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Background: Oral Epstein-Barr virus (EBV) status reflects host EBV activity and potentially links to EBV-associated diseases, however, factors influencing oral EBV loads or reactivation, such as environmental exposures or host factors, are not fully understood.Methods: A 2-stage, multicenter, cross-sectional study of 6558 subjects from 21 administrative cities of southern China and 3 populations from representative geographical areas in China (referred to as the south, north, and northeastern populations) was performed. The relationships between demographical factors and environmental exposures to EBV loads were analyzed by logistic regression models.Results: Current smoking, with a dose-response effect, was found to be strongly associated with higher oral EBV loads in the pooled data, with an odds ratio of 1.58 (95% confidence interval, 1.39-1.79), as well as in each of the separate populations. The odds ratio increased to 3.06 when current smokers in southern China were compared to never smokers in northern China. Additionally, higher oral EBV loads tended to be detected in older participants, male participants, and participants in southern China.Conclusions: This study provided evidence linking the effect of host-environmental factors, particularly smoking, to oral EBV activity. It could strengthen our understanding of the possible causal roles of EBV-related diseases, which may help to prevent or mitigate EBV-associated diseases. [ABSTRACT FROM AUTHOR]

Objects: Nasopharyngeal carcinoma (NPC) incidence exhibits a remarkable sex disparity, with higher risk among males. Whether this pattern can be partly explained by female reproductive history is unclear.Methods: A population-based case-control study of NPC was conducted in southern China between 2010 and 2014, including 674 histopathologically verified female NPC cases and 690 female controls randomly selected from population-based registries. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated using logistic regression after adjusting for potential confounders.Results: Women who had 3, 4, or ≥5 pregnancies compared with 2 pregnancies were at significantly increased risk for NPC (ORs 1.56, 1.45 and 1.88, respectively). History of deliveries was similarly associated with a greater risk of NPC. These positive associations were more prominent in women who were younger than 50 years, had less than 10 years of education, or were white-collar workers. Increasing time since menopause was associated with a diminished NPC risk (Ptrend = 0.010). Women more than 15 years after menopause had a 0.35-fold (95% CI: 0.16-0.75) NPC risk compared with those 0-3 years after menopause.Conclusion: Contrary to our hypothesis, a history of pregnancy or delivery increased the risk of NPC and the risk decreased with increasing time since menopause. However, the non-linear relationship and no consistent risk patterns across strata indicate that the observed associations are unlikely to be causal, and may at least partially be ascribed to residual confounding by socioeconomic factors. [ABSTRACT FROM AUTHOR]