancomycin is reserved for treatment of infections caused by multiresistant MRSA strains and for patients with suspected endocarditis or severe sepsis. Although a number of the newer antibiotics such as linezolid and quinopristin/dalfopristin have been shown to have good activity against MRSA, these agents should only be used with specialist advice.     

Predicting methicillin resistance and the effect of inadequate empiric therapy on survival in patients with Staphylococcus aureus bacteremia

BACKGROUND: The restriction of vancomycin hydrochloride use is recommended as a measure to decrease the emergence of vancomycin resistance in gram-positive organisms; however, vancomycin also is the treatment of choice for methicillin-resistant Staphylococcus aureus (MRSA) infections. If vancomycin use is restricted to patients with documented infections due to methicillin-resistant organisms, then patients with MRSA infections may not initially receive vancomycin. This study was performed to determine factors that predict MRSA bacteremia and if ineffective empiric antibiotic therapy increased the risk of death in patients with S aureus bacteremia. METHODS: We conducted a retrospective cohort study of all patients with clinically significant S aureus bacteremia (132 episodes in 128 patients) diagnosed between October 1, 1995, and January 1, 1998, at an urban acute care Veterans Affairs medical center (approximately 200 acute care beds) in Baltimore, Md. During the study period, vancomycin was a restricted antibiotic. Empiric use had to be approved by an attending physician specializing in infectious diseases. RESULTS: Compared with patients who had methicillin-sensitive S aureus bacteremia, patients with MRSA bacteremia were significantly older (70 vs 58 years; P<.01), more likely to have a history of MRSA (47% vs 6%; P<.01) and a nosocomial infection (76% vs 50%; P<.01), and less likely to use injection drugs (8% vs 32%; P<.01). In addition, compared with patients who had methicillin-sensitive S aureus bacteremia, patients with MRSA bacteremia were significantly less likely (45% vs 98%; P<.01) to receive effective antibiotic therapy during the first 48 hours of hospitalization. However, the risk of death due to ineffective empiric therapy was less than 1 (relative risk, 0.82; 95% confidence interval, 0.36-1.88) and did not change significantly when adjusted for age, occurrence of sepsis, or nosocomial infection. CONCLUSIONS: The results of this study support the safety of the restriction of vancomycin use in patients with clinically significant S aureus bacteremia. However, patients with a history of MRSA are more likely to have future MRSA infections and should receive empiric therapy using vancomycin for possible S aureus infections, particularly for nosocomial infections.     

Resistance to Non-glycopeptide Agents in Serious <Emphasis Type="BoldItalic">Staphylococcus aureus</Emphasis> Infections

The role of vancomycin in the treatment of serious Staphylococcus aureus infections, both methicillin-susceptible and methicillin-resistant, is becoming increasingly ineffective due to increasing MIC and failure. The development of reduced vancomycin susceptibility by S. aureus to glycopeptides highlights the need for clinicians to reexamine the roles of non-glycopeptide therapy. As the use of these alternative non-glycopeptides antimicrobials increases, it will become pertinent to monitor the rates of resistance. Large surveillance programs have provided data for resistance against S. aureus for the non-glycopeptides (daptomycin, ceftaroline, tigecycline, linezolid, and tedizolid). The current published literatures suggest that worldwide resistance rates to these non-glycopeptides for serious MRSA infections are still low. Implementation of antimicrobial stewardship programs will be crucial in prevention of resistance of these antimicrobials against S. aureus.     

Trimethoprim-sulfamethoxazole compared with vancomycin for the treatment of Staphylococcus aureus infection.

OBJECTIVE: To compare trimethoprim-sulfamethoxazole (TMP-SMZ) and vancomycin regarding efficacy and safety in the therapy of serious Staphylococcus aureus infections. DESIGN: Randomized, double-blind comparative trial. SETTING: A tertiary-care hospital. PATIENTS: One hundred and one intravenous drug users hospitalized with S. aureus infection. MEASUREMENTS: Cure and failure rates; blood and wound cultures; minimum inhibitory and bactericidal concentrations; serum inhibitory and bactericidal titers; temperature; leukocyte count; durations of treatment and hospitalization; and toxicity. RESULTS: Of 228 intravenous drug users, 101 had S. aureus infection and were included in the efficacy analysis (43 received TMP-SMZ and 58 received vancomycin). Methicillin-resistant S. aureus (MRSA) accounted for 47% of S. aureus isolates, and 65% of patients were bacteremic. Infections were cured in 57 of 58 vancomycin recipients and in 37 of 43 TMP-SMZ recipients (P less than 0.02). Failure occurred mostly in patients with tricuspid valve endocarditis and only in those with infection caused by methicillin-sensitive S. aureus (MSSA). The mean duration of bacteremia was 6.7 days in TMP-SMZ recipients and 4.3 days in vancomycin recipients. Among 222 subjects hospitalized for at least 24 hours, toxicity rates were similar for TMP-SMZ (23%) and vancomycin (20%) recipients; nausea and vomiting were associated with TMP-SMZ and inflammation at the intravenous site was associated with vancomycin. Forty-four percent of TMP-SMZ recipients and 29% of vancomycin recipients experienced side effects in the efficacy cohort (P greater than 0.05). CONCLUSIONS: Vancomycin is superior to TMP-SMZ in efficacy and safety when treating intravenous drug users who have staphylococcal infections. However, all treatment failures occurred in patients with MSSA infection at any site. Therefore, TMP-SMZ may be considered as an alternative to vancomycin in selected cases of MRSA infection.     

Vancomycin-resistant Staphylococcus aureus: a new model of antibiotic resistance

Vancomycin has been the most reliable therapeutic agent against infections caused by meticillin-resistant Staphylococcus aureus (MRSA). However, in 1996 the first MRSA to acquire resistance to vancomycin, was isolated from a Japanese patient. The patient had contracted a post-operative wound infection that was refractory to long-term vancomycin therapy. Subsequent isolation of several vancomycin resistant S. aureus (VRSA) strains from USA, France, Korea, South Africa, and Brazil has confirmed that emergence of vancomycin resistance in S aureus is a global issue. A certain group of S. aureus, designated hetero-VRSA, frequently generate VRSA upon exposure to vancomycin, and are associated with infections that are potentially refractory to vancomycin therapy. Presence of hetero-VRSA may be an important indicator of the insidious decline of the clinical effectiveness of vancomycin in the hospitals. Vancomycin resistance is acquired by mutation and thickening of cell wall due to accumulation of excess amounts of peptidoglycan. This seems to be a common resistance mechanism for all VRSA strains isolated in the world so far.     

Clinical analysis of patients requiring long-term mechanical ventilation of over three months: ventilator-associated pneumonia as a primary complication

OBJECTIVE: To evaluate the clinical features, etiology, and prognosis of patients who required long-term mechanical ventilation (LMV) of over three months for respiratory failure following underlying disease, and observation of their clinical course until death. PATIENTS: Thirty-seven patients (27 males, 10 females) treated in the internal and medical intensive care unit at Kawasaki Medical School Kawasaki Hospital over the 16-year period from April 1985 to March 2001 were retrospectively studied. RESULTS: Many of these patients were elderly males with respiratory disease such as pulmonary emphysema or old pulmonary tuberculosis, which had developed into acute respiratory failure resulting in respiratory tract infection and initiation of mechanical ventilation. The survival rates of one year, three years and five years after the start of mechanical ventilation were 60%, 30%, and 16%, retrospectively, and the prognoses were poor. Respiratory tract infection was the most common and serious complication. Specifically, ventilator-associated pneumonia (VAP) was a complication in 21 patients and also the main-cause of death. VAP was observed 2.3 years after the initiation of mechanical ventilation with significant differences in the following risk factors being observed between VAP (+) and VAP (-) groups: chronic obstructive pulmonary disease, duration of mechanical ventilation, prior antibiotics, aspiration of gastric contents and use of histamine-type II receptor antagonist. The causative pathogens of VAP were Pseudomonas aeruginosa and Staphylococcus aureus, which were frequently isolated from tracheal aspirates. All patients with VAP caused by MRSA died shortly after contracting the infection. CONCLUSIONS: This study has demonstrated that appropriate treatment for respiratory tract infections such as VAP and the prevention of nasocomial infection due to MRSA is of paramount importance for patients requiring long-term mechanical ventilation of over three months.     

Aerosolized vancomycin for the treatment of MRSA after lung transplantation

Lung transplantation is the only life-prolonging therapy available for cystic fibrosis (CF) patients with end-stage lung disease. The presence of pathogens in the airways of CF patients prior to transplantation is the major risk factor for infection in the post-transplantation period, with methicillin-resistant Staphylococcus aureus (MRSA) having a growing impact. Aerosolized vancomycin has been used successfully in the treatment of MRSA in the CF population but its use after lung transplantation has not been previously reported. We report the case of a lung transplant recipient who was successfully treated for MRSA infection with aerosolized vancomycin.     

耐甲氧西林金黄色葡萄球菌（MRSA）感染机制研究进展

耐甲氧西林金黄色葡萄球菌（MRSA）是一种新型金黄色葡萄球菌,它会造成严重感染性疾病。MRSA对p内酰胺类抗生素耐药性的产生及毒力的加强使得它成为了临床治疗的-大痼疾。一些虽然低效但较少产生耐药的抗生素的出现使得MRSA治疗有了新的选择。同时,研究者正在逐渐阐明MRSA基因突变和病原学特征（耐药性、毒力等）的相关性。这些成果都将为今后MRSA的临床治疗以及新药和疫苗的开发提供宝贵的理论支持与指导。     

Methicillin-resistant Staphylococcus aureus prosthetic aortic valve endocarditis with paravalvular abscess treated with daptomycin

Prosthetic valves have been used extensively for severe cardiac valvular dysfunction for the past 3 decades. Prosthetic cardiac valves may be infected with organisms causing bacteremia, particularly gram-positive cocci. Staphylococcus epidermidis (coagulase negative staphylococci) and Staphylococcus aureus , both methicillin-susceptible S. aureus and methicillin-resistant S. aureus (MRSA) strains, are the most frequent pathogens causing prosthetic valve endocarditis (PVE). Vancomycin has been the cornerstone of therapy for serious MRSA infections including bacteremia and endocarditis. Clinicians have noted that MRSA bacteremias treated with vancomycin often fail to clear even with prolonged therapy. Persistent or prolonged MRSA bacteremia unresponsive to vancomycin therapy has led to the treatment of these infections by other agents, that is, quinupristin, dalfopristin, linezolid, or daptomycin. These antibiotics have been found particularly useful in treating MRSA bacteremias unresponsive to vancomycin therapy. We report a case of a patient who presented with MRSA PVE complicated by perivalvular aortic abscess with persistent MRSA bacteremia unresponsive to vancomycin therapy. The patient's MRSA bacteremia was cleared with daptomycin therapy (6 mg/kg/d). Because the patient refused surgery, daptomycin therapy was continued in hopes of curing the endocarditis and sterilizing the perivalvular aortic abscess. Transesophageal echocardiogram revealed a decrease in abscess in the aortic perivalvular abscess after 1 week of daptomycin therapy. The patient made an uneventful recovery. The cure of PVE and perivalvular abscesses usually requires removal of the prosthetic device and abscess drainage. In this case, in which surgery was not an option, medical therapy of PVE and a decrease in size of the aortic perivalvular abscess were accomplished with daptomycin therapy. Daptomycin is an alternative to vancomycin therapy in patients with prolonged or persistent MRSA bacteremia secondary to endocarditis or abscess.     

Ventilator-associated pneumonia: impact of organisms on clinical resolution and medical resources utilization

BACKGROUND: Clinical resolution of ventilator-associated pneumonia (VAP) determines the duration of treatment and mechanical ventilation. The aim of this study was to evaluate the influence of organisms and their susceptibility to treatment on outcomes. METHODS: Prospective observational study in three teaching ICUs. Sixty episodes of VAP with appropriate therapy (Haemophilus influenzae, 15 episodes; methicillin-sensitive Staphylococcus aureus [MSSA], 15 episodes; Pseudomonas aeruginosa, 15 episodes; and methicillin-resistant S aureus [MRSA], 15 episodes), and 30 episodes with initial inappropriate therapy, all due to P aeruginosa, were compared. The main outcome measures were clinical resolution variables and, in survivors, length of mechanical ventilation after VAP onset. RESULTS: A significant delay in the resolution of hypoxemia was observed in VAP episodes due to MRSA and P aeruginosa with inappropriate antibiotic therapy (IAT) (median time to resolution, 10 and 8 days, respectively) when compared with the remaining pathogens (median time to resolution, 2 days). A multiple regression model, adjusted for disease severity, confirmed the delayed clinical resolution for MRSA and P aeruginosa with IAT. Similar associations were documented for defervescence. Among survivors, the median duration of mechanical ventilation after VAP onset was significantly longer for MRSA (17 days) and P aeruginosa IAT (11 days) when compared with episodes due to H influenzae or MSSA (6 days). Multiple regression analysis, adjusted for disease severity, confirmed that MRSA required significantly (R(2) = 0.132; p < 0.01) longer respiratory support than other organisms. CONCLUSIONS: When treated promptly, the resolution of VAP due to MSSA, H influenzae, and P aeruginosa was comparable. The resolution of MRSA VAP, regardless of the appropriateness of initial antibiotic therapy, was associated with longer respiratory support.     

Linezolid vs vancomycin: analysis of two double-blind studies of patients with methicillin-resistant Staphylococcus aureus nosocomial pneumonia

OBJECTIVE: To assess the effect of baseline variables, including treatment, on outcome in patients with nosocomial pneumonia due to methicillin-resistant Staphylococcus aureus (MRSA). DESIGN: Retrospective analysis of data from two prospective, randomized, double-blind studies. SETTING: Multinational study with 134 sites. PATIENTS: A total of 1,019 patients with suspected Gram-positive nosocomial pneumonia, including 339 patients with documented S aureus pneumonia (S aureus subset) and 160 patients with documented MRSA pneumonia (MRSA subset). INTERVENTIONS: Linezolid, 600 mg, or vancomycin, 1 g, q12h for 7 to 21 days, each with aztreonam. MEASUREMENTS AND RESULTS: Outcome was measured by survival and clinical cure rates (assessed 12 to 28 days after the end of therapy). Logistic regression analysis was used to determine the effect of treatment and other baseline variables on outcome. Kaplan-Meier survival rates for linezolid vs vancomycin were 80.0% (60 of 75 patients) vs 63.5% (54 of 85 patients) for the MRSA subset (p = 0.03). Logistic regression analysis confirmed that the survival difference favoring linezolid remained significant after adjusting for baseline variables (odds ratio [OR], 2.2; 95% confidence interval [CI], 1.0 to 4.8; p = 0.05). Other baseline variables associated with significantly higher survival rates in MRSA pneumonia were serum creatinine levels less than or equal to two times the upper limit of normal and absence of cardiac comorbidities. Clinical cure rates for linezolid vs vancomycin (excluding indeterminate or missing outcomes) were 59.0% (36 of 61 patients) vs 35.5% (22 of 62 patients) for the MRSA subset (p < 0.01). Logistic regression analysis confirmed that the difference favoring linezolid remained significant after adjusting for baseline variables (OR, 3.3; 95% CI, 1.3 to 8.3; p = 0.01). Other baseline variables associated with significantly higher clinical cure rates in MRSA pneumonia were single-lobe pneumonia, absence of ventilator-associated pneumonia, and absence of oncologic and renal comorbidities. CONCLUSIONS: In this retrospective analysis, initial therapy with linezolid was associated with significantly better survival and clinical cure rates than was vancomycin in patients with nosocomial pneumonia due to MRSA.     

Treatment of infective endocarditis caused by methicillin-resistant Staphylococcus aureus: teicoplanin versus vancomycin in a retrospective study

Infective endocarditis caused by methicillin-resistant Staphylococcus aureus (MRSA) is increasing. Vancomycin and teicoplanin are 2 intravenous glycopeptides appropriate for its treatment. There is no human study comparing teicoplanin and vancomycin for the treatment of MRSA endocarditis. Between 1996 and 2006, 51 MRSA endocarditis patients were treated at the authors' hospital. There were 29 patients with nosocomial infection; 15 were treated with teicoplanin. Teicoplanin was used as the first therapeutic agent in 3 patients because of renal insufficiency. Vancomycin was used as the first therapeutic agent in 12 patients. Treatment was changed to teicoplanin because of adverse reactions in 10 and persistent bacteremia in 2 patients. Early operation was performed in 2 patients because of persistent MRSA bacteremia. Overall, 7 patients died in hospital. There was no statistically significant difference in hospital mortality rate (42% vs 47%) and bacteriologic failure rate (34% vs 40%) between 36 patients treated with vancomycin and 15 patients treated with teicoplanin. Teicoplanin can be an alternative therapy of MRSA infective endocarditis.     

Successful treatment of methicillin-resistant Staphylococcus aureus pulmonary infection with linezolid in a patient with cystic fibrosis

Methicillin-resistant Staphylococcus aureus (MRSA) is a significant cause of pulmonary infection in patients with cystic fibrosis (CF). Because these organisms are frequently multidrug-resistant, most patients require intravenous therapy with vancomycin. We report on the first case of successful treatment of a pulmonary exacerbation due to MRSA in a CF patient with a new antimicrobial, linezolid. We demonstrated equivalence of intravenous and oral dosing in this patient, suggesting that oral linezolid may be an excellent alternative to intravenous vancomycin for CF patients infected with MRSA.     

Community-acquired Staphylococcus aureus pneumonia accompanied by rapidly progressive glomerulonephritis and hemophagocytic syndrome

A 59-year-old woman without underlying disease was admitted to a local hospital because of lung abscess, cytopenias and renal failure. 3 days before admission, she was diagnosed as influenza infection and was under antiviral therapy. Blood cultures were positive for methicillin-sensitive Staphylococcus aureus (MSSA). She was transferred to our hospital on the 15th day at the local hospital because the clinical manifestations could not improve even though she was treated with multiple intravenous antibiotics directed against MSSA. Sputum cultures yielded methicillin-resistant S. aureus (MRSA) producing toxic shock syndrome toxin-1 (TSST-1) and serologic test indicated hypercytokinemia. She was diagnosed as rapidly progressive glomerulonephritis and hemophagocytic syndrome associated with staphylococcal infection. The pulmonary lesions, cytopenias and renal dysfunction improved as a result of long-term antimicrobial treatment including vancomycin, hemodialysis, short-term administration of corticosteroid and other supportive cares. She was finally weaned from hemodialysis on the 73rd hospital day. In recent years, the number of cases of S. aureus producing TSST-1 and enterotoxin has been increasing and in cases of staphylococcal infections, close attention should be given to toxin-mediated as well as non-toxin-mediated clinical manifestations.     

Vancomycin for surgical prophylaxis?

The increasing prevalence of methicillin-resistant Staphylococcus aureus (MRSA) has resulted in a reevaluation of the role of vancomycin for surgical prophylaxis. Two systematic reviews of randomized control studies have concluded that cephalosporins are as effective as vancomycin for the prevention of surgical site infections (SSIs). However, most of these studies were conducted more than 10 years ago and cannot be generalized to the current rates of MRSA. Several time-series analyses have recently evaluated the effectiveness of vancomycin for surgical prophylaxis in institutions with a high prevalence of MRSA. Decision analysis models have also been used to estimate thresholds of MRSA prevalence for which vancomycin would minimize the incidence and cost of SSIs. Combination therapy and the emergence of resistant pathogens following vancomycin prophylaxis are reviewed. Vancomycin is not recommended for routine use in surgical prophylaxis but may be considered as a component of a MRSA prevention bundle for SSIs in selective circumstances.     

Clinical practice: colonization, fomites, and virulence: rethinking the pathogenesis of community-associated methicillin-resistant Staphylococcus aureus infection.

Community-associated methicillin-resistant Staphylococcus aureus (MRSA) infection is increasingly common worldwide and causes considerable morbidity and mortality. Of concern, community-associated MRSA infections are often recurrent and are highly transmissible to close contacts. The traditional tenet of pathogenesis is that MRSA colonization precedes infection. This has prompted persons involved in efforts to prevent community-associated MRSA infection to incorporate the use of intranasal topical antibiotics for nasal decolonization. However, data from outbreaks of community-associated MRSA infection suggest that skin-skin and skin-fomite contact represent important and common alternative routes of acquisition of the infecting strain. Furthermore, strain characteristics of the most successful community-associated MRSA strain, USA300, may contribute to a distinct pathogenesis. As we develop strategies to prevent community-associated MRSA infection, we must reconsider the pathogenesis of S. aureus. Reliance on models of health care-associated MRSA transmission for prevention of community-associated MRSA infection may result in the development of flawed strategies that attenuate our ability to prevent this serious and potentially deadly infection.     

Bacteremic pneumonia due to Staphylococcus aureus: A comparison of disease caused by methicillin-resistant and methicillin-susceptible organisms.

We performed a prospective study of all patients with bacteremic pneumonia due to Staphylococcus aureus over a period of 6 years during an outbreak of methicillin-resistant S. aureus (MRSA). Patients with bacteremic pneumonia due to MRSA (32 cases) or methicillin-susceptible S. aureus (MSSA; 54 cases) were compared. The patients with MRSA pneumonia were older and were more likely than those with MSSA pneumonia to have predisposing factors for acquisition of the infection. There were no differences in clinical findings, radiological pattern, or complications in clinical evolution among patients with MRSA and MSSA pneumonia. Mortality was significantly higher among MSSA-infected patients treated with vancomycin than among those treated with cloxacillin (47% vs. none; P<.01). Multivariate analysis (stepwise logistic regression method) showed a relationship between mortality and the following variables: septic shock (odds ratio [OR], 61), vancomycin treatment (OR, 14), and respiratory distress (OR, 8).