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Table 3 Joint effects of inhalants and high exposure of cigarette smoking on nasopharyngeal carcinoma

From: Household inhalants exposure and nasopharyngeal carcinoma risk: a large-scale case-control study in Guangdong, China

Exposure factors Never smokers Ever smokers ≥20 pack years
Case Control OR (95 % CI)a Case Control OR (95 % CI)a
Incense use  
 Never 142 331 1.00 (reference) 72 101 1.76 (1.16, 2.68)
 Frequent 489 506 1.83 (1.41, 2.38) 390 247 3.66 (2.65, 5.06)
Synergistic indexb   SI = 1.67 (1.01, 2.76)  
Wood stove use  
 No 265 629 1.00 (reference) 180 198 2.46 (1.80, 3.37)
 Yes 574 561 2.30 (1.82, 2.90) 386 289 3.22 (2.39, 4.34)
Synergistic indexb SI = 0.81 (0.57, 1.13)  
  1. aORs (odds ratios) were adjusted for age (years, continuous variable), sex (male, female), education (high school or less, college or more), housing type (block, bungalow), salted fish (less than monthly, monthly, weekly or more), preserved vegetables (less than monthly, monthly, weekly or more), tea (less than monthly, monthly, weekly or more), herbal tea (less than monthly, monthly, weekly or more), slow-cooked soup (less than monthly, monthly, weekly or more), and family history of NPC (no, yes)
  2. bThe synergy index for household inhalant exposure and cumulative cigarette smoking pack-years