Regional Distribution of Different Types of Human Papillomavirus in Cervixes of Chinese Women: A Meta-analysis

Cervical cancer is a common gynecological malignancy that has shown a gradual increase in morbidity in recent years in China. High-risk human papillomaviruses (HR-HPVs) play a vital role in cervical cancer development and commercial vaccines are available. The overall HPV infection and geographical distribution characteristics of cervical Cancer among Chinese females have not been reported that may guide the application of the vaccines. This study systematically retrieves literature on HPV type and cervical cancer in China published from 2005 to 2017. Data are analyzed according to provinces and administrative areas for the meta-analysis. (1) SPSS17.0 software is used for the statistical data analysis. (2) χ2 inspection is also employed to analyze the infection rate of different HPV types of different cervical lesion groups in seven regions of China. Results show that China’s HR-HPV16, 58, 18, 52, 33, 31, 53, 56, 59, 51, 35, and 68 infection rates are 60.49%, 11.16%, 9.68%, 7.05%, 5.61%, 3.62%, 2.88%, 2.32%, 1.96%, 1.74%, 1.53%, and 1.52%, respectively. Differences in the HR-HPV infection rate of cervical cancer were observed among different areas, especially for HPV 31, 33, 52, and 58. The genotypes of the top five HR-HPV infection rates in cervical cancer also show differences in different regions. The results offer a basis for the prevention and treatment of cervical cancer in different parts of China. HPV type distribution in relation to cervical cancer varies among different regions and parts of China. Therefore, use of available or development of new vaccines suitable for regional types is necessary to improve the efficacy of the vaccines in preventing the primary HPV infection in different areas of China.


Introduction
Cervical cancer is one of the most common gynecologic malignant tumors and has become the most common cause of cancer-related deaths in women in developing countries, where approximately 85% of cases occur. Cervical cancer more frequently occurs in younger women and causes serious harm to women's health [1]. Unlike other tumors, cervical cancer has the characteristics of definite cause and longer reversing precancerous period. Thus, the early detection and timely treatment of cervical cancer may improve patient prognosis to some extent. Human papillomavirus (HPV) infection is an essential factor of cervical intraepithelial neoplasia (CIN) and cervical cancer. The HPV infection rate and distribution of HPV subtypes vary in different countries and regions. Infection of high-risk HPV (HR-HPV) infection (e.g., HPV 16,18,31,and 45) is the main cause of the occurrence and development of cervical cancer. Although the important HR-HPV types (e.g., HPV l6 and 18) show consistency in the geographic area distribution, the main HPV subtypes differ in different parts of the world [2,3]. Hence, prevention and control measures with regional specificity to target infection of HPV subtypes are urgently needed.
China is the most populous country in the world with a high prevalence of cervical cancer. However, only a few studies with comprehensive analyses of the latest literature on the HPV infection condition of Chinese women have been conducted. To more comprehensively understand/map the geographic distribution of HPV types in different regions of China and relate the finding with HPV vaccine application. The current study analyzes literature on HR-HPV [4] infection of cervical cancer among Chinese women in different regions published in PubMed from 2005 to 2017. A meta-analysis was conducted to evaluate the status of HPV subtype infection in different Chinese regions. The results will provide evidence for vaccine application and other possible formulations of prevention and control measures that target the HPV subtype infection in various parts of China.

Search Strategy and Eligibility Criteria
As the primary data source, literature published from January 2005 to August 2017 were searched with the subject terms of "HPV", "cervical neoplasms/cervical cancer", "China"and their entry termsin the PubMed database. Two independent reviewers screened all articles by title and abstract based on theinclusion and exclusioncriteria. Duplicate records were automatically removed by a reference management software. Any disagreements between the two reviewers on paper selection were discussed by explicit selection rules, and fulltextswere reviewed if necessary. Fulltexts of eligible articles were retrieved and assessed by tworeviewers following the set processes.

Inclusion and Exclusion Criteria for the Literature
Inclusion criteria: (1) The research objects come from China, with clear source areas. The case number in a study includes the general screening patients, which may be suffering from cervical disease, precancerous lesions of the uterine cervix, and patients with cervical cancer. (2) The pathological or cytological classification of cervical lesions is definite, which includes invasive cervical cancer (ICC), high-level cervical intraepithelial neoplasia (HSIL), low-level cervical intraepithelial neoplasia (LSIL), and normal control group (i.e., healthy people and patients with cervicitis). Several studies may contain two or more pathological or cytological classifications. The ICC can be further divided into squamous cell carcinoma (SCC), glandular cell carcinoma or glands squamous cell carcinoma (ADC/ASC), and endometrial carcinoma (EC). HSIL is equivalent to the cervical intraepithelial neoplasia grade 2 (CIN2), cervical intraepithelial neoplasia grade 3 (CIN3), cervical glands intraepithelial neoplasia grade 2 (CGIN2), and cervical glands intraepithelial neoplasia grade 3 (CGIN3). Carcinoma in situ is classified as CIN3. LSIL is equivalent to the cervical intraepithelial neoplasia grade 1 (CIN1) and cervical glands intraepithelial neoplasia grade 1 (CGIN1). (3) The method for HPV classification is PCR. In this study, the specific case numbers of cervical lesions infection and infection of different HPV subtypes are connected. The essay methods should be sufficiently clear to introduce the HPV DNA detection process. The simple hybridization detection method based on non-amplification has been removed. (4) The minimum case number of each classification is 20. (5) If the article lacks specific information, then the authorsere contacted directly for specific details of the HPV classification data. If the data or partial data of the study were reported more than twice, then the largest sample size of the published article was included into the specific article.
Exclusion criteria: (1) Areview literature that lacksthe original source data. (2) Survey data that may have serious bias. (3) Experiment design in the original literature is not rigorous (e.g., the research data are incomplete). (4) Repeated case reports, vague data description, and investigation methods or data that do not conform to the research requirements.

Data Excerpt
The following key information serves as the excerpt for each paper: (1) The published year and journals name. (2) The specimen source (i.e., fresh or fixed tissue samples, cytology specimens, or their combination). (3) Pathological or cytological classification: the ICC (SCC/ADC/EC), HSIL (CIN 2/3, CGIN2/3), LSIL 1, CGIN1 (CIN), and normal control group (healthy crowd and cervicitis patients). (4) The total case number of each category and HR-HPV infection. 15 types of HR-HPV types were collected, namely, HPV 16,18,31,33,35,39,45,51,52,56,58,59,68,73,82, and other probable high-risk types (e.g., HPV 53, 66, and83). (5) Area: types. Therefore, the infection rate of different HPV types were analyzed in the HPV positive samples of cervical cancer. The specific positive ratio of HPV types equals the ratio of HPV positive cases of specific types and sample cases that have the results of this specific type. Therefore, the sample size is different forestimating the diverse typesin terms of HPV-positive rates.
SPSS17.0 software is used for the statistical analysis of the data when weighing and combining the infection rates for the different studies. χ² inspection is also employed to analyze the infection rate of different HPV types of different cervical lesion groups in seven regions of China to compare the HPV infection condition of different types.

Included Studies
A total of 316 articles were retrieved from the PubMed database through the keyword search. Approximately 136 articles were initially selected by reviewing their titles and abstracts. Finally, 30 articles were selected after reviewing their full text based on the inclusion criteria (Figure 1, Table1) .

Meta-analysis of the Total Infection Rate of HPV Genotypes in Cervixes
The meta-analysis includes 84,724 cervical biopsies or specimens of exfoliated cells, namely, 4,525 ICC cases, 10,194 Figure 2).

Meta-analysis of the Top Five High-Risk Types of Cervical Cancer in Seven Regions of China
Articles for Northeast China, North China, East China, South China, Central China, Northwest China, Southwest Chinawere obtained. A total of eight HR-HPV genotypes (i.e., HPV 16,18,31,33,52,58,59, and 68) of cervical cancer were selected by synthetically analyzing the top five high-risk types of cervical cancer in different regions. Table 3 shows that the top five genotypes of ICC in the seven regions are inconsistent. The top five HPV genotypes in the seven regions of China were generally HPV 16, 18, 31, 33, 52, 58, 59 and 68. A histogram was made to discuss the distribution of HPV subtypes in the control group (intraepithelial neoplasia) and cervical lesions (cervical cancer) ( Table 3 and Figure 3). Figure 2 shows that HPV 16  and 58 were included in the top five HPV genotype infection rates of cervical cancer in the seven regions, which indicates that they were the dominant types. These types were followed by HPV 31, 33, 59, and 68. Figure 3 also shows the top five high-risk infection rates.

. . . Comparison of the Infection Rate Difference of the Eight Genotypes in the Seven Regions
The chi-square test of R × C table in the SPSS statistical methods were utilized to compare the multiple sample rates. Finally, the chi-square segmentation method was implemented to readjust the inspection level of the alpha value [35]. The adjusted inspection level alpha was α' = 0.002273. The results are listed in Table 4.
The highest infection rate of HPV 16 is 75.56% in South China, which shows significant differences with the infection rates in Northeast China (63.13%, p = 0.001<α'), East China (51.42%, p = 0.000 <α') and Northwest China (55.07%, p = 0.001<α'); the infection rates in North China and Central China are 70.12% and 70.00%, which show significant differences compared with the infection rates of East China (51.42%, p = 0.000<α') and Northwest China (55.07%, p = 0.000 <α'). Moreover, the infection rate in Northeast China is 63.13%, which shows significant difference with the infection rate in East China (51.42%, p = 0.001<α'). The highest infection rate of HPV 31 is 6.77% in East China, which shows significant difference with the infection rates in North China (3.36%, p = 0.000 <α'), Northwest China (2.56%, p = 0.000 <α'), and Southwest China (0%, p = 0.000 <α'). The highest infection rate of HPV33 is 9.13% in North China, which is significantly different from the infection rates of Northeast China The infection rates of HPV 18 genotype showed no statistical differences among the different regions of China.

Discussion
The International Agency for Research on Cancer (IARC) of the World Health Organization has performed meta-analyses of HPV distribution in cervical cancer around the world since 2003 and regularly updates its data [36][37][38]. Results show that respective preponderant HPV types exist in different populations and regions, which indicate that regional differences existed in HPV prevention and treatment. The latest report concerning HPV distribution in mainland China was published in 2009 [39]. However, the data have not been updated, and the regional differences in the HPV types have not been analyzed in detail. China is the world's most populous country with a population of 1.36 billion, which accounts for approximately 18.84% of the world population. Therefore, determiningthe HPV infection status of the Chinese population is significant and important. Analysis of the HPV infection status of cervical cancer and associated lesions in Chinese population has also become necessary because of the different geographical types, races, and lifestyles in different regions of China. The latest summary of meta-analyses in existing literature [39] was published in 2009, and the number of people and cases included in this summary is relatively rare. The current study analyzes and summarizes the HPV infection studies in cervical lesions published from 2005 to 2017. A total of 84,414 cervical biopsies or exfoliated cells were included in this study, namely, 4,525 ICC cases, 10,194 HSIL cases, 5,259 LSIL cases, and 63,436 control subject cases without cervical lesions. This meta-analysis has the highest number of samples included to date, which may provide evidence for the prevention and treatment of cervical cancer and precancerous lesions for the Chinese people. In this study, the eight most prevalent of HPV genotypes in ICC and HSIL are HPV 16, 58, 18, 52, 33, 31, 53, and 56, and the second highest infection rate is HPV 58. In the LSIL and control group, the most prevalent is HPV 52 (Figure 2).
This meta-analysis shows that HPV 16 is the most common infection type among Chinese women with different cervical lesions. The HPV16 infection rates in the ICC, HSIL, LSIL, and normal group are 60.49%, 41.77%, 18.75%, and 2.39% respectively, which are higher than the WHO worldwide data, global and Asian meta-analyses [3,36,40]. In the study, the five most frequent HR-HPV types with cervical cancer are HPV 16, 58, 18, 52, and 33. Based on WHO worldwide data, the five most frequent HR-HPV types in patients with cervical cancer are HPV 16, 18, 33, 45, and 31. By contrast, WHO data indicate that the five most frequent HPV types in Chinese women cervical cancer are HPV 16, 18, 58, 33, and 52 in 2007 [2]. Clifford et al. determined that the most common genotypes of HPV infection in cervical cancer are HPV 16, 18, 45, 31, and 33 in 2003 [37] (Figure 4). The five most common types of HPV infection in Chinese patients with cervical cancer are HPV 16,18,58,33, and 52 in the study by Bao et al. in 2008 [41]. The infection rate of HPV 16 and 18 accounted for 70.17% of the total, which is similar to the findings of Bao. Compared with a similar study by Bao et al, changes were also observed in the five most common types of HPV infection in patients with cervical cancer. The results of the study show that HPV 58 and 52 infection rates are higher than Bao's, and HPV18 infection rate has declined. These results are similar to many other studies indicating that HPV 18 is uncommon and that HPV 58 and HPV 52 are more prevalent than HPV 18 in general population and cancer patients in China [42][43][44][45]. In western countries, HPV 45 is one of the five most frequent HR-HPV genotypes in cervical cancer. In China, the infection rate of HPV 45 is very low in patients with cervical cancer. In addition, the infection rates of the HPV 58 and 52 genotypes in China are higher than those in western countries and the world average. Thus, the national difference should be considered in the prevention and control of HPV and vaccine research in China.
These results indicate that the infection spectrum of HR-HPV types in cervical cancer has changed over the past nine years, which may be due to the difference in the experimental method utilized in the included studies. These differences need further research.
These results show that the HPV infection spectra in cervical cancer are relatively different in different countries and parts of China. Given the geography and population distribution, China can be divided into seven regions (i.e., East China, North China, Central China, South China, Southwest China, Northwest China, and Northeast China). The HPV infection spectra in cervical cancer (Figure 3) (Table 4).
These results indicate that the HPV infection spectra in cervical cancer have significant differences in different nations and regions of China. In particular, HPV 68 ranks third in the infection rate in cervical cancer in Central China but shows an extremely low infection rate in other areas. This phenomenon suggests that HPV68 may be the primary infection genotype of Central China, and the regional differences should be considered when performing HPV prevention, control, and vaccine research in China. The current study has certain differences with that of Chen et al in 2009 [39], which shows that the HPV 59 infection rate ranks third in North China and Northwest China. By contrast, this study shows that the HPV 59 infection rate is lower. This scenario suggests that the HPV infection spectra in cervical cancer vary in different regions of China, which may be due to the different experimental methods applied in the included studies. This difference requires further research and observation.
The HPV58 infection rate in seven regions are much higher than other types, which need to pay attention to. This result is similar to the result reported by Chan in 2014 [46]. Therefore, HPV58 genotype may be a kind of high-risk genotype with high infection rate besides HPV 18 and HPV16, suggesting that reducing the infection rate of HPV58 plays a significant role in reducing the occurrence of cervical cancer development. The aforementioned results suggest that the corresponding prevention treatment measures should be taken in the progress of HPV prevention or research and application of vaccines in different parts of China according to the primary infection types in these areas. HPV bivalent, tetravalent, or multivalent vaccines should be researched according to the regional differences and economic states.
As the only vaccine that can prevent malignant tumors thus far, the HPV vaccine is a milestone in the prevention and treatment of cervical cancer [47]. Currently, three HPV vaccines are available worldwide. The bivalent HPV vaccine (Cervarix; GlaxoSmithKline, Boronia, VIC, Australia) can protect against HPV 16 and 18, whereas the quadrivalent HPV (4vHPV) vaccine (Gardasil; CSL, Parkville, VIC, and Merck, Macquarie Park, NSW, Australia) can protect against HPV 6, 11, 16, and 18. A nine-valent HPV (9vHPV) vaccine, which includes HPV types 6,11,16,18,31,33,45,52, and 58, protecting against the five additional high-risk cancer-causing Cervixes of Chinese Women: A Meta-analysis HPV types, was approved by the US Food and Drug Administration in 2014 (Gardasil 9) [48]. Studies in Australia [49][50][51] showed that the prevalence of HPV 6, 11, 16, and 18 declined significantly for the population that had received the 4vHPV vaccine. Given the vast territory and large population of China, the HPV vaccine application is highly significant and has broad prospects. However, many developing countries, including China, have failed to adopt the vaccine largely because of its remarkably high price [47]. The 9vHPV vaccine is more expensive than the bivalent HPV vaccine and 4vHPV. Moreover, HPV 45 infection in Chinese patients, which is included in 9vHPV, has much lower prevalence than that in western countries and worldwide. Accordingly, the 9vHPV vaccine is unsuitable for Chinese women.
The development of a HPV vaccine suitable for Chinese population is significant. Particularly, the development of vaccines with regional advantages according to the primary HPV infection types is necessary to improve the preventive and treatment measures in different areas of China.

Conclusion
HPV 16 is the most common infection type in different cervical lesions, however, the infection rate of HPV 16 genotypes has clear regional differences. HPV 58 and HPV 52 are more prevalent than HPV 18 in general population and cancer patients in China, which need to pay more attention to. Compared to Western countries, the infection rate of HPV 45 is very low in patients with cervical cancer in China. Results of the study show that the HPV infection spectra in cervical cancer have significant differences in different nations and regions of China, This conclusion may be equally adapted to other countries and regions in the world. Therefore, the development of a HPV vaccine suitable for Chinese population is significant which could reduce the burden on the country and the government. Developing vaccines with regional advantages and according to the primary HPV infection types is necessary to improve the preventive and treatment measures in different areas of China, it may be suitable for other countries and regions.