760 HPV-positive cases), and HPV-12 (1/45 HPV-positive cases) were found (Table 3). Discussion A great variation in HPV rates detected in the oral mucosa of healthy individuals was reported, and it depends on the population studied and the choice of method. It is also known that HPV occurrence in the normal oral mucosa comprises sublinical and/or latent infections; Moreover, HPV infections of low viral load are frequent in the oral cavity [4]. Given the abundance of literature describing results concerning HPV prevalence in the oral cavity and oropharynx all over the world, data presented in this study are to be compared to similar surveys, which were conducted on adolescents aged 10–18 years old using the same MY-PCR method. In the present study, HPV-11 genotype was detected at surprisingly high rate (38/45 HPV-positive cases), while HPV-6 type, frequently reported to be present in the oropharynx, was detected only in three cases (3/45 HPV- positive cases). In our concurrent study, HPV-6 genotype has been identified in 30% cases of juvenile-onset recurrent respiratory papillomatosis among 47 patients investigated (3–12 year old) [6]. Concordant results concerning high HPV-11 prevalence in normal oral mucosa were not reported in literature. One should keep in mind that in some cases, localized HPV-11 infection may lead to severe clinical symptoms, such as recurrent respiratory papilloma- tosis mentioned above, or genital warts if infection is transmitted [12]. Another important finding of our study was the HPV-57 type present in three HPV-positive samples (3/45 HPV-positive cases). This HPV type had been previously found in numerous locations (inverted papillomas of the maxillary sinus, an oral verruca, and a genital condyloma) [14]. In rare cases, both HPV-11 and HPV−57 types are detected in malignant tumors. HPV-11 is known, especially for transformation of cells of the larynx and lungs, while HPV-57 of the nasal cavity. It was also surprising to detect HPV-12 genotype in one specimen, because in the majority of studies, it was not mentioned to infect buccal mucosa [9, 21] and is rather Table 3 Prevalence of HPV genotypes in the study sample Eur J Pediatr (2011) 170:757–761 considered to be etiologically significant in cutaneous epidermodysplasia verruciformis (EV)-associated HPV (EV-HPV). However, HPV-12 tends also to persistently infect within oral mucosa as shown in the study on HPV prevalence in Japan [10]. In the present study HPV-HR genotypes were not detected, whereas their presence was reported at relatively high rate in similar studies by other researchers [19, 20]. It may be due to the MY-PCR method, solely employed in our experimental procedure. It has been reported that type- specific nested PCR greatly improves detection limit of HPV-16 in buccal samples, setting it below ten viral DNA copies [16]. However, in one study performed with the sole usage of MY09 and MY11 oligonucleotides in PCR reaction, HPV-16 DNA was detected in one sample (among 662 screened). The detection limit was set at 100 viral copies in that study [10]. These results could support ours, in which case, indeed HPV-HR types were not present in the study sample of Polish adolescents or HPV-HR DNA load was significantly lower (several viral copies) than the viral load of detected HPV-LR genotypes. The overall HPV prevalence in the study group was 1.08%, and its distribution was even among different strata of age. This observation remains in opposition to those from other studies establishing that HPV prevalence depends strongly upon age [19]. Whereas the HPV prevalence reported herein is low and consistent with the results mentioned above; where the mean HPV prevalence in the 12–15 year-old group of American adolescents was 1.5% [19]. In the present study correlations between HPV, preva- lence and other variables were not observed. Concordant results were described in a number of studies [19, 20]; where sociodemographic gender, sexual intercourse (only adolescents over 13 years old were asked the question about their sexual activity), smoking cigarettes, and drinking were taken into account. In our study correlation of HPV, prevalence with upper respiratory chronic diseases (such as asthma, tuberculosis, mucoviscidosis) was also sought but was not observed. However, it is noteworthy that in several schools, localized in small towns around Poznań and in Poznań itself, the number of HPV-positive children/adolescents was elevated (not included in Table 2). 38/45 3/45 3/45 1/45 HPV genotype N (HPV-positive cases) % (out of N=4,150) HPV genotype/all HPV cases HPV11 HPV6 HPV57 HPV12 All HPV cases 38 3 3 1 45 0.92 0.07 0.07 0.02 1.08