Nationwide Survey for Current Status of Laboratory Diagnosis of Clostridioides difficile Infection in Korea.

BACKGROUND: The interest in Clostridioides difficile infection (CDI) has increased, and the choice of assays became wider since the first national survey in Korea on CDI diagnosis in 2015. We conducted a survey of the domestic CDI assays with more varied questions to understand the current situation in Korea. METHODS: In April 2018, about 50 questions on the current status of CDI assays and details on implementation and perceptions were written, and a survey questionnaire was administered to laboratory medicine specialists in 200 institutions. RESULTS: One-hundred and fifty institutions responded to the questionnaire, of which 90 (60.0%) including one commercial laboratory, performed CDI assays. The toxin AB enzyme immunoassay (toxin AB EIA), nucleic acid amplification test (NAAT), and C. difficile culture, glutamate dehydrogenase assay, alone or in combination with other assays, were used in 75 (84.3%), 52 (58.4%), 35 (36.0%), and 23 (25.8%), respectively, and 65 (73.0%) institutions performed a combination of two or more assays. The sensitivity of toxin AB EIA was more negatively perceived, and that on specificity was more positively perceived. The perception of sensitivity and specificity of NAAT was mostly positive. Perception on the algorithm test projected it as useful but in need of countermeasures. Sixty-three (73.3%) institutions responded that they performed surveillance on CDI. CONCLUSION: This study provides useful evidence on the current status of CDI laboratory diagnosis in Korea as well as on items that require improvement and is thought to aid in standardizing and improving the CDI laboratory diagnosis in Korea.

Evaluation of the VIDAS glutamate dehydrogenase assay for the detection of Clostridium difficile.

We evaluated the performance of the VIDAS GDH assay for the detection of Clostridium difficile. In total, 350 fecal specimens collected from patients clinically suspected of having CDI were analyzed by C. difficile culture and enzyme-linked fluorescent immunoassay (VIDAS GDH); the results were compared with those of toxigenic C. difficile culture (TC), PCR (Xpert C. difficile assay), and toxin AB EIA (VIDAS CDAB). The numbers of culture-positive and culture-negative samples were 108 and 242, respectively. The concordance between the GDH assay and C. difficile culture was 90.3%. With PCR, 12 more samples were found to be positive in GDH-positive/C. difficile culture-negative specimens. Thus, the concordance between GDH assay and C. difficile culture/PCR was 93.7%. The sensitivity, specificity, positive predictive value, and negative predictive value of the VIDAS GDH assay were 97.2%, 87.2%, 77.2%, and 98.6%, respectively, based on the C. difficile culture, and 97.5%, 91.7%, 86.0%, and 98.6%, respectively, based on C. difficile culture/PCR. Positivity rates of the GDH assay were partially associated with those of semi-quantitative C. difficile cultures, which were maximized in grade 3 (>100 colony-forming unit [CFU]) compared with grade 1 (<10 CFU). We evaluated the two-step or three-step algorithm using GDH assay as a first step. No toxin EIA-positive case was found among GDH-negative samples, and 60.8% (48/79) were TC- and/or PCR-positive among the GDH-positive/toxin EIA-negative samples. Thus, approximately 25% of the 350 samples required a confirmatory test (TC or PCR) in the GDH-toxin EIA algorithm, whereas only 2.3% of the total samples in GDH-PCR algorithm was discrepant and required another confirmatory test like TC.

Comparative evaluation of two molecular multiplex syndromic panels with acute gastroenteritis.

We compared the Allplex Gastrointestinal V/B1/B2 Assays and Seeplex Diarrhea V/B1/B2 ACE Detection Assays in patients with acute gastroenteritis (AGE). Of the total 432 specimens, 48.8% and 54.9% samples were positive for any bacterial or viral target using Seeplex and Allplex, respectively (P = 0.002). The overall percent agreement (OPA) between the two panels was >95% and the lowest OPA was 95.4% for CdB. Allplex identified 40 samples positive for Salmonella spp., while Seeplex and OBC identified only 27 (67.5%) and 8 (20%), respectively. Shigella spp. were detected by assays in six samples, but none were identified using culture. Clostridium perfringens with Seeplex was detected in 70 (16.2%). It remained an informative species in identifying AGE although cpe gene showed only 9.8% positivity. Pathogenic Escherichia coli with Allplex could be detected in 40 (9.3%) samples, which could provide valuable information for the diagnosis of AGE.

Comparison of BD GeneOhm Cdiff and Seegene Seeplex ACE PCR assays using toxigenic Clostridium difficile culture for direct detection of tcdB from stool specimens.

We evaluated the performances of 2 PCR assays (BD GeneOhm and Seegene ACE) for direct detection of tcdB from stool specimens. The concordance rate between BD and Seegene was 96.3%. The sensitivities, specificities, positive predictive values (PPVs), and negative predictive values (NPVs) of BD and Seegene were 95.7%, 96.5%, 91.8%, and 98.2% and 90.0%, 97.1%, 92.6%, and 96.0%, respectively.

Characterization of cases of Clostridium difficile infection (CDI) presenting at an emergency room: molecular and clinical features differentiate community-onset hospital-associated and community-associated CDI in a tertiary care hospital.

Definition of community-onset, hospital-acquired Clostridium difficile infection (CO-HA-CDI) is difficult in patients presenting with diarrhea at hospitals or outpatient clinics, especially 4 to 12 weeks after the last discharge. We performed C. difficile stool culture for 272 diarrheic patients visiting the emergency room (ER) between January 2006 and June 2010. C. difficile was isolated from 36 cases (13.2%), and isolation rates increased year by year, from 10.1% in 2008 to 12.4% in 2009 and 16.7% in 2010. Among 32 toxin-positive isolates, 13 (40.6%) and 19 (59.4%) were associated with CO-HA-CDI and community-acquired CDI (CA-CDI), respectively, if cases with CDI diagnosed within 12 weeks after discharge were considered hospital associated. The majority (70%) of CO-HA-CDI cases occurred within 2 weeks after hospital discharge, although the interval from discharge to onset of symptoms was as long as 10 weeks. We found via tcdA and tcdB and repetitive sequence PCR analysis, that toxin A-positive/toxin B-positive isolates were the most prevalent in both CO-HA-CDI (53.8%) and CA-CDI (94.7%) cases. Toxin A-negative/toxin B-positive isolates were also still highly associated with HA-CDI cases but were also observed in CA-CDI cases. Younger age, fewer underlying diseases, lack of prior antibiotic use, and genetic diversity of isolates in repetitive sequence PCR were the main characteristics in CA-CDI cases visiting the ER.

Laboratory Diagnostic Methods for Clostridioides difficile Infection: the First Systematic Review and Meta-analysis in Korea.

BACKGROUND: Various methods are used for the diagnosis of Clostridioides difficile infection (CDI). We systematically analyzed and investigated the performance of current laboratory diagnostic methods for CDI. METHODS: We performed systematic review and meta-analysis of studies in PubMed, Web of Science, Cochrane Library, and KoreaMed. The following methods were evaluated: glutamate dehydrogenase (GDH) enzyme immunoassays (GDH EIAs), toxin A and B detection by enzyme immunoassays (toxin AB EIAs), and nucleic acid amplification tests (NAATs) for C. difficile toxin genes. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of each method were calculated. RESULTS: Based on 39 studies, the pooled sensitivities/specificities were 92.7%/94.6%, 57.9%/97.0%, and 90.0%/95.8% for GDH EIAs, toxin AB EIAs, and NAATs, respectively, compared with those of toxigenic culture. The pooled sensitivities of automated EIAs were significantly higher than those of non-automated EIAs for both GDH and toxins A and B. The pooled sensitivity of Xpert C. difficile was significantly higher than those of other NAATs. PPVs increased as CDI prevalence increased, and NPVs were excellent when CDI prevalence was low; at CDI prevalence of 5%, PPV=37%-65% and NPV=97%-100%; at CDI prevalence of 50%, PPV=92%-97% and NPV=65%-98%. CONCLUSIONS: Toxin AB EIAs still show unsatisfactory sensitivity, whereas GDH EIAs and NAATs show relatively high sensitivity. However, toxin AB EIAs are the most specific tests. This study may provide useful information for CDI diagnosis.

A randomized intervention of montelukast for post-bronchiolitis: effect on eosinophil degranulation.

OBJECTIVE: To investigate the effect of montelukast on eosinophil degranulation and recurrent wheezing episodes in post-respiratory syncytial virus (RSV) bronchiolitis. STUDY DESIGN: Two hundred infants (age, 6-24 months) who were hospitalized with their first episode of acute RSV bronchiolitis were randomized in a double-blind, placebo-controlled, parallel comparison of 4-mg montelukast granules (RSV-MONT group) or matching placebo (RSV-PLC group) administered for 3 months. Serum eosinophil-derived neurotoxin (EDN) levels were measured (primary outcome), and recurrent wheezing was documented (secondary outcome) for 12 months. Comparisons were made with control subjects (control group, n = 50). RESULTS: At the end of the 3-month treatment period, the RSV-PLC group (n = 71) exhibited significantly elevated EDN levels (P < .0001), and the RSV-MONT group (n = 79) showed significantly decreased EDN levels (P < .01) when compared with the initial levels. As a result, EDN levels in the 2 RSV groups significantly differed at this point (P < .0001) and remained different for the entire 12-month follow-up period. Cumulative recurrent wheezing episodes at 12 months were significantly lower in the RSV-MONT group (P = .039). CONCLUSION: Montelukast treatment reduces eosinophil degranulation and is associated with a decrease in recurrent wheezing episodes in post-RSV bronchiolitis.

Clinical and epidemiological comparison of human metapneumovirus and respiratory syncytial virus in seoul, Korea, 2003-2008.

Human metapneumovirus (HMPV) shares clinical and epidemiological characteristics with well-known respiratory syncytial virus (RSV). The aim of this study was to investigate the clinical and epidemiological differences between HMPV- and RSV-induced wheezing illnesses. A total of 1,008 nasopharyngeal aspirate specimens was collected from 1,008 pediatric patients hospitalized with acute respiratory tract infection at Inje University Sanggye Paik Hospital from December 2003 to April 2008, and tested for seven common respiratory viruses. Conditions classified as wheezing illness were bronchiolitis, reactive airways disease, and bronchial asthma. HMPV caused a significantly lower proportion of wheezing illness when compared to RSV (48.1% vs. 82.2%, P<0.05). HMPV-induced wheezing illness occurred predominantly in older patients when compared to RSV patients (P<0.001). RSV infections peaked in the fall and winter followed by peaks of HMPV infection in winter and spring. Eosinophil counts were significantly higher (P<0.01) in RSV patients when compared to HMPV patients. These results show that human metapneumovirus patients exhibit several different clinical and epidemiological characteristics, such as higher proportion of wheezing illness, age and seasonal incidence, and eosinophil counts, when compared to RSV patients.

[The incidence and clinical features of Clostridium difficile infection; single center study].

BACKGROUND/AIMS: Clostridium difficile is the predominant cause of nosocomial diarrhea. Recently, the incidence of Clostridium difficile infection (CDI) increases in Europe and North America. A retrospective study was performed to evaluate the change of incidence and clinical features of CDI in Korea. METHODS: From January 2003 to December 2008, inpatients diagnosed with CDI in Seoul Paik hospital were enrolled. The diagnosis of CDI was made when patients complained diarrhea with any positive results in C. difficile toxin assay, stool culture, or endoscopy. The incidence, recurrence rate, and clinical features were compared between early period (2003-2005) and late period (2006-2008). RESULTS: The incidence of CDI was 21.73 cases per 10,000 admitted patients in early period group, and significantly increased to 71.71 cases per 10,000 admitted patients in late period group (p < 0.01). The hospital stay duration at the time of CDI diagnosis was shorter in late period group. Cephalosporin had the highest ratio as the causative antibiotics of CDI. However, there was no difference in recurrence rate between early and late period groups. Recurrence associated clinical factor was serum albumin level. CONCLUSIONS: The incidence of CDI showed increasing tendency during recent 6 years. The awareness of increasing disease burden is the first step in control of CDI.

Algorithm combining toxin immunoassay and stool culture for diagnosis of Clostridium difficile infection.

Enzyme immunoassays (EIA) to detect glutamate dehydrogenase or toxins A (TcdA) and B (TcdB), a cytotoxicity assay, and bacteriologic culture have disadvantages when applied individually to diagnosis of Clostridium difficile infections. Stool specimens (n = 1,596) were subjected to toxin detection via an enzyme-linked fluorescent immunoassay (ELFA; Vidas CDAB assay) and bacteriologic culture for toxigenic C. difficile in a three-step algorithm with additional toxigenic culture. Isolates (n = 163) from ELFA-negative stool specimens were examined via ELFA for toxin production. We amplified tcdA and tcdB from C. difficile isolates and tcdB from stool specimens that were ELFA positive or equivocal and culture negative, and we compared the results to those obtained with the three-step algorithm. More than 26% of stool specimens (419/1,596) were culture positive, yielding 248 isolates (59.2%) with both toxin genes (tcdA- and tcdB-positive isolates), 88 isolates (21.0%) with either tcdA or tcdB, and 83 (19.8%) that had no toxin genes (tcdA- and tcdB-negative isolates). Among 49 (culture-negative/ELFA-positive or -equivocal) stool specimens, 53.1% (26/49) represented tcdB-positive isolates. Therefore, the total number of PCR-positive cases was 362, and 27.1% (98/362) of these were detected through toxigenic culture. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were 63.3%, 96.7%, 90.5%, and 92.4% (ELFA alone); 92.8%, 93.3%, 80.2%, and 97.8% (culture); and 70.7%, 91.4%, 95.5%, and 100% (three-step algorithm ELFA and bacterial culture with toxigenic culture), respectively, with culture and PCR for tcdA and tcdB as the standards. Thus, sensitivity and specificity were highest using culture and ELFA, respectively, but we recommend the three-step algorithm comprising EIA to detect both toxins and toxigenic culture for C. difficile as a practical method for achieving better PPV and NPV.

Comparison of VIDAS CDAB and CDA immunoassay for the detection of Clostridium difficile in a tcdA- tcdB+ C. difficile prevalent area.

Enzyme immunoassays for TcdA and/or TcdB are widely used for diagnosis of C. difficile infection. This study compared the performance of the new VIDAS C. difficile Toxin A & B assay (CDAB) with that of the existing VIDAS C. difficile Toxin A II assay (CDA) in a tcdA(-)tcdB(+) prevalent area. A total of 555 fecal samples were cultured and tested using CDAB and CDA. C. difficile was isolated in 150 samples and the concordance rate was 81.8% (454/555) between CDAB and CDA. PCR assays for tcdA and/or tcdB were used as a confirmatory test on C. difficile strains recovered from culture positive cases (n=150) and on fecal specimens in culture negative/CDAB positive or equivocal cases (n=27). The number of tcdA(+)tcdB(+), tcdA(-)tcdB(+), and tcdA(-)tcdB(-) strains on culture positive isolates (n=150) were 75 (50.0%), 41 (27.3%), and 34 (22.7%), respectively. PCR assays for tcdB gene alone in stool specimens (n=27) showed positivity in five cases. The sensitivity of VIDAS CDAB was higher than that of VIDAS CDA (65.3% vs. 29.8%), by more than 2-fold. The specificity of CDAB was almost the same as CDA (93.8% vs. 94.5%). Toxigenic culture of C. difficile isolates in culture positive/VIDAS CDAB negative cases (n=62) additionally detected 22 VIDAS CDAB positive and 9 VIDAS CDAB equivocal cases. The VIDAS CDAB assay detects more tcdA(+)tcdB(+) strains (60% vs. 45.3%) and tcdA(-)tcdB(+) strains (70.7% vs. 0%) compared with VIDAS CDA.

Laboratory Diagnosis of Clostridium difficile Infection in Korea: The First National Survey.

In May 2015, we conducted a voluntary online survey on laboratory diagnostic assays for Clostridium difficile infection (CDI) across clinical microbiology laboratories in Korea. Responses were obtained from 66 laboratories, including 61 hospitals and five commercial laboratories. Among them, nine laboratories reported having not conducted CDI assays. The toxin AB enzyme immunoassay (toxin AB EIA), nucleic acid amplification test (NAAT), and C. difficile culture, alone or in combination with other assays, were used in 51 (89.5%), 37 (64.9%), and 37 (64.9%) of the remaining 57 laboratories, respectively, and 23 (40.4%) of the laboratories performed all three assays. Only one laboratory used the glutamate dehydrogenase assay. Nine laboratories used the toxin AB EIA as a stand-alone assay. The median (range) of examined specimens in one month for the toxin AB EIA, NAAT, and C. difficile culture was 160 (50-2,060), 70 (7-720), and 130 (9-750), respectively. These findings serve as valuable basic data regarding the current status of laboratory diagnosis of CDI in Korea, offering guidance for improved implementation.

Emerging toxin A-B+ variant strain of Clostridium difficile responsible for pseudomembranous colitis at a tertiary care hospital in Korea.

Sixty percent to 80% of Clostridium difficile isolates in Korea have been reported to be toxigenic. However, over 1 year, we encountered a high number of tcdA-tcB+ strains associated with pseudomembranous colitis (PMC). C. difficile was isolated from 224 of 471 specimens (47.6%) from 371 patients. A subset of the culture-positive specimens (n = 106), containing no duplicate cases, was randomly selected for tcdA and tcdB polymerase chain reaction (PCR) assays. PCR results showed that tcdA+tcdB+ and tcdA-tcdB+ strains accounted for 39.6% (42/106) and 50.9% (54/106), respectively. Endoscopy, performed on 55/106 patients, revealed 29 with PMC, 5 with colitis, 14 with other colon diseases, and 7 normal cases. Among the 29 PMC cases, 21 (72.4%) were associated with tcdA-tcdB+ strains (P = 0.0016). These results revealed the possible emergence of tcdA-tcdB+ C. difficile strains in Korea, and these variant strains could evoke a higher rate of PMC than tcdA+tcdB+ strains.

Multicentre study of the prevalence of toxigenic Clostridium difficile in Korea: results of a retrospective study 2000-2005.

The prevalence of toxigenic Clostridium difficile in Korea has been reported to be approximately 60-80%. Although the prevalence of the tcdA(-)tcdB(+) C. difficile strain was less then 5% prior to the year 2000, it has become an emerging nosocomial pathogen in Korea. Therefore, we have attempted to determine the multicentre nationwide prevalence of tcdA(+)tcdB(+) and tcdA(-)tcdB(+) C. difficile for epidemiological purposes. C. difficile strains (n=724, 30 from 2000, 80 from 2001, 74 from 2002, 76 from 2003, 179 from 2004, 285 from 2005) were obtained retrospectively from January 2000 to December 2005 from in-patients at 6 hospitals, all of whom were suspected of having C. difficile-associated disease (CDAD), colitis or pseudomembranous colitis. The numbers of participating hospitals varied yearly (1 in 2000, 2 in 2001-2003, 3 in 2004, 5 in 2005). The hospitals were located in Seoul (n=4), Kyunggi Province (n=1) and Busan (n=1), Korea. PCR assays for tcdA and tcdB genes were conducted using 724 unduplicated C. difficile isolates. The mean prevalence of tcdA(+)tcdB(+) and tcdA(-)tcdB(+) C. difficile strains over the 6 years was 51.8 % (38.4-59.3%) and 25.8%(10-56.0%), respectively. The mean prevalence of tcdA(-)tcdB(+) C. difficile strains was less than 7% until 2002, but began to increase in 2003 (13.2%) and achieved a peak in 2004 (50.3%). In 2005, the mean prevalence of tcdA(+)tcdB(+) and tcdA(-)tcdB(+) C. difficile strains was 47.7% (30.9-60.3%) and 27.0% (17.6-54.8%), respectively. This nationwide epidemiological study showed that tcdA(-)tcdB(+) C. difficile strains have already spread extensively throughout Korea, and our results provide basic data regarding the controversies currently surrounding the toxigenicity of tcdA(-)tcdB(+) C. difficile. The use of enzyme immunoassays capable of detecting both TcdA and TcdB is strongly recommended for the diagnosis of CDAD in microbiology laboratories, in order to control the spread of the tcdA(-)tcdB(+) strains of C. difficile.

Species distribution and susceptibility to azole antifungals of Candida bloodstream isolates from eight university hospitals in Korea.

PURPOSE: The incidence of Candida bloodstream infections (BSI) has increased over the past two decades. The rank order of occurrence and the susceptibility to antifungals of the various Candida species causing BSI are important factors driving the establishment of empirical treatment protocols; however, very limited multi-institutional data are available on Candida bloodstream isolates in Korea. MATERIALS AND METHODS: We investigated the susceptibility to azole antifungals and species distribution of 143 Candida bloodstream isolates recovered from eight university hospitals over a six-month period. Minimal inhibitory concentrations (MICs) of fluconazole, itraconazole, and voriconazole for each isolate were determined by the broth microdilution method of the Clinical and Laboratory Standards Institute (CLSI). RESULTS: The Candida species recovered most frequently from the blood cultures was C. albicans (49%), followed by C. parapsilosis (22%), C. tropicalis (14%), and C. glabrata (11%). The MIC ranges for the Candida isolates were 0.125 to 64 microg/mL for fluconazole, 0.03 to 2 microg/mL for itraconazole, and 0.03 to 1 microg/mL for voriconazole. Overall, resistance to fluconazole was found in only 2% of the Candida isolates (3/143), while the dose-dependent susceptibility was found in 6% (8/143). The resistance and dose-dependent susceptibility of itraconazole were found in 4% (6/143) and 14% (20/143) of the isolates, respectively. All bloodstream isolates were susceptible to voriconazole (MIC, < or = 1 microg/mL). CONCLUSION: Our findings show that C. albicans is the most common cause of Candida-related BSI, followed by C. parapsilosis, and that the rates of resistance to azole antifungals are still low among bloodstream isolates in Korea.

Prevalence and clinical implications of Staphylococcus aureus with a vancomycin MIC of 4 microg/ml in Korea.

In addition to vancomycin-intermediate Staphylococcus aureus (VISA), S. aureus with a vancomycin MIC of 4 microg/ml has been reported to be the cause of therapeutic failure. This study was designed to determine the prevalence of methicillin-resistant S. aureus (MRSA) with a vancomycin MIC of 4 microg/ml and to clarify the clinical characteristics of infections caused by these isolates. During the 8-week period from April to May, 2001, 27 hospitals participated in a nationwide surveillance program for VISA and vancomycin-resistant S. aureus (VRSA) in Korea. After screening on brain-heart infusion agar containing 4 microg/ml of vancomycin as previously described, 100 isolates with confluent growth were tested. The medical records of the patients involved were reviewed. Even though VISA or VRSA was not detected among 3,756 MRSA isolates, 18 (0.5%) had a vancomycin MIC of 4 microg/ml. The infections in 12 of these patients, excluding 5 that were colonized, were 8 chronic osteomyelitis, 1 surgical site infection, 1 pneumonia, 1 intra-abdominal infection, and 1 catheter-related infection. Although 11 cases were exposed to glycopeptides for a long time (median 56 days), the site of infection became culture-negative in only 1 case. Two patients died of their S. aureus infections. MRSA with a vancomycin MIC of 4 microg/ml was rare. Chronic osteomyelitis was the most common type of infection, and prolonged exposure to glycopeptides was associated with reduced susceptibility to vancomycin.

Evaluation of Xpert C. difficile, BD MAX Cdiff, IMDx C. difficile for Abbott m2000, and Illumigene C. difficile Assays for Direct Detection of Toxigenic Clostridium difficile in Stool Specimens.

BACKGROUND: We evaluated the performance of four commercial nucleic acid amplification tests (NAATs: Xpert C. difficile, BD MAX Cdiff, IMDx C. difficile for Abbott m2000, and Illumigene C. difficile) for direct and rapid detection of Clostridium difficile toxin genes. METHODS: We compared four NAATs on the same set of 339 stool specimens (303 prospective and 36 retrospective specimens) with toxigenic culture (TC). RESULTS: Concordance rate among four NAATs was 90.3% (306/339). Based on TC results, the sensitivity and specificity were 90.0% and 92.9% for Xpert; 86.3% and 89.3% for Max; 84.3% and 94.4% for IMDx; and 82.4% and 93.7% for Illumigene, respectively. For 306 concordant cases, there were 11 TC-negative/NAATs co-positive cases and 6 TC-positive/NAATs co-negative cases. Among 33 discordant cases, 18 were only single positive in each NAAT (Xpert, 1; Max, 12; IMDx, 1; Illumigene, 4). Positivity rates of the four NAATs were associated with those of semi-quantitative cultures, which were maximized in grade 3 (>100 colony-forming unit [CFU]) compared with grade 1 (<10 CFU). CONCLUSIONS: Commercial NAATs may be rapid and reliable methods for direct detection of tcdA and/or tcdB in stool specimens compared with TC. Some differences in the sensitivity of the NAATs may partly depend on the number of toxigenic C. difficile in stool specimens.

Analytical and Clinical Validation of Six Commercial Middle East Respiratory Syndrome Coronavirus RNA Detection Kits Based on Real-Time Reverse-Transcription PCR.

BACKGROUND: During the 2015 outbreak of Middle East Respiratory Syndrome coronavirus (MERS-CoV), six different commercial MERS-CoV RNA detection kits based on real-time reverse-transcription polymerase chain reaction (rRT-PCR) were available in Korea. We performed analytical and clinical validations of these kits. METHODS: PowerChek (Kogene Biotech, Korea), DiaPlexQ (SolGent, Korea), Anyplex (Seegene, Korea), AccuPower (Bioneer, Korea), LightMix (Roche Molecular Diagnostics, Switzerland), and UltraFast kits (Nanobiosys, Korea) were evaluated. Limits of detection (LOD) with 95% probability values were estimated by testing 16 replicates of upstream of the envelope gene (upE) and open reading frame 1a (ORF1a) RNA transcripts. Specificity was estimated by using 28 nasopharyngeal swabs that were positive for other respiratory viruses. Clinical sensitivity was evaluated by using 18 lower respiratory specimens. The sensitivity test panel and the high inhibition panel were composed of nine specimens each, including eight and six specimens that were positive for MERS-CoV, respectively. RESULTS: The LODs for upE ranged from 21.88 to 263.03 copies/reaction, and those for ORF1a ranged from 6.92 to 128.82 copies/reaction. No cross-reactivity with other respiratory viruses was found. All six kits correctly identified 8 of 8 (100%) positive clinical specimens. Based on results from the high inhibition panel, PowerChek and AccuPower were the least sensitive to the presence of PCR inhibition. CONCLUSIONS: The overall sensitivity and specificity of all six assay systems were sufficient for diagnosing MERS-CoV infection. However, the analytical sensitivity and detection ability in specimens with PCR inhibition could be improved with the use of appropriate internal controls.

Metallo-beta-lactamase-producing Gram-negative bacilli in Korean Nationwide Surveillance of Antimicrobial Resistance group hospitals in 2003: continued prevalence of VIM-producing Pseudomonas spp. and increase of IMP-producing Acinetobacter spp.

Metallo-beta-lactamase (MBL)-producing Pseudomonas spp. and Acinetobacter spp. were prevalent in Korean hospitals. In this study, the prevalence and presence of MBL-producing isolates among imipenem-nonsusceptible and imipenem-susceptible isolates, respectively, were screened. The genetic and phenotypic characteristics of MBL-producing isolates were determined. Among imipenem-nonsusceptible isolates, 52 (11.1%) of 467 Pseudomonas spp. were blaVIM-like allele-positive, and 33 (15.1%) of 218 Acinetobacter spp. were either blaVIM- or blaIMP-like allele-positive. One blaVIM-like allele-positive isolate of Acinetobacter spp. was detected among 84 imipenem-susceptible Acinetobacter isolates. The minimum inhibitory concentration for 90% of isolates of imipenem was higher (>128 microg/mL) for Pseudomonas spp. than Acinetobacter spp. (16 microg/mL), although both had blaVIM-like allele. The source of MBL-producing isolates was mostly the sputum and urine of patients in the intensive care unit. Pulsed-field gel electrophoresis analysis suggested the intra- and inter-hospital spread of MBL-producing strains at some hospitals. In conclusion, blaVIM-like allele-positive P. aeruginosa remained highly prevalent, and the proportion of blaIMP-like allele-positive Acinetobacter spp. has increased significantly in most Korean hospitals.