Special organism isolation: attempting to bridge the gap

Control of antimicrobial resistance in the health care system

Resistance continues to spread in nosocomial pathogens in acute care hospitals and other key settings of managed health care systems. Appropriate control measures for such resistant organisms depend, in part, on the pathways by which resistance has arisen. Unfortunately, these pathways differ greatly from organism to organism and setting to setting. Although the epidemiology of resistant organisms sometimes is similar to that of susceptible organisms of the same kind, in some situations it may be quite different. This article highlights some of the pathways leading to the development of resistance in bacteria and the relevance of these mechanisms to measures for the control of resistant bacteria in hospital and community settings.

An analysis of 110 serious enterococcal infections. Epidemiology, antibiotic susceptibility, and outcome

A prospective, observational study of 110 patients with serious infections due to Enterococcus spp. in 6 university and community teaching hospitals in Connecticut was conducted to define the epidemiology of community and nosocomial serious enterococcal infections and to determine risk factors, including antibiotic resistances, that contribute to outcome. Serious community and nosocomial enterococcal infections involved a variety of sites, and antibiotic resistance was common. Types of infection by major organ system were cardiovascular, 54% (catheter-related bacteremia 28%, primary bacteremia 18%, endocarditis 6%, septic thrombophlebitis 1%); intra-abdominal, 13% (including cholangitis, 6%); renal, 13%; skin and soft tissue, 5%; bone and joint, 4%; pleuropulmonary, 4%; central nervous system, 3%; deep surgical wound, 3%; and endometritis, 2%. Sixty-one percent of infections were nosocomial; 48% of these occurred in the intensive care unit. Enterococcus faecium was responsible for 20% of all infections. Antibiotic resistances among the infections included high-level gentamicin resistance (26%), ampicillin resistance (10%), and vancomycin resistance (8%). Clinical cure was achieved in 64% of patients; 6.8% of patients relapsed, 6.8% had recurrence of the infection with a different pathogen, and overall mortality was 23%. Ampicillin resistance and a high acute physiology and chronic health evaluation (APACHE) II score were highly predictive of lack of cure.

Penicillin-resistant pneumococci--an emerging threat to successful therapy

Pneumococci highly resistant to penicillin G [minimum inhibitory concentration (MIC) > or = 2 mg L-1] have become prevalent in many parts of the world since their emergence and spread in the late 1970s. In the USA, such organisms are seen primarily in two populations: infants and children, and adults with AIDS. Surveys in both rural and urban areas have revealed presence of these organisms, as well as an increasing frequency of Streptococcus pneumoniae strains relatively resistant to penicillin (MIC 0.1-1.0 mg L-1--now defined by some as 'intermediate' resistance). Predisposing factors are not yet clear. Prior antimicrobial therapy was given to some of the children and most of the adults who are colonized or infected with resistant strains. Prior or concurrent use of cotrimoxazole prophylaxis for Pneumocystis carinii pneumonia has been frequent in our cases in adults, most of whom had a concurrent diagnosis of AIDS. Children with disease often have a history of long-term prophylaxis with a beta-lactam drug (for sickle cell disease, etc). Many strains are also resistant to newer cephalosporins like cefotaxime and ceftriaxone (MIC > or = 2 mg L-1). The organisms are frequently multi-resistant, with high MIC values common as well for chloramphenicol and variable for tetracycline, macrolides, cotrimoxazole, and fluoroquinolones. Only to vancomycin are the organisms consistently susceptible. These findings raise alarms about the future of pneumococcal disease in both community and nosocomial disease. Increasing prevalence in otitis and pneumonia in children and in community-acquired pneumonia in adults may lead to use of vancomycin as empirical therapy for these clinical situations. This would increase the selective pressure for emergence of vancomycin-resistant organisms, whether S. pneumoniae or others. Moreover, the pneumococcus was a common cause of hospital infection prior to the introduction of penicillin. The potential now exists for nosocomial pneumococcal infection again to become a feared and ominous occurrence.