S. aureus and E. coli were identified in previous studies as the two most common blood culture isolates from hospitalized patients in the United States and Europe [4, 5, 12, 13]. In the current study, coagulase-negative staphylococci were the most common blood culture isolates from laboratories in the United States (42.0% of isolates) (Table 1). However, given that coagulase-negative staphylococci isolated from blood cultures are often contaminants (>85% are clinically insignificant) [5] our results agree generally with those previously published. As TSN collects all laboratory data, year-round, it may present a more accurate description of laboratory testing than do centralized point prevalence studies that often exclude the majority of isolates identified by laboratories in a year [12, 13]. Accepting the over-representation of contaminant coagulase-negative staphylococci in clinical laboratories in the United States as observed in TSN Database-USA, the rank order of other pathogens is similar to previous reports describing centralized surveillance studies [12, 13] and hospital review studies [4, 5]. Six organisms, coagulase-negative staphylococci, S. aureus, E. faecalis, E. coli, K. pneumoniae, and E. faecium accounted for >80% of blood culture isolates. Previously, SENTRY has reported similar results for laboratories in the United States, Canada, Latin America, and Europe [12, 13]. In the current study, overall frequencies of isolation were 78.1% gram-positive bacteria and 21.9% gram-negative bacteria.
Oxacillin-resistant S. aureus are extremely important causes of bloodstream infections and evidence has been presented that oxacillin-resistant S. aureus (Table 3) are increasing globally among bloodstream isolates and among isolates from other anatomical sites [12, 17]. Fluoroquinolone resistance has increased in a consistent step-wise manner in the United States and Europe for Enterobacteriaceae, P. aeruginosa, and S. aureus [12, 13, 18, 19]. It is important for clinicians to be updated with current data concerning the susceptibility of commonly prescribed agents such as the fluoroquinolones and also to be aware of trends in longitudinal data. The rates of change in resistance by pathogen and region can help set priorities for focused intervention efforts.
Early clinical suspicion, rigorous diagnostic measures, aggressive initiation of appropriate antimicrobial therapy, comprehensive supportive care, and measures aimed at reversing predisposing causes (e.g., amelioration of an underlying disease, removal of foreign bodies, drainage of abscesses) are the cornerstone of successful management of patients with sepsis syndrome [5, 10]. The selection of antimicrobials to be used for empiric therapy should be based on the local rates of susceptibility and on the site of infection [10]. Early initiation of appropriate antimicrobial treatment is critical in decreasing morbidity and mortality among patients with bloodstream infections due to gram-negative organisms [14]. The initiation of such therapy is almost always empirical, requiring knowledge of the likely pathogen(s) and their usual antimicrobial susceptibility patterns [10, 20]. Combinations of antimicrobial agents are recommended for empiric therapy for patients with bloodstream infections, particularly for those patients with the most adverse prognostic factors [10]. Combination therapy is recommended to cover the broad range of possible pathogens which may be difficult to distinguish clinically, because of the possibility of polymicrobial infections, because they may prevent the emergence of resistance, and because they may have additive or synergistic antimicrobial activity. For the patient with a nosocomial bloodstream infection, initial treatment should consist of an aminoglycoside initially paired with a broad-spectrum β-lactam. Expanded-spectrum cephalosporins are the β-lactam of choice for the non-neutropenic patient because of the greater likelihood of Klebsiella and Staphylococcus infections in these patients [10]. The regimen of an aminoglycoside paired with a penicillin or cephalosporin having antipseudomonal activity is preferred for neutropenic patients, patients with severe chronic obstructive pulmonary disease or bronchiestatis, patients receiving assisted ventilation, and patients with extensive burns [10].
The in vitro potency of ceftriaxone and cefotaxime against E. coli and Klebsiella suggests that single-agent therapy directed against those bacteria may be successful even in severely compromised hosts [10]. The superior pharmacokinetic and pharmacodynamic properties that exist for ceftriaxone when compared with cefotaxime may be a consideration when choosing between these two agents [18]. In the nosocomial setting, extensive data also confirmed the efficacy of ceftriaxone with or without an aminoglycoside in serious Gram-negative infections, pneumonia, spontaneous bacterial peritonitis and as surgical prophylaxis [21]. Ceftriaxone, cefotaxime, and cefepime all have similar indications for pneumonia, skin and skin structure infections, and urinary tract infections; however only ceftriaxone and cefotaxime have an indication for the sepsis syndrome. In the current study, susceptibilities of isolates to one or both agents in combinations of ceftriaxone, ceftazdime, cefepime, piperacillin-tazobactam or ciprofloxacin plus gentamicin were consistent (range, 74.8–76.3%) but lower than similar β-lactam or ciprofloxacin combinations with vancomycin (range, 93.5–96.6%). Ceftazidime, cefepime, imipenem and meropenem appear most active against P. aeruginosa [10].
