Statistical analysis

All statistical analyses were carried out using SPSS (Version 16.0, SPSS Inc., Chicago, USA). The association between gender and infection was analyzed by the Chi-square test. A p value of ≤ 0.05 was considered to indicate statistically significant differences. The McNemar test was, in turn, performed to compare PCR and ELISA results. Moreover, the agreement between ELISA and PCR was assessed by the calculation of Kappa statistic (Cohen’s kappa coefficient or κ). The strength of agreement based on κ was judged according to the following guidelines: κ ≤ 0.20 without consistency, 0.21 ≤ κ ≤ 0.40 poor agreement, 0.41 ≤ κ ≤ 0.60 moderate agreement, 0.61 ≤ κ ≤ 0.80 good agreement, κ > 0.80 very good agreement (Petrie and Watson 1999).