Eur J Pediatr (2011) 170:757–761 Table 1 General characteristics of the study sample Gender Age (years) Place of residencea Socio-economic status (SES)—on the basis of complex indicator)b Sexual intercoursec Variables Boys Girls 10–12 (primary school) 13–15 (secondary school) 16–18 (high school) Village Town: 21,000–500,000 inhabitants City over 500,000 inhabitants Low Average High No Yes, once Yes, more than once 0.086 3.56 5.595 0.41 2.29 Number 2,028 2,122 1,313 1,551 1,286 1,603 1,675 807 1,338 1,301 1,401 2,356 103 264 df 1 2 2 2 2 759 % 48.87 51.13 31.64 37.37 30.99 38.63 40.36 19.45 32.24 31.35 33.76 86.52 3.78 9.69 P value 0.7690 0.1685 0.0610 0.8150 0.3180 a 65 individuals did not state their place of residence (blank space in the questionnaire) b One hundred and ten individuals did not state their SES (blank space in the questionnaire) c Only adolescents (13–15 and 16–18 age categories) were asked with question about sexual intercourse (N=2,837). 114 individuals did not want to answer this question (blank space in the questionnaire), thus N=2,723 in this category of 450-bp HPV amplicon and were excluded from further analysis to avoid overestimation of positive results. It might have been due to the lack of viral DNA stability and/or too low viral DNA copy numbers very close to the detection threshold using MY-PCR method. In any case, the 450-bp HPV amplicon was redetected in 45 probes. The presence of HPV DNA was additionally confirmed and checked for HPV genotypes by direct DNA sequencing from PCR reaction tube (without purification from MY09 and MY11 oligonucleotides), even though the ethidium bromide signal from the 450-bp HPV amplicon had been very weak (hardly Table 2 HPV prevalence and selected features of the study sample visible) in agarose gel after electrophoresis of several probes. In general, “seq files” contained sequences of perfect readability covering over 300–400 nucleotides; in three cases, only 50–100 nucleotides could have beed read because of numerous “N” nucleotides (background noise). With the help of the corresponding chromatogram file, they were easily corrected. In either case, assigning HPV genotype to each sequence was possible. In our study group, none of HPV-HR types was detected, while among HPV-LR types, HPV-11 (38/45 HPV-positive cases), HPV-6 (3/45 HPV-positive cases), HPV-57 (3/45 Number of HPV-infected individuals Chi-square Variables Gender Age Place of residence SES Sexual intercourse* Category Boys Girls 10–12 13–15 16–18 Village: up to 20,000 inhabitants Town: 21,000–500,000 inhabitants City: over 500,000 inhabitants Low Average High No Yes, once Yes, more than once 21 24 9 22 14 13 17 15 13 16 16 34 0 2 *Only adolescents (13–15 and 16–18 age categories) were asked with question about sexual intercourse (N=2,837). 114 individuals did not want to answer this question (blank space in the questionnaire), thus N=2,723 in this category