758 cavity, 24 HPV genotypes (HPV-1, 2, 3, 4, 6, 7, 10, 11, 13, 16, 18, 30, 31, 32, 33, 35, 45, 52, 55, 57, 59, 69, 72 and 73) have been shown to be present in benign lesions and 12 HPV genotypes (HPV-2, 3, 6, 11, 13, 16, 18, 31, 33, 35, 52 and 57) in malignant lesions [9]. According to Syrjanen et al. the list of HPV genotypes found in the oral cavity is even longer and includes also HPV-58 genotype [21]. Many reports about oral HPV prevalence in the oropharynx in geographically distant human populations are available from cross-sectional surveys [3, 10, 17, 19, 20, 22]. However, different methodological approaches make difficult to compare HPV frequencies and patterns of HPV genotypes in normal oral mucosa among studied groups. Therefore, HPV prevalence varies from one study to another and remains controversial [4]. It should be noted that there are very few population-based screening programs restricted to small areas in Poland [2]. The purpose of the present study was to investigate the prevalence and genotypes of HPV in the oral cavity of children and adolescents in the Wielkopolska region, Poland. It is the first epidomiological cross-sectional survey con- ducted in children and adolescents in Poland. Our data provide novel information, still missing in Poland [11], about HPV occurrence in the oral cavity/oropharynx in young Polish population, aged 10–18. Materials and methods Sampling design Data were collected in years 2008–2009 as part of a large ongoing cross-sectional population-based survey of adoles- cents in the Wielkopolska region named ADOPOLNOR (www.adopolnor.eu). This region, with 3.4 million popula- tion, is situated in the central west of Poland and covers 29,826.51 km2. The study population consisted of 2,028 boys and 2,122 girls, aged 10–18 years, pupils of all types of schools, residing in rural and urban areas of the Wielkopolska region. The examination included body height and weight measurements and an extensive questionnaire where adoles- cents reported their state of health, health-risk behaviours, such as smoking cigarettes, drinking alcohol, taking drugs, and practicing risky sexual activities and socioeconomic life conditions of their households. Biological samples—collection and preparation Oral squamous cells from all the studied subjects (n= 4150) were collected as an oral rinse with a saline solution (5 mL) and processed to cellular DNA extraction, as previously described [7]. DNA concentration obtained from buccal swabs ranged from 10 to 30 ng/ul. Eur J Pediatr (2011) 170:757–761 Detection of HPV DNA by MY-PCR, sequencing and preparation of DNA standards All these steps were performed as described in previous studies [6, 13]. Statistical analyses For statistical analysis, all subjects were grouped by age (10–12; 13–15, and 16–18 years), type of school, and residence. The urbanization factor was categorized as follows: place of residence—village (up to 20,000 residents), town (up to 500,000 residents), and city (over 500,000 residents). The school type was classified into primary, lower secondary, and higher secondary. The Pearson's chi-square test was used to estimate relation between HPV prevalence and variables of interest. Compu- tations were performed using the Statistica 7.1 software package (StatSoft. Inc. 2005 Statistica for Windows). Statistical decisions were taken with a 5%-error probability. Results The study sample included 4,150 children and adolescents of caucasian race. This racial homogeneity is typical for Polish population and relatively rare in the world. There were slightly more girls than boys in the study sample (51.13% versus 48.87%). For more detailed description of sociodemographic data of the participants evaluated in the investigation, refer to Table 1. The total prevalence of HPV in the oral cavity was 1.08% and four different HPV genotypes were detected. More HPV-positive individuals were among girls (53.3%). No correlation was found between HPV prevalence and diseases of upper respiratory tract diagnosed by clinicians in the study group (including chronic diseases, such as asthma, tuberculosis, mucoviscidosis; these variables were not included in Table 2). The distribution of positive cases for infections with HPV was almost even as far as the different sizes of places of residence in the Wielkopolska region is concerned. For details, see Table 2. Correlations between HPV prevalence in the oral cavity and age, gender, socioeconomical status, as well as several risk factors enhancing HPV-related cell transformation, as described in literature (smoking, alcohol consumption, and sexual intercourse history), were sought, but none was observed. Smoking and alcohol consumption categories were not included in Table 2. After the initial MY-PCR amplification, over 53 samples could be classified as positive for HPV DNA presence. In order to confirm these results, a second round of MY-PCR was performed; eight probes were negative for the presence