BOLD in Africa: What has it taught us?

The Burden of Obstructive Lung Disease (BOLD) study was set up with the primary objective of measuring the prevalence of Chronic Obstructive Pulmonary Disease (COPD) and its risk factors around the world. With the exception of one centre in South Africa, centres in Africa were only recruited in a second phase funded by the Wellcome Trust after 2006. So far, there is no reason to believe that the causes of chronic airflow limitation act differently in Africa than elsewhere, though exposure to these does vary considerably across the continent. Smoking is still a major cause of airflow limitation wherever smoking is prevalent. A history of tuberculosis is also strongly associated with airflow limitation as well as with the restrictive pattern that might be associated with loss of lung tissue. There has been no association found with the burning of biomass fuels. Although a surprise to some people, this is consistent with the low prevalence of chronic airflow limitation (CAL) in areas where biomass fuels are commonly used for cooking and heating and with the results from another much larger study in China. Other topics that still need to be fully explored in the African context are the risks posed by occupational exposures and the potential role of asthma as a risk for chronic irreversible obstruction in later life. Most of the indications are, however, that the high prevalence of low lung volumes is a greater problem in much of sub-Saharan Africa than airflow obstruction. A full interpretation of this finding will need to wait for the outcome of the BOLD II study that is just starting.