New oral treatments with very high cure rates have the potential to revolutionize global management of hepatitis C virus (HCV), but population-based data on HCV infection are missing in many low and middle-income countries (LMIC).
Methods
Between 2004 and 2009, dried blood spots were collected from age-stratified female population samples of 9 countries: China, Mongolia, Poland, Guinea, Nepal, Pakistan, Algeria, Georgia and Iran. HCV antibodies were detected by a multiplex serology assay using bead-based technology.
Results
Crude HCV prevalence ranged from 17.4% in Mongolia to 0.0% in Iran. In a pooled model adjusted by age and country, in which associations with risk factors were not statistically heterogeneous across countries, the only significant determinants of HCV positivity were age (prevalence ratio for ≥45 versus <35 years = 2.84, 95%CI 2.18-3.71) and parity (parous versus nulliparous = 1.73, 95%CI 1.02-2.93). Statistically significant increases in HCV positivity by age, but not parity, were seen in each of the three countries with the highest number of HCV infections: Mongolia, Pakistan, China. There were no associations with sexual partners nor HPV infection. HCV prevalence in women aged ≥45 years correlated well with recent estimates of female HCV-related liver cancer incidence, with the slight exception of Pakistan, which showed a higher HCV prevalence (5.2%) than expected.
Conclusions
HCV prevalence varies enormously in women worldwide. Medical interventions/hospitalizations linked to childbirth may have represented a route of HCV transmission, but not sexual intercourse. Combining dried blood spot collection with high-throughput HCV assays can facilitate seroepidemiological studies in LMIC where data is otherwise scarce.
Keywords
Hepatitis C virusEpidemiologySerologyLiver cancer
Background
About 180 million people, some 3% of the world’s population, are estimated to have been exposed to hepatitis C virus (HCV) [1–3]. Of these, 130–150 million (~80%) are chronically HCV infected and at risk for development of hepatitis-C related liver cirrhosis or cancer, which kill approximately 700,000 people each year [4]. Although new HCV treatments offering very high cure rates with short durations and few side effects have the potential to drastically reduce HCV-related mortality, access to diagnosis and expensive treatment remain low, so that the number of people living with HCV is actually reported to be increasing [1].
In 2016, the World Health Assembly adopted a strategy to eliminate viral hepatitis as a major public health threat by 2030, noting that national data on hepatitis virus infection are often lacking [5]. In addition, available HCV surveys often over-represent low-risk groups, particularly younger low-risk persons (e.g. pregnant women and blood donors), whereas HCV prevalence is known to increase steadily with age owing to the combination of accumulating risk of exposure and a high probability of infection becoming chronic [6].
Common routes of HCV infection are unsafe injections, inadequate sterilization of medical equipment, and the transfusion of unscreened blood and blood products that have been common in high-income countries till the 1980s and also more recently in low- and medium-income countries (LMIC). Because these practices are largely specific to a given country’s medical system, HCV prevalence and the timing of infection spread may differ between bordering countries [2], and national level data on HCV infection is required to inform public health decisions.
Hence, we exploited a series of standardized seroepidemiological surveys in order to describe HCV prevalence and risk factors among the general female population of a heterogeneous range of countries around the world. HCV seropositivity was determined using a high throughput assay that has been shown to provide an accurate and cost-effective tool for assessment of HCV antibodies in large epidemiologic studies [7], and we went on to compare country-specific HCV prevalence with recently generated country-specific estimates of HCV-related liver cancer incidence.
Methods
Population
Between 2004 and 2009, studies were undertaken in 11 areas in 9 countries with the primary aim to estimate the prevalence of genital human papillomavirus virus (HPV) infection, according to a similar protocol developed and co-ordinated by the International Agency for Research on Cancer (IARC). Population sampling methods have been previously described for the individual study centres: Shanxi, China [8]; Shenyang, China [9]; Shenzhen, China [10]; Ulaanbaatar, Mongolia [11]; Warsaw, Poland [12]; Conakry, Guinea [13]; Bharatpur, Nepal [14]; Karachi, Pakistan [15]; Zeralda, Algeria [16]; Tbilisi, Georgia [17]; and Tehran, Iran [18]. In each area, an attempt was made to obtain an age-stratified population-based sample that included at least 100 women in each 5-year age group, from 15-19 up to 65 years and older. The number of included women is sometimes higher than that in the original reports due to relaxing of selection criteria for adequacy of genital specimens. Data from Mongolia have been previously reported in validation studies of the present HCV serological assay [7, 19]. Trained interviewers administered a face-to-face questionnaire that included information on sociodemographic characteristics, sexual behaviour, reproductive and contraceptive history, and smoking habits. All participants signed informed consent forms according to the recommendations of the IARC Ethics Committee, and of the local ethical review committees in each of the participating countries, which also approved each of the original studies.
Specimen collection
Each participant had a blood sample collected by venopuncture. In Mongolia, this sample was drawn from the cubital fossa into vacuum containers without anticoagulant [19], whereas in all other areas, samples were obtained by fingerstick. In both instances, full blood was then immediately applied to DBS (dried blood spot) filter paper card (Whatman 903 Protein Saver Blood Collection Cards; Schleicher & Schuell) to entirely fill five 14.5 mm diameter circles. DBS cards were dried at room temperature, placed in separate plastic paper zip lock envelopes containing a silica desiccant, and shipped at ambient temperature to the German Cancer Research Center (DKFZ) in Heidelberg, Germany, and stored at -20°C until serological analysis.
Study participants were also invited for a pelvic examination (although a subset, particularly self-reported virgins, declined) and collection of cervical exfoliated cells for HPV DNA testing, performed in the Department of Pathology, VU University Medical Center, Amsterdam, the Netherlands, according to a general primer GP5+/6 + –mediated PCR [20].
HCV serology
Antibodies were eluted from DBS cards according to a previously reported protocol that has been shown to result in high agreement (>96% for HCV antigens) of seropositivity in paired DBS and serum results [19]. In brief, one punch of 6 mm diameter from each DBS was eluted in one well of a 96-well plate in 100 μL PBS at 4oC overnight, and 16 μl of eluate subsequently mixed with 80 μL DBS preincubation buffer.
A multiplex serology assay [19] including antigens to HCV (strain H77, subtype 1a) Core and NS3 proteins was performed as previously described [7]. In brief, full-length coding sequences of Core and NS3 were expressed as double fusion proteins with an N-terminal-GST and a C-terminal tag epitope derived from the large T-antigen of SV40 in E. coli. Fusion proteins were loaded and affinity-purified on glutathione-casein coupled spectrally distinct fluorescence-labeled polystyrene beads (SeroMap; Luminex). DBS eluates were incubated with pooled antigen loaded bead sets. Bound antibodies were quantified with biotinylated goat anti-human IgA, IgM, IgG (Dianova), and R-phycoerythrin–labeled streptavidin in a Luminex 100 analyzer as the median R-phycoerythrin fluorescence intensity (MFI) from at least 100 beads of the same bead set. Antigen-specific MFI values were calculated as previously described [21].
DBS-specific cut-off values for HCV Core (MFI ≥ 967) and NS3 (MFI ≥ 310) were defined as the mean MFI plus three SDs from 235 reference sera that tested negative by a commercial HCV antibody screening assay [19]. Women that were positive for both Core and NS3 proteins were defined as being HCV-positive. In an evaluation against a set of 432 reference sera, this cut-off has been proven to perform similarly, in a single step, to a commercial HCV antibody screening assay (MEIA) followed by RNA confirmation (98% sensitivity, 99% specificity) [7].
When a subset of 2,988 DBS samples from 8 study areas were re-tested on a second occasion to evaluate assay reproducibility, 2,982 (99.8%) were concordantly classified (2,940 HCV-negative, 42 HCV-positive).
Statistical analyses
HPV prevalence was standardized by age using the world standard population (in 5-year age groups from 15-19 to 60-65 years) as a reference [22]. Prevalence ratios (PR) for HCV seropositivity and corresponding 95% confidence intervals (CI) were calculated using unconditional logistic regression adjusted for age (5-year groups) and study area. Heterogeneity of PRs between study areas was tested by calculating the difference between the log likelihood of the model that considered the interaction term between the areas and risk factor of interest and the log likelihood of the model that included the exposure only, and comparing it to the chi-squared distribution with degrees of freedom equal to the number of areas minus one.
Country-specific estimates of HCV-related liver cancer incidence in women were extracted from Plummer et al, Lancet Global Health, 2016 [23], derived by combining country-specific estimates of HCV attributable fraction in liver cancer with Globocan 2012 [24] estimates of female liver cancer incidence.
Results
HCV serology results were obtained for a total of 12,204 women, with study-specific sample sizes varying from 1,516 for Shenzhen, China, down to 892 for Iran (Table 1). Overall median age was 34 years, varying from 30 to 38 years by study center (Table 1). A total of 274 women (2.2%) were HCV-positive. Crude HCV prevalence ranged from 17.4% in Mongolia down to 0.0% in Iran (Table 1). Age-standardization reduced HCV prevalence estimates (by increasing the relative weight of younger age groups, who were less often HCV-positive), but did not change relative differences in HCV positivity between centers.
Table 2 shows the relationship of selected characteristics of study women with HCV positivity. In a model adjusted by age and study area, as appropriate, the only significant determinants of HCV positivity were age group (PR for ≥45 versus <35 years = 2.84, 95% CI 2.18-3.71) and parity (PR for parous versus nulliparous =1.73, 95% CI 1.02-2.93). However, no risk trend was found by number of births. Associations of HCV positivity with risk factors were not statistically heterogeneous across study areas (p values for heterogeneity = 0.17, 0.88, 0.59 and 0.25 for age, sexual partners, parity and induced abortion, respectively).
Table 2
Prevalence ratios (PR) for HCV positivity and corresponding 95% confidence intervals (CI) according to selected women’s characteristics
Risk factor
N tested
HCV positive
N (%)
Adjusted PRa
95% CI
Age
12,164
<35
6,249
79 (1.3)
1
-
35-44
2,894
78 (2.7)
1.86
1.39-2.50
≥45
3,021
117 (3.9)
2.84
2.18-3.71
χ12for trend
p < 0.001
Education level
12,156
None
1,713
24 (1.4)
1
-
Primary
1,552
21 (1.3)
0.96
0.52-1.77
Secondary and higher
8,891
229 (2.6)
0.86
0.46-1.60
Lifetime number of sexual partnersb
10,926
0
1,086
1 (0.1)
0.21
0.03-1.55
1
7,513
146 (1.9)
1
-
2
1,305
60 (4.6)
1.12
0.84-1.49
3+
1,022
65 (6.4)
1.08
0.81-1.44
χ12for trend
p = 0.367
Number of births (parity)
11,199
Nulliparous
2,207
21 (0.9)
1
-
1
3,228
55 (1.7)
1.68d
0.98-2.90
2
2,644
75 (2.8)
1.81d
1.01-3.26
3+
3,120
119 (3.8)
1.84d
1.01-3.38
χ12for trend
p = 0.171
Induced abortionc
9,166
0
5,433
95 (1.7)
1
-
1
1,750
46 (2.6)
0.97
0.69-1.37
2+
1,983
112 (5.6)
1.24
0.93-1.66
χ12for trend
p = 0.121
Smoking status
12,153
Never
10,860
235 (2.2)
1
-
Ever
1,293
38 (2.9)
1.21
0.88-1.66
HPV DNA-positive
9,984
No
8,264
183 (2.2)
1
-
Yes
1,720
65 (3.8)
1.04
0.80-1.36
aAdjusted for age (5-year groups) and geographical area, as appropriate
bAlgeria excluded because of missing data
cAlgeria and Guinea excluded because of missing data
dCombined PR for ≥ 1 versus 0 = 1.73 (1.02-2.93)
Findings by age group and parity are also shown separately for Mongolia, Pakistan and China (the three countries with the highest number of HCV-positive women) in Table 3. Statistically significant increases in HCV positivity by age were seen in each of the three countries, but the rise between women <35 to those 35-44 years of age was especially steep in Pakistan. Increases in HCV positivity in parous women were only observed in Mongolia and Pakistan and did not meet statistical significance (Table 3).
Table 3
HCV positivity by age and number of births, separately for Mongolia, Pakistan and China
Mongolia
Pakistan
China
Risk factor
N tested
HCV positive
N (%)
Adjusted PRa
and 95% CI
N tested
HCV positive
N (%)
Adjusted PRa
and 95% CI
N tested
HCV positive
N (%)
Adjusted PRa
and 95% CI
Age
1,075
963
3,445
<35
511
55 (10.8)
1
479
7 (1.5)
1
1,915
5 (0.3)
1
35-44
289
54 (18.7)
1.74 (1.23-2.45)
254
12 (4.7)
3.23 (1.29-8.11)
755
4 (0.5)
2.03 (0.55-7.54)
≥45
275
78 (28.4)
2.63 (1.93-3.60)
230
12 (5.2)
3.57 (1.42-8.95)
775
9 (1.2)
4.45 (1.49-13.2)
χ12for trend
p < 0.001
p = 0.005
p = 0.007
Number of births
1,056
955
3,225
0
228
16 (7.0)
1
136
1 (0.7)
1
942
2 (0.2)
1
≥1
828
169 (20.4)
1.62 (0.86-3.04)
819
30 (3.7)
3.06 (0.39-24.1)
2,283
16 (0.7)
0.48 (0.06-3.82)
aAdjusted for age (5 years groups), as appropriate
Age-specific HCV prevalence estimates are shown by study country in Fig. 1, in order of highest to lowest HCV prevalence among women aged ≥45 years, and are plotted against country-specific estimates of female HCV-related liver cancer incidence rates. Age-specific increases in HCV prevalence were observable in Mongolia, Pakistan, Guinea, Poland and China. HCV prevalence estimates in women aged ≥45 years correlated well with female HCV-related liver cancer incidence rates, ranging between the extremes of Mongolia (28.4% HCV prevalence versus 20.9 cases of HCV liver cancer per 100,000 women) and Iran (0.0% HCV prevalence versus 0.2 cases of HCV liver cancer per 100,000 women). The only slight exception to this correlation was Pakistan, which showed a high HCV prevalence (5.2%) in comparison to a relatively low estimate of female HCV-related liver cancer (1.3 cases per 100,000 women).
Fig. 1
Correlation of age-specific HCV prevalence with HCV-related liver cancer incidence in women ≥45 years
Discussion
Benefiting from a standardized population-based sampling protocol and a validated serological assay, we describe important variation in HCV seroprevalence in women around the world and robustly confirm the absence of a sexual transmission route for HCV infection. Crude population-based HCV prevalence ranged from 17% in Mongolia down to 0% in Iran and correlated with country-specific estimates of female HCV-related liver cancer incidence, which are also highest in Mongolia (20.9 per 100,000 women) and lowest in Iran (0.2 per 100,000 women) in women aged ≥45 years. Furthermore, when available, our estimates were compatible with previous population-based estimates of HCV prevalence in the evaluated countries.
The extreme HCV prevalence in Mongolia was expected and has been previously described [7]. Indeed, Mongolia has the highest burden of HCV-related liver cancer in the world [23], driven by a long-lasting epidemic due to iatrogenic transmission of HCV through mass vaccination campaigns (e.g. smallpox, polio [25], blood transfusions [26, 27]) and extensive use of injected treatments [28]. At the lower extreme, we confirm an anti-HCV prevalence of less than 1% reported from a wide-range of other population-based studies in Iran [29], where a low fraction of liver cancers are estimated to be attributable to HCV [30].
The relatively high HCV prevalence found in Karachi, Pakistan (~5% in women aged 45+ years) is similar to that in previous large population-based surveys in Karachi [31, 32] and nationwide in Pakistan [33]. Indeed, HCV was reported to be the predominant cause of liver cancer in Pakistan [34, 35]. Given this high HCV prevalence, however, current estimates of HCV-related liver cancer incidence in Pakistani women are lower than expected. This may be due to limitations in liver cancer incidence data for Pakistan [24], or to a more recent iatrogenic spread of the virus compared to, for instance, Mongolia. Indeed the proportion of HCV-positive hepatocellular carcinoma is still increasing in Pakistan [34].
HCV prevalence estimates were highly consistent across the three Chinese sites (0.4-0.6%) and compatible with estimates of 0.4-1.0% in large population-based surveys of women performed since 2006 [36–39]. HCV prevalence is especially low below age 45. Thus, improvements in transfusion practices implemented in China in the mid-1990s, notably prohibition of paid donations of plasma and blood that were associated with mass transmission of HCV and HIV, appear to have largely controlled the HCV epidemic. Indeed, population-based HCV prevalence [36], and proportion of liver cancer attributed to HCV [34], appears to be relatively low and decreasing over time in China.
HCV prevalence in women in Tbilisi, Georgia (1.3%) is compatible with that from a previous population-based survey in which the vast majority of HCV infections in Tbilisi were observed to occur among male intravenous drug users [40]. Indeed, increasing intravenous drug use is feared to be an important source of recent HCV transmission in many former Soviet republics [41]. Estimates of 0.8% HCV prevalence in Warsaw, Poland are similar to that in a nationwide study of 42,274 women (0.8% [42]), and with that modelled from meta-analytical data [43].
No population-based data are available for Algeria, but our HCV prevalence estimates (0.1%) compare well to the 0.2% and 0.6% reported among 1,000 [44] and 3,044 [45] pregnant women, respectively. This would suggest Algeria to have an HCV prevalence similar to its neighbors Morocco and Tunisia [46], and much lower than in Egypt [2], for which much more population-based data is available.
No population-based data are available for Nepal, but our HCV prevalence estimate of 0.2% compares well to the 0.1% reported among 2,007 female blood donors [47], suggesting that Nepal has largely escaped an epidemic of HCV to date.
Lastly, this study provides the first report on HCV infection in Guinea, for which the 0.9% HCV prevalence is lower than previous regional estimates for West sub-Saharan Africa (2.8% [1] and 5.3% [2]), which are nonetheless very sensitive to the lack of relevant data from this region of the world. Lower HCV prevalence among women aged under 45 years in Guinea may represent a cohort effect of reduced HCV transmission in younger generations.
HCV infection increased with age in most countries, presumably due to accumulating risk of exposure. This confirms steady increases up to the age of 60 years reported in a meta-analysis of age-specific HCV infection from Mongolia and Poland [43], and in large studies in China [36–39].
Given the orientation of the surveys towards studying HPV, questionnaires did not include variables that would be useful to studying specific iatrogenic transmission routes. Nevertheless, to our knowledge, this is the first study to suggest the existence of a possible association between HCV infection and parity, which persisted even after adjustment for center and age, which may represent a risk of HCV transmission by medical interventions/hospitalizations linked to childbirth. On the other hand, we were able to robustly confirm the absence of sexual transmission of HCV in the general female population, through the null association with number of sexual partners, and presence of cervical HPV infection, as proxies of sexual intercourse.
Our data arises entirely from females in selected towns, and may not be representative of males or other areas in the same country. In most populations around the world, HCV prevalence in females has been estimated to be similar or lower than that in males [43]. However, at least Mongolia [43] and China [38] may represent exceptions to this rule. In any case, we propose that our population-based sampling procedures provide a more representative picture than studies limited to typically young pregnant women or blood donors.
HCV genotypes are known to vary between the different worldwide regions represented by this study. Nevertheless, the cross-reactivity of serological assays for NS3 and Core proteins of genotypes 1a, 1b and 2a does not suggest that their performance should be affected by the existence of HCV serotypes [7]. Furthermore, the assay was shown to be highly reproducible when a large subset of samples were re-tested on a second occasion, and has been well-validated against commercial HCV tests [7] and for use with dried blood spots [19]. Taken together, we believe that this protocol represents a useful model for obtaining HCV prevalence data from low- and middle-income settings where data is scarce, for both men and women alike. Indeed, DBS do not require blood centrifugation and allow storage and shipment at ambient temperature, thus facilitating field work for seroepidemiological studies in environments with limited technical infrastructure, and the research serological assay is both high-throughput and cost-effective.
Conclusions
HCV prevalence varied enormously across the female populations represented in our study. Medical interventions/hospitalizations linked to childbirth may have represented a route of HCV transmission, at least in some settings, but not sexual intercourse. Combining dried blood spot collection with high-throughput HCV assays can facilitate seroepidemiological studies in LMIC where data is otherwise scarce. Indeed, the availability of population-based HCV estimates is going to become increasingly relevant in the next years, as countries consider the cost and public health priority of going beyond the prevention of HCV transmission by ensuring safety of medical interventions, towards screen-and-treat approaches that can benefit from a new generation of highly performant oral HCV treatment regimens [5].
Abbreviations
CI:
confidence interval
DBS:
dried blood spot
DKFZ:
German Cancer Research Center
HCV:
hepatitis C virus
HPV:
human papillomavirus virus
IARC:
International Agency for Research on Cancer
LMIC:
low and middle-income countries
MFI:
median R-phycoerythrin fluorescence intensity
PR:
prevalence ratio
Declarations
Acknowledgements
We would like to thank Vanessa Tenet for data management and analysis.
Funding
Not applicable.
Availability of data and material
All data generated or analyzed during this study are included in this published article.
Authors’ contributions
GMC conceived the study, supervised the data analysis and drafted the manuscript, in collaboration with SF. BD, TW and M Pawlita developed and performed the HCV assay. YLQ, DK, DH, NK, NK, SAR, ATS and WZ are the local principal investigators for each of the study centres responsible for acquiring the primary epidemiological data and samples. M Plummer was responsible for estimates of HCV-related liver cancer rates. All authors read, gave feedback and approved the final version of the manuscript.
Competing interests
The authors declare they have no competing interests.
Consent for publication
Not applicable.
Ethics approval and consent to participate
All participants signed informed consent forms according to the recommendations of the IARC Ethics Committee, and of the local ethical review committees in each of the participating countries, which also approved each of the original studies.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
Authors’ Affiliations
(1)
International Agency for Research on Cancer
(2)
Infection, Inflammation and Cancer Program, German Cancer Research Center (DKFZ)
(3)
Cancer Institute of the Chinese Academy of Medical Sciences
(4)
Iv. Javakhishvili Tbilisi State University
(5)
Institut National de Sante Publique
(6)
Department of Obstetrics and Gynaecology, Centre Hospitalier Universitaire de Donka
(7)
Infertility and Reproductive Health Research Centre, Shahid Beheshti University of Medical Sciences
(8)
Department of Surgery, The Aga Khan University
(9)
Centre de Recherche du CHUM, Département de Médecine Sociale et Préventive Université de Montréal
(10)
Kist Medical College
(11)
The Maria Sklodowska-Curie Memorial Cancer Center and Institute of Oncology
References
Mohd Hanafiah K, Groeger J, Flaxman AD, Wiersma ST. Global epidemiology of hepatitis C virus infection: new estimates of age-specific antibody to HCV seroprevalence. Hepatology. 2013;57:1333–42. doi:https://doi.org/10.1002/hep.26141.View ArticlePubMedGoogle Scholar
Lozano R, Naghavi M, Foreman K, Lim S, Shibuya K, Aboyans V, et al. Global and regional mortality from 235 causes of death for 20 age groups in 1990 and 2010: a systematic analysis for the Global Burden of Disease Study 2010. Lancet. 2012;380:2095–128. doi:https://doi.org/10.1016/s0140-6736(12)61728-0.View ArticlePubMedGoogle Scholar
WHO. Global health sector strategy on viral hepatitis 2016–2021. Geneva: WHO Press; 2016.Google Scholar
Dondog B, Schnitzler P, Michael KM, Clifford G, Franceschi S, Pawlita M, et al. Hepatitis C Virus Seroprevalence in Mongolian Women Assessed by a Novel Multiplex Antibody Detection Assay. Cancer Epidemiol Biomarkers Prev. 2015;24:1360–5. doi:https://doi.org/10.1158/1055-9965.epi-15-0351.View ArticlePubMedGoogle Scholar
Dai M, Bao YP, Li N, Clifford GM, Vaccarella S, Snijders PJF, et al. Human papillomavirus infection in Shanxi Province, People's Republic of China: a population-based study. Br J Cancer. 2006;95:96–101.View ArticlePubMedPubMed CentralGoogle Scholar
Li LK, Dai M, Clifford GM, Yao WQ, Arslan A, Li N, et al. Human papillomavirus infection in Shenyang City, People's Republic of China: A population-based study. Br J Cancer. 2006;95:1593–7.View ArticlePubMedPubMed CentralGoogle Scholar
Wu RF, Dai M, Qiao YL, Clifford GM, Liu ZH, Arslan A, et al. Human papillomavirus infection in women in Shenzhen City, People's Republic of China, a population typical of recent Chinese urbanisation. Int J Cancer. 2007;121:1306–11.View ArticlePubMedGoogle Scholar
Dondog B, Clifford GM, Vaccarella S, Waterboer T, Unurjargal D, Avirmed D, et al. Human papillomavirus infection in Ulaanbaatar, Mongolia: a population-based study. Cancer Epidemiol Biomarkers Prev. 2008;17:1731–8.View ArticlePubMedGoogle Scholar
Bardin A, Vaccarella S, Clifford GM, Lissowska J, Rekosz M, Bobkiewicz P, et al. Human papillomavirus infection in women with and without cervical cancer in Warsaw, Poland. Eur J Cancer. 2008;44:557–64.View ArticlePubMedGoogle Scholar
Keita N, Clifford GM, Koulibaly M, Douno K, Kabba I, Haba M, et al. HPV infection in women with and without cervical cancer in Conakry, Guinea. Br J Cancer. 2009;101:202–8.View ArticlePubMedPubMed CentralGoogle Scholar
Sherpa AT, Clifford GM, Vaccarella S, Shrestha S, Nygard M, Karki BS, et al. Human papillomavirus infection in women with and without cervical cancer in Nepal. Cancer Causes Control. 2010;21:323–30.View ArticlePubMedGoogle Scholar
Raza SA, Franceschi S, Pallardy S, Malik FR, Avan BI, Zafar A, et al. Human papillomavirus infection in women with and without cervical cancer in Karachi, Pakistan. Br J Cancer. 2010;102:1657–60.View ArticlePubMedPubMed CentralGoogle Scholar
Hammouda D, Clifford GM, Pallardy S, Ayyach G, Chekiri A, Boudrich A, et al. Human papillomavirus infection in a population-based sample of women in Algiers, Algeria. Int J Cancer. 2011;128:2224–9.View ArticlePubMedGoogle Scholar
Alibegashvili T, Clifford GM, Vaccarella S, Baidoshvili A, Gogiashvili L, Tsagareli Z, et al. Human papillomavirus infection in women with and without cervical cancer in Tbilisi, Georgia. Cancer Epidemiol. 2011;35:465–70.View ArticlePubMedGoogle Scholar
Khodakarami N, Clifford GM, Yavari P, Farzaneh F, Salehpour S, Broutet N, et al. Human papillomavirus infection in women with and without cervical cancer in Tehran, Iran. Int J Cancer. 2012;131:E156–61.View ArticlePubMedGoogle Scholar
Waterboer T, Dondog B, Michael KM, Michel A, Schmitt M, Vaccarella S, et al. Dried blood spot samples for seroepidemiology of infections with human papillomaviruses, Helicobacter pylori, Hepatitis C Virus, and JC Virus. Cancer Epidemiol Biomarkers Prev. 2012;21:287–93.View ArticlePubMedGoogle Scholar
Jacobs MV, Walboomers JM, Snijders PJ, Voorhorst FJ, Verheijen RH, Fransen-Daalmeijer N, et al. Distribution of 37 mucosotropic HPV types in women with cytologically normal cervical smears: the age-related patterns for high-risk and low-risk types. Int J Cancer. 2000;87:221–7.View ArticlePubMedGoogle Scholar
Waterboer T, Sehr P, Michael KM, Franceschi S, Nieland JD, Joos TO, et al. Multiplex human papillomavirus serology based on in situ-purified glutathione s-transferase fusion proteins. Clin Chem. 2005;51:1845–53.View ArticlePubMedGoogle Scholar
Doll R, Payne P, Waterhouse J. Cancer Incidence in Five Continents: A Technical Report. Berlin: Springer-Verlag (for UICC); 1966.View ArticleGoogle Scholar
Plummer M, de Martel C, Vignat J, Ferlay J, Bray F, Franceschi S. Global burden of cancers attributable to infections in 2012: a synthetic analysis. Lancet Glob Health. 2016;4:e609–e616. doi:https://doi.org/10.1016/S2214-109X(16)30143-7.
Ferlay J, Soerjomataram I, Ervik M, Dikshit R, Eser S, Mathers C, et al. 2013. GLOBOCAN 2012 v1.0, Cancer Incidence and Mortality Worldwide: IARC CancerBase No. 11 [Internet]. on International Agency for Research on Cancer. http://gco.iarc.fr/today/home. Accessed 27 July 2016.
Kurbanov F, Tanaka Y, Elkady A, Oyunsuren T, Mizokami M. Tracing hepatitis C and Delta viruses to estimate their contribution in HCC rates in Mongolia. J Viral Hepat. 2007;14:667–74.View ArticlePubMedGoogle Scholar
Tsatsralt-Od B, Takahashi M, Nishizawa T, Inoue J, Ulaankhuu D, Okamoto H. High prevalence of hepatitis B, C and delta virus infections among blood donors in Mongolia. Arch Virol. 2005;150:2513–28.View ArticlePubMedGoogle Scholar
Tserenpuntsag B, Nelson K, Lamjav O, Triner W, Smith P, Kacica M, et al. Prevalence of and risk factors for hepatitis B and C infection among Mongolian blood donors. Transfusion. 2010;50:92–9.View ArticlePubMedGoogle Scholar
Logez S, Soyolgerel G, Fields R, Luby S, Hutin Y. Rapid assessment of injection practices in Mongolia. Am J Infect Control. 2004;32:31–7.View ArticlePubMedGoogle Scholar
Hajiani E, Masjedizadeh R, Hashemi J, Azmi M, Rajabi T. Risk factors for hepatocellular carcinoma in Southern Iran. Saudi Med J. 2005;26:974–7.PubMedGoogle Scholar
Abdullah F, Pasha H, Memon A, Shah U. Increasing frequency of anti-hcv seropositivity in a cross-section of people in Karachi, Pakistan. Pak J Med Sci. 2011;27:767–70.Google Scholar
Afzal MS. 2016. Are efforts up to the mark? A cirrhotic state and knowledge about HCV prevalence in general population of Pakistan. Asian Pacific Journal of Tropical Medicine 9:616-618. doi:http://dx.doi.org/https://doi.org/10.1016/j.apjtm.2016.04.013.
Qureshi H, Bile KM, Jooma R, Alam SE, Afridi HU. Prevalence of hepatitis B and C viral infections in Pakistan: findings of a national survey appealing for effective prevention and control measures. East Mediterr Health J. 2010;16(Suppl):S15–23.PubMedGoogle Scholar
de Martel C, Maucort-Boulch D, Plummer M, Franceschi S. 2015. Worldwide relative contribution of hepatitis B and C viruses in hepatocellular carcinoma. Hepatology 62:1190-1200. doi:https://doi.org/10.1002/hep.27969 [doi].
Chen Y, Li L, Cui F, Xing W, Wang L, Jia Z, et al. A sero-epidemiological study on hepatitis C in China. Chin J Epidemiol. 2011;32:888–91.Google Scholar
Ke X, Liguo Z, Fenyang T, Changjun B, Yefei Z, Minquan C, et al. Rate of infection and related risk factors on hepatitis C virus in three counties of Jiangsu province. Chin J Epidemiol. 2014;35:1212–7.Google Scholar
Stvilia K, Tsertsvadze T, Sharvadze L, Aladashvili M, del Rio C, Kuniholm MH, et al. Prevalence of hepatitis C, HIV, and risk behaviors for blood-borne infections: a population-based survey of the adult population of T'bilisi, Republic of Georgia. J Urban Health. 2006;83:289–98. doi:https://doi.org/10.1007/s11524-006-9032-y.View ArticlePubMedPubMed CentralGoogle Scholar
Walewska-Zielecka B, Religioni U, Juszczyk G, Czerw A, Wawrzyniak Z, Soszynski P. Diagnosis of hepatitis C virus infection in pregnant women in the healthcare system in Poland: Is it worth the effort? Medicine (Baltimore). 2016;95, e4331. doi:https://doi.org/10.1097/md.0000000000004331.View ArticleGoogle Scholar
Saraswat V, Norris S, de Knegt RJ, Sanchez Avila JF, Sonderup M, Zuckerman E, et al. Historical epidemiology of hepatitis C virus (HCV) in select countries - volume 2. J Viral Hepat. 2015;22 Suppl 1:6–25. doi:https://doi.org/10.1111/jvh.12350.View ArticlePubMedGoogle Scholar
Ayed Z, Houinato D, Hocine M, Ranger-Rogez S, Denis F. Prevalence of serum markers of hepatitis B and C in blood donors and pregnant women in Algeria. Bull Soc Pathol Exot. 1995;88:225–8.PubMedGoogle Scholar
