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Table 2 Univariate and multivariable Cox analyses for risk factors of NPC

From: Plasma Epstein-Barr virus DNA and risk of nasopharyngeal carcinoma in a prospective seropositive population

Variables Participants(n) Person-Years NPC Cases(n) Incidence Rate Per 100,000
Person-Years
Crude HR(95%CIs) P-value Fully Adjusted HR(95%CIs)b P-value
Sex
 male 649 4009.16 18 448.97 Reference   Reference  
 female 714 4405.70 12 272.37 0.611 (0.294–1.269) 0.186 1.381 (0.413–4.617) 0.601
Age
 30–49 688 4470.52 15 335.53 Reference   Reference  
 50–69 675 3944.34 15 380.29 1.099 (0.537–2.250) 0.796 0.832 (0.389–1.783) 0.637
Smoking
 never 799 4929.13 11 223.16 Reference   Reference  
 current or former 564 3485.73 19 545.08 2.415 (1.149–5.076) 0.020 3.566 (1.055–12.060) 0.041
Salted food
 monthly or less 1171 7073.05 25 353.45 Reference   Reference  
 weekly and more 192 1341.81 5 372.63 1.050 (0.402–2.745) 0.921 0.867 (0.329–2.288) 0.774
Family history
 no 1302 8025.25 25 311.52 Reference   Reference  
 yes 61 389.61 5 1283.34 4.227 (1.618–11.043) 0.003 2.838 (1.029–7.826) 0.044
Education
  ≤ 6 year 488 2967.21 14 471.82 Reference   Reference  
  > 6 year 875 5447.65 16 293.70 0.638 (0.312–1.308) 0.220 0.433 (0.191–0.982) 0.045
EBV DNA (copies/ml)
  ≤ 3(undetectable) 1324 8171.70 23 281.46 Reference   Reference  
  > 3 (detectable) 39 243.16 7 2878.70 10.476 (4.495–24.414) < 0.0001 10.049 (4.227–23.887) < 0.0001
  > 3–999 35 223.31 5 2239.01 8.123 (3.088–21.370)   7.627 (2.83–20.558)  
  ≥ 1000 4 19.85 2 10,074.47 37.763 (8.890–160.414) < 0.0001a 39.789 (8.406–188.348) < 0.0001
  1. aP trend for the comparision among EBV DNA undetectable group, DNA levels at > 3–999 copies/ml and DNA levels ≥1000 copies/ml
  2. b Maximum adjustment: all the aforementioned variables were used for adjustment including sex, age, smoking status, NPC family history, salted food,education level, EBV DNA