Table 2.
Radiologic and Laboratory Findings of Subjects With False-Negative NAATs
| Symptom Onset to First NAAT | ||||
|---|---|---|---|---|
| Finding, n (%) or median (IQR) | Total (n = 60) | 0–5 Days (n = 38) | >5 Days (n = 22) | P Value |
| Radiologic Characteristics | ||||
| CXR performed within 24 hours of the initial negative test | 32 (53) | 22 (58) | 10 (45) | .43 |
| No abnormalities | 9 (28) | 5 (28) | 4 (29) | .18 |
| Bilateral opacity | 19 (59) | 9 (50) | 10 (71) | |
| Other abnormality | 4 (13) | 4 (22) | 0 (0) | |
| CT chest performed within 24 hours of initial negative testa | 14 (23) | 10 (26) | 4 (18) | .54 |
| Negative for pneumonia | 0 (0) | 0 (0) | 0 (0) | .13 |
| Atypical | 5 (36) | 5 (50) | 0 (0) | |
| Indeterminate | 4 (29) | 3 (30) | 1 (25) | |
| Typical | 5 (36) | 2 (20) | 3 (75) | |
| Laboratory Characteristics | ||||
| Number of Tests Required for Diagnosis | ||||
| 2 tests | 43 (72) | 28 (74) | 15 (68) | .61 |
| 3 tests | 12 (20) | 8 (21) | 4 (18) | |
| 4 tests | 5 (8) | 2 (5) | 3 (14) | |
| Time between onset of symptoms and final diagnosis, days | 10 (5–14) | 6 (3–10) | 14 (10–16) | <.01 |
| Time between first test and final diagnosis, days | 2 (1–7) | 4 (1–7) | 1 (1–8) | .18 |
| Ct Value at Diagnosis | ||||
| Strong on NP | 10 (17) | 8 (21) | 2 (9) | .21 |
| Moderate on NP | 6 (10) | 4 (11) | 2 (9) | |
| Weak on NPb | 30 (50) | 17 (45) | 13 (59) | |
| Unknown on NP | 5 (8) | 5 (13) | 0 (0) | |
| Diagnosed on NAAT from LRT specimen | 9 (15) | 4 (11) | 5 (23) | |
Bold indicates statistically significant values.
Abbreviations: CT chest, computed tomography of the chest; Ct, cycle threshold; CXR, chest x-ray; LRT, lower respiratory tract; IQR, interquartile range; NAAT, nucleic acid amplification test; NP, nasopharyngeal.
aCT chest findings as reported using the Radiological Society of North America (RSNA) criteria [18].
bIncludes patients for whom only the E target was detected at the time of the first positive test.