Comparison of EVD diagnostic systems
| Assay system | |||
|---|---|---|---|
| Category | RT-LAMP* (Nagasaki University-Toshiba Medical Systems Corp, Japan) | RDT† (ReEBOV Antigen Rapid Test, US) | Reference: rRT-PCR‡ |
| Validated sample number in study | 100 (for field validation study) | 293 (WHO independent evaluation by 2 ref. laboratories) 106 (for field validation study) | Widely used as the WHO benchmark assay |
| Characteristics of target population | Conakry and its surrounding prefectures in Guinea | Sierra Leone | |
| Samples validated for testing | Fresh/frozen blood, plasma (44 samples tested), oral swab (56 samples tested) | Fresh venous whole blood (147) frozen specimen(146) for WHO evaluation Fresh/frozen whole blood (fingerstick, venous) for field validation study | Plasma collected in EDTA§, cell-free body-fluids, swab washes |
| Reference PCR test for validation study | LightMix Modular Ebola Virus Zaire 2014 (TIB Molbiol, Germany) SmartCycler II system (Cepheid, USA) | RealStar Filovirus Screen RT-PCR Kit 1.0 Altona Diagnostics (GmbH, Germany) SmartCycler II system (Cepheid, USA) | – |
| Sensitivity (%) | 100 (92.5–100)¶ | 100 (92.1–100)** | – |
| 100 (87.7–100)†† | |||
| Specificity (%) | 100 (93.3–100)¶ | 92.2 (88.0–95.3)** | – |
| 92.2 (83.8–97.1)†† | |||
| Positive predictive value (%) | 100 (92.5–100)¶ | 71.4 (58.7–82.1)** | – |
| 82.4 (65.5–93.2)†† | |||
| 97.3 (90.6–9.7)‡‡ | |||
| Negative predictive value (%) | 100 (93.3–100)¶ | 100 (98.3–100)** | – |
| 100 (94.9–100)†† | |||
| 73.3 (66.9–79.8)‡‡ | |||
| Detected Ct* range shown in study | 17.1–37.5 (≓ 5.3×108–1.9×104 RNA copies/mL) | 15.9–26.3 (median 21.3 (19.2–23.4)) | 13.4–33.0 (median 21.1 (19.1–24.5)) |
| Probable limit of Ct*** value for detection | 2.0×105 RNA copies/mL | 2.11×108 RNA copies/mL (WHO evaluation) | Limit of detection not assessed by the WHO during EUAL assessment. 1PFU (approximately 3400 copies) of ZEBOV/mL plasma (FDA EUA) |
| Throughput (time to results) | <1 hour including the platform assay <15 min for positive (9–22.5 min) | 15–25 min | 4–6 hours for negative, less for positive |
| Maximum number of samples processed/day | 72 samples/system (6 samples×12 run/8 hours) | 60–100 specimens/operator | Approximately 50 specimens/system |
| Transport and stage condition (for reagents) | Non–cold chain system in development (at least 6-month reagent shelf life at below 35°C) | Cold chain required (2–8°C, not frozen, 6 months stable) | Cold chain required (−2°C, 9-month reagent shelf life) |
| Power supply | Operational by battery charge (1.5 hours operational by 1 time charge=1 day operation by 4 time charge) | No electricity | Electricity only |
| Portability | 1.75 kg | Negligible | >10 kg (laptop-PC) |
*RT-LAMP, reverse transcription—loop mediated amplification method.
†RDT, rapid diagnostic test.
‡rRT-PCR, real-time reverse transcription-PCR.
§EDTA, ethylenediamine-tetraacetic acid.
¶The indicated results were from the RT-LAMP test with the primers for the untranscribed trailer region with 100 samples.26
**The indicated results were obtained by the WHO evaluation test at the reference laboratory with 277 samples (whole blood).17
††The indicated values were obtained by the field validation study with 105 fingerstick samples.17
‡‡The indicated values were obtained by the field validation study with 176 samples (whole blood).18
***Ct, cycle threshold.
EVD, Ebola virus disease; EUA, emergency use authorisation; FDA, Food and Drug Administration.