Sociodemographic characteristics and risk factor analysis of Demodex infestation (Acari: Demodicidae).

To identify sociodemographic characteristics and risk factor of Demodex infestation, 756 students aged 13-22 years in Xi'an, China were sampled for the school-based cross-sectional study. Demodex was examined using the cellophane tape method (CTP). The results showed that the total detection rate of Demodex was 67.6%. Logistic regression analysis revealed that five variables (gender, residence, sharing sanitary ware, frequency of face-wash per day, and use of facial cleanser) were found to be uncorrelated with Demodex infestation, whereas three variables (age, skin type, and skin disease) were found to be independent correlates. Students aged over 18 years had 22.1 times higher odds of Demodex infestation compared to those under 16 years and students aged 16-18 years also had 2.1 times higher odds compared to those aged 13-15 years. Odds of having a Demodex infestation for oily or mixed skin were 2.1 times those for dry or neutral skin. Students with a facial skin disease had 3.0 times higher odds of being infested with Demodex compared to those without. The inception rate of students with facial dermatoses increased in parallel with increasing mite count. The inception rates were 21.3%, 40.7%, 59.2%, and 67.7% in the negative, mild, moderate, and severe infestation groups, respectively (χ(2)=60.6, P<0.001). Specifically, the amount of infested mites and inception rate of acne vulgaris were positively correlated (R(2)=0.57, moderate infestation odds ratio (OR)=7.1, severe infestation OR=10.3). It was concluded that Demodex prevalence increases with age, and Demodex presents in nearly all adult human. Sebaceous hyperplasia with oily or mixed skin seems to favour Demodex proliferation. Demodex infestation could be associated with acne vulgaris. The CTP is a good sampling method for studies of Demodex prevalence.