John D. Rihs

Staphylococcus aureus nasal carriage and infection in patients on hemodialysis: efficacy of antibiotic prophylaxis

We conducted a five-year prospective controlled study of prophylaxis of Staphylococcus aureus nasal carriage and infection among patients in a hemodialysis unit. Carriers tended to have chronic colonization with a single phage type. S. aureus infections occurred significantly more frequently in carriers than in noncarriers and, in 93 percent of the infected carriers, were caused by the same phage type as that carried in the nares. Neither intravenous vancomycin nor topical bacitracin was found to be efficacious in eradicating nasal carriage. However, oral rifampin given for five days decreased S. aureus carriage over a one-month follow-up period, but within three months colonization of the nares recurred in most carriers, often with an S. aureus of the original phage type. Carriers were then randomly assigned to receive either rifampin or no prophylaxis. Rifampin was readministered at three-month intervals if culture of the anterior nares yielded S. aureus. Infections with S. aureus occurred significantly more frequently in carriers given no prophylaxis than in those given a full course of rifampin. S. aureus resistant to rifampin was isolated from the anterior nares of four patients, but these isolates were not implicated in any infections. The incidence of infection at the dialysis access site, skin, and soft tissue of patients on hemodialysis can be decreased by interventions directed at nasal carriage of S. aureus.

National Survey on the Susceptibility of Bacteroides fragilis Group: Report and Analysis of Trends in the United States from 1997 to 2004

ABSTRACT The susceptibility trends for the species of the Bacteroides fragilis group against various antibiotics from 1997 to 2004 were determined by using data for 5,225 isolates referred by 10 medical centers. The antibiotic test panel included ertapenem, imipenem, meropenem, ampicillin-sulbactam, piperacillin-tazobactam, cefoxitin, clindamycin, moxifloxacin, tigecycline, chloramphenicol, and metronidazole. From 1997 to 2004 there were decreases in the geometric mean (GM) MICs of imipenem, meropenem, piperacillin-tazobactam, and cefoxitin for many of the species within the group. B. distasonis showed the highest rates of resistance to most of the β-lactams. B. fragilis, B. ovatus, and B. thetaiotaomicron showed significantly higher GM MICs and rates of resistance to clindamycin over time. The rate of resistance to moxifloxacin of B. vulgatus was very high (MIC range for the 8-year study period, 38% to 66%). B. fragilis, B. ovatus, and B. distasonis and other Bacteroides spp. exhibited significant increases in the rates of resistance to moxifloxacin over the 8 years. Resistance rates and GM MICs for tigecycline were low and stable during the 5-year period over which this agent was studied. All isolates were susceptible to chloramphenicol (MICs < 16 μg/ml). In 2002, one isolate resistant to metronidazole (MIC = 64 μg/ml) was noted. These data indicate changes in susceptibility over time; surprisingly, some antimicrobial agents are more active now than they were 5 years ago.

Association with prior fluoroquinolone therapy of widespread ciprofloxacin resistance among gram-negative isolates in a Veterans Affairs medical center.

We performed a case-control study of risk factors for the acquisition of ciprofloxacin-resistant gram-negative isolates in a Veterans Affairs medical center. Sixty-five patients with resistant isolates and 50 control patients were identified. Prior fluoroquinolone use was significantly more frequent among patients with resistant isolates than it was among controls (58 versus 20%; P = 0.0001). The association with prior quinolone use was stronger in the long-term-care division (81 versus 32%; P = 0.0005) than it was in the acute-care division (29 versus 0%; P = 0.015). On multivariate analysis, prior receipt of a fluoroquinolone was the single most significant risk factor for isolation of a ciprofloxacin-resistant gram-negative organism (P = 0.0001).

Lessons Learned from the Anaerobe Survey: Historical Perspective and Review of the Most Recent Data (2005–2007)

BACKGROUND The rationale and lessons learned through the evolution of the National Survey for the Susceptibility of Bacteroides fragilis Group from its initiation in 1981 through 2007 are reviewed here. The survey was conceived in 1980 to track emerging antimicrobial resistance in Bacteroides species. METHODS Data from the last 11 years of the survey (1997-2007), including 6574 isolates from 13 medical centers, were analyzed for in vitro antimicrobial resistance to both frequently used and newly developed anti-anaerobic agents. The minimum inhibitory concentrations of the antibiotics were determined using agar dilution in accordance with Clinical and Laboratory Standards Institute recommendations. RESULTS The analyses revealed that the carbapenems (imipenem, meropenem, ertapenem, and doripenem) and piperacillin-tazobactam were the most active agents against these pathogens, with resistance rates of 0.9%-2.3%. In the most recent 3 years of the survey (2005-2007), resistance to some agents was shown to depend on the species, such as ampicillin-sulbactam against Bacteroides distasonis (20.6%) and tigecycline against Bacteroides uniformis and Bacteroides eggerthii ( approximately 7%). Very high resistance rates (>50%) were noted for moxifloxacin and trovafloxacin, particularly against Bacteroides vulgatus. During that period of study, non-B. fragilis Bacteroides species had >40% resistance to clindamycin. Metronidazole-resistant Bacteroides strains were also first reported during that period. CONCLUSIONS In summary, resistance to antibiotics was greater among non-B. fragilis Bacteroides species than among B. fragilis and was especially greater among species with a low frequency of isolation, such as Bacteroides caccae and B. uniformis. The emergence of resistance among the non-B. fragilis Bacteroides species underscores the need for speciation of B. fragilis group isolates and for clinicians to be aware of associations between species and drug resistance.

Isolation of Staphylococcus aureus from the Urinary Tract: Association of Isolation with Symptomatic Urinary Tract Infection and Subsequent Staphylococcal Bacteremia

BACKGROUND Staphylococcus aureus is frequently isolated from urine samples obtained from long-term care patients. The significance of staphylococcal bacteriuria is uncertain. We hypothesized that S. aureus is a urinary pathogen and that colonized urine could be a source of future staphylococcal infection. METHODS We performed a cohort study of 102 patients at a long-term care Veterans Affairs facility for whom S. aureus had been isolated from clinical urine culture. Patients were observed via urine and nasal cultures that were performed every 2 months. We determined the occurrence of (1) symptomatic urinary tract infection concurrent with isolation of S. aureus (by predetermined criteria), (2) staphylococcal bacteremia concomitant with isolation of S. aureus from urine, and (3) subsequent episodes of staphylococcal infection. RESULTS Of 102 patients, 82% had undergone recent urinary catheterization. Thirty-three percent of patients had symptomatic urinary tract infection at the time of initial isolation of S. aureus, and 13% were bacteremic. Eight-six percent of the initial urine isolates were methicillin-resistant S. aureus. Seventy-one patients had follow-up culture data; 58% of cultures were positive for S. aureus at > or =2 months (median duration of staphylococcal bacteriuria, 4.3 months). Sixteen patients had subsequent staphylococcal infections, occurring up to 12 months after initial isolation of S. aureus; 8 late-onset infections were bacteremic. In 5 of 8 patients, the late blood isolate was found to have matched the initial urine isolate by pulsed-field gel electrophoresis typing. CONCLUSIONS S. aureus is a cause of urinary tract infection among patients with urinary tract catheterization. The majority of isolates are methicillin-resistant S. aureus. S. aureus bacteriuria can lead to subsequent invasive infection. The efficacy of antistaphylococcal therapy in preventing late-onset staphylococcal infection in patients with persistent staphylococcal bacteriuria should be tested in controlled trials.

Control of an Outbreak of Infection Due to Extended-Spectrum β-Lactamase-Producing Escherichia coli in a Liver Transplantation Unit

We report an outbreak of infection due to genotypically identical extended-spectrum beta-lactamase--producing Escherichia coli among patients in a liver transplantation unit. Control of the outbreak was achieved by a combination of contact isolation, feedback on hand hygiene, and gut decontamination with an orally administered fluoroquinolone. These interventions led to abrupt curtailment of the outbreak.

Evaluation of housestaff physicians' preparation and interpretation of sputum Gram stains for community-acquired pneumonia

Objective:To evaluate the preparation and interpretation of sputum Gram stains by housestaff physicians in the assessment of patients with community-acquired pneumonia.Design:A prospective, multicenter study.Setting:Two university-affiliated hospitals in Pittsburgh.Patients:Ninety-nine cases of clinically and radiographically established pneumonia occurring in 97 patients.Diagnostic test assessment:Housestaff and microbiology personnel prepared a Gram stain for each case of pneumonia. Housestaff assessed the presence and identity of a predominant microbial organism on the slides they prepared. Two senior staff microbiologists, blinded to patient and preparer, evaluated all slides for preparation, sputum purulence, and identification of the predominant organism. Two reference standards were used to assess the sensitivity, specificity, and predictive values of housestaff’s Gram-stain interpretations: 1) senior staff microbiologists’ determinations of the microbes present using the slides without benefit of culture results, and 2) the etiologic agent derived from results of sputum culture, blood culture, or serology.Measurements and main results:Housestaff physicians completed a Gram stain in 58% of the pneumonia episodes. Gram stains were not made in 42% of cases, primarily because patients were unable to produce sputum. Fifteen percent of housestaff’s smears were judged inadequately prepared, compared with 3% for the laboratory personnel (p<0.01). Housestaff obtained purulent sputum samples significantly more often than did nursing personnel (58% versus 38%; p<0.01). Housestaff’s Gram stains were 90% sensitive for detecting pneumococcus, with a 50% falsepositive rate. The sensitivity of the Gram stain was less for identification of Haemophilus influenzaethan for identification of Streptococcus pneumoniae.A single antimicrobial agent was chosen as initial therapy for 50% of the patients in whom housestaff identified a predominant organism, compared with 30% in whom a predominant organism was not identified (p≤0.05).Conclusions:Although housestaff obtained purulent sputum samples more frequently than did nursing personnel, they made systematic errors in the preparation and interpretation of Gram-stained slides. Housestaff physicians should receive formal training in the preparation and interpretation of Gram stains; the specific defects elucidated in this study warrant special attention.

Lack of efficacy of mupirocin in the prevention of infections with staphylococcus aureus in liver transplant recipients and candidates

Background. Infections with Staphylococcus aureus are a significant problem in patients in liver transplant units. An association between prior nasal carriage with S. aureus and subsequent infections has been documented previously in liver transplant recipients and patients with cirrhosis. However, the role of decolonization with mupirocin applied intranasally for the prevention of S. aureus infections in these patients has not been determined. Methods. S. aureus nasal carriage was prospectively sought in 70 consecutive liver transplant candidates. Mupirocin two times per day for 5 days was administered to the carriers. Follow-up nasal cultures to document decolonization were performed 5 days after the final application of mupirocin. The primary endpoint was the development of S. aureus infections. Results. Thirty-one of 70 patients (44%) were found to be nasal carriers and 27 of 31 nasal carriers (87%) were successfully decolonized. However, 12 of 27 patients (37%) successfully decolonized became recolonized with S. aureus, and an additional nine patients who were initially noncarriers became newly colonized with S. aureus during the study period. Despite the use of mupirocin, 16 of 70 patients (23%) developed an infection with S. aureus. No isolate was found to be mupirocin resistant. Conclusion. Elimination of S. aureus nasal carriage by mupirocin did not prevent S. aureus infections in patients in our liver transplant unit.

In vitro activities of newer quinolones against bacteroides group organisms.

ABSTRACT The activities of BMS-284576, clinafloxacin, moxifloxacin, sitafloxacin, trovafloxacin, imipenem, cefoxitin, and clindamycin against 589 Bacteroides fragilis group isolates were determined. The activity of BMS-284576 was comparable to that of trovafloxacin. Sitafloxacin and clinafloxacin were the most active quinolones, and moxifloxacin was the least active. B. fragilis was the most susceptible of the species, and Bacteroides vulgatus was the most resistant. Association of specific antibiotic resistance with Bacteroides species was noted for all quinolones.

The efficacy of topical antibiotic prophylaxis for contaminated head and neck surgery

This study was undertaken to determine the feasibility of using perioperative topical antibiotics in contaminated head and neck surgery and to standardize the culture methodology (both qualitative and quantitative) which could serve as bacteriologic endpoints for evaluation. Following preliminary studies to establish oral cavity indicator organisms and the impact of a single antibiotic mouthwash dose on oral microflora, 10 consecutive patients undergoing contaminated head and neck surgery were recruited into a clinical trial where clindamycin mouthwash and intraoperative irrigation containing clindamycin were used instead of traditional parenteral antibiotics. The bacteriologic efficacy of topical clindamycin was assessed by comparing the presence of four indicator microorganisms (two aerobic and two anaerobic) cultured from two oral cavity culture sites before and after antibiotic prophylaxis