Antimicrobial Culture and Susceptibility Testing Has Little Value for Routine Management of Secondary Bacterial Peritonitis

S258 Antimicrobial Culture and Susceptibility Testing Has Little Value for Routine Management of Secondary Bacterial Peritonitis Steve H. Dougherty From the Department of Surgery, Texas Tech University Health Sciences Center at El Paso, El Paso, Texas The traditional surgical practice of routinely culturing specimens from patients with communityacquired intraabdominal infections, such as appendicitis, contributes little to the management of the individual patient, either initially or later when infectious complications have developed. Instead of performing routine cultures for peritonitis, a modified approach that still facilitates hospital surveillance for microbial resistance patterns should be used. The traditional surgical practice of routinely culturing specimens from patients with community-acquired intraabdominal infections, such as appendicitis, has come under increasing scrutiny. It is arguable that the results of such routine culturing seldom influence the management of the individual patient, either initially or later when infectious complications have developed. If such is the case, of course, routine culturing may not be cost-effective and should be abandoned. This review will explore these issues. Broad-Spectrum Empirical Antibiotic Therapy for Peritonitis Although some 400 species of bacteria may be isolated from the gut, especially the colon, apparently only a few species are actually involved in intraperitoneal infections, usually a combination of enteric aerobes and anaerobes [1]. Escherichia coli is the most common enteric aerobe isolated, while Bacteroides fragilis is the most frequently isolated anaerobe. Over the last two decades, the use of broad-spectrum empirical antibiotic therapy directed against these organisms has become commonplace in the treatment of secondary bacterial peritonitis. The basis of this empirical approach to the drug management of peritonitis has largely been experimental. Animal studies performed since the mid-1970s have shown that peritonitis can be roughly divided into two stages: an early liquid or freeflowing stage followed in 7 – 14 days by an abscess stage [2, 3]. During the early stage, E. coli predominates numerically and is the organism most commonly recovered from the bloodstream. The natural mortality associated with this stage is Ç40%, and virtually all surviving animals develop intraabdominal abscesses. The numerically dominant organism in the late or abscess stage, however, is B. fragilis (mean concentrations Reprints or correspondence: Dr. Steve H. Dougherty, Department of Surgery, Texas Tech University Health Sciences Center at El Paso, 4800 Alberta Avenue, El Paso, Texas 79905. Clinical Infectious Diseases 1997;25(Suppl 2):S258–61 q 1997 by The University of Chicago. All rights reserved. 1058–4838/97/2503–0054$03.00 / 9c36$$se66 as high as 109 organisms/mL of pus), although the presence of facultative organisms is apparently also necessary for abscess formation to occur [4]. Such results suggest that gram-negative aerobic organisms are responsible for early mortality due to acute peritonitis whereas anaerobic organisms are more important during abscess formation. Both types of bacteria, though, are present during each stage. It is of interest that a similar pattern has been recognized clinically: the longer peritonitis has been present, the more likely the recovery of anaerobes from the septic focus. In one study, the number of aerobic strains from peritoneal cultures outnumbered anaerobes when the duration of illness was õ3 days. When the illness had lasted ú3 days, however, anaerobes outnumbered aerobes [5]. Working with the rat peritonitis model, Weinstein et al. [6] and Nichols et al. [7] showed that antibiotics effective against aerobes reduce early mortality but not late abscess formation. In contrast, antibiotics effective mainly against anaerobes do not reduce early mortality but do prevent abscesses in surviving animals. An antibiotic regimen (an aminoglycoside plus clindamycin) effective against both aerobes and anaerobes reduced both early mortality and late abscess formation. Indeed, comparable favorable results can be obtained with almost any drug or drug combination whose spectrum of antimicrobial coverage is similar [8]. Animal studies such as these suggest that intraabdominal sepsis of enteric origin is managed effectively with empirical antibiotics directed against the aerobic and anaerobic gut flora. Though perhaps less definitive, the results of clinical trials on the antibiotic management of peritonitis have generally paralleled the findings of the animal studies. Thadepalli et al. [9] conducted a prospective, randomized study comparing the use of cephalothin-kanamycin vs. clindamycin-kanamycin as presumptive therapy for penetrating bowel injuries. The drugs were administered parenterally before laparotomy. Anaerobic infections were almost twice as frequent in the cephalothinkanamycin group as they were among patients receiving anaerobic coverage with clindamycin-kanamycin. The overall septic complication rate was also significantly lower among the clindamycin-kanamycin group, the difference being due almost entirely to a reduction in infections involving anaerobic or mixed flora. 08-12-97 16:34:21 cida UC: CID CID 1997;25 (Suppl 2) Routine Bacterial Cultures for Peritonitis Berne et al. [10] conducted a comparative trial of gentamicin-clindamycin vs. two different cephalosporin regimens in the management of perforated or gangrenous appendicitis. Patients who received gentamicin-clindamycin therapy had far fewer septic complications than those who received therapy with the cephalosporin regimens. Primary therapy failed for 15% (7/47) of patients treated with cefoperazone and for 23% (11/48) treated with cefamandole but for only 2% (1/52) treated with gentamicin-clindamycin. In a follow-up to this report, Heseltine et al. [11] studied the causes of treatment failure and found that most were associated with the recovery of resistant B. fragilis from intraoperative cultures. In a retrospective study of perforated appendicitis, David et al. [12] found that children treated with ampicillin, gentamicin, and clindamycin had markedly fewer wound infections (2%) and abscesses (5%) than those receiving only ampicillin and/ or gentamicin (wound infections, 36%; abscesses, 18%). Thus, broad-spectrum empirical drug therapy for peritonitis appears to be effective. Indeed, it is the very success of this approach, with its failure rate of only 10% – 15%, that has led surgeons to question the necessity of performing intraperitoneal cultures when empirical therapy is being used [13 – 16]. Surgeons perceive that routine culturing does not affect antibiotic selection or clinical outcome. By the time that culture and susceptibility results become available, especially anaerobic susceptibilities that may take up to 4 days and are seldom routinely performed by hospitals anyway, clinical outcom (...truncated)