False-positive Cultures Research Articles

Nurses’ Knowledge of Blood Culture Sampling Procedure

Background : False-positive blood culture results due to contaminated samples have shown to increase patients’ health costs, including the use of broad spectrum antibiotics and prolonged hospital length of stay. While previous research have suggested that increasing staff knowledge on proper specimen collection lowers contamination rates significantly, staff’s current knowledge of hospital-recommended sample collection procedure have yet to be assessed in Dr. Dr. Hasan Sadikin General Hospital, Bandung, Indonesia. Methods : This was a cross-sectional descriptive study on 81 Emergency Department nurses in Dr. Hasan Sadikin General Hospital, Indonesia. Subjects were asked to complete a questionnaire in order to measure their knowledge of blood culture sampling procedure in accordance with the hospital’s standard operating procedure. Results : Among 81 subjects enrolled, 51 managed to adequately describe the prerequisites in proper blood culture sampling procedure and their purpose as dictated by Dr. Hasan Sadikin General Hospital’s standard operating procedure. Conclusions : Up to 67% of nurses conducting blood sampling procedure in Dr. Hasan Sadikin General Hospital’s Emergency Department understood the prerequisites of hospital-recommended blood culture sampling procedure and their purpose.

Comment on "A Case of Healthcare Associated Pneumonia Caused by Chryseobacterium indologenes in an Immunocompetent Patient".

I am writing regarding the publication of S. A. Nemil et al., “A Case of Healthcare Associated Pneumonia Caused by Chryseobacterium indologenes in an Immunocompetent Patient” [1]. In the published case report, the authors state that the patient acquired a Healthcare Associated Pneumonia (HAP) caused by Chryseobacterium indologenes. Notwithstanding that the patient had a HAP, the evidence that the infection was caused by C. indologenes is insufficient and could possibly be questionable. (a) According to the authors both E. coli and C. indologenes were isolated from a transtracheal aspirate (TTA) sample; however it is suggested that the infection was caused only by C. indologenes. (b) The transtracheal aspirate (TTA) samples are ideal for bacteriology investigation; however an organism growth on a single TTA sample is not proof of the pathogen that causes the infection. The interpretation of the relevance of bacterial growth depends on the pathogen and it is high if the isolate is a typical pathogenic organism that causes respiratory tract infection/chest infection and significantly low if the isolated organism is an uncommon bacterium (Chryseobacterium indologenes). Chryseobacterium indologenes is an opportunistic pathogen, not normally present in the human microflora, although it is widely distributed in nature. The patient was not immunocompromised and therefore is more susceptible to an organism with low pathogenicity. Important information regarding the microbiology culture growth (quantitative or semiquantitative) and presence of inflammation were not reported in the document in order to estimate the significance of the culture. The presence of two organisms on the same culture reduces further the clinical significance of the culture result. In addition the diagnostic utility of TTA is likely decreased in a patient with a chronic airway disease, such as bronchiectasis, in which case a false-positive culture result should be expected due to common colonization below the level of the larynx [2]. (c) According to the authors the antimicrobial susceptibility test revealed that the “C. indologenes was resistant to carbapenems and sensitive to levofloxacin. Levofloxacin was added to antimicrobial therapy on the 6th day of admission. On follow-up, after the second day of therapy modification, improvement on blood gas parameters was observed and the patient was extubated.” The authors speculate that the patient had an infection caused by C. indologenes due to the patient not responding to the previous antibiotic treatment. The patient's antimicrobial therapy was modified to ertapenem on the 3rd day of admission (when urine culture yielded ESBL and after 3 days treatment with piperacillin-tazobactam), possibly indicating that the patient was possibly close to or less than 72 hours on ertapenem treatment when levofloxacin was added. It would be interesting to know if the 82-year-old patient had hypoalbuminaemia. Hypoalbuminaemia is rarely considered in clinical decisions but ertapenem is highly albumin bound (85–95%) and data from multiple studies showed that hypoalbuminaemia may have a profound effect on pharmacokinetics (failure to attain pharmacodynamic targets) and therefore could possibly lead to treatment failure or a delayed clinical response [3, 4]. In addition a large proportion of C. indologenes isolates are susceptible to piperacillin-tazobactam (the patient was initially treated with piperacillin-tazobactam) [5, 6]; however the C. indologenes susceptibility to piperacillin-tazobactam is not documented. On conclusion, the interpretation of the relevance of bacterial growth of uncommon bacterium with low pathogenicity (C. indologenes) in transtracheal aspirates needs to be carefully interpreted, including clinical cases when there is a clear clinical improvement after targeted antimicrobial therapy to the uncommon bacterium has been applied.

PS-214 Does A Total Sterile Collection Bundle Reduce False Positive Blood Culture Rates And Antibiotic Use In Neonatal Intensive Care?

Background and aim In neonatal intensive care coagulase negative Staphylococcus species can be both blood culture contaminant and pathogen. False positive cultures can result in clinical uncertainty and unnecessary antibiotic use. Our aim was to assess the effect of a total sterile blood culture collection bundle on the incidence of false positive blood cultures in a regional surgical neonatal intensive care unit. Method Clinical data of all infants who had blood cultures taken before and after the introduction of the collection bundle (sterile technique and 2% Chlorhexidine) were collected. The rates of false positive blood cultures, defined as the presence of a skin commensal and <3 predefined clinical signs (Modi et al . 2009), were compared. Results In total 367 blood cultures from 294 babies were assessed, 197 pre-intervention (PRE) and 170 following bundle introduction (POST). The median birth weight and gestation were similar in both groups. The rate of false positive cultures in the total PRE group was 9/197 (4.6%) compared to 1/170 (0.6%) in the POST group (p < 0.05). In infants <28 weeks’ the rates reduced from 4/29 (13.8%) to 0/30 (0%) (p < 0.05). Unnecessary antibiotic exposure rate was 7.7% in the PRE group versus 0.0% in the POST group (p < 0.05). Conclusion Implementation of this collection bundle reduced the number of false positive blood culture results. This has a potential benefit in reducing unnecessary antibiotic use and associated health care costs.

Prevalence of serious bacterial infections in return visits to the emergency department among infants aged 90 days or younger.

The main objective of this study was to describe the epidemiology of return visits (RVs) in well-appearing infants to an urban emergency department (ED) who were evaluated for serious bacterial infection (SBI) at their index ED visit. We conducted a retrospective chart review on infants aged 90 days and younger who were evaluated for SBI at their initial ED visit from 2003 through 2009. A parent database of all febrile infants evaluated for SBI was queried to identify patients who had an RV within 7 days of the index visit. We collected demographic variables including age, sex, and past medical history as well as laboratory test results including white blood cell count, blood, urine, and cerebrospinal fluid cultures and viral studies. Of eligible febrile infants, 10.8% (350/3220) had an RV to the ED within 7 days. The prevalence of SBI in the RV cohort was 6.0% (21/350), which included 1.7% (6/350) bacteremia, 3.7% (13/350) urinary tract infection, and 0.6% (2/350) combined urinary tract infection and bacteremia. The blood culture contamination rate was 88%. Infants aged 90 days or younger who are evaluated for SBI have high RV rates. A substantial number of RVs are due to contaminated blood cultures. Future studies should be conducted to identify predictors for false-positive blood cultures.

Incidence of Culture Positive Propionibacterium acnes in Shoulder Arthroscopy

Objectives:Accurate detection and diagnosis of Propionibacterium acnes infection after shoulder surgery is often challenging. Aspiration and tissue cultures yield both false negative and false positive cultures and determination of infection is not always straightforward. The purpose of our study was to measure P. acnes positive cultures from patients undergoing arthroscopic surgery, with no previous surgical history on that shoulder. Our hypothesis was that P. acnes would not be found in patients who had not previously had shoulder surgery.Methods:Seven samples were collected from 57 consecutive patients undergoing shoulder arthroscopy, without any previous shoulder surgery. An air swab was taken as a control for this study. Two skin swabs (one after skin preparation and one prior to skin closure), aspiration of joint fluid, and three samples of debrided tissue were obtained for culture. All samples were placed on three different aerobic plates and held for 48 hours. Samples were also plated on anaerobic plates and placed into a Thioglycollate broth and held for 28 days. All bacteria cultures were identified. Isolated P. acnes were tested for biotype with a Microscan Rapid Anaerobic ID and then streaked on brucella agar/ ANA CDC agar to measure hemolysis. The biotype isolated was also tested with Epsilometer tests.Results:Fifty-seven patients underwent arthroscopic shoulder surgery for subacromial decompression (22.8%), rotator cuff repair (57.9%), labrum or instability repair (19.3%). The mean age of the patients was 51 years (range 17-81). A total of 81 samples (21.8%) were positive for P. acnes in the timeframe of zero to fourteen days (Table 1). All positive cultures were non-hemolytic. Diagnosis, history of corticosteroid injection, or antibiotic received had no significant bearing on culture results. Positive skin cultures for P. acnes increased from 10.5 % before incision to 31.9 % at closure. This was even more pronounced in males as skin cultures increased from 31.3% before incision to 62.96% at closure. Fifteen (26.3%) patients had more than three cultures positive. None of the patients in this study have had signs or symptoms to suggest clinical infection of P. acnes.Conclusion:There was high rate (21.8 %) of positive culture for P. acnes culture positives in a group of patients that we would not expect to find bacteria. When samples are held for 28 days, this percent increased to 25.3%. This either represents false positives via contamination, inadequate skin preparation or may represent colonization as no patients have clinical symptoms of infection. These findings make the interpretation of positive P. acnes culture even more challenging when managing a patient with shoulder pain after surgery. The consequence of treating a false positive is not benign. There was also a remarkable increase in positive rate from culture obtained from the skin at the beginning of surgery (10.5%) as compared to at the end (31.9%). Future studies should examine alternate surgical skin preparation.

Investigating the Impact of Blood Culture Bundles on the Incidence of Blood Culture Contamination Rates

Blood cultures are integral diagnostic procedures for identifying serious infections and selecting antimicrobials. Positive blood cultures are the initial step in attaining a conclusive diagnosis of sepsis. Relative risk is blood culture contamination, false-positive blood culture results, diagnostic error delays, treatment errors, excessive lab testing, and increased length of stay. A complicating issue is the increased use of central venous access devices (CVADs). The purpose of this descriptive, comparative study is to evaluate the effectiveness of blood culture bundles on blood cultures drawn through a CVAD and contamination rates. The study revealed a decrease in blood culture contamination rates by 61%.

Reducing blood culture contamination rate: a quality assurance project in a Malaysian tertiary hospital

Blood cultures contamination is a common scenario in Malaysian hospitals. Reducing the contamination rate of blood culture will reduce false-positive blood culture, prevent inappropriate antibiotic prescription and reduce patient management cost. This is a 6 months study specifically focused on the effects of changing the type of skin antiseptics used (70% isopropyl alcohol plus 2% chlorhexidine replacing 70% isopropyl alcohol plus povidone-iodine) and improving the knowledge and techniques of blood culture taking in a tertiary hospital. the remedial measures introduced were successful in achieving 4.34% contamination rate, which is 2.03% less than pre-remedial contamination rate (6.37%). There was a statistically significant reduction in the number of contaminants (p = 0.02) with five-fold rise in the significant blood cultures results. Better choice of skin antiseptics and good blood culture knowledge and technique may contribute to reduce number of contamination rate in blood culture.

Do We Need This Blood Culture?

This study describes blood culture collection rates, results, and microbiology laboratory charges for 4 leading pediatric inpatient diagnoses (asthma, bronchiolitis, pneumonia, and skin and soft tissue infection [SSTI]) in low-risk patients. This retrospective cohort study was conducted at an urban, academic, quaternary children's hospital. The study period was from January 1, 2011, to December 31, 2011. Inclusion criteria were as follows: 6 months to 18 years of age and primary diagnosis of asthma (International Classification of Diseases, Ninth Revision [ICD-9] codes 493.91-493.92), bronchiolitis (ICD-9 codes 466.11 and 466.19), SSTI (ICD-9 codes 680.00-686.99), or pneumonia (community-acquired pneumonia; ICD-9 codes 481.00-486.00). Patients with complex chronic conditions were excluded. Data were collected via administrative billing data and chart review. Descriptive statistics were performed; χ(2) tests were used for categorical variables, and nonparametric tests were used for continuous variables because of non-normal distributions. Administrative data review included 5159 encounters, with 1629 (32%) inpatient encounters and 3530 (68%) emergency department/outpatient encounters. Twenty-one percent (n = 343) of inpatient encounters had blood cultures performed, whereas 3% (n = 111) of emergency department/outpatient encounters had blood culture testing performed. Inpatient blood culture utilization varied according to diagnosis: asthma, 4%; bronchiolitis, 15%; pneumonia, 36%; and SSTI, 46%. Charts were reviewed for all 343 inpatients with blood culture testing. Results of all the blood cultures obtained for asthma and bronchiolitis admissions were negative, with 98% and 99% negative or false-positive (contaminant) for SSTI and community-acquired pneumonia, respectively. The approximate financial impact of blood culture utilization (according to gross microbiology laboratory charges) approximated $100 000 over the year for all 4 diagnoses. There was a high rate of negative or false-positive blood culture results for these common inpatient diagnoses. In addition, there was a low rate of clinically significant true-positive (pathogenic) culture results. These results identify points of potential blood culture overutilization.

Performance Characteristics of Broth-only Cultures After Revision Total Joint Arthroplasty

Surgeons frequently obtain intraoperative cultures at the time of revision total joint arthroplasty. The use of broth or liquid medium before applying the sample to the agar medium may be associated with contamination and false-positive cultures; however, the degree to which this is the case is not known. We (1) calculated the performance characteristics of broth-only cultures (sensitivity, specificity, positive predictive value, and negative predictive value) and (2) characterized the organisms identified in broth to determine whether a specific organism showed increased proclivity for true-positive periprosthetic joint infection (PJI). A single-institution retrospective chart review was performed on 257 revision total joint arthroplasties from 2009 through 2010. One hundred ninety (74%) had cultures for review. All culture results, as well as treatment, if any, were documented and patients were followed for a minimum of 1year for evidence of PJI. Cultures were measured as either positive from the broth only or broth negative. The true diagnosis of infection was determined by the Musculoskeletal Infection Society criteria during the preoperative workup or postoperatively at 1year for purposes of calculating the performance characteristics of the broth-only culture. The sensitivity, specificity, positive predictive value, and negative predictive value were 19%, 88%, 13%, and 92%, respectively. The most common organism identified was coagulase-negative Staphylococcus (16 of 24 cases, 67%). Coagulase-negative Staphylococcus was present in all three true-positive cases; however, it was also found in 13 of the false-positive cases. The broth-only positive cultures showed poor sensitivity and positive predictive value but good specificity and negative predictive value. The good specificity indicates that it can help to rule in the presence of PJI; however, the poor sensitivity makes broth-only culture an unreliable screening test. We recommend that broth-only culture results be carefully scrutinized and decisions on the diagnosis and treatment of infection should be based specifically on the Musculoskeletal Infection Society criteria. Level IV, diagnostic study. See Instructions for Authors for a complete description of levels of evidence.

Taking blood cultures from a newly established intravenous catheter in the emergency department does not increase the rate of contaminated blood cultures

It has been suggested that blood cultures drawn from vascular catheters have a higher false positive rate than those drawn by venepuncture. In the face of institutionally imposed practice change prohibiting obtaining blood cultures from intravenous (i.v.) catheters in the ED, our aim of was to compare the rate of contaminated blood cultures between those taken from recently placed i.v. catheters and those taken by direct venepuncture. Prospective, non-randomised, observational study comparing the rate of contaminated blood cultures for specimens taken from recently placed (<1 h) i.v. catheters and direct venepuncture in adult ED patients. Outcome of interest was the rate of false positive cultures. Analysis was by comparison of proportions (χ(2) -test). Four hundred seventy-two blood culture sets were studied. There were 65 positive cultures, of which 49 (75%; 95% confidence interval [CI], 63-85%) were classified as true positive. The overall rate of contaminated blood cultures was 3.4% (95% CI, 2.0-5.6%). There was no difference in false positive rate between blood cultures taken via venepuncture and those taken from a recently placed i.v. cannula (P = 0.52; odds ratio, 0.9; 95% CI, 0.33-2.44). We found no difference in contaminated blood culture rate between recently placed i.v. catheters and direct venepuncture when infection control procedures were followed.

Recognizing Laboratory Cross-Contamination

Mycobacterium tuberculosis (MTB) isolation from clinical specimens is the standard for TB diagnosis. Positive MTB cultures are rarely questioned, but false-positive culture rates range from 2% to 4%. In December 2011, two smear-negative, culture-positive TB cases were reported to the Oklahoma State Department of Health (OSDH) in people without TB signs or symptoms. OSDH TB control officers interviewed physicians and laboratory personnel, reviewed patient charts, traced epidemiologic links, and performed microbiologic studies to determine if these were true TB cases. Both specimens were found to have been processed on the same day, at the same laboratory, under the same hood, and by the same technician sequentially after a strongly smear-positive TB specimen. No epidemiologic links were identified among the three patients. Spoligotyping and 24-locus mycobacterial interspersed repetitive unit typing of the three specimens were identical. Only liquid media grew MTB in the two questionable specimens. A laboratory splash incident was suspected, whereby all three liquid media sample lids were open during inoculation rather than being opened one at a time, causing cross-contamination. Also, the two specimens were incubated for 2-3 weeks longer than standard protocol before MTB growth was observed. Patient 1 was not treated for TB because her physician doubted the culture result. Patient 2, an organ transplant recipient, began four-drug anti-TB therapy, and an investigation was initiated for transplant-associated TB. Adherence to strict laboratory techniques and recognizing the possibility of false-positive MTB cultures, especially when inconsistent with clinical data, are essential in preventing erroneous TB diagnoses.

Identifying and Classifying Bloodstream Infections Among Hemodialysis Patients

Bloodstream infections (BSIs) are a prominent clinical problem in patients undergoing hemodialysis. These infections appear to be more common among patients who have a central line as their dialysis access and can be associated with substantial morbidity and mortality. Accurately diagnosing BSIs clearly influences patient management, but is also an important part of an infection prevention program; particularly as facility BSI rates are becoming a recognized quality measure for which dialysis facilities might be held accountable. Blood cultures remain the gold standard for diagnosing BSIs and a number of practices can affect the sensitivity and specificity of this important laboratory test. Optimizing the collection of blood cultures can assist providers with interpretation of positive blood cultures and can help minimize the impact of false-positive and false-negative cultures. This review will describe differences between BSI definitions, examine the use of blood cultures to identify these infections including the use of recommended best practices to maximize culture yield, and highlight characteristics that can assist in the clinical interpretation of positive blood cultures.

Statistical Evaluation of Two Microbiological Diagnostic Methods of Pulmonary Tuberculosis After Implementation of a Directly Observed Treatment Short-course Program

ObjectivesTo evaluate the diagnostic accuracy of smear and culture tests of clinical samples of pulmonary tuberculosis after the introduction of the directly observed treatment short-course (DOTS) program. MethodsUsing sputum samples from 572 individuals as a self-selected population, both Ziehl–Neelsen staining and culturing on Lowenstein–Jensen medium were carried out as diagnostic procedures. Using Bayes' rule, the obtained data set was analyzed. ResultsOf the 572 samples, 33 (0.05769) were true positive (results of both tests positive) cases; 22 samples (0.03846) were false positive (smear test positive and culture test negative) cases; 62 samples (0.10839) were false negative (smear test negative and culture test positive) cases; and 455 samples (0.79545) were true negative (results of both tests negative) cases. Values of test statistics, sensitivity, and specificity were used to compute several inherent other Bayesian test statistics. The a priori probability or prevalence value of tuberculosis in the targeted population was 0.166. The a posteriori probability value computed arithmetically was 0.6614 and that obtained by the graphical method was 0.62. ConclusionsThe smear test was found to be dependable for 95.4% with stable TB infections, and it was not dependable for 34.7% without stable TB infections. The culture test could be regarded as the gold standard for 96.15% as seen with the data set, which was obtained after the implementation of the DOTS program.

Reducing the Blood Culture Contamination Rate in a Pediatric Emergency Department and Subsequent Cost Savings

Blood culture contamination in the pediatric population remains a significant quality and safety issue because false-positive blood cultures lead to unnecessary use of resources and testing. In addition, few studies describe interventions to reduce peripheral blood culture contamination rates in this population. We hypothesized that the introduction of a standardized sterile collection process would reduce the pediatric emergency department's peripheral blood culture contamination rate and unnecessary use of resources. A sterile blood culture collection process was designed by analyzing current practice and identifying areas in which sterile technique could be introduced. To spread the new technique, a web-based educational model was developed and disseminated. Subsequently, all nursing staff members were expected to perform peripheral blood cultures by using the modified sterile technique. The peripheral blood culture contamination rate was reduced from 3.9% during the baseline period to 1.6% during the intervention period (P < .0001), with yearly estimated savings of ~$250,000 in hospital charges. Subsequent to our intervention, there was a significant reduction of the peripheral blood culture contamination rate as well as considerable cost savings to the institution. When performed in a standardized fashion by using sterile technique, blood culture collection with low contamination rates can be performed via the insertion of an intravenous catheter.

Pseudo-Outbreak of Vancomycin-Resistant-Enterococcus (VRE) Colonization in a Neonatal Intensive Care Unit Using Spectra VRE Surveillance Medium

From November 2011 through March 2012, we surveyed 272 babies in our neonatal intensive care unit for rectal colonization with vancomycin-resistant enterococci (VRE). Using Spectra VRE medium (Remel Diagnostics, Lenexa, KS), we identified one neonate colonized with vancomycin-resistant Enterococcus faecium. In addition, 55 (13%) of the surveillance cultures yielded false-positive results with vancomycin-susceptible Enterococcus faecalis. During the same time period, 580 rectal swabs were collected from adult patients resulting in 20 (3%) false-positive cultures. The difference in false-positive rates between cultures from babies and adults was statistically significant (P < 0.001), prompting an investigation of factors that might influence the elevated false-positive rate in the neonates including patient demographics, nutrition, and topical ointments applied at the time of testing. Older neonates, with a median age of 6 weeks, were more likely to have false-positive cultures than younger neonates with a median age of 3 weeks (P < 0.001). The younger neonates receiving Similac Expert Care products were less likely to have false-positive surveillance cultures than those receiving other formulas (P < 0.001). Application of topical products was not associated with false-positive cultures. The false-positive E. faecalis strains were typed by Diversilab Rep-PCR (bioMérieux, Marcy l'Etoile, France) and found to represent eight different groups of isolates. The utility of the Spectra VRE media appeared to be significantly impacted by the age of the patients screened.

Strategies on reducing blood culture contamination

Blood culture contamination (BCC) is a common problem in hospitals; contaminated or false-positive blood cultures may confuse the clinicians, precipitate unnecessary antibiotics usage as well as prolonging the hospital stay for patients. Although it is not possible to eliminate BCC, it is important that we introduce methods to reduce BCC. These methods include changes to the sampling technique to increase the chance of sterility, selection of appropriate skin prep kits, using a trained phlebotomy team rather than junior doctors, and introducing an interactive approach, along with clinical clues and laboratory tests for the classification of blood culture results to minimize BCC rate.

Application of broad-spectrum PCR amplification and direct sequencing for identification of the infrequent bacterial cultures from clinical sources, targeting the bacterial 16S rRNA gene with universal primes

Objectives To identify the infrequent strains in clinical isolates by broad-spectrum PCR amplification and direct sequencing targeting the bacterial 16S rRNA gene. Methods Total 48 clinical isolates and 7 false-positive blood culture samples were collected from 7 different hospitals or institutions from December 2010 to September 2011.The bacterial 16S rRNA gene were amplified and sequenced by universal prime sets of 27f-1492r and 27f-1525r，and MicroSeq 500 16S rRNA gene kit.The homology analysis was used by the Basic Local Alignment Search Tool, and comparing to gene sequence of the type strain.provided by the List of Prokaryotic names with Standing in Nomenclature.The criteria for the bacterial identification was interpreted according to the Clinical and Laboratory Standards Institute （CLSI） MM18-A. Results All of the 48 cultured strains were succeeded amplifying and sequencing the targeted 16S rRNA genes.According to the criteria of CLSI MM18-A, total 35 strains were specified to the species level, 11 strains were specified to the genus level, and the other 2 strains were specified to possible novel genus and species.Combining the analysis the sequence of other housekeeping gene with the results of biochemical results, total 42 strains can be specified to the species level, including some clinical important pathogens, such as Streptobacillus, Capnocytophaga, Nocardia, Mycobacterium, Roseomonas and Campylobacter.Two false-positive blood culture samples were managed to amplify 16S rRNA genes and finally identified as Streptococcus pneumoniae.We also identified one novel subspecies of Campylobacter fetus, and some new valid-published species, such as Acinetobacter parvus,Mycobacterium phocaicum,Roseomonas mucosa and Halomonas johnsoniae. Conclusions The 16S rRNA gene sequence based identification has unique advantages over the phenotypic methods.It is universal to almost of all the bacteria, and can provide the genetic classified information. It is very suitable for the clinical infrequent and special bacterial cultures, such as the slow-growing, fastidious, or un-cultured bacteria.（Chin J Lab Med,2012,35:612-619） Key words: RNA，ribosomal，16S; Polymerase chain reaction; Sequence analysis; Bacteriological techniques

Epidemiologic surveillance to detect false-positive Mycobacterium tuberculosis cultures

This study was aimed to investigate the ability of potential indices from epidemiologic surveillance to detect false-positive cultures of Mycobacterium tuberculosis (MTB). All clinical specimens for mycobacterial culture from April 1 to August 31, 2010, were reviewed. Single-positive cultures without relevant clinical and pathologic information were categorized as suspected false-positive cultures. Genotyping methods were used to confirm false-positive cultures. The performance of epidemiologic surveillance indices to detect potential false-positive cultures was evaluated. A total of 14,462 specimens were sent to the laboratory and 214 batches were processed in 107 work days (average 67.6 specimens per batch, ranging from 21 to 130 specimens per batch). Seventy-one single-positive cultures were identified, among which 5 cultures of multidrug-resistant MTB in 1 batch were false-positive, confirmed by genotyping methods. Epidemiologic surveillance with statistical process control charts for single-positive cultures per day showed good performance in epidemiologic surveillance. The false-positive rate was 38.5% in the 13 potential false-positive cultures according to the statistical process control chart for single-positive cultures per day. Although the incidence of tuberculous disease is high in Taiwan, clustering of multidrug-resistant MTB in 1 batch or clustering of single-positive cultures still suggested the occurrence of false-positive MTB cultures. Therefore, epidemiologic surveillance for the clustering of single-positive cultures with the statistical process control chart could be used to monitor the occurrence of false-positive results.

Reducing False-Positive Peripheral Blood Cultures in a Pediatric Emergency Department

False-positive peripheral blood cultures due to contamination pose clinical and financial consequences for patients, families, and hospitals. Educating staff who draw peripheral blood cultures about hospital policy, using a blood culture-drawing kit, having a dedicated team obtaining peripheral blood cultures, and following up with staff who draw a contaminated peripheral blood cultures have been shown to reduce the rate of false-positive peripheral blood cultures. The objective of this study was to reduce the rate of false-positive peripheral blood cultures in a pediatric emergency department using the previously mentioned measures. This quality-improvement initiative used a retrospective chart-review approach to examine false-positive peripheral blood cultures drawn in 2009. In June 2010 a month-long education campaign about the initiative was conducted for nurses and clinical assistant staff to reduce false-positive peripheral blood cultures. From July 2010 through June 2011, monthly retrospective chart audits of false-positive peripheral blood cultures were completed in conjunction with bimonthly e-mail communication about the study, development of a blood culture-drawing kit, and follow-up with staff who drew the false-positive cultures. In 2009 the false-positive peripheral blood culture rate in the emergency department was 2.1%. After educational interventions and use of a blood culture-drawing kit, the rate of false-positive peripheral blood cultures decreased to 1.4%. The decline in contaminated blood cultures shows that the interventions described significantly reduced the rate of false-positive peripheral blood cultures in the emergency department.

Case of laboratory cross-contamination of Mycobacterium tuberculosis in the broth-based culture system

We experienced a case of laboratory cross-contamination of Mycobacterium tuberculosis on the broth based culture system. These false-positive cultures were confirmed by analysis of DNA fingerprinting, RFLP method, which showed the same pattern in three specimens with that of the first manipulated specimen in our laboratory on that day, out of 7 specimens examed. We found possible several process causing cross-contamination where mixture of the foreign body could occur in buffer or NALC-NaOH. False-positive cultures for Mycobacterium tuberculosis may lead to unnecessary, potentially toxic, costly treatment, and changing the treatment strategy. So we must critically interpret a single positive culture, especially by liquid media.