Facial dermatosis associated with Demodex: a case-control study

Facial dermatosis associated with Demodex : a case-control study 1 first-author †E-mail:zhaoyae@mail.xjtu.edu.cn †E-mail:zhaoyae@mail.xjtu.edu.cn zhaoyae@mail.xjtu.edu.cn 1 2 3 1 4 3 3 3 Department of Immunology and Pathogen Biology, Xi’an Jiaotong University College of Medicine, Xi’an 710061, China Department of Immunology and Pathogen Biology, Xi’an Jiaotong University College of Medicine, Xi’an 710061, China Xi’an Center for Disease Control and Prevention, Xi’an 710054, China Xi’an Center for Disease Control and Prevention, Xi’an 710054, China Department of Dermatology, the Second Affiliated Hospital, Xi’an Jiaotong University College of Medicine, Xi’an 710004, China Department of Dermatology, the Second Affiliated Hospital, Xi’an Jiaotong University College of Medicine, Xi’an 710004, China Department of Clinical Laboratory, Chengdu First People’s Hospital, Chengdu 610041, China Department of Clinical Laboratory, Chengdu First People’s Hospital, Chengdu 610041, China Demodex has been considered to be related with multiple skin disorders, but controversy persists. In this case-control study, a survey was conducted with 860 dermatosis patients aged 12 to 84 years in Xi’an, China to identify the association between facial dermatosis and Demodex . Amongst the patients, 539 suffered from facial dermatosis and 321 suffered from non-facial dermatosis. Demodex mites were sampled and examined using the skin pressurization method. Multivariate regression analysis was applied to analyze the association between facial dermatosis and Demodex infestation, and to identify the risk factors of Demodex infestation. The results showed that total detection rate of Demodex was 43.0%. Patients aged above 30 years had higher odds of Demodex infestation than those under 30 years. Compared to patients with neutral skin, patients with mixed, oily, or dry skin were more likely to be infested with Demodex (odds ratios (ORs) were 2.5, 2.4, and 1.6, respectively). Moreover, Demodex infestation was found to be statistically associated with rosacea (OR=8.1), steroid-induced dermatitis (OR=2.7), seborrheic dermatitis (OR=2.2), and primary irritation dermatitis (OR=2.1). In particular, ORs calculated from the severe infestation (≥5 mites/cm 2 ) rate were significantly higher than those of the total rate. Therefore, we concluded that Demodex is associated with rosacea, steroid-induced dermatitis, seborrheic dermatitis, and primary irritation dermatitis. The rate of severe infestation is found to be more correlated with various dermatosis than the total infestation rate. The risk factors of Demodex infestation, age, and skin types were identified. Our study also suggested that good hygiene practice might reduce the chances of demodicosis and Demodex infestation. Facial dermatosis Demodex infestation Association Case-control study Age Introduction 1 The Demodex mites belong to the family Demodicidae (Acari: Cheyletoidea). Demodex folliculorum ( D.f .) and Demodex brevis ( D.b .) are two Demodex mites of permanent parasites found on humans (Desch and Nutting, 1972 1972 ). D.f . occupies the hair follicles above the level of the sebaceous glands, while D.b . exists principally in depth of sebaceous and meibomian glands. These two Demodex species have been retrieved from almost every area of human skin but have a predilection for the face. The mites can be found in any age groups except newborns who are presumably infested soon after birth by direct contact (Bonnar et al., 1991 1991 ). The mite population increases with host age, and in the adult population, these two Demodex species parasitize the normal skin with a prevalence of 100% and a usual density < 5 mites/cm 2 . Demodex mites are usually considered to play a pathogenic role when present in an excessive number or penetrating into the dermis (Ayres and Ayres, 1961 1961 ; Ecker and Winkelmann, 1979 1979 ; Bonnar et al., 1993 1993 ; Forton and Seys, 1993 1993 ; Erbagci and Ozgoztasi, 1998 1998 ). They have been implicated in the occurrence of a wide range of clinical features, including pityriasis folliculorum (Ayres and Ayres, 1961 1961 ), papulopustular and granulomatous rosacea (Bonnar et al., 1993 1993 ; Forton and Seys, 1993 1993 ), inflammatory papule (Seifert, 1978 1978 ), folliculitis (Purcell et al., 1986 1986 ), seborrheic dermatitis (Karincaoglu et al., 2009 2009 ), perioral dermatitis (Dolenc-Voljc et al., 2005 2005 ), and blepharitis (Post and Juhlin, 1963 1963 ; Zhao et al., 2011a 2011a ), although much controversy persists (Bonnar et al., 1993 1993 ; Forton and Seys, 1993 1993 ; Forton et al., 2005 2005 ; Hsu et al., 2009 2009 ). A definitive diagnosis of demodicosis requires a compatible clinical picture and the presence of more than 5 mites/cm 2 (Forton and Seys, 1993 1993 ). In order to confirm the association of various facial dermatosis with Demodex mites, we investigated 860 dermatosis patients in Xi’an, China by a case-control study and conducted multivariate logistic regression analysis. Materials and methods 1 Study population 2 In the study, final diagnoses of the 860 outpatients aged 12 to 84 years were made by four dermatologists who had clinical experience for 10‒35 years in Department of Dermatology at the Second Affiliated Hospital of Xi’an Jiaotong University College of Medicine between October 2008 and December 2009. There were 539 patients with facial dermatosis (patient group) and 321 with non-facial dermatosis (NFD, control group) included. Diagnosis of dermatosis 2 Pathogenicity of Demodex has been under dispute for a long time and few demodicosis diagnoses have been made by a dermatologist at our clinic. In this study, we investigated the correlation between each of the following six kinds of facial dermatosis probably and Demodex . Rosacea is a common skin condition of uncertain etiology, which usually affects the center of face among the middle-aged, causing transient or permanent facial erythema, telangiectasia, edema, papules and pustules, nodus and scar. Based on pathogenesis progress, erythematotelangiectatic rosacea, papulopustular rosacea, and phymatous rosacea appear subsequently. In this study, a total of 91 cases of rosacea were diagnosed, with 9 erythematotelangiectatic rosacea, 65 papulopustular rosacea, and 17 phymatous rosacea. Steroid-induced dermatitis (SID), a dermatosis with obvious “anti-jump phenomenon”, is caused by long-time inappropriate external use of hormone drugs (such as cortisone and prednisone). A total of 26 cases of SID were diagnosed. Seborrheic dermatitis (Seb D) is a common condition with uncertain etiology that makes the skin greasy, scaly, and flaky. A total of 153 cases of Seb D were diagnosed. Facial dermatitis is a facial dermatosis characterized by red, itchy, and blistering skin. It consists of two types: primary irritation dermatitis (PID) and sensitization dermatitis (SD). We identified 106 cases of PID and 34 cases of SD. Acne vulgaris (AV) is a chronic inflammation of unknown etiology, predilecting young adults. It is characterized by skin with comedones, papules, pustules, nodules, cysts, etc., mostly affecting follicles and sebaceous glands. A total of 129 cases of AV were diagnosed. Questionnaire and Demodex examination 2 The questionnaire covered information about age, gender, family address, telephone number, residence pattern, hygiene practices (sharing of sanitary ware, frequency of face-washing every day, and the use of facial cleanser), eating habits (alcohol, sweetmeat, spicy food (such as hot pepper, zingiber) consumptions), skin types (neutral, dry, oily, or mixed), and the dermatosis (rosacea, SID, Seb D, PID, AV, SD, and NFD) considered in this study. All the participants signed the written consent form. Ethical permission was not required for this study because the skin pressurization method was a non-invasive sampling technique routinely used in etiological agent. Skin pressurization method was employed in the process of Demodex examination for all patients. It is convenient, quick, and is widely applied in the fast diagnosis of outpatients in Mainland China. It was conducted with the following steps. First, squeeze the left nasolabial fold and nasal ala (about 1 cm 2 ) with the thumb to get some sebum. Second, place the sebum on the slide and add a drop of liquid paraffin. Finally, place the cover glass and examine the sample with a microscope (4×10). A positive diagnosis was made only after observing the Demodex mites (any of the developmental stages: egg, larva, nymph, adult of D.f . or D.b .) under microscopic magnification. Based on the limit value found by standardized skin surface biopsy ( n < 5 mites/cm 2 ) (Forton and Seys, 1993 1993 ), we decided to apply the same limit value for our sampling method. The Demodex density was classified as severe (≥5 mites/cm 2 ) and mild (1‒4 mites/cm 2 ). Statistical analysis 2 The focus of the study was the occurrence of Demodex infestation. The Demodex infestation rate was calculated by sociodemographic characteristics of patients. χ 2 test was applied to compare the Demodex infestation rates of cases and controls. Seven independent variables (age, gender, residence, eating habits, hygienic practice, skin type, and dermatosis) were included in the logistic regression model to identify significant correlates of Demodex infestation and to calculate odds ratios (ORs) and P values, with a 0.05 significant level. Correlation between Demodex density and the age of patients was shown by a scatterplot. Associations between the rate of severe Demodex infestation and each of the six skin diseases (rosacea, SID, Seb D, PID, AV, SD) were estimated. We also estimated the correlation between the rate of severe Demodex infestation and age amongst the AV patients. Results 1 General information 2 In this study, 860 dermatosis patients completed the questionnaire effectively. The total infestation rate of Demodex mites was 43.0% (370/860). Constituent ratio of D.f . infestation was the highest (52.4%, 194/370), followed by the infestation rate of D.b . (26.5%, 98/370), and the mixed infestation rate was the lowest (21.1%, 78/370). The three constituent ratios were significantly different ( χ 2 =93.5, P < 0.01). Multivariate logistic regression analysis 2 Results of multivariate logistic regression analysis revealed that after controlling for the covariates (Table 1 1 ), three variables (gender, residence pattern, eating habit) were found to be uncorrelated with Demodex infestation, whereas each of the other four variables (age, hygiene practice, skin type, and facial dermatosis) was still correlated with Demodex infestation. In particular, patients aged above 30 years had higher odds of Demodex infestation than those under 30 years. Compared to patients with neutral skin type, patients with mixed skin type were more prone to Demodex infestation (odds ratio (OR)=2.5), followed by those with oily skin (OR=2.4) and then dry skin (OR=1.6). Characteristics 2 Description Frequency Proportion (%) Infestation rate (%) OR (95% CI) P -value 6 Age (year) 2 12–20 92 10.7 31.5 2 21–30 262 30.5 35.9 1.2 (0.7–2.0) 0.450 2 31–40 225 26.2 50.7 2.2 (1.3–3.7) 0.002 2 41–50 166 19.3 47.6 2.0 (1.2–3.4) 0.012 2 51–60 75 8.7 45.3 1.8 (1.0–3.4) 0.067 2 61–84 40 4.6 50.0 2.2 (1.0–4.6) 0.043 2 Gender 2 Male 236 27.4 44.5 2 Female 624 72.6 42.5 0.9 (0.7–1.2) 0.593 2 Residence 2 Urban 836 97.2 43.1 2 Rural 24 2.8 41.7 1.1 (0. 5–2.4) 0.892 6 Eating habit 2 Drinker No 171 19.9 43.9 Yes 689 80.1 42.8 1.0 (0.7–1.5) 0.805 2 Spicy diet No 555 64.5 42.5 Yes 305 35.5 43.9 0.9 (0.7–1.3) 0.689 2 Sweetmeat No 416 48.4 44.2 Yes 444 51.6 41.9 1.1 (0.8–1.4) 0.489 7 Hygienic practice 2 With private sanitary ware 553 64.3 39.4 2 Without private sanitary ware 307 35.7 49.5 1.5 (1.1–2.0) 0.004 2 Washing face once a day 73 8.5 56.2 2 Washing face twice a day 666 77.4 43.8 0.6 (0.4–1.0) 0.046 2 Washing face three times a day 121 14.1 30.6 0.3 (0.2–0.6) 0.001 2 Facial cleanser user 228 26.5 47.8 2 Otherwise 632 73.5 41.3 0.8 (0.6–1.0) 0.004 4 Skin type 2 Neutral 194 22.6 28.4 2 Dry 118 13.7 38.1 1.6 (1.0–2.5) 0.000 2 Oily 254 29.5 48.8 2.4 (1.6–3.6) 0.000 2 Mixed 294 34.2 49.7 2.5 (1.7–3.7) 0.000 7 Dermatosis 2 NFD 321 37.3 30.5 2 Rosacea 91 10.6 78.0 8.1 (4.7–14.0) 0.000 2 SID 26 3.0 53.9 2.7 (1.2–6.0) 0.018 2 Seb D 153 17.8 49.7 2.2 (1.5–3.3) 0.000 2 PID 106 12.3 48.1 2.1 (1.3–3.3) 0.001 2 AV 129 15.0 40.3 1.5 (1.0–2.3) 0.047 2 SD 34 4.0 23.5 0.7 (0.3–1.6) 0.398 Table 1 1 also demonstrated that Demodex infestation was statistically associated with the developments of rosacea (OR=8.1), SID (OR=2.7), Seb D (OR=2.2), PID (OR=2.1), and AV (OR=1.5), whereas no significant statistical correlation was found between SD and Demodex infestation (OR=0.7). Association between Demodex infestation and age of patients 2 Fig. 1 1 showed that Demodex infestation rates increased with age among the 12‒30 years old patients and remained stable amongst the older patients. Although we found no significant differences between the four subgroups amongst the patients aged 31 to 84 years, the average infestation rates between the patients aged 12‒30 years and 31‒84 years were significantly different. Similarly, it was shown that Demodex density changed in the same direction as the infestation rates, except that the density decreased with age amongst patients older than 60 years. X [age group (median) (year)]: 12–20 (15), 21–30 (25), 31–40 (35), 41–50 (45), 51–60 (55), 61–84 (72); Y [infestation rate (%), ♦]: 31.5 (29/92), 35.9 (94/262), 50.7 (114/225), 47.6 (79/166), 45.3 (34/75), 50.0 (20/40); y 1 [mild density constituent ratio (%), ■]: 93.1 (27/29), 73.4 (69/94), 63.2 (72/114), 69.6 (55/79), 64.7 (22/34), 80.0 (16/20); y 2 [severe density constituent ratio (%), ▲]: 6.9 (2/29), 26.6 (25/94), 36.8 (42/114), 30.4 (24/79), 35.3 (12/34), 20.0 (4/20) Correlation between severe Demodex infestation and dermatosis 2 As shown in Table 2 2 , the severe infestation (≥5 mites/cm 2 ) was statistically correlated with rosacea, SID, Seb D, and PID, while not with SD and AV. Patients aged 12–84 years Continuity correction χ 2 value Dermatosis Frequency Infestation rate (%) χ 2 P OR (95% CI)  NFD 321 5.0  Rosacea 91 38.5 73.3 0.000 11.9 (6.2–23.0)  SID 26 19.2 6.1 * * 0.012 4.5 (1.5–13.6)  Seb D 153 16.3 16.9 0.000 3.7 (1.9–7.2)  PID 106 13.2 8.2 0.004 2.9 (1.4–6.2)  AV 129 9.3 2.9 0.086 2.0 (0.9–4.3)  SD 34 5.9 0.0 * * 1.000 1.2 (0.3–5.4) Relationship between Demodex infestation and age among acne patients 2 As shown in Table 3 3 , both the total infestation rates and the severe infestation rates were higher amongst the 31‒84 year-old acne patients than amongst the 12‒30 year-old ones. Acne patients had a higher infestation rate than patients with non-facial dermatosis in both age groups. Regarding severe infestation, the rates were not significantly different between the acne patients and ones with non-facial dermatosis amongst those aged 12‒30 years, whereas ORs of older (31‒84 years old) acne patients and the control patients were statistically different. Continuity correction χ 2 value Demodex density Age (year) Dermatosis Frequency Infestation rate (%) χ 2 P OR (95% CI) 4 Total (≥1 mite/cm 2 ) 2 12–30 NFD 131 20.6 AV 110 35.5 6.6 0.010 2.1 (1.2–3.8) 2 31–84 NFD 190 37.4 AV 19 68.4 6.9 0.008 3.6 (1.3–10.0) 4 Severe (≥5 mites/cm 2 ) 2 12–30 NFD 131 0.8 AV 110 5.5 3.2 * * 0.076 7.5 (0.9–63.3) 2 31–84 NFD 190 7.9 AV 19 31.6 8.3 * * 0.004 5.4 (1.8–16.2) Discussion 1 Demodex infestation can cause indistinguishable multiple skin disorders with white follicular scales, papules, and pustules as their frequent clinical picture (Ayres, 1930 1930 ; Ayres and Ayres, 1961 1961 ; Seifert, 1978 1978 ). Yet it is still under debate whether Demodex is the cause of many kinds of skin diseases (Bonnar et al., 1993 1993 ; Forton and Seys, 1993 1993 ; Forton et al., 2005 2005 ; Hsu et al., 2009 2009 ). Based on the results of the present study, we conclude that rosacea, SID, Seb D, and PID are significantly associated with Demodex infestation, while SD is not. Until now, the dispute mainly focuses on the contradiction of high Demodex infestation rate in the population (few studies reported 100%) (Forton and Seys, 1993 1993 ) and the low incidence of demodicosis. Some studies even showed that a few patients with excessive Demodex had no obvious clinical symptoms (Zhang et al., 2008 2008 ). Three factors might explain the low incidence of demodicosis. First, the density of Demodex infestation is important. The mild cases, the majority of the infested, tend to ignore the symptoms and hence seldom seek medical advice. For instance, pityriasis folliculorum, the most frequent demodicosis (Forton et al., 2005 2005 ), is rarely diagnosed in our hospital. The severe infestation could make great contribution to demodicosis. Although Forton and Seys ( 1993 1993 ) proposed that the mite density of ≥5 mites/cm 2 can be a diagnostic criterion, Erbagci and Ozgoztasi ( 1998 1998 ) suggested that a certain density might not be an appropriate criterion in the diagnosis of demodicosis. Nevertheless, in our study, the correlation between severe infestation (≥5 mites/cm 2 ) rate and various kinds of dermatosis was obviously higher than that between the total infestation (≥1 mite/cm 2 ) rate and the dermatosis (OR values were 11.9 and 8.1 in rosacea, 4.5 and 2.7 in SID, 3.7 and 2.2 in Seb D, 2.9 and 2.1 in PID, respectively). Second, due to the Chinese dermatologists’ denial of Demodex pathogenicity, probably the demodicoses are often misdiagnosed or confused with other facial dermatoses in our clinical practice, thus leading to the nosological question of the demodicoses. One possible interpretation is that demodicosis is included in such related dermatosis as rosacea, SID, Seb D, PID, etc. The other one is that the same patient can have two pathologies at the same time. Thirdly, the susceptibility of hosts could affect the effect of Demodex infestation. Akilov and Mumcuoglu ( 2003 2003 ) have evidenced that people with the Cw2 and Cw4 haplotypes are more susceptible to demodicosis compared to people without the Cw2 and Cw4 haplotypes. In particular, the risk of developing clinical symptoms of demodicosis is 5.0 times higher for people with the Cw2 haplotype and 3.1 times higher for those with the Cw4 haplotype, whereas individuals who have the human leucocyte antigen (HLA) A2 phenotype are 2.9 times more resistant to demodicosis. The role of Demodex mites as risk factors for rosacea has been confirmed recently (OR=7.6) (Zhao et al., 2010 2010 ). The conclusion was drawn from 48 selected studies (9 in English and 39 in Chinese) conducted in 10 countries by meta synthetic quantitative study, which involved 28 527 participants (4 307 rosacea patients and 24 220 controls). That finding was confirmed by the present study (OR=8.1). The hypothesis that SID and Seb D were associated with Demodex mites has not been confirmed at present, but our results were consistent with those of Dolenc-Voljc et al. ( 2005 2005 ) and Karincaoglu et al. ( 2008 2008 ; 2009 2009 ). It is worth clarifying that although English papers about the association between Demodex infestation and AV are very few and mostly give negative conclusions (Baysal et al., 1997 1997 ; Okyay et al., 2006 2006 ), a great number of Chinese papers have reported a positive association between Demodex infestation and the development of AV (Yang et al., 2006 2006 ; Ma et al., 2009 2009 ; Wang et al., 2010 2010 ; Zhao et al., 2011b 2011b ). Moreover, effective acaricidal treatments have also supplied indirect proof of a causal relationship between Demodex infestation and AV (Yang et al., 2006 2006 ; Ma et al., 2009 2009 ). In this study, a significant association between Demodex infestation and AV was established according to the total infestation rate (OR=1.5, 95% CI 1.0–2.3; P < 0.05), whereas a weaker correlation was obtained according to the severe infestation rate (OR=2.0, 95% CI 0.9–4.3; P > 0.05). The weaker correlation might be a result of statistical bias, because severe infestation of Demodex is rather rare amongst the 12‒30 year-old patients in our study. For the younger age group (12‒30 years old), we found no significant difference in the rate of severe infestation between the group with AV and the group with non-facial dermatosis (OR=7.5, 95% CI 0.9–63.3; P > 0.05). After the 12‒30 year-old patients with adolescent acne and non-facial dermatosis were excluded, the severe infestation rate of AV patients became significantly higher than that of non-facial dermatosis in the 31‒84 years age group (OR=5.4, 95% CI 1.8–16.2; P < 0.05). Therefore, any conclusions about the association between Demodex infestation and AV require further study. In addition, we found that Demodex infestation could be affected by age, skin type, and hygienic practice. The infestation rate and the density of Demodex change with age. In our study, the Demodex detection rate increased along with age amongst the 12‒30 year-old patients, which was in agreement with the study of 102 students aged 18‒27 years reported by Okyay et al. ( 2006 2006 ) and 2 248 medical students aged 19‒24 reported by Hu and Wang ( 2001 2001 ). However, the high Demodex detection rate remained stable in the 31‒84 year-old patients, which differed from the particularly big increase in the infestation rate of both Demodex species during the hosts’ fifth and sixth decades reported by Aylesworth and Vance ( 1982 1982 ). At the same time, the Demodex density kept a high level amongst the 30‒60 year-old patients, significantly higher than that amongst the 12‒30 year-old ones and those older than 60 (Fig. 1 1 ). This might be attributed to the development of sebum secretion, which is more mature at the age of 30‒60 years than at 12‒30 years, and less functional above 60 years. Skin type is closely related with Demodex infestation. Our study revealed that the detection rate of mites in dermatosis patients with oily or mixed skin was higher than that in patients with neutral or dry skin. This corresponded to the conclusions of some previous studies (Cao et al., 2009 2009 ; Peng et al., 2009 2009 ). A possible reason is that Demodex mainly consumes living cells in follicles and sebaceous glands. The destruction of massive epithelial cells could lead to compensatory hyperplasia and secretion enhancement. To make it worse, the movement of chelae and claws of the mites in the pilosebaceous unit would stimulate sebaceous follicles and enhance the secretion. Conversely, the detection rate of mites in dermatosis patients with dry skin was found to be higher than that in patients with neutral skin in our study. The reason might be that the dry skin is only a false sensation (Forton et al., 2005 2005 ), which is a result of the opisthosomes of numerous Demodex protruding at the follicular orifices. In addition to age and skin type, individual hygienic practice was also found to be statistically correlated with Demodex infestation, which coincided with Wang and Zhang ( 2006 2006 ) and Cheng et al. ( 2008 2008 ), but was not in accordance with Andrews ( 1982 1982 ) and Xu and Zhang ( 2005 2005 ). One possible explanation is that using private sanitary ware, increasing the frequency of face-washing every day, and the use of facial cleanser can help clean up the Demodex mites on skin-surface and reduce mite population and the chance of cross infestation, regardless of the parasites in the hair follicles and sebaceous glands. Therefore, to draw a definite conclusion about the effect of individual hygienic practice, we need to conduct further studies. Regarding the influence of eating habits, Okyay et al. ( 2006 2006 ) reported that Demodex infestation was associated with alcohol intake, but did not give a definite conclusion due to the small size of the alcohol-consuming group. It was also reported that spicy food (such as hot pepper) contributed to a higher infestation rate because spicy food might make epithelial hyperplasia of follicular and sebaceous glands, which could provide plenty of nutrition for Demodex reproduction (Wu et al., 2008 2008 ; He et al., 2009 2009 ; Tian, 2010 2010 ). However, we have found no statistical correlation between eating habits (alcohol, spicy food, and sweetmeat consumptions) and Demodex infestation in the present study. The association between eating habits and Demodex infestation needs to be further investigated. Gender and residence patterns were also not statistically correlated with Demodex infestation according to our results, which is in accordance with the conclusions of some previous studies (Andrews, 1982 1982 ; Okyay et al., 2006 2006 ). In conclusion, Demodex infestation is significantly associated with the development of rosacea, SID, Seb D, and PID. 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Sociodemographic characteristics and risk factor analysis of Demodex infestation (Acari: Demodicidae) . J Zhejiang Univ-Sci B (Biomed & Biotechnol) , 2011 . 12 ( 12 ): 998 - 1007 . DOI: 10.1631/jzus.B1100079 http://doi.org/10.1631/jzus.B1100079 . Sociodemographic characteristics and risk factor analysis of Demodex infestation (Acari: Demodicidae) 10.1631/jzus.B1100179 Project supported by the National Natural Science Foundation of China (No. 30872199), and the Natural Science Foundation of Shaanxi Province (No. 2006C247), China 2011-08-29 2011-11-18 2011-09-29 2022-01-05 Copyright © Zhejiang University and Springer-Verlag Berlin Heidelberg 2011 2011 Journal of Zhejiang University-SCIENCE B (Biomedicine and Biotechnology) 12 12