Tropical Epidemiology: A System for Continuous Demographic Monitoring of a Study Population

Health and demographic surveillance systems in low- and middle-income countries: history, state of the art and future prospects

Health and Demographic Surveillance Systems (HDSS) have been developed in several low- and middle-income countries (LMICs) in Africa and Asia. This paper reviews their history, state of the art and future potential and highlights substantial areas of contribution by the late Professor Peter Byass.Historically, HDSS appeared in the second half of the twentieth century, responding to a dearth of accurate population data in poorly resourced settings to contextualise the study of interventions to improve health and well-being. The progress of the development of this network is described starting with Pholela, and progressing through Gwembe, Balabgarh, Niakhar, Matlab, Navrongo, Agincourt, Farafenni, and Butajira, and the emergence of the INDEPTH Network in the early 1990'sThe paper describes the HDSS methodology, data, strengths, and limitations. The strengths are particularly their temporal coverage, detail, dense linkage, and the fact that they exist in chronically under-documented populations in LMICs where HDSS sites operate. The main limitations are generalisability to a national population and a potential Hawthorne effect, whereby the project itself may have changed characteristics of the population.The future will include advances in HDSS data harmonisation, accessibility, and protection. Key applications of the data are to validate and assess bias in other datasets. A strong collaboration between a national HDSS network and the national statistics office is modelled in South Africa and Sierra Leone, and it is possible that other low- to middle-income countries will see the benefit and take this approach.

Health & Demographic Surveillance System Profile: Farafenni Health and Demographic Surveillance System in The Gambia

The Farafenni Health and Demographic Surveillance System (Farafenni HDSS) is located 170 km from the coast in a rural area of The Gambia, north of the River Gambia. It was set up in 1981 by the UK Medical Research Council Laboratories to generate demographic and health information required for the evaluation of a village-based, primary health care programme in 40 villages. Regular updates of demographic events and residency status have subsequently been conducted every 4 months. The surveillance area was extended in 2002 to include Farafenni Town and surrounding villages to support randomized, controlled trials. With over three decades of prospective surveillance, and through specific scientific investigations, the platform (population ≈ 50,000) has generated data on: morbidity and mortality due to malaria in children and during pregnancy; non-communicable disease among adults; reproductive health; and levels and trends in childhood and maternal mortality. Other information routinely collected includes causes of death through verbal autopsy, and household socioeconomic indicators. The current portfolio of the platform includes tracking Millennium Development Goal 4 (MDG4) attainments in rural Gambia and cause-of-death determination.

Dying to count: mortality surveillance in resource-poor settings

Reliable cause-specific mortality data constitute a crucial resource for health monitoring, service planning and prioritisation. However, in the majority of the world's poorest settings, systematic health and vital event surveillance systems are weak or non-existent. As such, deaths are not counted and causes of death remain unregistered for more than two-thirds of the world's population.For researchers, health workers and policy makers in resource-poor settings, therefore, attempts to measure mortality have to be implemented from first principles. As a result, there is wide variation in mortality surveillance methodologies in different settings, and lack of standardisation and rigorous validation of these methods hinder meaningful comparison of mortality data between settings and over time.With a particular focus on Health and Demographic Surveillance Systems (HDSSs), this paper summarises recent research and conceptual development of certain methodological aspects of mortality surveillance stemming from a series of empirical investigations. The paper describes the advantages and limitations of various methods in particular contexts, and argues that there is no single methodology to satisfy all data needs. Rather, methodological decisions about mortality measurement should be a synthesis of all available knowledge relating to clearly defined concepts of why data are being collected, how they can be used and when they are of good enough quality to inform public health action.

Patterns of mortality in Bavi, Vietnam, 1999-2001

AIMS

Demographic data including detailed mortality patterns for Vietnam are relatively sparse, mainly coming from national census data. This paper describes detailed mortality findings from a sample drawn from the population of one district of northern Vietnam, over the three-year period 1999-2001.

METHODS

These data were based on quarterly household visits to collect data on vital events, covering 142,318 person-years of observation over a three-year period.

RESULTS

Crude mortality was 5.1 per 1,000 person-years (4.7 for females and 5.6 for males). Infant mortality was 21.6 per 1,000 live births and crude birth rate was 14.7 per 1,000. Life expectancy at birth was 75.2 years (78.8 year for females and 71.1 for males). Residents of mountainous and highland areas experienced lower mortality than riverside and island dwellers.

CONCLUSIONS

These findings are discussed in the light of two major demographic factors: the legacy of the Vietnam War and, more recently, the effect of Vietnam's two-child policy. Although these mortality estimates seem low, there is good reason to believe that they accurately reflect the current state of this population. Vietnam as a whole enjoys low mortality in relation to its socioeconomic status compared with neighbouring countries.

Validity and completeness of death reporting and registration in a rural district of Vietnam

AIMS

Assessment was made of the validity of mortality estimates based on data collected during 1999-2000 by quarterly follow-up visits and compared with other methods (re-census, communal death registration, and neighbourhood survey).

METHODS

This study was carried out within a longitudinal epidemiological laboratory in Bavi, District, Vietnam (called FilaBavi), covering a sample of 11,089 households with 51,024 inhabitants. Deaths within FilaBavi during 1999-2000 were collected by four methods and compared: quarterly household follow-ups, the re-census carried out in 2001, the Commune Population Registration System (CPRS), and a neighbourhood survey.

RESULTS

Within these four methods, a total of 471 deaths were detected in the FilaBavi sample. Quarterly household follow-ups detected 470 deaths (99.8%). The re-census missed 19 deaths, of which eight were infants, and two-thirds of the missed deaths fell in 1999. The CPRS missed 89 cases (19%), the majority being infant and elderly deaths. The neighbourhood survey over-reported deaths.

CONCLUSIONS

Quarterly follow-ups were the best method for death registration. The re-census approach was less complete, with problems of recall bias. The completeness and quality of death registration by CPRS was low, especially for infant and elderly mortality.

The role of demographic surveillance systems (DSS) in assessing the health of communities: an example from rural Ethiopia

Longitudinal demographic surveillance systems (DSSs) in selected populations can provide important information in situations where routine health information is incomplete or absent, particularly in developing countries. The Butajira Rural Health Project is one such example, initiated in rural Ethiopia in 1987. DSSs rely on regular community-based surveillance as a means of vital event registration, among a sufficient population base to draw meaningful conclusions about rates and trends in relatively rare events such as maternal death. Enquiries into specific health problems can also then use this framework to quantify particular issues or evaluate interventions. Demographic characteristics and trends for a rural Ethiopian population over a 10-y period are presented as an illustration of the DSS approach, based on 336 000 person-years observed. Overall life expectancy at birth was 50 y. Demographic parameters generally showed modest trends towards improvement over the 10-y period. The DSS approach is useful in characterising populations at the community level over a period of time, providing important information for health planning and intervention. Methodological issues underlying this approach need further exploration and development.