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Swiss Population* (n = 201) US Population† (n = 258) Data collection period December 1999 to February 2000 January to March 2002 Study design Prospective cohort Prospective cohort Setting University primary care clinic that serves an urban population of 150,000 in Lausanne, Switzerland Emergency department or urgent care ambulatory patients in a large tertiary care university hospital in San Francisco, California Inclusion criteria Adult outpatients with influenza-like illness as determined by the primary care physician Consecutive adults with symptoms of an acute respiratory tract infection (cough, sinus pain, congestion/rhinorrhea, sore throat or fever) developing in past 3 weeks Outcome Presence of influenza A or B Presence of influenza A or B Reference standard Culture PCR Prevalence of influenza 104 (52.8) 53 (20.5) Men 101 (50) 103‡ (40) Mean age, years (range) 34.3 (17–86) 38.8 (18–90) Fever 116 (58) 54 (21) Cough 186 (93) 235 (91) Sore throat 151 (75) 181 (70) Myalgia 181 (90) 154 (60) Rhinitis 163 (81) 185 (72) Headache 169 (84) 190 (74) Chills/sweating 166 (83) 158 (61) Fatigue 184 (92) 197 (76) Onset <48 hours 106 (53) 45 (17) Senn, 200514 Stein, 20055 Combined Datasets Total patients (n) 201 258 459 Male 0.77 (0.44–1.34) 0.74 (0.39–1.4) 0.9 (0.61–1.33) Fever 4.24 (2.33–7.71) 3.84 (1.98–7.45) 5.55 (3.65–8.45) Myalgia 2.76 (1.01–7.49) 4.22 (1.96–9.1) 5.35 (2.99–9.56) Chills/sweating 2.05 (0.97–4.35) 3.37 (1.6–7.06) 3.43 (2.08–5.66) Cough 3.2 (0.98–10.41) 1.8 (0.51–6.31) 2.45 (1.05–5.7) Fatigue 0.95 (0.35–2.57) 2.35 (1.00–5.52) 2.28 (1.26–4.10) Rhinitis 0.96 (0.47–1.94) 2.22 (1.02–4.82) 1.65 (1.02–2.65) Headache 1.09 (0.51–2.31) 1.7 (0.8–3.6) 1.64 (1.00–2.68) Sore throat 0.99 (0.52–1.87) 0.98 (0.51–1.89) 1.07 (0.7–1.65) Onset <48 hours 3.20 (1.79–5.69) 1.76 (0.85–3.65) 3.69 (2.44–5.58) Values provided as odds ratio (95% CI) unless otherwise indicated.
Bold values are significant at P ≤.05.
- Table 3.
Clinical Decision Rules Based on Multivariate Models from Combined Dataset (Flu Scores 1 to 3) and Multivariate Model of Monto et al13 (Flu Scores 4 and 5)
Clinical Variable Beta Odds ratio (95% CI) Points Flu score 1 Fever 1.225 3.40 (1.97–5.89) 7 Cough 0.912 2.49 (0.95–6.49) 5 Onset <48 hours 0.727 2.07 (1.17–3.65) 4 Myalgias 1.386 4.00 (1.91–8.39) 8 Constant −3.423 Flu score 2 Fever 0.763 2.14 (1.13–4.06) 2 Myalgia 1.304 3.68 (1.72–7.90) 4 Chills/sweats 0.430 1.54 (0.79–2.97) 2 Fever, cough, acute 1.443 4.23 (1.95–9.19) 4 Constant −2.686 Flu score 3 Onset <48 hours 0.721 2.06 (1.19–3.55) 1 Myalgia 1.260 3.53 (1.65–7.53) 2 Chills/sweats 0.401 1.49 (0.78–2.87) 1 Fever and cough 1.361 3.90 (2.27–6.70) 2 Constant −2.808 Flu score 4 Fever (temp ≥37.8°C) 1.182 3.26 3.0 Cough 1.047 2.85 3.0 Nasal congestion 0.683 1.98 2.0 Age ≥55 years 0.470 1.60 1.5 Weakness 0.432 1.54 1.5 Onset <48 hours 0.425 1.53 1.5 Male 0.239 1.27 1.0 Sore throat −0.329 0.72 −1.0 Flu score 5 Fever 1.182 3.26 3 Cough 1.047 2.85 3 Nasal congestion 0.683 1.98 2 Age ≥55 years 0.470 1.60 1 Weakness 0.432 1.54 1 Onset <48 hours 0.425 1.53 1 Male sex 0.239 1.27 1 Sore throat −0.329 0.72 −1 - Table 4.
Performance of Clinical Prediction Rules and Simple Heuristics for the Diagnosis of Influenza
Derivation group Validation group All patients Flu/Total (%) LR In Group (%) Flu/Total (%) LR In Group (%) Flu/Total (%, 95% CI) LR In Group (%) Flu score 1 Low risk (0–11) 7/86 (8.1) 0.17 26.4 1/34 (2.9) 0.06 25.6 8/120 (6.7, 3.4–12.6) 0.14 26.1 Moderate risk (12–15) 24/106 (22.6) 0.57 32.5 16/46 (34.8) 0.98 34.6 40/152 (26.3, 20.0–33.8) 0.69 33.1 High risk (16–24) 79/134 (59.0) 2.82 41.1 30/53 (56.6) 2.39 39.8 109/187 (58.3, 51.1–65.1) 2.69 40.7 Flu score 2 Low risk (0–2) 6/77 (7.8) 0.17 23.6 1/32 (3.1) 0.06 24.1 7/109 (6.4, 3.1–12.7) 0.13 23.7 Moderate risk (4–6) 44/149 (29.5) 0.82 45.7 16/56 (28.6) 0.73 42.1 60/205 (29.3, 23.5–35.8) 0.80 44.7 High risk (8–12) 60/100 (60.0) 2.95 30.7 30/45 (66.7) 3.66 33.8 90/145 (62.1, 54.0–69.6) 3.15 31.6 Flu score 3 Low risk (0–2) 10/109 (9.2) 0.20 33.4 2/40 (5.0) 0.10 30.1 12/149 (8.1, 4.7–13.5) 0.17 32.5 Moderate risk (3) 25/90 (27.8) 0.76 27.6 14/39 (35.9) 1.02 29.3 39/129 (30.2, 23.0–38.6) 0.83 28.1 High risk (4–6) 75/127 (59.1) 2.83 39.0 31/54 (57.4) 2.47 40.6 106/181 (58.6, 51.3–65.5) 2.72 39.4 Flu score 4 Low risk (−1–3) 4/36 (11.1) 0.25 11.1 1/19 (5.3) 0.10 14.3 5/55 (9.1, 4.0–19.6) 0.19 12.0 Moderate risk (4–8) 36/166 (21.7) 0.55 51.2 17/65 (26.2) 0.65 48.9 53/231 (22.9, 18.0–28.8) 0.57 50.5 High risk (9–11) 69/122 (56.6) 2.57 37.7 29/49 (59.2) 2.65 36.8 98/171 (57.1, 49.8–64.5) 2.59 37.4 Flu score 5 Low risk (0–11) 3/28 (10.7) 0.24 8.6 0/17 (0.0) 0.0 12.8 3/45 (6.7, 2.3–17.9) 0.14 9.8 Moderate risk (12–16) 59/220 (26.8) 0.72 67.9 26/84 (31.0) 0.82 63.2 85/304 (28.0, 23.2–33.3) 0.75 66.5 High risk (17+) 47/76 (61.8) 3.20 23.5 21/32 (65.6) 4.27 24.1 68/108 (63.0, 53.6–71.5) 3.28 23.6 Heuristics Fever, cough Positive (both present) NA NA 96/157 (61.1, 53.4–68.4) 3.03 34.2 Negative (0 or 1 present) NA NA 61/302 (20.2, 16.1–25.1) 0.49 65.8 Fever, cough, and acute-onset Positive (all 3 present) NA NA 64/86 (74.4, 64.3–82.5) 5.59 18.7 Negative (0, 1, or 2 present) NA NA 93/373 (24.9, 20.8–29.6) 0.64 81.3 - Table 5.
Predictive Values Based on Integration of Pretest Probability and Diagnostic Test With Flu Score 3* Using Test and Treatment Thresholds of 10% and 50%, Respectively
Season/Risk Category Probability of Influenza (%) Comment Not flu season (2.5%) Low risk (0–2) 0.4 Neither test nor treat Moderate risk (3) 2.1 Neither test nor treat High risk (4–6) 6.5 Neither test nor treat Shoulder (10%) Low risk (0–2) 1.9 Neither test nor treat Moderate risk (3) 8.4 Neither test nor treat High risk (4–6) 23 Order rapid test. Probability of flu is 84% if positive and 8% if negative. Flu season (30%) Low risk (0–2) 6.8* Neither test nor treat Moderate risk (3) 26 Order rapid test. Probability of flu is 84% if positive and 8% if negative. High risk (4–6) 54 Treat empirically via option 1 (consider empiric therapy if high risk for complications) or option 2 (consider rapid test [95% if positive and 25% if negative]). ↵* Flu score 3 assigns 2 points for fever plus cough, 2 points for myalgias, and 1 point each for duration <48 hours and chills or sweats.
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