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Table 1 Sociodemographic characteristics and symptoms of enrollees ≥ 5 years of age reported at enrollment, by Polymerase Chain Reaction (PCR)-confirmed Influenza status

From: Classification and Regression Tree (CART) analysis to predict influenza in primary care patients

  Overall Developmental sample Validation sample
Characteristics   PCR-negative for influenza PCR-confirmed influenza P valuea   
  Total n = 3531 n = 642   Total Total
  N = 4173 (84.6 %) (15.4 %)   (N = 2087) (N = 2086)
  N (%) n (%) n (%)   N (%) N (%)
Vaccinated by self-report 354 (8.7) 311 (87.8) 43 (12.2) 0.08 173 (8.5) 181 (8.9)
Unvaccinated 3714 (91.3) 3131 (84.3) 583 (15.7)    
Smokerb 436 (15.6) 386 (88.5) 50 (11.5) 0.07 215 (15.2) 221 (16)
Non-smoker 2358 (84.4) 2010 (85.2) 348 (14.8)    
Smoker in the household 481 (11.6) 428 (89.0) 53 (11.0) 0.004 223 (10.7) 258 (12.4)
No smoker in the household 3667 (88.4) 3081 (84.0) 586 (16.0)    
Asthma diagnosis 1098 (26.8) 949 (86.4) 149 (13.6) 0.04 543 (26.4) 555 (27.1)
No asthma diagnosis 3007 (73.3) 2521 (83.8) 486 (16.2)    
Any high risk condition 1147 (85.0) 1004 (87.5) 143 (12.5) 0.14 569 (84.4) 578 (85.5)
No high risk condition 203 (15.0) 170 (83.7) 33 (16.3)    
Symptoms reported at enrollment   
 Fever 2910 (69.7) 2327 (80.0) 583 (20.0) <.001 1461 (70) 1449 (69.5)
 No fever 1263 (30.3) 1204 (95.3) 59 (4.7)    
 Cough 3818 (91.5) 3189 (83.5) 629 (16.5) <.001 1912 (91.6) 1906 (91.4)
 No cough 355 (8.5) 342 (96.3) 13 (3.7)    
 Fatigue 3610 (86.5) 3003 (83.2) 607 (16.8) <.001 1795 (86) 1815 (87)
 No fatigue 563 (13.5) 528 (93.8) 35 (6.2)    
 Wheezing 1550 (37.1) 1292 (83.3) 258 (16.7) 0.08 773 (37) 777 (37.2)
 No wheezing 2623 (62.9) 2239 (85.4) 384 (14.6)    
 Sore throat 3105 (74.4) 2639 (85.0) 466 (15.0) 0.25 1543 (73.9) 1562 (74.9)
 No sore throat 1068 (25.6) 892 (83.5) 176 (16.5)    
 Nasal Congestion 3351 (80.3) 2823 (84.2) 528 (15.8) 0.18 1690 (81) 1661 (79.6)
 No nasal congestion 821 (19.7) 707 (86.1) 114 (13.9)    
 Shortness of breath 1899 (45.5) 1598 (84.2) 301 (15.8) 0.45 911 (43.7) 988 (47.4)
 No shortness of breath 2272 (54.5) 1931 (85.0) 341 (15.0)    
Age, years, Mean (SD) 34.1 (22.2) 34.5 (22.2) 31.9 (21.8) 0.007 34.8 (22.3) 33.5 (22)
  1. aFor difference between influenza cases and controls
  2. bAsked of those ≥18 years only