Bacteremia due to Rochalimaea henselae in a child: practical identification of isolates in the clinical laboratory.

Two closely related species of Rochalimaea, Rochalimaea quintana and Rochalimaea henselae, are nutritionally fastidious but can be cultivated on bacteriologic media from the blood of patients with diverse clinical presentations. We report a case of culture-proven R. henselae bacteremia in a child with persistent fever. Serologic evidence of infection by R. henselae was ascertained by testing sera at two intervals for immunoglobulin G or immunoglobulin M antibodies by enzyme immunoassay and immunoblot. The case isolate and a collection of other strains (R. henselae, R. quintana, and related organisms) were used to test commercial identification systems for their comparative utility in the identification of Rochalimaea spp. on a practical basis. Of six systems designed for testing of either fastidious or anaerobic isolates of bacteria, the MicroScan Rapid Anaerobe Panel was the only system that distinguished R. henselae from R. quintana. Four of five others gave reactions that were unique within their data bases but did not distinguish Rochalimaea isolates at the species level.     

Evaluation of the MicroScan Urinary Combo Panel and API 20E system for identification of glucose-nonfermenting gram-negative bacilli isolated from clinical veterinary materials

Many isolates of glucose-nonfermenting gram-negative bacilli (NFB) cultured from clinical veterinary specimens are not identified because of the large number of identification tests required. We evaluated two commercial identification systems to determine if they could accurately identify NFB isolated from animals. Of 182 strains of NFB, the MicroScan Urinary Combo Panel (MicroScan, Inc., Campbell, Calif.) correctly identified 72%, and the API 20E system (Analytab Products, Plainview, N.Y.) correctly identified 74%. Of the 118 strains of the three most common species of NFB isolated from animals, the MicroScan Urinary Combo Panel identified 86% correctly, and the API 20E system identified 92% correctly. The use of either of these systems could improve the accuracy of identification of NFB from clinical veterinary materials.     

Evaluation of the MicroScan system for identification of staphylococci

Conventional biochemical tests were compared with reactions in a multiple test system, MicroScan Walkaway (Dade Diagnostic Inc. MicroScan Divison, West Sacramento, California) in conjugation with the Combo Pos ID Panels (Dade Diagnostic Inc. MicroScan Divison, West Sacramento, California), in order to evaluate the accuracy for the identification of 99 clinical isolates of Staphylococcus spp. and five reference strains. False-negative or positive reactions were detected from Voges-Proskauer, urease and mannose tests. A good correlation was found among the two identification systems for the fermentation of trehalose, lactose, raffinose, as well as for arginine dyhydrolase, esculin hydrolisis and nitrate reduction. From the results of the present study, it is concluded that the MicroScan Walkaway system is a reliable method for identification of staphylococci (94.23%), although 8.2% could be identified to the species level only after use of additional test.     

Identification of clinical isolates of actinomyces species by amplified 16S ribosomal DNA restriction analysis

Amplified 16S ribosomal DNA (rDNA) restriction analysis (ARDRA), using enzymes HaeIII and HpaII, was applied to 176 fresh and 299 stored clinical isolates of putative Actinomyces spp. referred to the Anaerobe Reference Unit of the Public Health Laboratory Service for confirmation of identity. Results were compared with ARDRA results obtained previously for reference strains and with conventional phenotypic reactions. Identities of some strains were confirmed by analysis of partial 16S rDNA sequences. Of the 475 isolates, 331 (70%) were clearly assigned to recognized Actinomyces species, including 94 isolates assigned to six recently described species. A further 52 isolates in 12 ARDRA profiles were designated as apparently resembling recognized species, and 44 isolates, in 18 novel profiles, were confirmed as members of genera other than Actinomyces. The identities of 48 isolates in nine profiles remain uncertain, and they may represent novel species of Actinomyces. For the majority of species, phenotypic results, published reactions for the species, and ARDRA profiles concurred. However, of 113 stored isolates originally identified as A. meyeri or resembling A. meyeri by phenotypic tests, only 21 were confirmed as A. meyeri by ARDRA; 63 were reassigned as A. turicensis, 7 as other recognized species, and 22 as unidentified actinomycetes. Analyses of incidence and clinical associations of Actinomyces spp. add to the currently sparse knowledge of some recently described species.     

Identification of the emerging pathogen Vibrio vulnificus biotype 3 by commercially available phenotypic methods

Identification of the emerging pathogen Vibrio vulnificus biotype 3 has become a challenge for clinical laboratories in the last few years. In this study, the abilities of five commercial systems to identify this new species have been evaluated for the first time, using a unique collection of strains. Fifty-one well-documented wild strains of V. vulnificus biotype 3 were processed using API 20 NE, GNI+ Vitek 1 cards, ID-GNB Vitek 2 cards, Neg Combo 20 Microscan panels, and NMIC/ID-5 BD Phoenix panels. The numbers of strains identified as V. vulnificus by ID-GNB, NMIC/ID-5, and GNI+ were 50 (98.0%), 46 (90.2%), and 7 (13.7%), respectively. Neg Combo 20 Microscan panels and API 20 NE were unable to identify any of the strains of this emerging pathogen to the species level and mostly misidentifies them as other species of the Vibrionaceae family. Data on the phenotypic pattern of V. vulnificus biotype 3 when processed in all five systems as presented here could help clinical laboratories in identifying this new pathogen.     

A comparison of Sensititre™ Anaerobe MIC plate with ATB ANA® test for the routine susceptibility testing of common anaerobe pathogens

The accuracy of the Thermo Scientific? Sensititre? Anaerobe MIC plate was assessed against the ATB ANA® test (bioMérieux) on 56 clinically relevant anaerobic strains collected at Geneva University Hospitals. The overall categorical agreement between both methods reached 95%. The Sensititre? Anaerobe MIC plate had excellent accuracy for most antibiotics tested. When the Sensititre? Anaerobe MIC plate disagreed with ATB ANA® test, the gradient strip method resolved the antimicrobial susceptibility categories of all the antibiotics tested, except for piperacillin, piperacillin-tazobactam, and penicillin, in favor of the Sensititre? Anaerobe MIC plate (58% [21 out of 36]). Several very major errors were observed for piperacillin (12.5% [7 out of 56]), piperacillin-tazobactam (12.5% [7 out of 56]), and penicillin (2% [1 out of 56]). The gradient strip method revealed that the categorical differences for piperacillin, piperacillin-tazobactam, and penicillin were at least partly explained by heterogeneity in resistance expression. The Sensititre? Anaerobe MIC plate offers therefore a useful alternative to the ATB ANA® test for the routine antimicrobial susceptibility testing of anaerobes in clinical microbiology laboratories.     

Evaluation of the IDS RapID SS/u system for rapid identification of urinary microorganisms

The accuracy of a new rapid identification system for common urinary pathogens was compared with that of conventional methods and of miniaturized 18-24-hour identification panels. The rapid system, RapID SS/u (Innovative Diagnostic System Inc., Atlanta, GA) is a non-growth-dependent micro-method that identifies selected gram-negative bacilli, gram-positive cocci, and yeasts in two hours by detection of constitutive enzymes acting on chromogenic substrates. A total of 185 representative clinical urinary isolates were tested, including 24 gram-positive cocci, 140 gram-negative bacilli, and 21 yeasts. Identifications by the rapid system were compared with the ones obtained by reference conventional methods for gram-positive cocci and yeasts. For gram-negative bacilli, identifications were compared with the ones obtained by MicroScan Combo Panel (American MicroScan, Mahwah, NJ), and all discrepancies were resolved by testing with API 20E (Analytab Products, Plainview, NY). Overall, the RapID SS/u system correctly identified to genus 160 of 185 isolates (86.5%). For 14 additional isolates (7.6%) the system provided probability overlap identifications that required further testing. Two (1%) isolates failed to be identified, and nine isolates (4.9%) were misidentified by the system. Discrepancies involved five strains of Citrobacter, one Enterobacter, one Morganella, and one Providencia species. The authors conclude that the RapID SS/u system provided rapid and accurate genus identification of most microorganisms commonly isolated from urine.     

Comparison of media in the Anaerobe-Tek and Presumpto plate systems and evaluation of the Anaerobe-Tek system for identification of commonly encountered anaerobes.

Using a variety of sporeforming and nonsporeforming anaerobic bacteria, we compared 10 differential agar media of the Anaerobe-Tek (A/T) system recently marketed by Flow Laboratories, Inc. (McLean, Va.) with 10 comparable media in Presumpto quadrant plates (Presumpto 1, 2, and 3) developed by the Centers for Disease Control Anaerobic Bacteria Branch. The A/T identification system was evaluated by comparing the species identity of anaerobes determined as recommended by the manufacturer's instruction manual with the identity of the strains obtained by the Centers for Disease Control Anaerobe Reference Laboratory by using conventional procedures. We also compared reactions obtained with the Presumpto plates with a chopped meat glucose broth culture as a source of inoculum with those obtained by using a turbid cell suspension from growth on blood agar as inoculum. The agreement of results for the 16 characteristics compared ranged from 92.8 to 100%. Comparison of test results obtained with 10 media in the Presumpto plate and A/T systems from the examination of 223 strains of anaerobes, representing 54 different taxa, showed the following agreement between A/T and CDC systems: catalase production, esculin hydrolysis, glucose fermentation, and lecithinase production (100%); inhibition of growth by bile agar (99.6%); lipase production (99%); DNase (98.7%); fermentation of lactose and mannitol (98.2%); starch hydrolysis (96.9%); gelatin hydrolysis (96.4%); and casein hydrolysis (94.6%). Of the 204 strains of common anaerobes tested with the A/T system, only 70% were correctly identified to the species level. However, several strains could have been identified correctly with the A/T system if data on certain other characteristics had been included in the A/T data base.     

Clinical comparison of anaerobic blood-culture media for detecting bacteraemia due to viridans streptococci and oral anaerobes

Brain heart infusion cysteine broth, with and without Panmede (a papain digest of ox liver) and Fastidious Anaerobe Broth, with and without Liquoid, were compared by inoculating the broths with blood collected from each of 51 patients, 2 min after dental extraction. Bacteraemia caused by viridans streptococci or oral non-sporing anaerobes or both was detected in 39 patients (76%). Detection of bacteraemia caused by viridans streptococci and anaerobes was more rapidly achieved by the addition of Panmede to brain heart infusion broth. Significantly more cases of bacteraemia caused by viridans streptococci were detected by use of the Panmede-containing medium than by use of Fastidious Anaerobe Broth after incubation of the broths for only 1 day. Use of brain heart infusion cysteine broth with and without Panmede, and Fastidious Anaerobe Broth permitted detection of bacteraemia caused by viridans streptococci in 26, 11 and 22 patients respectively during incubation for 2 weeks. Bacteraemia caused by anaerobes was detected by use of these three media in 24, 13 and 23 patients respectively. The addition of Liquoid to Fastidious Anaerobe Broth had no significant effect on the detection of bacteraemia caused by viridans streptococci or anaerobes. The Panmede-containing blood-culture medium should be a useful anaerobic broth in the investigation of patients with suspected endocarditis, because viridans streptococci are also rapidly detected.     

Evaluation of the BBL Crystal Anaerobe identification system.

The BBL Crystal Anaerobe (ANR) identification system was evaluated, and the results were compared with those from conventional anaerobic methods. We tested 322 clinically significant anaerobic bacteria according to the manufacturer's instructions. The system identified correctly 286 of 322 (88.8%) of the anaerobic bacteria tested. Of these, 263 of 322 (81.7%) were identified correctly on initial testing and 49 were identified correctly only to the genus level; on repeat testing, 23 of 49 (46.9%) were identified correctly to both the genus and the species levels. A total of 26 (8.5%) were misidentified at the species level, and 10 (3.1%) were not identified. Performance characteristics for individual strains varied. The system correctly identified all tested strains of Campylobacter, Desulfomonas, Desulfovibrio, Leptotrichia, Mobiluncus, Peptostreptococcus, Porphyromonas, Provetella, Propionibacterium, Tisierella, and Veillonella and 36 of 37 (97.3%) Actinomyces strains, 42 of 46 (91.3%) B. fragilis group strains, 79 of 103 (76.7%) Clostridium strains, (however, the system failed to identify any of the 7 C. innocuum and 9 C. tetani strains tested), and 8 of 15 (53.3%) Bacteroides strains. This system was easy to use, did not involve the addition of reagents, and was faster than conventional anaerobic procedures. It would be a useful addition to the anaerobe laboratory of most hospitals.     

Performance of serological and molecular tests within acute HIV infection

BackgroundEarly diagnosis of acute HIV infection can be challenging and is critical in regards to early therapeutic decision making.ObjectivesTo evaluate the performance of different HIV tests in detecting early infections.Study designA total of 83 leftover specimens of 61 study participants who seroconverted were used in this sub-study. 35 HIV RNA positive but still seronegative specimens (acute infections) were used for analysis of the sensitivity of the different assays in detecting early infections and 42 HIV RNA and antibody negative specimens were used for specificity analysis.ResultsFour (11%) specimens out of 35 acute infections were reactive with the Enzygnost^® Anti-HIV 1/2 Plus and 12/35 (34%) with the Vironostika^® HIV Ag/Ab. 16 (46%) specimens were confirmed as acute by the INNOTEST^® HIV antigen mAb Antigen test. Only three (9%), 10 (29%) and 9 (27%) specimens were reactive with the Determine HIV-1/2 Ag/Ab Combo, SD Bioline HIV Ag/Ab Combo test and the HIV Combo test, respectively. The specificity of the different tests were 100%, 95%, 100%, 93%, 100% and 93% for Enzygnost^® Anti-HIV 1/2 Plus, Vironostika^® HIV Ag/Ab, INNO-Test HIV antigen mAb, Determine HIV-1/2 Ag/Ab Combo, SD Bioline HIV Ag/Ab Combo test and HIV Combo test respectively.ConclusionRNA test, 4th generation ELISA and Single Ag test are the most sensitive tests for detection of an acute infection. As an alternative, the HIV Combo test is generally slightly more sensitive compared to its previous version, but the SD Bioline HIV Ag/Ab Combo tests has the best performance compared to the other simple rapid tests (SRTs) but none of them are precise in detecting Ag in the determination of acute infections.     

Evaluation of autoSCAN-W/A and the Vitek GNI+ AutoMicrobic system for identification of non-glucose-fermenting gram-negative bacilli

The autoSCAN-W/A (W/A; Dade Behring Microscan Inc., West Sacramento, Calif.) and Vitek AutoMicrobic System (Vitek AMS; bioMérieux Vitek Systems, Inc., Hazelwood, Mo.) are both fully automated microbiology systems. We evaluated the accuracy of these two systems in identifying nonglucose-fermenting gram-negative bacilli. We used the W/A with conventional-panel Neg Combo type 12 and Vitek GNI+ identification systems. A total of 301 isolates from 25 different species were tested. Of these, 299 isolates were identified in the databases of both systems. The conventional biochemical methods were used for reference. The W/A correctly identified 215 isolates (71. 4%) to the species level at initial testing with a high probability of >/=85%. The Vitek GNI+ correctly identified 216 isolates (71.8%) to the species level at initial testing with a high probability of >/=90%. After additional testing that was recommended by the manufacturer's protocol, the correct identifications of the W/A and Vitek GNI+ improved to 96.0 and 92.3%, respectively. The major misidentified species were Sphingomonas paucimobilis and Agrobacterium radiobacter in the W/A system and Acinetobacter lwoffii, Chryseobacterium indologenes, and Comamonas acidovorans in the Vitek GNI+ system. The error rates were 4.0 and 7.6%, respectively. The overall accuracy for both systems was above 90% if the supplemental tests were applied. There was no significant difference in accuracy (P > 0.05) between the two systems.     

Comparison of four commercial brucella agar media for growth of anaerobic organisms.

Four different commercial brucella blood agar plating media (Anaerobe Systems, BBL Microbiology Systems, Remel, and Scott Laboratories) were compared for the abilities to recover anaerobic organisms from clinical specimens and to support the growth of American Type Culture Collection anaerobic stock cultures. Following 24 h of incubation in an anaerobe chamber, Anaerobe Systems prereduced, anaerobically sterilized brucella plates yielded 63% of the total clinical anaerobe isolates, the Scott medium yielded 51%, the Remel medium yielded 42%, and the BBL medium yielded 37%. Poor growth of Peptostreptococcus magnus, P. anaerobius, Fusobacterium necrophorum, F. nucleatum, and pigmented Bacteroides spp. was observed on brucella media obtained from BBL, Remel, and Scott. Data obtained with stock anaerobic cultures showed that Anaerobe Systems plates yielded good growth and produced a larger colony size with all of the strains tested in 1 day, whereas poor growth of Peptostreptococcus spp., B. melaninogenicus, and Fusobacterium spp. was noted on brucella media from BBL, Remel, and Scott.     

Comparison of PRAS II, RapID ANA, and API 20A systems for identification of anaerobic bacteria.

This study evaluated the PRAS II, RapID ANA, and API 20A systems for the identification of anaerobic bacteria. A total of 80 isolates (68 fresh clinical isolates and 12 stock cultures) were examined and included 25 Bacteriodes spp., 7 Fusobacterium spp., 12 Clostridium spp., 2 Veillonella spp., 16 gram-positive cocci, and 18 gram-positive nonsporeforming bacilli. All isolates were initially identified by the procedures outlined in Holdeman et al. (ed.), Anaerobe Laboratory Manual, Virginia Polytechnic Institute and State University, Blacksburg, Va., 1977; identifications from the PRAS II, RapID ANA, and API 20A systems were compared with these initial identifications. If no supplemental tests were required, the RapID ANA and API 20A systems had incubation times of 4 and 24 h, respectively; the PRAS II system generally required 2 to 5 days of incubation, depending on the growth rate of the isolate. PRAS II identified 74% correct to species level, 14% correct to genus only, and 6% incorrect; 6% could not be identified. PRAS II data were reevaluated according to a revised data base that was provided after completion of the study; PRAS II (revised) identified 82% correct to species, 12% correct to genus only, and 6% incorrect. RapID ANA identified 62% correct to the species level, 28% correct to genus only, and 10% incorrect. API 20A identified 71% correct to the species level, 10% correct to genus only, and 3% incorrect; 16% could not identified. The API 20A is a more established system for identification of anaerobic bacteria; PRAS II and RapID ANA appear to be promising new methods for the identification of anaerobic bacteria.     

Cost savings associated with testing of antibodies, antigens, and nucleic acids for diagnosis of acute HIV infection

Efforts to identify all persons infected with HIV in the United States are driven by the hope that early diagnosis will lower risk behaviors and decrease HIV transmission. Identification of HIV-infected people earlier in the course of their infection with HIV antigen/antibody (Ag/Ab) combination assays (4th-generation HIV assays) should help achieve this goal. We compared HIV RNA nucleic acid test (NAT) results to the results of a 4th-generation Ag/Ab assay (Architect HIV Ag/Ab Combo [HIV Combo] assay; Abbott Diagnostics) in 2,744 HIV antibody-negative samples. Fourteen people with acute HIV infection (HIV antibody negative/NAT positive) were identified; the HIV Combo assay detected nine of these individuals and was falsely negative in the remaining five. All five persons missed by the HIV Combo assay were in the stage of exponential increase in plasma virus associated with acute HIV infection (3, 7, 20, 35, 48). In contrast, most acutely infected persons detected by the HIV Combo assay demonstrated either a plateauing or decreasing plasma viral load. The HIV Combo assay also classified as positive five other samples which were negative by NAT. Taken together, the HIV Combo assay had a sensitivity of 73.7% and a specificity of 99.8%. Using published data, we estimated secondary transmission events had HIV infection in these five individuals remained undiagnosed. Screening of our population with NAT cost more than screening with the HIV Combo assay but achieved new diagnoses that we predict resulted in health care savings that far exceed screening costs. These findings support the use of more sensitive assays, like NAT, in HIV screening of populations with a high prevalence of acute HIV infection.     

Comparison of the autoSCAN-W/A rapid bacterial identification system and the Vitek AutoMicrobic system for identification of gram-negative bacilli

The autoSCAN-W/A (W/A; Baxter MicroScan, West Sacramento, Calif.) with the new fluorometric Rapid Neg Combo 1 (RNC) panel is a fully automated fluorometric system for identification of both enteric and nonenteric gram-negative bacilli within 2 h. We compared the W/A with the Vitek AutoMicrobic System (Vitek AMS; Vitek Systems, Inc., Hazelwood, Mo.) for identification of 383 clinical isolates of gram-negative bacilli. The API 20E (Analytab Products, Plainview, N.Y.) and conventional biochemical testing were used as the reference systems. The W/A correctly identified 336 isolates (87.7%) to the species level and classified an additional 29 isolates (7.6%) as correct with low probability (overall identification = 95.3%); the Vitek AMS correctly identified 355 isolates (92.7%) to the species level and classified an additional 8 isolates (2.1%) as correct with low probability (overall identification = 94.8%). A common set of 134 isolates of gram-negative bacilli was tested in both participating laboratories as a means of assessing interlaboratory agreement with both the W/A and the Vitek AMS. The overall agreements between the two laboratories were 86% with the W/A and 92% with the Vitek AMS. The W/A performed comparably to the Vitek AMS for identification of most gram-negative bacilli, actually exceeding the Vitek AMS for identification of nonenteric bacilli. Rapid time to identification and a high level of automation make the W/A an attractive system for clinical microbiology laboratories.     

Evaluation of MicroScan Rapid Pos Combo panels for identification of staphylococci.

MicroScan Rapid Pos Combo panels (Baxter Diagnostics, Inc., MicroScan, West Sacramento, Calif.) contain substrates conjugated with fluorophores and substrates with a fluorescent pH indicator. AutoSCAn W/A, an automated panel processor equipped with a fluorometer, reads the panels after 2 h of incubation and can identify staphylococci to the species level. We tested 239 strains belonging to 17 species of staphylococci. All the strains were identified by conventional methods (W.E. Kloos and K.H. Schleifer, J. Clin. Microbiol. 1:82-88, 1975) and by the MicroScan Rapid ID system. The system correctly identified 219 (91.6%) strains; nine (3.8%) identification results were probably correct, and six (2.5%) results were incorrect. The system designated five (2.1%) strains as rare biotypes. The automated MicroScan Rapid ID system is useful and reliable in identifying most human isolates of staphylococci encountered in the clinical laboratory.     

Evaluation of the rapid CORYNE identification system for Corynebacterium species and other coryneforms.

The Rapid CORYNE system for identification of aerobic, nonsporeforming, gram-positive rods was evaluated according to the manufacturer's instructions with 177 organisms. After inoculation with a heavy suspension of growth, strips containing 20 cupules were incubated for 24 h, reagents were added, and the results of 21 biochemical reactions were recorded as numerical profiles. The strains consisted of pathogenic species of the genus Corynebacterium, primarily C. diphtheriae (n = 29), opportunistic species of Corynebacterium including C. jeikeium (n = 75), recognized species of non-corynebacteria such as Gardnerella and Arcanobacterium (n = 51), and Centers for Disease Control (CDC) coryneform groups (n = 22). Results from single tests read after 24 h yielded correct identifications to species level with no additional tests for 26 (89.7%) of the pathogenic species; 64 (85.3%) of the opportunistic organisms; 51 (100%) of the non-corynebacteria, and 8 (36.4%) of the CDC coryneform groups. Supplemental tests produced the correct identification for three additional pathogenic isolates (100% total) and four additional isolates from the opportunistic species (90.6% total). Twelve of the 15 isolates not identified by the system were in the CDC coryneform groups. Four of the six misidentified and one of the unidentified isolates were C. matruchotii, which was not included in the data base. The system is an excellent rapid alternative to conventional biochemical tests.     

Four methods for identification of gram-negative nonfermenting rods: organisms more commonly encountered in clinical specimens.

Four commercial kits, Oxi/Ferm (OF), API 20E (AP), Minitek (MT; BBL Microbiology Systems), and Flow N/F (NF), were evaluated, without additional tests, for identification of 258 gram-negative nonfermentative rods. OF and MT were read after 48 h of incubation, and AP and NF were read after both 24 and 48 h of incubation, respectively. Overall, OF correctly identified 51% of strains, with 46% as part (but not first) of a spectrum of identifications (SI), and 3% incorrect species identification. MT yielded 85% correct identification, with 15% SI. Of 126 glucose-positive strains, or those with greater than or equal to 3 positive AP reactions after 24 h, 60% were correctly identified, with 40% SI; incubation for an additional 24 h raised the rate of correct identification to 99%, with 1% SI. A total of 132 strains yield less than 3 positive AP reactions after 24 h and were identified after 48 h only; of these, 82% were correctly identified, with 17% SI and 1% incorrect species identification. NF correctly identified 79% of cultures after 24 h, with 21% SI; corresponding figures after an additional 24 h of incubation were 80% and 20%, respectively. All four commercial methods show promise; OF is easiest to inoculate, but requires extra tests for optimal identification. AP reliably identifies the majority of clinically important nonfermenters, with fairly good species identification of saccharolytic strains after 24 h. MT yields reliable identification of most nonfermenters and has the advantage of flexibility. NF is easy to inoculate, yields satisfactory identification rates, and may be read after 24 h of incubation.     

Performance comparison of the 4th generation Bio-Rad Laboratories GS HIV Combo Ag/Ab EIA on the EVOLIS™ automated system versus Abbott ARCHITECT HIV Ag/Ab Combo,Ortho Anti-HIV 1 + 2 EIA on Vitros ECi and Siemens HIV-1/O/2 enhanced on Advia Centaur

BackgroundA multisite study was conducted to evaluate the performance of the Bio-Rad 4th generation GS HIV Combo Ag/Ab EIA versus Abbott 4th generation ARCHITECT HIV Ag/Ab Combo. The performance of two 3rd generation EIAs, Ortho Diagnostics Anti-HIV 1 + 2 EIA and Siemens HIV 1/O/2 was also evaluated.ObjectiveStudy objective was comparison of analytical HIV-1 p24 antigen detection, sensitivity in HIV-1 seroconversion panels, specificity in blood donors and two HIV false reactive panels.Study designAnalytical sensitivity was evaluated with International HIV-1 p24 antigen standards, the AFFSAPS (pg/mL) and WHO 90/636 (IU/mL) standards; sensitivity in acute infection was compared on 55 seroconversion samples, and specificity was evaluated on 1000 negative blood donors and two false reactive panels.ResultsGS HIV Combo Ag/Ab demonstrated better analytical HIV antigen sensitivity compared to ARCHITECT HIV Ag/Ab Combo: 0.41 IU/mL versus 1.2 IU/mL (WHO) and 12.7 pg/mL versus 20.1 pg/mL (AFSSAPS); GS HIV Combo Ag/Ab EIA also demonstrated slightly better specificity compared to ARCHITECT HIV Ag/Ab Combo (100% versus 99.7%). The 4th generation HIV Combo tests detected seroconversion 7–11 days earlier than the 3rd generation HIV antibody only EIAs.ConclusionBoth 4th generation immunoassays demonstrated excellent performance in sensitivity, with the reduction of the serological window period (7–11 days earlier detection than the 3rd generation HIV tests). However, GS HIV Combo Ag/Ab demonstrated improved HIV antigen analytical sensitivity and slightly better specificity when compared to ARCHITECT HIV Ag/Ab Combo assay, with higher positive predictive values (PPV) for low prevalence populations.