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Table 4 Performance metrics of influenza clinical case definitions in subjects 6–49 years ( n= 523)

From: Determination of clinical and demographic predictors of laboratory-confirmed influenza with subtype analysis

   Laboratory influenza     
  Clinical test diagnosis     
Clinical test result Positive Negative SN (%) (95% CI) SP (%) (95% CI) PPV (%) (95% CI) NPV (%) (95% CI)
At least 1 criteriona Positive 157 363 100.0 (undefined) b 0.8 (0.0–1.6) 30.2 (26.3–34.1) 100.0 (undefined) b
Negative 0 3
At least 2 criteriaa Positive 149 292 94.9 (93.0–96.8) 20.2 (16.8–23.7) 33.8 (29.7–37.8) 90.2 (87.7–92.8)
Negative 8 74
At least 3 criteriaa Positive 91 73 58.0 (53.7–62.2) 80.1 (76.6–83.5) 55.5 (51.2–59.7) 81.6 (78.3–84.9)
Negative 66 293
All 4 criteriaa Positive 23 5 14.6 (11.6–17.7) 98.6 (97.6–99.6) 82.1 (78.9–85.4) 72.9 (69.1–76.7)
Negative 134 361
Exact 2 criteria c
Acute onset and fever Positive 31 22 19.7 (16.3–23.2) 94.0 (92.0–96.0) 58.5 (54.3–62.7) 73.2 (69.4–77.0)
Negative 126 344
Acute onset and cough Positive 86 85 54.8 (50.5–59.0) 76.8 (73.2–80.4) 50.3 (46.0–54.6) 79.8 (76.4–83.3)
Negative 71 281
Acute onset and body aches Positive 64 68 40.8 (36.6–45.0) 81.4 (78.1–84.8) 48.5 (44.2–52.8) 76.2 (72.6–79.9)
Negative 93 298
Fever and cough Positive 51 29 32.5 (28.5–36.5) 92.1 (89.8–94.4) 63.8 (59.6–67.9) 76.1 (72.4–79.7)
Negative 106 337
Fever and body aches Positive 42 25 26.8 (23.0–30.5) 93.2 (91.0–95.3) 62.7 (58.5–66.8) 74.8 (71.1–78.5)
Negative 115 341
Cough and body aches Positive 126 224 80.3 (76.8–83.7) 38.8 (34.6–43.0) 36.0 (31.9–40.1) 82.1 (78.8–85.4)
Negative 31 142
Cough + any of other 3 criteria Positive 149 264 94.9 (93.0–96.8) 27.9 (24.0–31.7) 36.1 (32.0–40.2) 92.7 (90.5–95.0)
Negative 8 102
Exact 3 criteria c
Acute onset, fever, cough Positive 31 14 19.7 (16.3–23.2) 96.2 (94.5–97.8) 68.9 (64.9–72.9) 73.6 (69.9–77.4)
Negative 126 352
Acute onset, cough, body aches Positive 64 47 40.8 (36.6–45.0) 87.2 (84.3–90.0) 57.7 (53.4–61.9) 77.4 (73.8–81.0)
Negative 93 319
Acute onset, fever, body aches Positive 23 9 14.6 (11.6–17.7) 97.5 (96.2–98.9) 71.9 (68.0–75.7) 72.7 (68.9–76.5)
Negative 134 357
Fever, cough, body aches Positive 42 18 26.8 (23.0–30.5) 95.1 (93.2–96.9) 70.0 (66.1–74.0) 75.2 (71.5–78.9)
Negative 115 348
CDC ILI case definition d
Total study population Positive 83 82 37.7 (33.6–41.9) 85.6 (82.6–88.6) 50.3 (46.0–54.6) 78.0 (74.5–81.6)
Negative 137 487
Subjects ages 3–5 years Positive 3 15 25.0 (21.3–28.7) 71.7 (67.8–75.6) 16.7 (13.4–19.9) 80.9 (77.5–84.2)
Negative 9 38
Subjects ages 6–49 years Positive 63 52 40.1 (35.9–44.3) 85.8 (82.8–88.8) 54.8 (50.5–59.0) 77.0 (73.4–80.6)
Negative 94 314
Subjects ages 50–80 years Positive 17 15 33.3 (29.3–37.4) 90.0 (87.4–92.6) 53.1 (48.8–57.4) 79.9 (76.4–83.3)
Negative 34 135
  1. NOTE. CDC, Centers for Disease Control and Prevention; CI, confidence interval; ILI, influenza-like illness; NPV, negative predictive value; PPV, positive predictive value; SN, sensitivity; SP, specificity. The first 15 clinical tests displayed are defined according to combinations of 4 influenza predictors (“criteria”) present in a subject: acute onset, fever, cough, and body aches. CI calculated for a proportion estimate as follows: (estimate) ± 1.96 x √(estimate x (1 – estimate)/n). aPositive test defined by at least n of the 4 criteria of interest being met. bCI undefined; cannot be calculated for a proportion of 1.0. cThe exact criteria listed are met, regardless of whether the other unlisted criteria are met. dCDC ILI definition = temperature ≥37.8 °C and either cough or sore throat in absence of another known cause. Presence of another known cause is not assessable in this study. This case definition’s performance was evaluated in and is reported for all age groups included in the study.