Hepatitis C viraemic and seroprevalence and risk factors for positivity in Northwest Cambodia: a household cross-sectional serosurvey

Background Despite a dramatic reduction in HCV drug costs and simplified models of care, many countries lack important information on prevalence and risk factors to structure effective HCV services. Methods A cross-sectional, multi-stage cluster survey of HCV seroprevalence in adults 18 years and above was conducted, with an oversampling of those 45 years and above. One hundred forty-seven clusters of 25 households were randomly selected in two sets (set 1=24 clusters ≥18; set 2=123 clusters, ≥45). A multi-variable analysis assessed risk factors for sero-positivity among participants ≥45. The study occurred in rural Moung Ruessei Health Operational District, Battambang Province, Western Cambodia. Results A total of 5098 individuals and 3616 households participated in the survey. The overall seroprevalence was 2.6% (CI95% 2.3–3.0) for those ≥18 years, 5.1% (CI95% 4.6–5.7) for adults ≥ 45 years, and 0.6% (CI95% 0.3–0.9) for adults 18–44. Viraemic prevalence was 1.9% (CI95% 1.6–2.1), 3.6% (CI95% 3.2–4.0), and 0.5% (CI95% 0.2–0.8), respectively. Men had higher prevalence than women: ≥18 years male seroprevalence was 3.0 (CI95% 2.5–3.5) versus 2.3 (CI95% 1.9–2.7) for women. Knowledge of HCV was poor: 64.7% of all respondents and 57.0% of seropositive participants reported never having heard of HCV. Risk factor characteristics for the population ≥45 years included: advancing age (p< 0.001), low education (higher than secondary school OR 0.7 [95% CI 0.6–0.8]), any dental or gum treatment (OR 1.6 [95% CI 1.3–1.8]), historical routine medical care (medical injection after 1990 OR 0.7 [95% CI 0.6–0.9]; surgery after 1990 OR 0.7 [95% CI0.5–0.9]), and historical blood donation or transfusion (blood donation after 1980 OR 0.4 [95% CI 0.2–0.8]); blood transfusion after 1990 OR 0.7 [95% CI 0.4–1.1]). Conclusions This study provides the first large-scale general adult population prevalence data on HCV infection in Cambodia. The results confirm the link between high prevalence and age ≥45 years, lower socio-economic status and past routine medical interventions (particularly those received before 1990 and 1980). This survey suggests high HCV prevalence in certain populations in Cambodia and can be used to guide national and local HCV policy discussion.


Background
Until very recently, the global Hepatitis C Virus (HCV) epidemic, responsible for an estimated 71 million chronic infections and 30% of the 1.34 million deaths due to viral hepatitis, was largely thought insurmountable [1]. Though newer Direct Acting Antivirals (DAA) are safer, more effective and easier for patients than previous HCV treatment, the extremely high treatment cost (up to $150,000 per patient) prohibited their widespread access and use, particularly outside of well-resourced health systems [1,2].
However, recent developments are restructuring the public health approach to HCV. Two common DAAs, Sofosbuvir (Sof) and Daclatasvir (Dac), have reduced dramatically in cost (Sof was $84,000/treatment in 2013, and is only $85 in 2019) [3]. Adjusted models-of-care in low-resource settings are treating more patients, as effectively, for a fraction of previous prices (cost-per-cure in a 2018 Cambodian cohort dropped from $1172 to $370) [4]. Widespread access to treatment is becoming a more realistic goal, encouraging Ministries of Health (MoH) and donors in low-resource settings to expand HCV treatment as part of the global push towards the elimination of viral hepatitis by 2030, a goal adopted in 2016 by the World Health Assembly [1,5].
The HCV burden in Cambodia has long been thought high. However, prevalence estimates in the general population are lacking. Several studies have attempted to understand the magnitude of HCV prevalence in Cambodia, but most have methodological limitations or focus on specific sub-populations rather than on the general population, with considerable variation in their estimates of prevalence rates [6][7][8][9]. Anecdotal clinical evidence has suggested increased HCV risk based on historic exposures to unsafe transfusions or routine medical practices, but this hypothesis has not been tested in the general population.
In This study establishes a robust estimate of the HCV burden and seropositivity risk factors for the general population in three rural districts of northwestern Cambodia.

Study setting
The survey was conducted from April to August 2018 in the health operational district of Moung Ruessei, Battambang province, located in northwestern Cambodia near the border of Thailand. The three surveyed (administrative) districts included 175 villages, 20 communes, and 13 health center catchment areas. The area population consisted of an estimated 202790 individuals in 42072 households; village sizes ranged from 139 to 3979 inhabitants (29-822 households). 1

Study population, survey design and sample size
This was a cross-sectional population-based survey, using a multi-stage cluster design with probability proportional to size (PPS) and random sampling of villages (using ENA software version 2011) and random sampling of households (25 per cluster). All consenting adults 18 years and above (including visitors 2 ) were eligible for inclusion in the survey. The sampling methodology enabled an oversampling of the population ≥45 years old to account for higher expected prevalence in this population.
Sample sizes were calculated using EpiInfo software, with an estimated 7% HCV prevalence among adults ≥45 years and 1.6% HCV prevalence among all adults ≥18 years, at 95% confidence, precision = 1.0% (≥45 years) and 0.8% (≥18 years), a non-response rate of 15%, and an average household size of 4.7. A total of 147 clusters were selected (123 clusters targeting the population ≥45 and 24 clusters for the population ≥18). The final sample size required 4784 individuals (1610 aged ≥18 and 3174 aged ≥45), 3628 households (577 including ≥18 and 3051 including ≥45). 1 Census 2016, Cambodian Ministry of Planning 2 Defined as any person who slept in the household the previous night

Data collection
Fifteen teams (1 surveyor, 1 nurse) administered face-toface standardized, pre-piloted electronic questionnaires to households and individuals. Questionnaires included information on socio-demography, migration, knowledge of HCV prevention and treatment, and individual history of HCV exposure and risk factors. Data were entered and collected using electronic tablets and then exported to a secure Kobo platform.

Statistical analysis
Statistical analyses were conducted using probabilities/ sampling weights calculated for each stage of the sampling: village, household and individual. The sampling stratum considered the cluster, and analysis considered the finite population correction factor.
We conducted a multivariate analysis, accounting for the sampling design, to identify risk factors for HCV serological infection among the population ≥45 years. 3 Risk factors for seropositivity identified a priori demographic variables (age, gender, occupation, education level, ID poor card status 4 ), spatial variables (health centers catchment area, distance to Moung Ruessei referral hospital, distance to the health center from the catchment area), medical variables (history of blood transfusion and blood donation, history and location/provider type for medical injections, surgery and delivery, dental and gum treatment, type of contraception, miscarriage and abortion) and behavioral variables (tattoos, piercing, IV drug use, pedicures, manicures and frequenting of barbershops). The association between the seroprevalence and the explanatory covariates was quantified by fitting a linear multivariate regression model. The multivariate analysis retained variables from the univariate analysis with p-value less than 0.2. Estimates of the regression coefficients of the model and odds ratios with their standard error are presented. In the final model, 'unknown' levels of medical variables (history of blood transfusion and blood donation, surgery and dental and gum treatment) were few and are recoded as 'none'. Statistical analyses were conducted using R version 3.4.1 (R Development Core Team, 2014). Accounting for the sampling design, the survey package (Analysis of Complex Survey Samples, Thomas Lumley) version 3.34 estimated parameters, including standard errors (Horvitz-Thompson-type standard errors are used everywhere in the survey package [10]. Confidence interval calculations usually used the scaled Chi squared distribution for the log likelihood from a binomial distribution [11]).
The list of villages and population data was provided by the Provincial Health Department 2016 and 2017 census data. Household lists (official household registers or notebooks) were provided by chiefs of villages and updated to include any new or temporary residents.

Community engagement
Prior to the start of the survey, meetings were organized with local authorities at all levels to introduce the objectives of the survey and to discuss the timeline and request for support. Mobilisers (identified by the chief of each village) visited selected households prior to the data survey to request the household's presence.

Laboratory procedures
Sero-infection was assessed for all participants using the SD Bioline® HCV rapid diagnostic test [12], performed according to the manufacturer's instructions, using capillary blood collected by fingerpick by trained nurses.
Seropositive participants were invited to the nearest health center to assess their HCV viral load; HIV and HBV diagnostics were also offered to ensure smooth linkage to care but results were not tracked. Specimens were stored and transported to the MSF laboratory in Moung Ruessei hospital in cold chain (2-8°C). Samples were centrifuged the same day and stored in a refrigerator (2-8°C) before their analysis within 24 h. Viral load was assessed using the Xpert© HCV viral load assay with GeneXpert© Instrument Systems (Cepheid, Sweden).

Linkage to treatment and care
Patients with detectable viral load were invited to the MSF/MoH HCV program at Moung Ruessei hospital to receive their results and initiate treatment, if desired (the survey reimbursed transport costs). Besides initial and final visits at the hospital, care was provided at the closest health facility to the patient's home.

Ethical considerations
This study received ethical approval from the MSF Ethical Review Board (ID: 1816), as well as the Cambodian National Ethics Committee for Health Research (NECHR; 23 February 2018 NECHR minutes). 3 We focused on this older cohort for the risk factor analysis both because 1) in the ≥ 18 age group there were very low rates of positivity and, among those positive, insufficient numbers of affirmative responses in the respective risk factor categories to enable meaningful analysis and 2) the ≥45 years population was of primary programmatic and advocacy interest due to the assumption (justified by the results of this survey) of the elevated comparative prevalence in this population as compared to the younger cohort. 4 The ID poor card is a system in Cambodia to identify impoverished households eligible to receive public assistance. For the purposes of this survey, there were three possible types of ID poor card status: 1) ID poor card 1, 2) ID poor card 2 and 3) Poor letter (whereby the village chief or another local leader provided a letter confirming the impoverished status of the family). The difference between ID poor card 1 and 2 is a matter of severity of poverty levels; the poor letter is written in the absence of having an official designation as ID poor card 1 or 2, for example in sudden or unexpected circumstances

Participation
A total of 5098 (of 5215) individuals and 3616 (of 3668) households participated in the survey, with an individual and household response rate of 97.8 and 98.6%, respectively. The percentage of households absent or refusing was equal, at 0.7%, as was the percentage of individual absenteeism or refusal, at 1.1%.

Study population
This section extrapolates the demographics of the surveyed population to the population as a whole to confirm the representativeness of the survey sample. The surveyed individuals and households represented a population of 112398 inhabitants living in Moung Ruessei district consisting of 49903 males and 62494 females, with an overall sex ratio of 0.80 (Table 1). This age and gender distribution in the study was similar to the population as a whole. 5 The percentage of the study population never attending school was~50%, irrespective of gender (Table 2). Women achieved more education than men (24.6% of women have attended higher than secondary school, versus 10.3% of men).
Roughly a third (28.9%) of the population was part of a social welfare program ( Table 2).
More than a quarter of the population was away from home sometime within the previous year ( Table 3). The percentage of the population away for 1 month or longer was substantial: 9.0% were away 1 to 6 months and 7.0% were away more than 6 months.' (Table 3).

Geographical pattern
Among adults ≥45 years old, geographic variation in seroprevalence was noted at the level of the health center catchment area, ranging from the lowest prevalence, in Prey Svay, of 3.0 (CI95% [1.3-4.6]) to the highest in Prey Toch, at 9.4 (CI95% [6.7-12.1]) ( Table 5). Nevertheless, this analysis was unable to quantify any clear geographic patterns in seroprevalence. Exploratory analyses showed no identifiable trends in prevalence according to the distance from the catchment area to Moung Ruessei referral hospital, or to the health center (Fig. 2).

Knowledge of HCV
Most participants, 3302/5103 (64.7%), reported never having heard of HCV. 6 This percentage was lower amongst seropositive participants (57.0%). Among those who reporting having heard of HCV, knowledge of HCV transmission was similarly reported between seropositive and seronegative participants (55.8% versus 53.2%). The percentage of all survey participants who had both heard of HCV and accurately reported the transmission pathways ranged from 12.6 to 17.5%. Among the 1801 participants who had heard of HCV, 1139 participants (63.2%) responded that they know how HCV can be prevented. Although most participants correctly reported HCV prevention methods ("not sharing needles or syringes with other people," "using a condom," and "using sterile or unused medical devices": 93.1, 80.0, 88.2%, respectively), a majority (85.4, 82.2%) also reported that "getting a vaccine," and "washing your hands thoroughly," were other ways to prevent transmission.  Seropositivity risk factor analysis Table 6 presents socio-demographic characteristics and risk factors associated with seroprevalence in the multivariate linear regression model (accounting for the sampling design) for adults ≥45 years. Seroprevalence increased with age (p< 0.001) and was associated with socio-economic status, being lower among people who achieved an education level higher than secondary school than those who never attended school (OR 0.7 [95% CI 0.6-0.8]); there was also some evidence that seroprevalence was lower among people with an ID poor card 1 compared to those not part of a welfare program (OR 0.8 [95% CI 0.6-1.0], p< 0.05). Seroprevalence was higher among people who had their first medical injection before 1990 (injection after 1990 OR 0.7 [95% CI 0.6-0.9]), their first surgery before 1990 (surgery after 1990 OR 0.7 [95% CI 0.5-0.9]); people who donated blood for the first time before 1980 (blood donation after 1980 OR 0.4 [95% CI 0.2-0.8]),a blood transfusion for the first time before 1990 (blood transfusion after 1990 OR 0.7 [95% CI 0.4-1.1]); and those who had dental and gum treatment (OR 1.6 [95% CI 1.3-1.8]). The degrees of freedom of the model was high (30) given the number of events (216). Nevertheless, the p-value of the Hosmer Lemeshow test that assesses the goodness-of-fit of the model was less than 0.05.

Discussion
This survey is the first of its kind in size and rigor in Cambodia, with findings that: HCV prevalence is higher in people ≥45 years (with prevalence increasing with older age) and among those with less education, that there is sometimes wide geographic variability in HCV estimates, and that HCV disease is poorly understood even among the seropositive.
The prevalence rates found were similar to estimates from some previous studies, but substantially different from others. The 2.6% prevalence seen in this population was far lower than the 14.7% seen in blood donors in 2009, and was half the rates (5.8 and 5.2%) from observational studies of people living with HIV (PLHIV) [7][8][9]. The only other survey of a general population cohort, from Siem Reap in 2012 (across only three northern villages; n=483), found double (5.2%) the seroprevalence of this cohort, though our survey confirmed several findings of that survey as well (higher prevalence in older cohorts, geographic variability in seroprevalence, similar viraemic prevalence) [13]. Notably, our results diverge from that smaller survey in the gender differences in seropositivity risk that we found, and the fact that the Siem Reap survey associated blood transfusions and surgical history with a higher risk of viremia, while ours associated these factors with seroprevalence.
Surveys in nearby Thailand have similarly found a wide range of HCV prevalence among different regions and groups. A recent large-scale survey of the general population in Phetchabun of adults aged 35-64 found 6.9% anti-HCV positive [14], though an earlier study found a 15.5% anti-HCV positivity rate in Phetchabun, compared to 3.6% in neighboring Khon Kaen Province [15]. More similarly to our results among older adults (but dissimilarly as it was among a sub-group), a 5.5% HCV seroprevalence was identified among HIV cohorts in Cambodia in a systematic review and meta-analysis [16]. Predictably, HCV seroprevalence was especially linked (among those ≥45 years) to routine medical care (dental), and procedures occurring prior to 1990 and 1980: injections, surgery, blood donation and transfusion. Though these findings may speak to historic trends, the fact that the study cannot determine when transmission occurred in this population means it is critical to generally reinforce infection prevention and control (IPC) measures in healthcare facilities and among staff at all levels.
Furthermore, programs for HCV screening and treatment should particularly consider older populations. Systematic testing of those aged ≥45 years, and treatment for the viraemic positives would contribute to the goal of HCV elimination in Cambodia and could substantially reduce the existing reservoir of HCV in the general population. Increasing overall awareness of HCV in the general population through information, education and communication (IEC) will also be a critical component of decreasing transmission and prevalence.
There have been many obstacles on the road to HCV elimination. For years, effective drugs were lacking, and then cost-prohibitive. Now, simplified care models make HCV interventions more efficient and cost-effective. Establishing baseline prevalence rates and identifying groups at highest risk for seropositivity using statistically rigorous methods like the ones described here provides the necessary evidence for HCV elimination programs.
The results of this study are sufficiently representative, demographically and geographically, to provide policyrelevant guidance on HCV screening strategies, treatment and elimination in Cambodia, and to contribute to global conversations on HCV epidemiology, treatment and disease reduction or elimination [13].

Limitations
There are several limitations to this study. There were not enough seropositive participants under 45 years to conduct a meaningful analysis of risk factors for infection in this age group. Also, children were not included. The timing of initial HCV infection cannot be identified and therefore it is not possible to describe historical HCV epidemiology from this survey.
Although the study ensured that all participants were provided with transport for follow-up testing and to initiate care and treatment, the study design did not maintain data regarding uptake of care or initiation of treatment. This decision was made after deliberation and taken in light of ethical concerns that participants could feel unfairly pressured to participate in the survey if they  were to be followed through the course of their decision regarding treatment initiation, since MSF both conducted the survey and, in collaboration with the MOH, provided treatment. Moreover, the survey is not representative of all Battambang Province or of other regions in Cambodia, and the surveyed geographic area may have had unique characteristics (such as a low distance [< 20 km] from most health centers to the hospital or largest town) and should not be considered representative of other regions. Care should be taken when interpreting results, though these findings point to important potential infection trends and are the most robust rural HCV estimates in the country to date.

Conclusion
This study provides the first large-scale general adult population prevalence data on HCV infection in Cambodia. The primary conclusions fill gaps in the understanding of HCV epidemiology in Cambodia with more precision and power than currently existing data. The results show high prevalence in adults age ≥45 years and confirm the link between high prevalence and increasing age, lower socio-economic status and past routine medical interventions (particularly those before 1990 and 1980). This survey serves as an alert to the potentially high prevalence of HCV infection in Cambodia and can be used to guide national and local HCV policy discussion.