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 202,790 individuals in 42,072 households; village sizes ranged from 139 to 3,979 inhabitants (29–822 households)[i].
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 Emergency Nutrition Assessment – ENA software version 2011) and random sampling of households (25 per cluster). All consenting adults 18 years and above (including visitors[ii]) were eligible for inclusion in the survey. The sampling methodology enabled an oversampling of the population greater than or equal to 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 above and 1.6% HCV prevalence among all adults 18 years and above, 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 4,784 individuals (1,610 aged ≥18 and 3,174 aged ≥45), 3,628 households (577 including ≥18 and 3,051 including ≥45).
Data collection
15 teams (each consisting of a surveyor plus a nurse) administered face-to-face 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 seropositivity risk factors. Data were entered and collected using electronic tablets and then exported to a secure Kobo platform.
Statistical analysis
Statistical analyses (description, prevalence calculation and seropositivity risk factor analysis) were conducted using probabilities/sampling weights calculated for each stage of the sampling: village, household and individual. The sampling stratum was considered the cluster, and analysis took into account the finite population correction factor.
We conducted a multivariate analysis to identify risk factors for HCV serological infection among the population ≥45 years. Risk factors for seropositivity identified a priori included demographic variables (age, gender, occupation, education level, ID poor card status[iii]), 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. Statistical analyses were conducted using R version 3.4.1 (R Development Core Team, 2014).
The list of villages and population data was provided by the Provincial Health Department (PHD), 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 the survey team’s requests for the involvement of each area/village/authority in the survey. Mobilisers (identified by the chief of each village) visited selected households prior to the data collection to request the household’s presence at home on the planned days of data collection.
Laboratory procedures
Sero-infection was assessed for all participants using the SD Bioline® HCV rapid diagnostic test (Labs), which was 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 at this time to ensure smooth linkage to clinical care. These results were not collected or tracked by the survey. Specimens were stored and transported to the MSF laboratory in Moung Russei 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 24h. 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 (transport costs for this travel were reimbursed by the survey). Outside of the initial and final visits at the hospital, follow up care was provided at the closest health facility to the patient’s place of residence.
Ethical considerations
Household and individual written consents were obtained before any inclusions in the survey. This study received ethical approval from the Médecins Sans Frontières Ethical Review Board (ID: 1816), as well as the Cambodian National Ethics Committee for Health Research (NECHR; 23 February 2018 NECHR meeting minutes).
[i] Census 2016, Cambodian Ministry of Planning
[ii] Defined as any person who slept in the household the previous night
[iii] 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