Ilstrup, D M

The Plus Aerobic/F resin bottle of the BACTEC 9240 automated blood culture system (Becton Dickinson Diagnostic Instrument Systems, Sparks, Md.) was compared with aerobic culture of the Isolator system (Wampole Laboratories, Cranbury, N.J.) for the detection of bloodstream microorganisms from 6,145 blood cultures collected from adult patients with suspected septicemia. The BACTEC resin bottles were incubated for 7 days, and the sediment from the Isolator tube was inoculated to sheep blood and chocolate agars which were incubated for 72 h and to inhibitory mold, brain heart infusion, and Sabouraud agars which were incubated for 21 days. A total of 622 microorganisms were recovered from 583 blood cultures. The BACTEC resin bottle recovered statistically significantly more pathogens overall than the Isolator system (P = 0.0006). When individual pathogens isolated from either system for a 7-day study period were assessed, it was determined that the BACTEC resin bottle detected statistically significantly more isolates of Staphylococcus aureus (P = 0.0113) and coagulase-negative Staphylococcus spp. (P = 0.0029) than the Isolator system. The BACTEC resin bottle also detected statistically significantly more bloodstream infections (septic episodes) caused by coagulase-negative Staphylococcus spp. (P = 0.0146). The Isolator system recovered statistically significantly more contaminants overall (P < 0.0001), and among this group of microorganisms, recovered statistically significantly more Bacillus spp. (P < 0.0001), coagulase-negative Staphylococcus spp. (P < 0.0001), and viridans group Streptococcus spp. (P = 0.0156). The Isolator system detected statistically significantly more isolates of Histoplasma capsulatum (P = 0.004), but all of these isolates were detected at > or = 7 days of incubation of fungal plates, i.e., after the system to system comparison study period (7 days). In blood culture sets which produced growth of the same pathogen in both systems, there was a statistically significant difference in median time to detection for all pathogens combined favoring the BACTEC resin bottle over the Isolator tube (P < 0.05). When assessing individual microorganisms, the median times for detection of S. aureus, Enterococcus spp., and Pseudomonas spp. were all statistically significantly less for the BACTEC system (P < 0.05). The BACTEC instrument had 79 (1.3%) false positive signals. The BACTEC system required less processing time than the Isolator system and eliminates the hands-on time for detection of positive cultures required with the Isolator system.

The relative value of routine anaerobic blood culture for recovery of organisms and identification of episodes of bloodstream infection was assessed in a three-component, high-volume blood culture system which employs aerobic and anaerobic bottles of BacT/Alert (Organon-Teknika, Durham, N.C.) and aerobic cultures of Isolator (Wampole Laboratories, Cranbury, N.J.). The results of 5,595 blood culture sets from patients with suspected bloodstream infection were analyzed. Compared with either the aerobic BacT/Alert bottle or aerobic culture of Isolator, the BacT/Alert anaerobic bottle recovered significantly fewer isolates (242 versus 294, P < 0.05; 242 versus 298, P < 0.05) but did not detect significantly fewer episodes of bloodstream infection (141 versus 157, P > 0.05; 141 versus 147, P > 0.05). The BacT/Alert anaerobic bottle recovered significantly more isolates of obligately anaerobic bacteria (16 versus 4, P < 0.05; 16 versus 0, P < 0.05) and detected significantly more episodes of bloodstream infection caused by obligately anaerobic bacteria (10 versus 3, P < 0.05; 10 versus 0, P < 0.05) than either the aerobic bottle of BacT/Alert or the aerobic culture of Isolator. The combination of the BacT/Alert anaerobic bottle and the aerobic culture of Isolator recovered as may isolates (374 versus 377) and detected as many episodes of bloodstream infection (194 versus 191) as the combination of the aerobic bottle of BacT/Alert and the aerobic culture of Isolator, and both of these combinations identified at least 8% more isolates and detected at least 3% more bloodstream infections than the combination of the BacT/Alert aerobic and anaerobic bottles. Further analysis of the data revealed that the utility of the BacT/Alert anaerobic bottle, especially when combined with the aerobic culture of Isolator, resulted from not only enhanced recovery of obligately anaerobic bacteria but also effective recovery of facultatively anaerobic bacteria. These results demonstrate the utility of the anaerobic BacT/Alert bottle for detecting bloodstream infection caused by either facultatively anaerobic bacteria or obligately anaerobic bacteria and support the routine inclusion of anaerobic blood culture in the three-component blood culture system used in our hospital.

The ESP 80A aerobic blood culture of the ESP automated blood culture system (Difco Laboratories. Detroit, Mich.) was compared with two manual aerobic blood culture systems, the Isolator (Wampole Laboratories, Cranbury, N.J.) and the Septi-Chek (Becton Dickinson, Cockeysville, Md.) systems, for the detection of bloodstream microorganisms from 5,845 blood samples for culture collected from adult patients with suspected septicemia. The bottles were incubated for 7 days, and the sediment from the Isolator tube was inoculated onto solid medium and this medium was incubated for 72 h. A total of 609 microorganisms were recovered from 546 blood cultures. There was no statistically significant difference in the total recovery of microorganisms for the ESP 80A system when compared with that for the Septi-Chek system (P = 0.083); however, the Isolator system recovered significantly more microorganisms overall than either the ESP 80A (P < 0.001) or the Septi-Chek (P < 0.001) system. When assessing individual probable pathogens, the Isolator system detected statistically significantly more Staphylococcus aureus and Candida spp. than either the ESP 80A or the Septi-Chek system (P < 0.05). Similarly, the Isolator system detected statistically significantly more bloodstream infections (septic episodes) caused by S. aureus and Candida spp. than either the ESP 80A or the Septi-Chek system (P < 0.05). In blood culture sets which produced growth of the same probable pathogens in the ESP 80A and the Isolator systems, there was no statistically significant difference in the median times to detection for all pathogens combined (P = 0.067). However, a similar comparison showed the Isolator and the ESP 80A systems to have statistically significantly shorter median detection times for all pathogens combined (P < 0.001) when they were independently compared with the Septi-Chek system. The ESP 80A system had 29 (0.5%) false-positive signals. The ESP system required less processing time than the Isolator system and eliminates the hands-on time for the detection of positive cultures required by the manual systems.

The performance characteristics of the Isolator (Wampole Laboratories, Cranbury, N.J.) and the BacT/Alert (Organon Teknika Corporation, Durham, N.C.) aerobic blood culture systems were compared for 6,009 blood culture sets obtained from patients with suspected bloodstream infections. The BacT/Alert aerobic bottle [BTA(O2)] was continuously agitated while it was incubated in 5% CO2 at 36 degrees C; culture plates prepared from the Isolator tube [I(O2)] were incubated in 5% CO2 at 37 degrees C. From 394 blood cultures, 416 clinically significant isolates of bacteria and yeasts were recovered. The overall yields for BTA(O2) and I(O2) were not significantly different (319 versus 336; P = 0.20). I(O2) recovered significantly more staphylococcus (P < 0.05) and yeast isolates (P < 0.01). BTA(O2) recovered significantly more aerobic and facultatively anaerobic gram-negative bacilli (P < 0.05). In blood culture sets which produced growth of the same organisms in both the BTA(O2) and I(O2) systems, the BTA(O2) system detected growth sooner, but more rapid identification was possible with the I(O2) system by virtue of earlier isolation of colonies on solid media.

Cytomegalovirus (CMV) viremia is a widely used laboratory marker of CMV disease following transplantation and is additionally used to trigger preemptive antiviral therapy. Despite this, the optimal method for diagnosing CMV viremia in transplantation recipients remains unknown. To determine the sampling frequency and blood volume required for the optimal diagnosis of viremia by shell vial assay, a prospective study of 46 viremic transplantation recipients was conducted. Blood specimens (2.5 and 5 ml) were collected twice, 3 h apart, at a median of 1.4 days (range, 1 to 3 days) after the triggering shell vial-positive blood had been collected. Considering a single 2.5-ml specimen, an average of only 40% of previously viremic patients had documented CMV in their blood: this increased to 50% when a second 2.5-ml sample of blood was collected 3 h later. The yields of two 2.5-ml versus two 5-ml samples were 50 versus 61%, respectively. Viremia as detected by shell vial assay is intermittent, and increasing the frequency and volume of blood sampling increases its diagnosis. These results have implications in diagnosis of CMV infection and its preemptive therapy.

The effect of age of MRC-5 cell monolayers in shell vials on the detection of cytomegalovirus (CMV) from urine was evaluated. When the AD169 strain of CMV was used, 8-day-old monolayers had a higher mean count of fluorescent foci than 15-day-old monolayers did (5.78 versus 2.86) (P less than 0.02) and were more frequently positive (21 of 23 shell vials versus 14 of 22 shell vials) (P less than 0.04). Commercial shell vials used for clinical specimens were evaluated in groups of 8- to 11-, 12- to 15-, and 8- to 15-day-old monolayers. When compared with laboratory-prepared shell vials ranging in age from 3 to 9 days, commercial shell vials had a lower number of fluorescent foci in all groups (P less than 0.03, P less than 0.0001, and P less than 0.0001, respectively), the 12- to 15- and 8- to 15-day-old groups were less frequently positive (P less than or equal to 0.02 and P less than 0.02, respectively), and all three groups were more susceptible to the toxic effects of urine (P less than 0.0001, P less than 0.01, and P less than 0.0001, respectively). For all 191 specimens cultured (8- to 15-day-old group), one or both monolayers were destroyed in 60 (31.4%) specimens compared with 9 (4.7%) specimens toxic to laboratory-prepared shell vials (P less than 0.0001). Both the decreased sensitivity of older MRC-5 cells and the increased sensitivity to the toxic effects of urine made commercial shell vial less sensitive than laboratory-prepared shell vials for the detection of CMV.

Urine specimens submitted for the diagnosis of cytomegalovirus infection were inoculated into shell vials that had been pretreated with a combination of dimethyl sulfoxide (DMSO) and dexamethasone (DEX). The results were compared with those for inoculated shell vials which had received no drug treatment. Of 664 specimens, 100 (15%) were positive for cytomegalovirus. Of the 100 strains of cytomegalovirus, 88 (88%) were detected in both DMSO-DEX-treated and untreated shell vials. Of the remaining 12 positive specimens, 6 were detected with untreated shell vials exclusively and 6 were detected with DMSO-DEX-treated shell vials alone (not significant by the sign test). The median number of fluorescent foci was not significantly higher in DMSO-DEX-treated shell vials compared with that in untreated cultures (Wilcoxon signed-rank test; P = 0.1). DMSO-DEX-treated monolayers did not enhance the sensitivity detection of cytomegalovirus in shell vial cell cultures.

Specimens submitted for the diagnosis of cytomegalovirus (CMV) infection were inoculated into three (blood) or two (urine, tissue, bronchoalveolar lavage [BAL]) shell vials seeded with MRC-5 cells for the diagnosis of CMV infection. We evaluated the detection of 993 specimens that were positive for CMV according to the number of shell vial cell cultures inoculated per specimen. For blood cultures, and considering one CMV-positive shell vial as 100%, inoculation of three shell vials versus one increased the detection rate of the virus by 51%. Inoculation of three shell vials compared with two yielded a 20% increase in the detection rate of CMV. For urine, tissue, and BAL specimens, inoculation of two shell vials compared with one resulted in increases of 7, 10, and 5%, respectively. For maximum detection of CMV in shell vial cell cultures, at least three vials should be inoculated with blood specimens, and two vials should be used for urine, tissue, and BAL samples.

Statistical methodology is viewed by the average laboratory scientist, or physician, sometimes with fear and trepidation, occasionally with loathing, and seldom with fondness. Statistics may never be loved by the medical community, but it does not have to be hated by them. It is true that statistical science is sometimes highly mathematical, always philosophical, and occasionally obtuse, but for the majority of medical studies it can be made palatable. The goal of this article has been to outline a finite set of methods of analysis that investigators should choose based on the nature of the variable being studied and the design of the experiment. The reader is encouraged to seek the advice of a professional statistician when there is any doubt about the appropriate method of analysis. A statistician can also help the investigator with problems that have nothing to do with statistical tests, such as quality control, choice of response variable and comparison groups, randomization, and blinding of assessment of response variables.