A total of 24,199 samples with HPV genotyping results were collected, the overall positive rate of HPV was 23.10%. Among the 24,199 samples, 1,661 cases with histopathologic diagnoses were included in this retrospective study. 456 women were diagnosed as negative by pathology, 1,199 women were CIN, and 6 women were cervical cancer. Among the women diagnosed with CIN, 899 (75.29%) were CIN1, 156 (13.06%) were CIN2, and 144 (11.65%) were CIN3. HPV-positive results reported for negative, CIN1, CIN2, CIN3 and SCC were 91.45%, 90.99%, 98.08%, 96.53% and 100%, respectively (χ2 = 14.577, P = 0.006). As the results showed in Fig. 2, the proportion of single HPV infection increased with the increase of CIN grade, in which negative, CIN1, CIN2, CIN3 and SCC were 64.75%, 58.19%, 60.78%, 69.06%, and 100% (χ2 = 5.906, P = 0.052), respectively. However, the results for multiple HPV infection were contrary to the results for single infection and CIN grade association. The overall percentage of multiple HPV infection was 38.77% (592/1661). As shown in Fig. 2, the percentage of multiple HPV infection in women diagnosed as normal, CIN1, CIN2, CIN3 and SCC were 35.25%, 41.81%, 39.22%, 30.94% and 0%, respectively (χ2 = 5.906, P = 0.052).

The single infection and multiple infection of HPV among different groups

In this study, the evaluation values of women infected with single HPV16 type in pathologically normal CIN1, CIN2, and CIN3 were 24.07%, 22.06%, 46.24%, and 55.21%, respectively. The proportion of women infected with monotype HPV16 increased significantly with the increase of CIN grade (trend chi-square test, P < 0.001).

It is also observed that HPV33 and HPV16 have the same trend, that is, HPV33 infection rate increases with the increase of CIN grade. The prevalence of HPV33 in normal, CIN1, CIN2 and CIN3 were 2.22%, 3.15%, 5.38% and 8.33%, respectively (trend chi-square test, P = 0.033). In addition, among women with pathological normal, CIN1, CIN2 and CIN3, the incidence of HPV16/18 (HPV16 and/or HPV18) was 33.33%, 29.41%, 50.54% and 59.38% respectively (trend chi-square test, P < 0.001). However, the prevalence of HPV51, 56 and 66 were lower than 8.00% in all the pathological CIN grades and decreased obviously with the increasing grade of CIN (chi-squared test for trend, P < 0.05). Then, in normal pathology, CIN1, CIN2, and CIN3, the incidence of other high-risk human papillomavirus (hrHPV) types (excluding 16 and 18) was 5.93%, 69.54%, 49.46%, and 40.63%, respectively. In conclusion, with the increase of CIN grade, the percentage of non-HPV16/18 of hrHPV also showed the same downward trend (Chi-square test of trend, P < 0.001).

In women with normal pathology, the total incidence rate of the five most common genotypes (HPV16, 52, 58, 18 and 51/56, with the frequency decreasing from 24.07 to 5.19%) was 67.41%. In CIN1 patients, the 5 most common HPV types were HPV16 (22.06%), HPV52 (17.02%), HPV58 (14.92%), HPV18 (7.35%) and HPV66 (7.14%), with a total incidence of 68.49%. The total incidence rate of five major hrHPV genotypes in CIN2 women was 89.25%, which was HPV16 (46.24%), HPV52 (15.05%), HPV58 (15.0%), HPV31 (7.53%), and HPV33 (5.38%), respectively. In the CIN3 group, the infection rate of the first five hrHPV genotypes accounted for 88.54%, and the prevalence rate was HPV16 (55.21%), HPV58 (11.46%), HPV52 (9.38%), HPV33 (8.33%), HPV31/18 (4.17%), respectively. Moreover, no monotypic infection of HPV45 and HPV6/11 was observed in CIN2 and CIN3 in this study. In addition, all of the six SCC cases were detected with single HPV16 genotype results. (Shown in Table 1)

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As shown in Fig. 3, HPV16 was the most common genotype in monotypic HPV infection, and its prevalence increases significantly with the severity of CIN (Chi-square test of trend, P < 0.001). Even though the prevalence of HPV33 in all CIN grades was lower than 10%, HPV33 also increased with the increase of CIN grade (Chi-square test of trend, P = 0.033). However, HPV18, 31, 52, 58 showed the opposite trends, which decreased with increasing grade of CIN. Besides, other HPV types also decreased with increasing grade of CIN (chi-squared test for trend, P < 0.001). Regarding single infection, the cumulative positive rate of HPV16, 18, 31, 33, 52 and 58 was 68.15%, 66.60%, 93.55% and 92.71% in pathologic normal group, CIN1, CIN2 and CIN3, respectively.

The distribution pattern of predominant HPV genotypes with single-type infection

To detect one CIN2 + cases, 2.8, 8.5, 3.2 and 7.1 women should receive colposcopy referrals if using HPV16, HPV18, HPV16/18 and non-HPV16/18, HPV others as screening methods for detecting cervical lesions, respectively. Meanwhile, to detect one CIN3 case, the referral numbers for HPV16, HPV18, HPV16/18, and HPV others were 5.0, 17.0, 5.9 and 15.4 women, respectively. The colposcopy referral rate for HPV others is 2.5 times and 3 times higher than HPV16 for detecting one CIN2 + case and one CIN3 case, respectively (Table 2).

In the present study, the average age of CIN2 and CIN3 were (41.51 ± 10.53) years and (40.75 ± 10.51) years, respectively. In CIN2, the main age was 35 ~ 44 years (36.46%) and 25 ~ 34 years (33.33%), and the prevalence of CIN2 decreased obviously with increasing age in women over 45 years old. While the peak of the incidence of CIN3 was observed at 25 ~ 34 years (33.68%), followed by 35 ~ 44 years (31.58%), and decreased obviously with increasing age. Moreover, no single type infection was identified under 25 years old in both CIN2 and CIN3 (Fig. 4).

The age distribution of the incidence of CIN2 and CIN3

When age-dependent prevalence for single-type HPV infection in negative, CIN1, CIN2 and CIN3 were evaluated, the top 5 most frequent HPV types in different age groups were analyzed and showed in Fig. 5. In general, the prevalence of HPV16 was the most frequent in all the age groups, except ≥ 65 years group in CIN3, in which two out of three patients were HPV58 infected and one was HPV16 infected. Among CIN1 patients, HPV16, 52 and 58 were the common predominant HPV types in all the age groups except ≥ 65 years. In CIN2 patients, the most prevalent HPV types in different age groups were HPV16, 52, 58, 33, 31 and 18, with relative proportion differed somewhat by age. In CIN3 patients, HPV16, 52, 58 and 33 were the common frequent types in the age groups of 25 ~ 34 years, 35 ~ 44 years and 45 ~ 54 years. Moreover, the prevalence of HPV16 in younger groups (25 ~ 34 years, 35 ~ 44 years and 45 ~ 54 years) was significantly higher than older groups (55 ~ 64 years and ≥ 65 years), while HPV58 showed the opposite trends.

HPV genotypes by age groups in CIN