Blood culture contamination in Tanzania, Malawi, and the United States: a microbiological tale of three cities

We conducted retrospective, comparative analyses of contamination rates for cultures of blood obtained in the emergency rooms of Muhimbili National Hospital (MNH) in Dar es Salaam, Tanzania; Lilongwe Central Hospital (LCH) in central Malawi; and the Duke University Medical Center (DUMC) in the United States. None of the emergency room patients had indwelling intravascular devices at the time that the blood samples for cultures were obtained. In addition, we reviewed the contamination rates for a cohort of patients already hospitalized in the DUMC inpatient medical service, most of whom had indwelling intravascular devices. The bloodstream infection rates among the patients at MNH (n = 513) and LCH (n = 486) were similar (~28%); the contamination rates at the two hospitals were 1.3% (7/513) and 0.8% (4/486), respectively. Of 54 microorganisms isolated from cultures of blood collected in the DUMC emergency room, 26 (48%) were identified as skin contaminants. Cultures of blood collected in the DUMC emergency room were significantly more likely to yield growth of contaminants than the cultures of blood collected in the emergency rooms at MNH and LCH combined (26/332 versus 11/1,003; P < 0.0001) or collected in the DUMC inpatient medical service (26/332 versus 7/283; P < 0.01). For the MNH and LCH blood cultures, lower contamination rates were observed when skin was disinfected with isopropyl alcohol plus tincture of iodine rather than isopropyl alcohol plus povidone-iodine. In conclusion, blood culture contamination was minimized in sub-Saharan African hospitals with substantially limited resources through scrupulous attention to aseptic skin cleansing and improved venipuncture techniques. Application of these principles when blood samples for culture are obtained in U.S. hospital emergency rooms should help mitigate blood culture contamination rates and the unnecessary microbiology workup of skin contaminants.     

Comparison of four antiseptic preparations for skin in the prevention of contamination of percutaneously drawn blood cultures: a randomized trial

A number of skin antiseptics have been used to prevent the contamination of blood cultures, but the comparative efficacies of these agents have not been extensively evaluated. We therefore sought to compare the efficacy of four skin antiseptics in preventing blood culture contamination in a randomized, crossover, investigator-blinded study conducted in an emergency department and the inpatient wards of a university hospital. The patient group included all patients from whom blood samples were obtained percutaneously for culture. Skin antisepsis was performed with 10% povidone-iodine, 70% isopropyl alcohol, tincture of iodine, or povidone-iodine with 70% ethyl alcohol (i.e., Persist). The blood culture contamination rate associated with each antiseptic was then determined. A total of 333 (2.62%) of 12,692 blood cultures were contaminated during the study period compared to 413 (3.21%) of 12,859 blood cultures obtained during the previous 12-month period (relative risk = 0.82; 95% confidence interval, 0.71 to 0.94; P = 0.006). During the study, the contamination rates were determined to be 2.93% with povidone-iodine, 2.58% with tincture of iodine, 2.50% with isopropyl alcohol, and 2.46% with Persist (P = 0.62). We detected no significant differences in the blood culture contamination rates among these four antiseptics, although there was some evidence suggesting greater efficacy among the alcohol-containing antiseptics. Among the evaluated antiseptics, isopropyl alcohol may be the optimal antiseptic for use prior to obtaining blood for culture, given its convenience, low cost, and tolerability.     

Effect of the Initial Specimen Diversion Technique on Blood Culture Contamination Rates

The initial specimen diversion technique (ISDT) was first described by Patton and Schmitt (J. Clin. Microbiol. 48:4501–4503, 2010, doi:10.1128/JCM.00910-10). This study looked at the effect of implementation of the ISDT on blood culture contamination rates at our center. We found a reduction of 30.34% in potential blood culture contaminants.     

A recommendation to perform a blood culture before the administration of intravenous antibiotics increased the detection of Staphylococcus aureus bacteremia

In 2004, the Surviving Sepsis Campaign was launched to increase awareness and improve the outcome of severe sepsis. Accordingly, in Jönköping County, Sweden, a strong recommendation to perform a blood culture before the start of intravenous antibiotic treatment was introduced in 2007. Moreover, a reminder was included in the laboratory report to consult an infectious disease specialist when Staphylococcus aureus was isolated from a blood culture. Retrospectively, patients with at least one blood culture growing S. aureus during 2002 through 2003 (pre intervention n?=?58) or during 2008 through 2009 (post intervention n?=?100) were included. Medical records were evaluated regarding clinical data and outcome. Blood culture isolates were characterized by antibiotic susceptibility testing (AST) and S. aureus protein A (spa) gene typing. The annual incidence of S. aureus bacteremia (SAB) increased from 28 per 100,000 inhabitants at the pre intervention period to 45 per 100,000 at the post intervention period (p?=?0.046). During post intervention, the SAB incidence was significantly higher in men (p?=?0.009). The mortality rate during hospital stay was 14 % during pre intervention and 18 % during post intervention (p?=?0.47). The most common spa types were t012 and t084. The Surviving Sepsis Campaign resulted in an increased number of detected cases of SAB. The mortality rate was the same before and after the intervention, and no spa type correlated to certain clinical manifestations or mortality.     

The threat of persistent bacteria and fungi contamination in tuberculosis sputum cultures

BackgroundTuberculosis (TB) sputum culture contaminants make it difficult to obtain pure TB isolates.We aimed to study and identify persistent TB sputum culture contaminants post the standard laboratory pre-culture sample decontamination techniques.MethodsThis was a longitudinal study of TB sputum culture contamination for a cohort of TB patients on standard treatment at: baseline, during TB treatment and post TB treatment. Sputum samples were decontaminated with 1.5%NaOH and neutralized using 6.8 Phosphate buffer solution.Sputum was then inoculated into MGIT (mycobactrial growth indicator tube) supplemented with 0.8ml PANTA. A drop of each positive MGIT culture was sub cultured onto blood agar and incubated for 48 hours at 35 -37OC.Any growth was identified using growth characteristics and colony morphology.ResultsFrom October 2017 through May 2019;we collected 8645 sputum samples of which 8624(99.8%) were eligible and inoculated into MGIT where 2444(28.3%)samples were TB culture positive and 255(10.4%)were positive for contaminants: 237 none-tuberculosis bacteria, 12 fungi and 6 mixed(none-tuberculous bacteria+fungi). There was no statistically significant difference between none tuberculosis bacteria and fungi in the treatment (OR=1.4,95%CI:0.26–7.47,p=0.690) and the post treatment TB phases(OR=2.02,95%CI:0.38–10.79,p=0.411)Vs baseline.ConclusionNone-tuberculous bacteria and fungi dominate the plethora of TB sputum culture contamination and persist beyond the standard laboratory pre-culture decontamination algorithm.     

Reducing blood culture contamination by a simple informational intervention

Compared to truly negative cultures, false-positive blood cultures not only increase laboratory work but also prolong lengths of patient stay and use of broad-spectrum antibiotics, both of which are likely to increase antibiotic resistance and patient morbidity. The increased patient suffering and surplus costs caused by blood culture contamination motivate substantial measures to decrease the rate of contamination, including the use of dedicated phlebotomy teams. The present study evaluated the effect of a simple informational intervention aimed at reducing blood culture contamination at Skåne University Hospital (SUS), Malmö, Sweden, during 3.5 months, focusing on departments collecting many blood cultures. The main examined outcomes of the study were pre- and postintervention contamination rates, analyzed with a multivariate logistic regression model adjusting for relevant determinants of contamination. A total of 51,264 blood culture sets were drawn from 14,826 patients during the study period (January 2006 to December 2009). The blood culture contamination rate preintervention was 2.59% and decreased to 2.23% postintervention (odds ratio, 0.86; 95% confidence interval, 0.76 to 0.98). A similar decrease in relevant bacterial isolates was not found postintervention. Contamination rates at three auxiliary hospitals did not decrease during the same period. The effect of the intervention on phlebotomists'' knowledge of blood culture routines was also evaluated, with a clear increase in level of knowledge among interviewed phlebotomists postintervention. The present study shows that a relatively simple informational intervention can have significant effects on the level of contaminated blood cultures, even in a setting with low rates of contamination where nurses and auxiliary nurses conduct phlebotomies.Blood cultures are commonly contaminated, with contaminated cultures representing as many as 50% of positive cultures (1). Compared to truly negative cultures, false-positive (contaminated) blood cultures not only increase laboratory work but also prolong lengths of patient stay and increase the use of broad-spectrum antibiotics, with negative consequences for antibiotic resistance and patient morbidity. Furthermore, false-positive results can cause confusion regarding antibiotic regimens, endangering patient safety (2, 5, 16).The dominating organism in blood culture contamination, coagulase-negative staphylococcus (CoNS), is also an increasingly important pathogen, which is a significant clinical problem because there is no true “gold standard” for determining contamination from relevant pathogens (1, 8, 13, 22). Although not applicable for clinical use for individual patients, a laboratory assessment definition of contamination for comparison of rates between institutions has been developed. Target rates should not exceed 3% (7), but many teaching hospitals have contamination rates exceeding 6% or more (2, 17, 21).Considering the potential savings in resource utilization, it is justified to invest considerable resources in reducing blood culture contamination (24). Since contamination most probably is a result of personnel introducing exogenous bacteria into the blood culture, education of phlebotomists is central to prevention. Many studies advocate the effectiveness of teams of specialized phlebotomists in reducing contamination rates (5, 18, 21). Feedback, intense education in correct phlebotomy routines, and long-term monitoring programs have also been shown to be effective (3, 4, 6, 10). In general, interventions seem less effective and contamination rates higher among nursing personnel conducting phlebotomy than those for specialized phlebotomy teams (5, 6, 15, 18, 21).In addition to presenting internationally comparable rates of blood culture contamination from a Swedish university hospital, the present study evaluates the effect of a simple informational intervention aimed at reducing blood culture contamination in a setting where phlebotomy for blood culture is conducted by nurses and auxiliary nurses, not by dedicated phlebotomy teams. The major examined outcome of the study was the effect of intervention on blood culture contamination rates. We also monitored the effect in a novel way, by assessing the impact of the intervention on phlebotomists'' knowledge of disinfection and phlebotomy routines.     

Bone marrow T cell colony-forming cells: studies of their origin and use in monitoring T cell-depleted bone marrow grafts.

Peripheral blood T cell colony forming cells (T-CFC) are mature T cells. When blood was fractionated into sheep red blood cell receptor positive (E+) and negative (E-) fractions, T cell colony growth was largely restricted to the E+ population. When bone marrow was similarly fractionated, many colonies grew from the E- cells but myeloid colonies also grew making interpretation of colony numbers difficult. We have, therefore, also assessed T cell proliferation during culture as an expansion index (EI) by determining the absolute number of T cells pre and post culture. This data shows that T cell expansion is on average nine times greater in the E- marrow fraction than in the E+ fraction. Studies are presented suggesting that this is because marrow E- cells contain appropriate accessory cells and that high numbers of T cells inhibit T cell growth. The cells giving rise to bone marrow T cell colonies thus appear to be contaminating mature T cells rather than pre-thymic progenitor cells. We have measured T cell expansion in culture as a sensitive assay of T cell contamination following procedures to remove T cells from bone marrow grafts for the prevention of graft versus host disease (GVHD).     

Blood Culture Contamination: Still Hazy After All These Years

Despite the availability of a few methods for direct pathogen detection from whole blood, a blood culture is still the main method for diagnosing bloodstream infections. Detection of organisms in a patient’s blood culture has both diagnostic and prognostic value and is one of the most important functions of the diagnostic microbiology laboratory. Blood cultures support growth of most bacteria and fungi in specialized nutrient broth, pathogen and non-pathogen alike. Thus, growth of microbes in a blood culture can signal the presence of a true bloodstream infection or skin commensal contaminant introduced during the collection of blood. Monitoring blood culture contamination rates is a critical process for microbiology laboratories. Contamination of blood cultures can lead to negative patient outcomes. Blood culture contamination leads to unnecessary antimicrobial therapy, prolonged hospital stays, additional laboratory tests, and additional costs. The National Health Safety Network recently issued a master organism list that takes effect beginning January 2021. This review focuses on discussion of blood culture contamination, the history of benchmarking of the quality metrics related to blood culture contamination, and the need to reduce the impacts of blood culture contamination with standardized benchmarks and best practices to prevent contamination.     

Effects of Volume and Site of Blood Draw on Blood Culture Results

Blood culture contamination greatly affects clinical decisions. Hence, it is of interest to assess the influence of factors such as the volume of blood drawn and the site of blood draw on the rates of blood culture contamination. In a retrospective study, blood cultures from infants and children up to 18 years of age who had at least one positive blood culture during the year 2006 were analyzed for their volume of blood drawn, patient''s weight, site of blood draw used, and blood culture results. Blood cultures were deemed adequate collections if they contained an appropriate weight-related volume of blood. Moreover, blood culture results were categorized as true pathogens, contaminants, and negative cultures; these were then compared and analyzed with respect to their volume and site of blood draw. A total of 5,023 blood cultures were collected during 2006, of which 843 were analyzed. There were 306 (36%) positive cultures among the 843 cultures analyzed. Of the 306 positive cultures, 98 (32%) were contaminants and 208 (68%) cultures grew significant pathogens. Thirty-five percent of the contaminant cultures had adequate volume compared to 60% in the true bacteremia group (P < 0.001). Also, of the 843 cultures, the rates of contamination among the different sites of blood draw were as follows: peripheral venipuncture, 36%; arterial, 10%; and central venous access, 7% (P = 0.155). The rate of contamination was higher with lower blood volumes, and there was no significant difference in the rates of contamination among the different sites of blood draw.Blood cultures are vital for identifying pathogens causing serious infections and in directing appropriate antibiotic therapy. Moreover, they remain the standard method for detecting bacteremia in the evaluation of sick patients (14). Unfortunately, blood culture contamination is a common occurrence and may lead to confusion regarding the significance of a positive blood culture. The most common contaminants are coagulase-negative staphylococcus species which are also becoming more prevalent as a primary pathogen in immunocompromised patients and in patients with indwelling intravascular devices (9, 15). The uncertain clinical significance of potential contaminants leads to longer hospital stays, unnecessary antibiotic therapy, and additional laboratory testing; as a result, the cost incurred by a hospital is many times that incurred by the laboratory (2).Many factors influence the yield of blood cultures, but the single most important factor is blood volume. Several studies have shown that the rate of isolation of pathogens from blood cultures increases with the quantity of blood submitted (12). Hence, a blood culture may be falsely negative from an inadequate-volume blood culture (6). Furthermore, the blood culture contamination rate inversely correlates with the volume of blood (3). The site and method of blood collection have also been known to influence the rate of contamination of blood cultures (8). Vascular-access devices, such as arterial and central venous catheters, pass through the skin and are susceptible to bacterial colonization. Hence, it is easy for these bacteria to colonize and multiply in and around these ports, and they can be pulled into blood specimens drawn from those sites. Hence, the primary aims of this study were to determine the volume of blood obtained for culture in routine clinical practice and to evaluate if inadequate blood volumes lead to an increased incidence of contaminants. Finally, this study also assessed whether the site of blood draw was related to an increased frequency of contaminated cultures.     

改构体aFGF对颈动脉窦损伤的保护作用

目的　探讨损伤大白鼠颈动脉窦压力感受器神经末梢后 ,改构体aFGF的保护作用。方法　将Wistar大鼠随机分成对照组、改构体aFGF1组、改构体aFGF2 组、改构体aFGF3 每组各 10只。改构体组分别经静脉注射 0 14 μg/ml、0 4 3μg/ml、1 30 μg/ml的改构体aFGF(1ml/ 10 0g) ,而对照组注射同剂量的生理盐水。 2 0min后 ,用蘸有 80 %乙醇的棉球轻轻擦拭右颈动脉窦区 ,损伤颈动脉窦压力感受器神经末梢 ,并放置 5min。观察记录各组损伤前后夹闭颈总动脉血压即 :收缩压 (SP)、舒张压(DP)、平均动脉压 (MP)和心率 (HR)的变化。结果　 (1)损伤右颈动脉窦前 ,夹闭右颈总动脉 ,实验组和对照组血压均升高 ,夹闭前后相比差异均有统计学意义 (P <0 0 1) ;(2 )损伤右颈动脉窦后 ,夹闭右颈总动脉 ,改构体aFGF1组、对照组血压不变 ,夹闭前后相比差异无统计学意义 (P >0 0 5 ) ;改构体aFGF2 组、改构体aFGF3 组血压升高 ,夹闭前后相比差异有统计学意义 (P <0 0 5 ) ,夹闭前后两组的血压差分别与对照组的差值相比有统计学意义 (P <0 0 5 )。在本实验中 ,HR均无明显变化。结论　改构体aFGF对颈动脉窦损伤有保护作用 ,并显示一定的量效关系     

Isopropyl alcohol compared with isopropyl alcohol plus povidone-iodine as skin preparation for prevention of blood culture contamination

Despite a number of studies on the efficacies of antiseptics for the prevention of blood culture contamination, it still remains unclear which antiseptic should be used. Although the combination of povidone-iodine and isopropyl alcohol has been traditionally used in many institutions, the application of povidone-iodine needs extra time, and there is little evidence that this combination could have an additive effect in reducing contamination rates. To elucidate the additive efficacy of povidone-iodine, we compared two antiseptics, 70% isopropyl alcohol only and 70% isopropyl alcohol plus povidone-iodine, in a prospective, nonrandomized, and partially blinded study in a community hospital in Japan between 1 October 2007 and 21 March 2008. All blood samples for culture were drawn by first-year residents who received formal training on collection techniques. Skin antisepsis was performed with 70% isopropyl alcohol plus povidone-iodine on all inpatient wards and with only 70% isopropyl alcohol in the emergency department. For the group of specimens from inpatient wards cultured, 13 (0.46%) of 2,797 cultures were considered contaminated. For the group of specimens from the emergency department cultured, 12 (0.42%) of 2,856 cultures were considered contaminated. There was no significant difference in the contamination rates between the two groups (relative risk, 0.90; 95% confidence interval, 0.41 to 1.98; P = 0.80). In conclusion, the use of a single application of 70% isopropyl alcohol is a sufficient and a more cost- and time-effective method of obtaining blood samples for culture than the use of a combination of isopropyl alcohol and povidone-iodine. The extremely low contamination rates in both groups suggest that the type of antiseptic used may not be as important as the use of proper technique.     

Catheter-drawn blood cultures: is withdrawing the heparin lock beneficial?

AIMS: To assess the potential benefit of withdrawing or flushing away the heparin lock before collecting blood for culture from a central venous catheter. METHODS: We compared the contamination rates of 152 pairs of blood samples aspirated from central venous catheters in afebrile renal dialysis or cancer patients. We also assessed the antimicrobial effect of 2000 U of heparin in Bactec Plus Aerobic/F culture bottles inoculated with a volunteer's blood plus one of six common bloodstream pathogens. RESULTS: There was no significant difference in contamination rates between first-drawn (26 of 152, 17.1%) and second-drawn (24 of 152, 15.8%) samples. There was no significance difference in yield (58 of 60 [97%] versus 52 of 53 [98%]) or time to flagging positive (16.6 versus 16.7 h) between the bottles with and without heparin. CONCLUSIONS: Our results do not support the practice of withdrawing or flushing away the heparin lock before collecting blood for culture from a central venous catheter.     

Evaluation of an intervention to improve blood culture practices: a cluster randomised trial

This study aimed to evaluate an intervention to improve blood culture practices. A cluster randomised trial in two parallel groups was performed at the Grenoble University Hospital, France. In October 2009, the results of a practices audit and the guidelines for the optimal use of blood cultures were disseminated to clinical departments. We compared two types of information dissemination: simple presentation or presentation associated with an infectious diseases (ID) specialist intervention. The principal endpoint was blood culture performance measured by the rate of patients having one positive blood culture and the rate of positive blood cultures. The cases of 130 patients in the “ID” group and 119 patients in the “simple presentation” group were audited during the second audit in April 2010. The rate of patients with one positive blood culture increased in both groups (13.62 % vs 9.89 % for the ID group, p?=?0.002, 15.90 % vs 13.47 % for the simple presentation group, p?=?0.009). The rate of positive blood cultures improved in both groups (6.68 % vs 5.96 % for the ID group, p?=?0.003, 6.52 % vs 6.21 % for the simple presentation group, p?=?0.017). The blood culture indication was significantly less often specified in the request form in the simple presentation group, while it remained stable in the ID group (p?=?0.04). The rate of positive blood cultures and the rate of patients having one positive blood culture improved in both groups. The ID specialist intervention did not have more of an impact on practices than a simple presentation of audit feedback and guidelines.     

Impact of Hourly Emergency Department Patient Volume on Blood Culture Contamination and Diagnostic Yield

Emergency departments (EDs) are an important diagnostic site for outpatients with potentially serious infections. EDs frequently experience high patient volumes, and crowding has been shown to negatively impact the delivery of early care for serious infections, such as pneumonia. Here, we hypothesized that other important factors in the early care of infectious diseases, the rate of blood culture contamination and the accurate detection of pathogens, would be sensitive to ED operational stress, as proper collection requires fastidious attention to technique and timing. We related all blood samples collected over 1 year and their rates of recovery of likely contaminants and pathogens to the number of patients being cared for in the ED at the time of sample collection. Likely pathogens and contaminants were classified through combined microbiological and manual chart review criteria. Zero-inflated Poisson regression was used to relate crowding to culture results. Blood samples were obtained from 7,586 patients over 82,521 adult and pediatric patient visits. The unadjusted rates of recovering a likely pathogen or a likely contaminant were 8.0% and 3.7%, respectively. Periods of increased crowding (3rd and 4th quartiles of hourly occupancy) were significantly associated (P < 0.01) with increased rates of contamination (relative risk, 1.23 compared to the least busy quartile). Collecting samples for culture during busy times was also associated with a reduced likelihood of recovering a likely pathogen (relative risk, 0.93 compared to the least busy quartile). ED crowding was associated with degraded performance of blood cultures, both increasing the rate of contamination and decreasing the diagnostic yield.     

Improving quality of patient care in an emergency department: a laboratory perspective

The purpose of our study was to improve the quality of care in an emergency department (ED) as measured by length of stay (LOS), total turnaround time (TAT) for laboratory result reporting, and the blood culture contamination rate. Data were included for patients who had at least 1 of 5 laboratory tests performed as part of their care. The study was conducted in 2 phases. First, phlebotomy was performed by a dedicated phlebotomist or nonlaboratory personnel. The second phase added a dedicated laboratory technologist. There was a significant reduction in total TAT for all tests (at least 46 and 75 minutes in the respective interventions), and blood culture contamination rates dropped from 5.0% to 1.1%, although the overall LOS did not change. Estimated cost avoidance is more than $400,000 annually. Quality of care in an ED is improved when samples are collected by a dedicated phlebotomist, but overall LOS does not change.     

Comparative evaluation of paired blood culture (aerobic/aerobic) and single blood culture, along with clinical importance in catheter versus peripheral line at a tertiary care hospital

Purpose: Paired blood culture (PBC) is uncommon practice in hospitals in India, leading to delayed and inadequate diagnosis. Also contamination remains a critical determinant in hampering the definitive diagnosis. Objectives: To establish the need of PBC over single blood culture (SBC) along with the degree of contamination, this comparative retrospective study was initiated. Materials and Methods: We processed 2553 PBC and 4350 SBC in BacT/ALERT 3D (bioMerieux) between October 2010 and June 2011. The positive cultures were identified in VITEK 2 Compact (bioMerieux). True positivity and contaminants were also analyzed in 486 samples received from catheter and peripheral line. Results: Out of 2553 PBC samples, positivity was seen in 350 (13.70%). In 4350 SBC samples, positivity was seen in 200 samples (4.59%). In PBC true pathogens were 267 (10.45%) and contaminants were 83 (3.25%), whereas in SBC 153 (3.51%) were true positives and contaminants were 47 (1.08%). Most of the blood cultures (99.27 %) grew within 72 h and 95.8% were isolated within 48 h. In 486 PBCs received from catheter/periphery (one each), catheter positivity was found in 85 (true positives were 48, false positives 37). In peripheral samples true positives were 50 and false positives were 8. Conclusion: Significantly higher positive rates were seen in PBCs compared with SBCs. Automated blood culture and identification methods significantly reduced the time required for processing of samples and also facilitated yield of diverse/rare organisms. Blood culture from catheter line had higher false positives than peripheral blood culture. Thus every positive result from a catheter must be correlated with clinical findings and requires further confirmation.     

The influence of sampling site and assay method on lactate concentration in response to rock climbing

The sport of rock climbing has increased in popularity and as a focus for research. Previous studies have examined the physiological determinants for successful performance. Variation is evident between studies over lactate sampling sites and assay methods. The aim of this study was to examine the limits of agreement between the YSI 2300 analyser and the Lactate Pro for finger and ear capillary blood samples in a climbing context. Forty-five (31 males and 14 females) participants volunteered to complete the climbing trial. Blood samples were collected simultaneously from finger and ear pre, post and 5 min post climb. The repeatability results indicated a good agreement across samples. Modelling analysis indicated the use of a −0.175 mmol l⁻¹ adjustment to move from Lactate Pro to YSI finger concentrations. To move from finger to ear concentrations, using the Lactate Pro, modelling analysis suggested a regression equation of Y = 0.827x + 0.769 adjustment for pre climb samples and Y = 0.955x + 0.566 for post climb concentrations. To better understand the physiological demands of climbing further research on natural rock is required. Results from this study suggest the Lactate Pro and blood sampling from the ear lobe could be of benefit to future rock climbing field studies.     

The effect of plasma exchange on the in vitro monocyte function of patients with immune complex diseases.

In vitro function tests were performed on peripheral blood monocytes isolated from patients with putative immune complex diseases undergoing therapeutic plasma exchange. Bacterial killing by monocytes improved significantly after plasma exchange (pre: 29 +/- 5%; post: 39 +/- 3%). The intracellular content of the acid hydrolase N-acetylglucosaminidase (NAG) after in vitro culture rose significantly following plasma exchange (pre: 48.3 +/- 21 nmol mg protein-1 hr-1; post: 76.6 +/- 30.6), although the amount of NAG released into the supernatant was unchanged. Plasma exchange also resulted in reduced levels of immune complexes (IC) and clinical improvement in most patients. The beneficial effect of plasma exchange in patients with IC diseases may be partly due to removal of IC which are known to influence the functional activity of cells of the mononuclear macrophage series.     

Discarding the Initial Aliquot of Blood Does Not Reduce Contamination Rates in Intravenous-Catheter-Drawn Blood Cultures

Although venipuncture is the preferred method for obtaining blood cultures, specimens often are obtained from intravenous catheters (IVC). For IVC-drawn blood cultures, some authorities recommend discarding the initial 5 to 10 ml of blood to reduce contamination and remove potential inhibitory substances. To determine whether this practice reduced contamination rates (CR), we assessed the results of IVC-drawn blood cultures for adults. Thirty milliliters of blood was obtained aseptically. The first 10 ml, rather than being discarded, was inoculated into an aerobic culture vial. Using a second sterile syringe, 20 ml of blood was obtained and inoculated in 10-ml aliquots to aerobic and anaerobic culture vials. Positive cultures were evaluated to assess clinical significance (true versus contaminant). Out of 653 IVC-drawn blood culture pairs, both vials were contaminated in 38 pairs (5.8%); only the “discard” vial was contaminated in 33 (5.1%); and only the “standard” vial was contaminated in 31 (4.7%). Overall CR were 10.9% for the discard vial versus 10.5% for the standard vial (P = 0.90). We conclude that discarding an initial aliquot of blood when obtaining blood cultures from IVCs does not reduce CR.The standard method for obtaining blood for culture is venipuncture using aseptic techniques. With greater utilization of intravenous access catheters (e.g., PICC, Hickman, etc.), blood cultures often are obtained from these devices, yet there is no standardized method for obtaining blood for culture by this technique. Several reports have demonstrated increased blood culture contamination rates (i.e., false-positive results) when blood cultures are obtained from catheters (4, 8, 10, 15), which, in turn, can lead to inappropriate antibiotic administration as well as additional unnecessary diagnostic testing. Some authorities recommend discarding the first 5 to 10 ml of blood when obtaining blood from intravenous catheters (IVCs) prior to inoculating the blood culture vials (17), whereas others do not (1, 9, 16). The purpose of discarding these aliquots of blood is to remove any substances that could potentially inhibit microbial growth (e.g., heparin) (6, 19) and to reduce blood culture contamination rates. However, there are few published systematic assessments of this issue, no consensus recommendations on how to draw blood cultures from an IVC, and no controlled comparative evaluations of different techniques to obtain blood culture samples from an IVC.It has been standard practice at our institution to discard the first 10 ml of blood prior to obtaining blood for culture from IVCs. If patients have repeated blood cultures, in which 10 ml of blood is discarded with each culture, nosocomial anemia may occur or worsen and result in added morbidity (1, 3, 11, 18, 21). To determine whether discarding the initial aliquot of blood from IVC-drawn blood cultures reduces contamination, we inoculated the initial 10-ml sample of blood that would have been discarded into an aerobic blood culture vial and compared contamination rates in these vials with contamination rates in the “standard” blood sample obtained for culture from the same patient.     

Molecular Typing of Coagulase-Negative Staphylococcal Blood and Skin Culture Isolates to Differentiate Between Bacteremia and Contamination

In order to determine whether a blood culture positive for coagulase-negative staphylococci (CNS) represents bacteremia or contamination, a prospective study was conducted using molecular typing to analyze CNS blood culture isolates and corresponding CNS skin isolates collected after skin disinfection from 431 subjects. CNS bacteremia was not found in any of the 301 subjects not suspected of having bacteremia. In 130 patients suspected of having bacteremia, the rate of actual CNS bacteremia was 6%. The overall rate of CNS blood culture contamination was 1%. Chart analysis showed good agreement between our microbiological definitions of bacteremia and the clinical definitions previously published. Bacteremia and contamination can be differentiated using pulsed-field gel electrophoresis and molecular typing of CNS isolates obtained from cultures of blood and corresponding skin samples.