Chlamydia trachomatis and Neisseria gonorrhoeae remain the most common bacterial sexually transmitted infections and the most commonly reported notifiable diseases in the United States. Recent estimates of national chlamydia prevalence among 14- to 39-year-olds range from 1.4% (95% confidence interval [CI], 1.1%–18.%) among men to 2.0% (95% CI, 1.5%–2.5%) among women.1 Substantial health disparities for infection are associated with race and socioeconomic status.1 Current screening options are not substantially reducing the overall burden of disease in the Unite States. Despite recommendations for annual screening of sexually active women younger than 26 years, less than 50% of those for whom screening is recommended are tested as suggested (http://www.cdc.gov/std/chlamydia/female-enrollees-00-08.htm). One strategy for improving control efforts is expansion of availability of screening services. In many primary care settings, access to screening is limited due to a lack of local testing options. Most of the diagnostic platforms that offer chlamydia and gonorrhea screening use medium high to high-volume (e.g., >96 samples/d) throughput analyzers requiring a substantial capital investment for instruments for specialty diagnostic menus. As a result, smaller health care settings often refer samples to large tertiary care facilities or commercial laboratories for testing. Options that can support lower throughput testing would allow screening to be performed locally that could improve timeliness of results for improved patient management.
The BD Viper LT System is a fully automated tabletop instrument that can perform either polymerase chain reaction or strand displacement amplification assays with real-time detection of amplified targets. The system has a footprint of 50 in. wide by 24 in. deep and can generate results in less than 4 hours. A prewarm and cooling step is required for specimen processing before loading onto the instrument to digest mucus and homogenize specimens. Nucleic acid isolation is performed using the same ferric oxide separation technology used by the Viper XTR.2 Amplification and detection of chlamydia and gonorrhea are carried out using the BD ProbeTec CT Qx (CTQ) and GC Qx (GCQ) Amplified DNA Assays that have been described for the Viper XTR.2,3 Here we present the findings of a study designed to compare the chlamydia and gonorrhea results obtained using the CTQ and GCQ amplified assays on the BD Viper LT System with the results obtained using the same assays with the high-throughput BD Viper XTR platform.
Samples were collected prospectively from symptomatic men and women at 4 clinical sites in the United States; Birmingham, AL; Houston, TX, Indianapolis, IN; and New Orleans, LA. Patients were classified as symptomatic if they reported symptoms such as dysuria, urethral discharge, coital pain/difficulty/bleeding, testicular or scrotum pain/swelling, abnormal vaginal discharge, or pelvic/uterine/adnexal pain. Consistent with the Centers for Disease Control and Prevention (CDC) 2014 recommendations for chlamydia and gonorrhea laboratory diagnostics,4 male urine and female vaginal swabs were assessed on the new Viper LT platform. In addition, female urine and liquid-based cytology medium (LBC) samples were also evaluated due to high demand for testing using these sample types. Because of lower priority in the CDC diagnostic recommendations and the increased discomfort that would result from multiple swab collection, urethral and endocervical swab (other than a single LBC) samples were not evaluated in this study. Urine specimens were aliquoted into 5 BD Qx urine preservative tubes at the clinical sites before transport to the laboratory (Fig. 1). From women, 5 patient-collected vaginal swabs in BD dry collection tubes were obtained followed by 2 endocervical samples. The endocervical samples were placed, one each, in PreservCyt solution (Hologic, San Diego, CA) and BD SurePath Preservative Fluid. The order of collection was randomized between the 2 LBC media.
Urine aliquots, vaginal swabs, and endocervical samples in LBC media were sent to BD. The 5 vaginal swabs per female participant were eluted into a total of 10 mL of Qx swab diluent buffer (Fig. 1). After elution, the medium was aliquoted into 4 tubes, 2 mL each. Each LBC sample was aliquoted into 4 Qx LBC diluent tubes following the package insert instructions for the CTQ/GCQ assays. A single urine aliquot was used at BD for chlamydia and gonorrhea testing on the XTR for determination of the infection status of each patient from whom samples were collected. Based on these results, panels were created for blinded testing at 3 clinical/academic sexually transmitted disease (STD) laboratories using the BD Viper LT system: Indiana University School of Medicine, Louisiana State University Health Sciences Center, and University of Alabama at Birmingham School of Medicine. The panels sent to each site contained aliquots from identical participants and the sites were blinded to the initial XTR results. At each site, the samples were tested using the CTQ and GCQ Assays on the LT System. An identical blinded panel was tested at BD on the XTR System. Viper LT results were compared with the Viper XTR results for each testing site by sample type and in aggregate. Conditional logistic regression was used to determine whether differences in performance by site were observed. In addition to the comparison of results, the rate of errors was assessed and environmental testing of potential carryover contamination was performed during the trial.
Specimens from a total of 170 men and 653 women were collected and screened to derive panels consisting of samples from 113 men and 106 women. Recruitment was focused on symptomatic patients to obtain a large number of participants with current infections. All men and 55% of the women were recruited from STD clinics; the remaining women were recruited from Family Planning clinics. The final panels comprised samples from 46 men and 54 women with chlamydia infection, 41 men and 30 women with gonorrhea, and 37 men and 33 women with no infection detected by the urine Viper XTR testing. Eleven men and 11 women tested positive for both chlamydia and gonorrhea. All specimens were stored at −20°C within package insert stability claims before the time of testing.
The results were analyzed to determine whether results could be pooled across testing sites. There were no statistical differences among the 3 testing sites (P values for all sample types and for both organisms were all >0.6). Therefore, testing results for all sites were pooled such that the results for each of the 3 aliquots of each panel member were included in the positive (PPA) and negative percent agreement (NPA) estimates. The CTQ and GCQ assays tested on the Viper LT System provided results similar to those obtained on the Viper XTR System (Table 1). The PPA for all sample types was at least 95.8% and at least 96.4% for chlamydia and gonorrhea, respectively, whereas the NPA was at least 95.0% for both organisms.
The rate of errors generated by the Viper LT system during the trial was captured as an indicator of the robustness of the platform. Of the 1611 sample runs, 3 (0.2%) had an extraction error and had to be repeated. On repeat testing, all 3 samples generated a compliant result. Another measure of the functionality of the system is the nominal occurrence of environmental contamination. This was assessed during the trial by periodic swabbing of thirteen predefined areas of the Viper LT workspace and surrounding laboratory surfaces. Of the 200 environmental samples tested across the 3 laboratoryies, there was a single (0.5%) contaminant (chlamydia) detected, which resolved after following the recommended cleaning procedure.
The performance of the Viper LT System compared favorably with the larger throughput Viper XTR platform using samples from symptomatic patients. The data from all currently approved assays suggest that although there may be minor differences in the actual estimate of performance between symptomatic and asymptomatic populations, the CIs always overlap suggesting that these differences are not statistically significant and likely not clinically meaningful. The PPA and NPA estimates were similar to the sensitivity and specificity estimates described for the Viper XTR in both Qx clinical trials2,3,5 and independent evaluations.6–9 The Viper LT System is intended for use in laboratories that benefit from the ability to run small batch sizes which is a much needed solution for laboratories with low- to mid-volume testing (e.g., 5000–30,000 samples per year). According to the CDC, the minority of cases of chlamydia were reported by STD clinics (5.5% and 17.2% in women and men, respectively). Most STD screening and reporting are being provided as part of family practice/HMO, family planning, and emergency department health care visits.10 These settings generate small to midlevel volume of tests and the availability of a platform designed to meet this need may increase adherence to screening recommendations11,12 through increased local testing and less reliance on referral of specimens to distant laboratories. In addition, the polymerase chain reaction capability of the Viper LT System will allow for further menu expansion and detection of other pathogens.
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