Article Figures & Data
Figures
- Fig. 1.
Effect of increasing concentration of target nucleic acid on IC signal. Samples containing increasing amounts of C. trachomatis (CT) target DNA, 25 copies of N. gonorrhoeae (NG) target DNA, and 20 copies of IC DNA per test sample were amplified in a Perkin-Elmer 9600 thermal cycler.C. trachomatis, N. gonorrhoeae, and IC amplification products were hybridized to separate microwell plates coated with target-specific oligonucleotide probes. The hybridized amplification products were detected colorimetrically with an avidin-horseradish peroxidase complex. The concentration of C. trachomatis target DNA is shown on the x axis (1.00E+01 is 101, 1.00E+02 is 102 etc.) and the absorbance at 450 nm is shown on the y axis. The broken line indicates the assay cutoff value.
- Fig. 2.
Distribution of IC signals in a set of clinical specimens. Specimens were tested by the COBAS AMPLICOR C. trachomatis and N. gonorrhoeae tests. The IC signal was evaluated in specimens that were negative for both C. trachomatis and N. gonorrhoeae. Each bar shows the number of specimens (on the y axis) having an IC absorbance less than the value the value shown directly below the bar (on thex axis) but greater than or equal the value to the immediate left (on the x axis). The bar over the 4.00 value includes specimens having signals equal to 4.00.
- Fig. 3.
Effect of IC cutoff on assay sensitivity. A set of clinical specimens was tested with the COBAS AMPLICOR C. trachomatis test. Different IC cutoff values were used to distinguish between inhibitory and noninhibitory specimens. Clinical sensitivity and the number of inhibitory, infection-positive specimens were calculated for each cutoff value. The IC cutoff is shown on thex axis, clinical sensitivity is shown on the lefty axis, and the number of inhibitory specimens is shown on the right y axis.
Tables
- Table 1.
Frequency of inhibition in infection-positive and -negative specimens
COBAS AMPLICOR test and specimen Infection-positive specimens Infection-negative specimens Total no. No. inhibitory (%) Retest Total no. No. inhibitory (%) Retest No. positive No. inhibitory No. negative No. inhibitory C. trachomatis Swab 117 4 (3.4) 1 3 839 82a (9.8) 22 46 Urine 118 7 (5.9) 6 1 847 79b (9.3) 68 9 N. gonorrhoeae Swab 115 1 (0.9) 1 0 831 63c (7.6) 24 38 Urine 118 8 (6.8) 6 2 836 70d (8.4) 62 6 M. tuberculosis Smear positive 154 1 (0.6) 1 0 29 0 (0.0) 0 0 Smear negative 125 3 (2.4) 1 2 4,068 217 (5.3) 96 121 HCV 1,036 61 (5.9) 50 11 929 107 (11.5) 98 9 ↵a Fourteen of the inhibitoryC. trachomatis swab specimens were not available for retesting.
↵b Two of the inhibitory C. trachomatis urine specimens were not available for retesting.
↵c One of the inhibitory N. gonorrhoeae swab specimens was not available for retesting.
↵d Two of the inhibitory N. gonorrhoeae urine specimens were not available for retesting.
- Table 2.
Enhancement of test sensitivity using IC
COBAS AMPLICOR test and specimen Sensitivity (%) Specificity (%) Without IC With IC Without IC With IC C. trachomatis Swab 94.8 (110/116) 97.4 (111/114) 99.0 (832/840) 99.0 (771/779) Urine 92.0 (104/113) 94.0 (110/117) 99.1 (844/852) 99.0 (828/836) N. gonorrhoeae Swab 93.9 (108/115) 94.8 (109/115) 98.0 (814/831) 97.9 (775/792) Urine 83.8 (98/117) 89.7 (104/116) 98.9 (828/837) 98.8 (818/828) M. tuberculosis Smear positive 98.7 (151/153) 98.7 (152/154) 90.0 (27/30) 89.7 (26/29) Smear negative 73.6 (92/125) 75.6 (93/123) 99.0 (4027/4068) 99.0 (3906/3947) HCV 72.6 (752/1036) 78.2 (802/1025) 98.2 (912/929) 98.2 (903/920)
