TABLE 2.
Accuracies of diagnostic tests for acute scrub typhus estimated using Bayesian LCMs
| Parametera | Accuracy (%) for model usingb: |
|
|---|---|---|
| On-admission sample alone | Paired samples | |
| In vitro culture for O. tsutsugamushi | ||
| Sensitivity | 24.1 (21.2–26.9) | 24.1 (21.2–25.9) |
| Specificity | 100 | 100 |
| PPV | 100 | 100 |
| NPV | 82.8 (79.7–85.2) | 82.8 (79.7–84.4) |
| Combination of PCR assaysc | ||
| Sensitivity | 69.2 (63.3–73.3) | 66.7 (61.3–70.0) |
| Specificity | 98.1 (95.5–100) | 97.2 (96.3–99.1) |
| PPV | 90.9 (77.3–100) | 86.4 (81.8–95.5) |
| NPV | 92.0 (89.4–92.9) | 91.2 (89.4–92.0) |
| IgM IFAd | ||
| Sensitivity | 69.0 (60.6–76.9) | 86.2 (75.8–92.6) |
| Specificity | 100 (99.1–100) | 100 (99.1–100) |
| PPV | 100 (95.0–100) | 100 (96.0–100) |
| NPV | 92.2 (88.7–94.8) | 96.4 (92.7–98.2) |
| IgM ELISAe | ||
| Sensitivity | 69.0 (60.6–76.9) | 85.7 (77.4–86.7) |
| Specificity | 100 (99.1–100) | 98.1 (97.2–100) |
| PPV | 100 (95.0–100) | 92.3 (88.5–100) |
| NPV | 92.2 (88.7–94.8) | 96.3 (93.6–96.3) |
| Presence of eschar | ||
| Sensitivity | 42.9 (37.9–46.7) | 41.4 (37.5–44.8) |
| Specificity | 98.1 (97.2–100) | 98.1 (98.1–99.1) |
| PPV | 85.7 (78.6–100) | 85.7 (85.7–92.9) |
| NPV | 86.8 (83.5–87.6) | 86.0 (83.5–87.6) |
PPV positive predictive value; NPV negative predictive value.
The values are medians and 95% CrIs.
A combination of PCR assays was defined as positive when at least two out of the three PCR assays (56-kDa nPCR assay, 47-kDa-based qPCR assay, and groEL-based qPCR assay) were positive.
In the model using on-admission samples alone, IgM IFA was defined as positive in those with an admission IgM IFA titer of ≥1:3,200. In the model using paired samples, IgM IFA was defined as positive in those with an admission IgM IFA titer of ≥1:3,200 or at least a 4-fold rise to ≥1:3,200 in the convalescent/discharge IgM IFA titer compared to the admission IgM IFA titer.
In the model using on-admission samples alone, IgM ELISA was defined as positive when the OD was ≥1.474 at a sample dilution of 1:400. In the model using paired samples, IgM ELISA was defined as positive when the OD was ≥1.474 at a sample dilution of 1:400 in either sample.