Table 3

Distribution and risk associated with formaldehyde exposure

ExposureAll subjectsEBV+ subjectsa (360 cases/94 controls)
No. cases (n = 375)No. controls (n = 325)RRb95% CIRRb95% CI
Ever exposed
Duration (overall)
 ≤10 years31211.3[0.69–2.3]2.8[0.83–9.7]
 >10 years43201.6[0.91–2.9]2.6[0.87–7.7]
ptrend = 0.08
Duration (excl. 10 yrs before dx/int)c
 ≤10 years34181.6[0.89–3.0]4.7[1.1–20]
 >10 years34201.2[0.67–2.2]1.7[0.65–6.0]
Cumulative exposured
ptrend = 0.10
Years since first exposure
 <20 years1972.3[0.95–5.8]2.3[0.52–10]
 ≥20 years55341.2[0.76–2.0]2.8[1.1–7.6]
Age at first exposure
 <25 years62381.3[0.80–2.0]2.6[1.1–6.5]
 ≥25 years1233.4[0.94–12]3.1[0.39–24]
  • a EBV seropositives defined as positive for one of the following anti-EBV antibodies known to be associated with NPC: viral capsid antigen IgA, EBV nuclear antigen1 IgA, early antigen IgA, DNA binding protein IgG, and anti-DNase IgG (see also description in “Materials and Methods”).

  • b Adjusted for age, sex, education, and ethnicity.

  • c Dx/int = date of diagnosis (for case) and date of interview (for controls).

  • d Defined as intensity × duration as specified in “Materials and Methods.”