Table 4. Performance of standard case definitions and sign/symptom combinations in the identification of influenza among hospitalized patients, Vadu, India, May 2009–April 2011.
| Definition, by patient age | Value (%) and 95% confidence interval |
|||
|---|---|---|---|---|
| Sensitivity | Specificity | Positive predictive valuea | Negative predictive valuea | |
| Age < 5 years (n = 337) | ||||
| Severe acute respiratory illness (measured fever only) | 11 (4.2–24.7) | 87 (82.2–90.3) | 11 (4.5–25.9) | 86 (80.6–89.6) |
| Severe acute respiratory illness (reported or measured fever) | 11 (4.2–24.7) | 86 (81.4–89.6) | 11 (4.1–24.1) | 86 (80.9–89.8) |
| Influenza-like illness (measured fever only) | 69 (53.5–81.4) | 43 (37.4–49.0) | 17 (11.9–23.5) | 90 (83.0–94.0) |
| Influenza-like illness (reported or measured fever) | 87 (73.2–94.4) | 5 (3.2–8.5) | 13 (9.2–17.3) | 72 (49.1–87.5) |
| Acute respiratory illness | 77 (61.6–87.3) | 26 (21.2–31.4) | 14 (10.1–19.4) | 88 (78.2–93.3) |
| Febrile acute respiratory illness (measured fever only) | 63 (47.8–75.6) | 44 (38.1–49.4) | 16 (11.3–22.5) | 88 (81.0–92.3) |
| Febrile acute respiratory illness (reported or measured fever) | 77 (61.6–87.3) | 27 (21.9–32.1) | 14 (10.1–19.6) | 88 (78.7–93.5) |
| Individual symptoms and symptom combinations | ||||
| Reported or measured fever | 95 (83.1–98.5) | 3 (1.4–5.5) | 14 (10.1–18.3) | 78 (45.2–93.6) |
| Measured fever (> 38 °C) | 88 (75.5–94.9) | 21 (16.3–25.6) | 16 (12.2–21.7) | 92 (81.9–96.3) |
| Cough | 77 (61.6–87.3) | 33 (27.3–38.1) | 15 (10.9–21.1) | 90 (81.8–94.5) |
| Sore throat | 51 (36.2–66.1) | 53 (47.3–58.8) | 16 (10.2–22.7) | 88 (81.7–92.0) |
| Shortness of breath | 11 (4.2–24.7) | 86 (81.1–89.4) | 10 (4.0–23.5) | 86 (80.9–89.8) |
| Cough and reported or measured fever | 77 (61.6–87.3) | 33 (28.1–39.1) | 16 (11.3–21.7) | 90 (82.0–94.6) |
| Sore throat and reported or measured fever | 51 (36.2–66.1) | 54 (47.7–59.2) | 16 (10.4–23.0) | 88 (81.7–92.0) |
| Age ≥ 5 years (n = 2842) | ||||
| Severe acute respiratory illness (measured fever only) | 3 (1.7–4.5) | 98 (97.4–98.7) | 39 (25.6–54.2) | 72 (70.2–74.1) |
| Severe acute respiratory illness (reported or measured fever) | 4 (2.5–5.7) | 97 (96.4–97.9) | 35 (24.3–47.2) | 72 (70.1–74.1) |
| Influenza-like illness (measured fever only) | 70 (66.3–73.5) | 53 (50.7–54.9) | 34 (31.6–36.9) | 84 (81.2–85.6) |
| Influenza-like illness (reported or measured fever) | 97 (95.2–98.0) | 3 (2.3–3.7) | 26 (24.1–27.7) | 76 (65.0–83.8) |
| Acute respiratory illness | 87 (83.8–89.1) | 36 (34.3–38.3) | 33 (30.5–35.1) | 89 (86.6–91.1) |
| Febrile acute respiratory illness (measured fever only) | 69 (65.0–72.2) | 53 (51.1–55.2) | 34 (31.3–36.5) | 83 (80.7–85.1) |
| Febrile acute respiratory illness (reported or measured fever) | 86 (83.1–88.5) | 37 (34.8–38.8) | 33 (30.6–35.2) | 89 (86.3–90.8) |
| Individual symptoms and symptom combinations | ||||
| Reported or measured fever | 98 (96.3–98.7) | 2 (1.0–2.1) | 26 (24.0–27.5) | 68 (52.0–79.9) |
| Measured fever (> 38 °C) | 80 (76.5–82.8) | 21 (19.5–22.9) | 26 (23.9–27.9) | 74 (70.3–78.1) |
| Cough | 80 (77.1–83.3) | 41 (39.3–43.4) | 33 (30.7–35.5) | 86 (83.9–88.4) |
| Sore throat | 58 (54.4–62.2) | 64 (61.7–65.7) | 37 (33.8–39.9) | 82 (79.7–83.7) |
| Shortness of breath | 4 (2.6–5.9) | 97 (96.0–97.6) | 33 (23.0–44.5) | 72 (70.1–74.1) |
| Myalgia | 73 (69.5–76.4) | 27 (25.3–29.0) | 26 (23.7–27.8) | 74 (70.1–77.0) |
| Headache | 86 (83.1–88.5) | 10 (9.0–11.6) | 25 (23.6–27.4) | 72 (66.4–76.4) |
| Cough and reported or measured fever | 80 (76.1–82.5) | 42 (40.2–44.3) | 33 (30.7–35.6) | 86 (83.7–88.2) |
| Sore throat and reported or measured fever | 58 (54.0–61.8) | 64 (62.1–66.1) | 37 (33.8–39.9) | 82 (79.7–83.7) |
| Influenza-like illness (measured fever) and either myalgia or headache | 63 (59.0–66.7) | 56 (53.9–58.6) | 29 (26.9–32.0) | 84 (82.1–85.7) |
| Influenza-like illness (reported or measured fever) and either myalgia or headache | 77 (73.8–80.4) | 45 (42.4–47.1) | 22 (20.1–23.7) | 78 (75.1–80.8) |
a Calculated for the period when > 10% of the tested patients were found positive for an influenza virus (June 2009–October 2010).