National hospital survey of anaerobic culture and susceptibility methods: III

Abstract

To assess the current status of anaerobic bacteriology in the United States, we surveyed, by means of a questionnaire, 150 hospitals selected at random with bed capacities of 200–1000 and we received responses from 98 (65%). Ninety-eight percent processed anaerobic culture specimens with 21% sending them to reference laboratories. Almost all these hospitals processed blood and wound cultures for anaerobes and all used selective media for identification, including BBE (52%), LKV (77%), and PEA (53%) agars. All hospital laboratories attempted identification of blood culture isolates including 80% that attempted speciation. Wound cultures for anaerobic bacteria and sterile site cultures were also processed for anaerobes by almost all labs. Identification of B. fragilis group species to species level was performed only in 56% of labs always and 37% sometimes. Preformed enzyme kits were used by 66% of labs and 30% used special potency disks for identification. Susceptibility testing was performed in-house by 21% of hospital labs and sent out to reference labs an additional 20%. Susceptibility testing was attempted for all blood culture isolates by both hospital (21% of total labs) and reference laboratories, but only performed by 17% for sterile body site and 14% of the time for wound isolates. Etest was used most often followed by broth microdilution. No labs used the agar dilution or disk elution methods. The antimicrobials most often tested in hospital labs, predicated on the commercial panel used, were penicillin/ampicillin and clindamycin (15/18; 83%; 15% of total labs), metronidazole (16/18; 89%; 16% of total labs) and cefotetan and ampicillin/sulbactam (12/18; 67%; 12% of total labs), piperacillin/tazobactam (7/18; 39%; 7% of total labs), cefoxitin (9/18; 50%), imipenem (8/18; 44%), and chloramphenicol (6/18; 33%). Our current survey suggests that while many labs are processing anaerobic cultures, especially blood cultures, the identification of isolates and the performance of antimicrobial susceptibility testing of isolates are in disarray and in dire need of improvement.

Introduction

While anaerobic bacteria are important clinical pathogens, clinical laboratories vary in their capabilities and interest in the isolation and identification of anaerobes and in their performance of anaerobic susceptibility testing [1], [2]. Recently, the controversy about the importance of obtaining anaerobic cultures has reemerged when Lassmann et al. [3] noted a 74% rise in anaerobic bacteremias at the Mayo Clinic and that in today's complex medical patients “the clinical context for anaerobic infections [is] less predictable than it once was.” This highlights the need for practice improvement [4]. Numerous studies have demonstrated that appropriate early therapy results in a better clinical outcome with lower mortality and morbidity and shortened length of stay for diverse conditions including bacteremia [5], [6]. With the rising resistance to a variety of commonly employed anti-anaerobe agents, including several case reports of clinical metronidazole resistance, also suggests that the availability of susceptibility testing is clinically relevant [7]. However, laboratorians that are often concerned about the cost of testing [2] often treat anaerobic bacteriology as the poor stepsister and as a consequence even guideline committees have suggested that anaerobic culture of community-acquired intraabdominal infections need not be performed [8]. In order to assess the current status of anaerobic culture and susceptibility methods, we performed a new national survey in randomly selected, large nonteaching hospitals across the United States.