Impact of Automated Blood Culture Systems on the Management of Bloodstream Infections: Results from a Crossover Diagnostic Clinical Trial

Bloodstream infections are associated with high rates of morbidity and mortality. Blood culture remains the gold standard for the diagnosis of BSIs. We report a prospective crossover diagnostic clinical trial comparing the performances of two blood culture incubation systems: Virtuo and Bactec FX. The primary outcome was the time to detection (TTD) (from the loading of the sample into the incubator to the positivity signal). Patients over 16 years old suspected of having bacteremia/fungemia were included. They were divided into two strata with a total of 9,957 blood extractions. Initially, each stratum was randomly assigned to one of the incubators and then alternated every 2 weeks for 6 months. Each sample was inoculated into an aerobic bottle and an anaerobic bottle. All bottles were processed equally according to the laboratory's standard procedures after they were flagged positive. We analyzed 4,797 samples in the Virtuo system and 5,160 in the Bactec FX system. The median TTD was significantly lower for the Virtuo group (Virtuo, 15.2 h; Bactec FX, 16.3 h [P < 0.0001]). The turnaround time (TAT) (from sample loading to the Gram stain report) was also reduced with Virtuo (Virtuo, 26.2 h; Bactec FX, 28.3 h [P < 0.004]). When considering only samples from patients with antimicrobial treatment prior to blood culture extraction, the TTD was shorter for Virtuo (median differences in the TTD of 4.5 h for all bottles and 8.7 h for aerobic bottles only [P = 0.0001]). In conclusion, virtuo provided shorter TTD and TAT than Bactec FX. The difference in the median TTD was increased when considering samples incubated in aerobic bottles from patients with antimicrobial treatment. This could have an important effect on the faster diagnosis of BSIs. IMPORTANCE Bloodstream infections are associated with high rates of morbidity and mortality. Blood culture remains the gold standard for its diagnosis. While the identification of the pathogen and its antibiotic susceptibility is required to confirm the optimal antimicrobial regimen, reductions in the times to the detection of positivity and reporting of Gram stain results may be important and time-saving to reduce inappropriate antimicrobial use, improve patient outcomes, and decrease health care costs. We report the first clinical diagnostic study of this scale in a "real-world" setting with a crossover design, comparing two automatic blood culture incubators using samples from patients with a suspected diagnosis of bacteremia/sepsis, as opposed to spiked vials. Our study design mimics that of clinical trials performed for drug marketing authorization, but patient randomization was replaced with the crossover design. A shorter time to detection could have an important effect on the faster identification of causative microorganisms of BSIs and antimicrobial stewardship.

A field experiment characterizing variable detection rates during plant surveys

Surveys aimed at finding threatened and invasive species can be challenging due to individual rarity and low and variable individual detection rates. Detection rate in plant surveys typically varies due to differences among observers, among the individual plants being surveyed (targets), and across background environments. Interactions among these 3 components may occur but are rarely estimated due to limited replication and control during data collection. We conducted an experiment to investigate sources of variation in detection of 2 Pilosella species that are invasive and sparsely distributed in the Alpine National Park, Australia. These species are superficially similar in appearance to other yellow-flowered plants occurring in this landscape. We controlled the presence and color of flowers on target Pilosella plants and controlled their placement in plots, which were selected for their variation in cover of non-target yellow flowers and dominant vegetation type. Observers mimicked Pilosella surveys in the plots and reported 1 categorical and 4 quantitative indicators of their survey experience level. We applied survival analysis to detection data to model the influence of both controlled and uncontrolled variables on detection rate. Orange- and yellow-flowering Pilosella in grass- and heath-dominated vegetation were detected at a higher rate than nonflowering Pilosella. However, this detection gain diminished as the cover of other co-occurring yellow-flowering species increased. Recent experience with Pilosella surveys improved detection rate. Detection experiments are a direct and accessible means of understanding detection processes and interpreting survey data for threatened and invasive species. Our detection findings have been used for survey planning and can inform progress toward eradication. Interaction of target and background characteristics determined detection rate, which enhanced predictions in the Pilosella eradication program and demonstrated the difficulty of transferring detection findings into untested environments.

Comparative evaluation of BACTEC FX, BacT/ALERT 3D, and BacT/ALERT VIRTUO automated blood culture systems using simulated blood cultures

BACKGROUND

To evaluate the performance of BACTEC FX, BacT/ALERT 3D, and VIRTUO systems using simulated blood culture (BC).

METHODS

Two experimental designs based on 'with' or 'without' added trough antibiotic concentrations in bottles were implemented.

RESULTS

For the experiment A, A shorter time to detection (TTD) was observed for most of organisms (17/22) in VIRTUO system. VIRTUO system was also faster than 3D and FX systems no matter in aerobic and anaerobic bottles. The anaerobic bottles had faster detection than aerobic bottles in 3D system (13.68 h vs 15.36 h, P < 0.001) and VIRTUO system (10.30 h vs 12.46 h, P = 0.001) but not in FX system (P = 0.38). When antibiotics were present, the bacterial recovery rate (RR) of FX, 3D and VIRTUO systems were 64.10% (50/78), 58.97% (46/78) and 43.59% (34/78), respectively (P = 0.027). the bacterial RR of various bottles were as follows: BPA vs. FA vs. SA [84.44%(38/45) vs. 55.56%(25/45) vs. 42.22(19/45), P < 0.001]; BFN vs. FN vs. SN [36.36%(12/33) vs. 63.64%(21/33) vs.45.45%(15/33), P = 0.078].

CONCLUSIONS

The VIRTUO system allowed faster growth detection for most of organisms compared with FX and 3D systems. When antibiotics were present, the bottles containing antibiotic-binding agent showed better bacterial RR, especially in BACTEC Plus Aerobic/F bottles.

Measuring Timeliness of Outbreak Response in the World Health Organization African Region, 2017-2019

Large-scale protracted outbreaks can be prevented through early detection, notification, and rapid control. We assessed trends in timeliness of detecting and responding to outbreaks in the African Region reported to the World Health Organization during 2017–2019. We computed the median time to each outbreak milestone and assessed the rates of change over time using univariable and multivariable Cox proportional hazard regression analyses. We selected 296 outbreaks from 348 public reported health events and evaluated 184 for time to detection, 232 for time to notification, and 201 for time to end. Time to detection and end decreased over time, whereas time to notification increased. Multiple factors can account for these findings, including scaling up support to member states after the World Health Organization established its Health Emergencies Programme and support given to countries from donors and partners to strengthen their core capacities for meeting International Health Regulations.

Comparative Growth Inhibition of Bread Spoilage Fungi by Different Preservative Concentrations Using a Rapid Turbidimetric Assay System

Bread and intermediate moisture bakery products are mainly spoiled by yeasts and filamentous fungi. The inoculum load and preservation system used determines their shelf life. To extend the shelf life of such commodities, the use of chemical preservatives is the most common way to try and control the initiation of mold spoilage of bread. This study has utilized a rapid turbidimetric assay system (Bioscreen C) to examine the temporal efficacy of calcium propionate (CP) and potassium sorbate (PS) for controlling the growth of important bread spoilage fungi. The objectives were to compare the temporal growth of strains of three important spoilage fungi Hyphopichia burtonii (HB17), Paecilomyces variotii (PV11), and Penicillium roqueforti (PR06) isolated from visibly molded bread to (a) different concentrations of CP and PS (0-128 mM), (b) temperatures (25°C, 30°C), (c) water activity (a_w; 0.95, 0.97), and (d) pH (5.0, 5.5). All three abiotic factors, pH, a_w, and temperature, and preservative concentrations influenced the relative growth of the species examined. In general, PS was more effective than CP in inhibiting the growth of the strains of these three species. In addition, the Time to Detection (TTD) for the efficacy of the preservatives under the interacting abiotic factors was compared. The strain of Paecilomyces variotii (PV10) was the most tolerant to the preservatives, with the shortest TTD values for both preservatives. P. roqueforti was the most sensitive with the longest TTD values under all conditions examined. These results are discussed in the context of the evolution of resistance to food-grade preservatives by such spoilage fungi in bakery products.

Factors related to residual gallbladder calculi formation using computed tomography and magnetic resonance imaging combined with clinical data

Objective

We aimed to investigate risk factors related to remnant gallbladder (RGB) stones.

Methods

This retrospective study included 73 patients with RGB, in groups with and without RGB calculi. Univariate analyses were used to identify nine variables associated with RGB calculi: sex, age, body mass index (BMI), time to detection, surgical method, length of RGB, angle of RGB and common hepatic duct (CHD), choledocholithiasis, and remnant cholecystitis. Multivariate logistic regression was performed to assess independent predictors of RGB stones. A receiver operating characteristic (ROC) curve was used to estimate model accuracy and determine cut-off values of independent predictors.

Results

We enrolled 73 patients, 33 with and 40 without RGB stones. Univariate analyses showed that age, BMI, time to detection, length of RGB, angle of RGB and CHD were predictors for RGB calculi. Multivariate analyses indicated that time to detection, length of RGB, and angle of RGB and CHD were independent predictors for RGB calculi. The area under the ROC curve of the model was 0.940. Cut-off values of the three indicators were 1.5 years, 2.25 cm, and 22.5°, respectively.

Conclusion

Time to detection, length of RGB, and angle of RGB and CHD were independent predictors of RGB calculi.

Current detection rates and time-to-detection of all identifiable BRCA carriers in the Greater London population

BACKGROUND

BRCA carrier identification offers opportunities for early diagnoses, targeted treatment and cancer prevention. We evaluate BRCA- carrier detection rates in general and Ashkenazi Jewish (AJ) populations across Greater London and estimate time-to-detection of all identifiable BRCA carriers.

METHODS

BRCA carrier data from 1993 to 2014 were obtained from National Health Service genetic laboratories and compared with modelled predictions of BRCA prevalence from published literature and geographical data from UK Office for National Statistics. Proportion of BRCA carriers identified was estimated. Prediction models were developed to fit BRCA detection rate data. BRCA carrier identification rates were evaluated for an 'Angelina Jolie effect'. Maps for four Greater London regions were constructed, and their relative BRCA detection rates were compared. Models developed were used to predict future time-to-identify all detectable BRCA carriers in AJ and general populations.

RESULTS

Until 2014, only 2.6% (3072/111 742 estimated) general population and 10.9% (548/4985 estimated) AJ population BRCA carriers have been identified in 16 696 608 (AJ=190 997) Greater London population. 57% general population and 54% AJ mutations were identified through cascade testing. Current detection rates mirror linear fit rather than parabolic model and will not identify all BRCA carriers. Addition of unselected ovarian/triple-negative breast cancer testing would take >250 years to identify all BRCA carriers. Doubling current detection rates can identify all 'detectable' BRCA carriers in the general population by year 2181, while parabolic and triple linear rates can identify 'detectable' BRCA carriers by 2084 and 2093, respectively. The linear fit model can identify 'detectable' AJ carriers by 2044. We did not find an Angelina Jolie effect on BRCA carrier detection rates. There was a significant difference in BRCA detection rates between geographical regions over time (P<0.001).

CONCLUSIONS

The majority of BRCA carriers have not been identified, missing key opportunities for prevention/earlier diagnosis. Enhanced and new strategies/approaches are needed.

Modeling for Predicting the Time to Detection of Staphylococcal Enterotoxin A in Cooked Chicken Product

Staphylococcal enterotoxins (SEs) produced by Staphylococcus aureus (S. aureus) are the cause of Saphylococcal food poisoning (SFP) outbreaks. Thus, estimation of the time to detection (TTD) of SEs, that is, the time required to reach the SEs detection limit, is essential for food preservation and quantitative risk assessment. This study was conducted to explore an appropriate method to predict the TTD of SEs in cooked chicken product under variable environmental conditions. An S. aureus strain that produces staphylococcal enterotoxin A (SEA) was inoculated into cooked chicken meat. Initial inoculating concentrations (approximately 102, 103, 104 CFU/g) of S. aureus and incubation temperatures (15 ± 1, 22 ± 1, 29 ± 1, and 36 ± 1°C) were chosen as environmental variables. The counting of S. aureus colonies and the detection of SEA were performed every 3 or 6 h during the incubation. The TTD of SEA was considered a response of S. aureus to environmental variables. Linear polynomial regression was used to model the effects of environmental variables on the TTD of SEA. Result showed that the correlation coefficient (R2) of the regressed equation is higher than 0.98, which means the obtained equation was reliable. Moreover, the minimum concentration of S. aureus for producing a detectable amount of SEA under various environmental conditions was approximately 6.32 log CFU/g, which was considered the threshold for S. aureus to produce SEA. Hence, the TTD of SEA could be obtained by calculating the time required to reach the threshold by using an established S. aureus growth predictive model. Both established methods were validated through internal and external validation. The results of graphical comparison, RMSE, SEP, Af , and Bf showed that the accuracy of both methods were acceptable, and linear polynomial regression method showed more accurately.

Implementation of the new VIRTUO blood culture system: evaluation and comparison to the 3D system using simulated blood cultures

PURPOSE

To evaluate the performances of the newly approved BacT/ALERT VIRTUO blood culture system for the recovery of bloodstream pathogens and compare it to the BacT/ALERT 3D system.

METHODS

Simulated blood cultures of eight clinically relevant microorganisms were used: Bacteroides fragilis (ATCC 25285), Escherichia coli (ATCC 25922), Haemophilus influenzae (ATCC 49247), Pseudomonas aeruginosa (ATCC 27853), Enterococcus faecalis (ATCC 29212), Staphylococcus aureus (ATCC 29213), Streptococcus pneumoniae (ATCC 49619) and Candida krusei (ATCC 6258). Criteria for comparison were culture positivity and time to detection (TTD). The effects of delayed entry on recovery and TTD were also evaluated.

RESULTS

The VIRTUO exhibited around 3 h faster detection time compared to the 3D system. (p < 0.01) for aerobic and facultative microorganisms. The difference in TTD was greatest for the B. fragilis, with a median difference of 46.67 h. The anaerobic bottle of the VIRTUO (FN Plus) did not support the growth of obligate aerobes, whereas the 3D did so. Delayed entry (studied with an E. Coli isolate) had no effect on the recovery rate but proportionally reduced TTD.

CONCLUSIONS

The VIRTUO performed better than the 3D in terms of TTD and hands-on-time. FN Plus vial appears to be more efficient than the SN bottle in the recovery of anaerobes.

Interplay between Mutations and Efflux in Drug Resistant Clinical Isolates of Mycobacterium tuberculosis

Numerous studies show efflux as a universal bacterial mechanism contributing to antibiotic resistance and also that the activity of the antibiotics subject to efflux can be enhanced by the combined use of efflux inhibitors. Nevertheless, the contribution of efflux to the overall drug resistance levels of clinical isolates of Mycobacterium tuberculosis is poorly understood and still is ignored by many. Here, we evaluated the contribution of drug efflux plus target-gene mutations to the drug resistance levels in clinical isolates of M. tuberculosis. A panel of 17 M. tuberculosis clinical strains were characterized for drug resistance associated mutations and antibiotic profiles in the presence and absence of efflux inhibitors. The correlation between the effect of the efflux inhibitors and the resistance levels was assessed by quantitative drug susceptibility testing. The bacterial growth/survival vs. growth inhibition was analyzed through the comparison between the time of growth in the presence and absence of an inhibitor. For the same mutation conferring antibiotic resistance, different MICs were observed and the different resistance levels found could be reduced by efflux inhibitors. Although susceptibility was not restored, the results demonstrate the existence of a broad-spectrum synergistic interaction between antibiotics and efflux inhibitors. The existence of efflux activity was confirmed by real-time fluorometry. Moreover, the efflux pump genes mmr, mmpL7, Rv1258c, p55, and efpA were shown to be overexpressed in the presence of antibiotics, demonstrating the contribution of these efflux pumps to the overall resistance phenotype of the M. tuberculosis clinical isolates studied, independently of the genotype of the strains. These results showed that the drug resistance levels of multi- and extensively-drug resistant M. tuberculosis clinical strains are a combination between drug efflux and the presence of target-gene mutations, a reality that is often disregarded by the tuberculosis specialists in favor of the almost undisputed importance of antibiotic target-gene mutations for the resistance in M. tuberculosis.

Incorporating detectability of threatened species into environmental impact assessment

Environmental impact assessment (EIA) is a key mechanism for protecting threatened plant and animal species. Many species are not perfectly detectable and, even when present, may remain undetected during EIA surveys, increasing the risk of site-level loss or extinction of species. Numerous methods now exist for estimating detectability of plants and animals. Despite this, regulations concerning survey protocol and effort during EIAs fail to adequately address issues of detectability. Probability of detection is intrinsically linked to survey effort; thus, minimum survey effort requirements are a useful way to address the risks of false absences. We utilized 2 methods for determining appropriate survey effort requirements during EIA surveys. One method determined the survey effort required to achieve a probability of detection of 0.95 when the species is present. The second method estimated the survey effort required to either detect the species or reduce the probability of presence to 0.05. We applied these methods to Pimelea spinscens subsp. spinescens, a critically endangered grassland plant species in Melbourne, Australia. We detected P. spinescens in only half of the surveys undertaken at sites where it was known to exist. Estimates of the survey effort required to detect the species or demonstrate its absence with any confidence were much higher than the effort traditionally invested in EIA surveys for this species. We argue that minimum survey requirements be established for all species listed under threatened species legislation and hope that our findings will provide an impetus for collecting, compiling, and synthesizing quantitative detectability estimates for a broad range of plant and animal species.

Microbial growth parameters obtained from the analysis of time to detection data using a novel rearrangement of the Baranyi-Roberts model

AIMS

To explore the predictions of a novel rearrangement of the Baranyi-Roberts model (BRM) with time to detection data obtained from optical density data of microbial growth.

METHODS AND RESULTS

Growth of Escherichia coli and Salmonella Typhimurium under mild conditions of temperature (25-37°C), salt (0·086, 0·51 and 1·03 mol l(-1)) and pH (6·85-4·5) was examined using optical density. Time to detection (TTD) data were fitted to a model based on a rearrangement of the BRM. Observations showed compatibility with standard viable count studies and produced highly accurate specific growth rates and lag phase durations. At high salt and low pH, however, there was a substantial dependency on the initial inoculum for the observation of visible growth. At 30 and 37°C, with 1·03 mol l(-1) salt, and at pH <5·75, no visible growth was recorded for E. coli at initial inoculum levels below 10(7) CFU ml(-1).

CONCLUSIONS

The rearranged BRM can be used directly with TTD data obtained from optical density measurements.

SIGNIFICANCE AND IMPACT OF THE STUDY

A distinct advantage of the rearranged model is that it allows for a very simple interpretation of easily obtainable data using standard nonlinear regression. The rearranged model gives to TTD data the same modelling capability that the BRM gives to plate count data.

Optimum Time to Detection of Bacteria and Yeast Species with BACTEC 9120 Culture System from Blood and Sterile Body Fluids

The culture results of 4,807 blood and 383 sterile body fluid specimens received in our laboratory during a 54-month period, were analyzed to determine the time required for culture to become positive, time at which a culture could safely be considered negative, and the spectrum of isolated organisms. The specimens were processed by automated BACTEC 9120 culture system. A total of 1,677 clinically significant microorganisms were isolated. Gram positive and negative bacterial isolation rates were found to be 62.55% and 32.20%, respectively. Yeasts were recovered in 5.24%. False positivity rate was 1.5%. Clinically significant isolates recovered on day four and five were 97.81% and 99.88%, respectively. At day five, the sensitivity was 99.94% and negative predictive value 99.96%. Our data support a five-day incubation protocol for recovery of all clinically significant organisms with sensitivity reduced by 0.06%, when compared with a six-day protocol.

Time to detection of Mycobacterium tuberculosis as an alternative to quantitative cultures

Testing new drugs is critical to improving the treatment of tuberculosis. Quantitative cultures of Mycobacterium tuberculosis on solid media have been used in Phase 1 and 2 trials, but are time and resource intensive. Time to detection (TTD) of growth of M. tuberculosis in automated liquid culture systems is an alternative. TTD has been shown to correlate with CFU in quantitative cultures, and is faster and simpler to perform. We compared TTD in the BACTEC 460 liquid culture system with CFU in a clinical trial that included 110 subjects. Comparing all sputum cultures collected between baseline and 2 months we found a strong negative correlation between log(10) CFU and TTD (rho = -0.91). In addition, when TTD at baseline was compared with 1 and 2 month sputum culture positivity, subjects whose cultures were negative after 1 and 2 months had a significantly longer median baseline TTD compared with subjects whose cultures were positive at 1 and 2 months (5 vs. 3 days and 3 vs. 2 days, respectively). TTD compares closely with CFU and represents a faster, simpler alternative to quantitative cultures.