Study area
The Nouna Health and Demographic Surveillance Site (NHDSS) has existed since 1992 and is in the rural western part of Burkina Faso (Figure 1). It currently covers 58 villages and one semi-urban town and covers a population of about 85,000 inhabitants. The NHDSS is part of Kossi province, which consists primarily of a rural population of multi-ethnic groups. The predominant activity is subsistence farming and cattle keeping. The region is a dry orchard savannah and has a sub-Sahelian climate, which is characterized by a hot climate with short rainy season lasting from June to September with rainfall varying between 400 to 1000 millimeters. The vegetation is mainly scattered short trees. The mean temperature varies from 26°C to 34°C, often reaching 40°C in April, the hottest period [11].
The NHDSS is a member of the INDEPTH Network, a global network of HDSSs with the aim of conducting longitudinal health and demographic evaluation of populations in low- and middle-income countries [16]. The health facilities within the NHDSS consist of one secondary care facility (the district hospital) and 14 primary health centers. The NHDSS has been used as a sampling frame for numerous studies in the fields of clinical research, epidemiology, health economics, and health-systems research. Nouna has a functional vital event registration system, which allows collecting data continuously on pregnancies, births, deaths, and migration [17].
The VA questionnaire
The Nouna questionnaire covers background characteristics of the deceased using structured filter questions on specific signs and symptoms experienced by the deceased up to the point of death. Additionally, a narrative section provides an opportunity to describe conditions not covered in the structured questions (see Additional file 1). Although the questionnaire is written in French, interviews with the HDSS population are performed by trained fieldworkers who translate the content into local languages. The Dioula language is the most spoken local language, but several other languages are common, such as Bwamu, Moore, and Fulfulde.
Verbal autopsy questionnaire data are collected every four to five months at the household level by interviewers. They are then coded by physicians familiar with the 10th revision of the WHO International Classification of Diseases codes (ICD-10).
We used the ICD-10 adopted in 1994 by the World Health Assembly. Its main use here is to classify causes of mortality as recorded at the registration of death. The ICD-10 also covers a conceptual framework of definitions, standards, and methods that have been closely linked and developed along with the classifications themselves. A restricted list based on ICD-10 has been used for the final physician coding (see Additional file 2).
Physicians' coding organization
The VA coding sessions were organized locally by gathering 12 physicians working in the district hospital with an average working experience as general practitioners of four years. One of these physicians with detailed public health background guided the coding process. All physicians had good knowledge of patient management covering the areas of general medicine, care for pediatric inpatients, care for HIV patients, and basic gynecological and obstetrical care for women. Nevertheless, the panel sought opinion from external specialists in the area of interest when required. Based on the number of available physicians, the panel consisted of three to four members. An agreement upon a given cause of death was only reached when two out of three members (66%) or three out of four members (75%) of the panel arrived at a consensus. Thus the panel coding process was more than majority-based and required that more than 50% of the panel members come up with the same cause of death. The cause was then ascribed to the final cause of death. The panel overwhelmingly agreed to classify the cause of death as undetermined if the available VA information did not allow them to make a final decision.
Study design
This study was designed as a comparative study using two methods of PCVA to ascertain causes of death respectively on two independent samples of VA questionnaires collected in 2009 and 2010.
The first sample, from 2009, was coded using the WHO-recommended method (Method 1). The second sample, from 2010, was coded using the extended method (Method 2).
Coding methods
Method 1: As recommended by WHO [3], two experienced local physicians interpret the answers to the questionnaire and independently determine the most probable cause of death. In the case of disagreement, a third physician is consulted. The cause of death is attributed only if supported by at least two physicians using ICD-10.
Method 2: In 2010, Method 1 was extended using a panel of physicians in the case of a coding discordance between referee physicians.
The VA coding procedure has been combined in a stepwise process shown in Figure 2.
Verbal autopsy data collection
Two key actors are generally involved in the process of VA data collection. Since the creation of Nouna HDSS, the event of death is registered in an active reporting system using community reporters, called community key informants (CKIs). Overall, 58 CKIs (one per village) report deaths occurring within households. Afterward, an assigned village interviewer collects information on the death. The trained field staff who visit households with a registered death have no medical background. As described above, they conduct the interview with the caregivers or relatives, translating the French VA questionnaire into the local language. The interview usually takes place several months after the event with the person who assisted the deceased before the death. Figure 3 presents the VA data collection flow chart in Nouna describing the interaction between fieldworkers and the community.
Quality control
Quality control is ensured by several checking mechanisms put in place at different stages of the data collection process. Whenever inconsistencies in collected information do not allow for a final diagnosis, a second interview is done by a field supervisor for consistency. Independently, the interview process at the household level is closely followed up by village supervisors in a random manner. At the data-entry level, attention is given to the attributed codes to reduce errors of coding.
Statistical method used
The concordance rate was obtained for each method by taking the total number of VAs coded where there is agreement among physician coders over the total number of VAs coded.
The proportion test for two independent samples was applied to compare the proportions of undetermined cause of death achieved using the different methods.