Analysis of parameters and validation of method for normalized interpretation of antimicrobial resistance.

The method of normalized resistance interpretation (NRI), uses the high-zone side of the susceptible peak in a zone diameter histogram as an internal calibrator to construct the real standard distribution of susceptible isolates even in the presence of resistant isolates. NRI parameters were optimized using control strain histograms from microbiology laboratories in Stockholm, Argentina, and the Philippines. A moving average based on four-zone values was slightly better than based on two-zone average values. The optimal peak adjustment from the switch position of the moving average was 1.0 for two-zone averages and 2.5 for four-zone averages. A comparison between true means and NRI-calculated means showed a highly significant correlation (R(2)=0.963). Coefficients of variation (CV), comparing the CV of the true distribution of control strain test results with the NRI calculated distribution, identified two types of aberrant histograms. NRI calculations on clinical isolates of Escherichia coli and Staphylococcus aureus from selected laboratories showed a good agreement between the local resistance interpretations with the NRI calculated levels. One type of deviation was most marked with cephalothin histograms for E. coli isolates where the regular zone breakpoints used cut through the population of susceptible strains. With proper markers for required quality of disc test results, the NRI method might be a valuable tool for both resistance surveillance and for quality control of the disc diffusion method.

Long-term antibiotic resistance surveillance of gram-negative pathogens suggests that temporal trends can be used as a resistance warning system.

Antibiotic resistance among Gram-negative bacteria and antibiotic consumption were investigated at the Karolinska Hospital, Stockholm, Sweden over a 12-y period. The investigation showed an increase in ciprofloxacin resistance of Escherichia coli from 0% in 1991 to 7% in 1997 and to 11% in 1999. Resistance among Pseudomonas aeruginosa isolates to ciprofloxacin increased from 2.5% in 1991 to 9.0% in 1997 and to 13% in 1999. Resistance levels for norfloxacin showed the same high statistical significance in terms of the temporal trend. A more detailed analysis showed higher resistance against norfloxacin in specific wards. Relationships between antibiotic use and antibiotic susceptibility showed different patterns. The increased ciprofloxacin resistance of E. coli and P. aeruginosa during the study period was paralleled by an increased consumption of quinolones. During the 12-y study period the total use of cephalosporins increased 2.5-fold, while the levels of E. coli resistance to cefuroxime and cefotaxime remained stable. A third pattern was seen with trimethoprim-sulfamethoxazole, namely increasing resistance of E. coli as the use of trimethoprim-sulfamethoxazole declined. The analysis of resistance levels and antibiotic consumption in the present study suggests different mechanisms for the increased resistance. The significant trend of increased resistance to antibiotics over time constitutes an important warning system.

Prophylactic intracameral cefuroxime. Efficacy in preventing endophthalmitis after cataract surgery.

PURPOSE: To evaluate the efficacy of prophylactic intracameral cefuroxime in preventing endophthalmitis in cataract surgery. SETTING: Department of Ophthalmology, St. Eriks Hospital, Stockholm, Sweden. METHODS: In a noncontrolled retrospective observational study, all cases of recorded postoperative endophthalmitis were related to the total number of uncombined cataract procedures from January 1996 to December 2000. RESULTS: Twenty cases of postoperative endophthalmitis occurred in 32180 procedures, yielding an overall rate of 0.06%. Cefuroxime-resistant organisms accounted for 12 of 13 culture-positive cases, and enterococci were the most common etiology. CONCLUSIONS: Intracameral cefuroxime 1 mg appeared to effectively inhibit sensitive bacterial strains and was associated with a low frequency of postoperative endophthalmitis. The causative organisms of future incidents of postoperative endophthalmitis will determine whether the present protocol must be reappraised.

Prophylactic intracameral cefuroxime. Evaluation of safety and kinetics in cataract surgery.

PURPOSE: To evaluate the safety and kinetics of prophylactic intracameral cefuroxime in cataract surgery. SETTING: Department of Ophthalmology, St. Eriks Hospital, Stockholm, Sweden. METHODS: In a nonrandomized observer-masked best-case trial, the visual rehabilitation and the evolution of laser flare intensity and corneal endothelial cell density after cataract surgery were assessed in 45 patients receiving intracameral cefuroxime and in 45 control patients. Immunoglobulin E-mediated sensitivity was evaluated using a skin prick test to cefuroxime in a screening program comprising all cataract patients operated on in 1997. Intracameral concentrations of cefuroxime in samples retrieved 30 seconds (n = 10) and 1 hour (n = 9) postoperatively were evaluated in an observer-masked fashion with a microbiological assay. RESULTS: Intracameral cefuroxime did not have a statistically significant effect on postoperative visual acuity, induced laser flare intensity, or endothelial cell loss compared with nonadministration of intracameral antibiotic prophylaxis. Three positive skin prick tests to cefuroxime were found in the 5813 screened cataract patients. The median aqueous humor concentration of cefuroxime at 30 seconds was 2742 mg/L, declining to 756 mg/L 1 hour after drug instillation. CONCLUSIONS: Intracameral cefuroxime 1 mg appears safe in terms of local toxicity. Immunoglobulin E-mediated allergy to cefuroxime is rare in the cataract population. The treatment achieved high aqueous concentrations even 1 hour after surgery.