The microbes that cause infectious diseases are complex, dynamic, and constantly evolving. They reproduce rapidly, mutate frequently, breach species barriers, adapt with relative ease to new hosts and new environments, and develop resistance to the drugs used to treat them. In their article "Meeting the challenge of epidemic infectious diseases outbreaks: an agenda for research", Kai-Lit Phua and Lai Kah Lee clearly demonstrate how social, behavioural and environmental factors, linked to a host of human activities, have accelerated and amplified these natural phenomena. By reviewing published and non-published information about outbreaks of Nipah virus in Malaysia, severe acute respiratory syndrome (SARS) and avian influenza in Asia, and the HIV pandemic, they provide a series of examples that demonstrate the various social, behavioural and environmental factors of these recent infectious disease outbreaks. They then analyse some of these same determinants in important historical epidemics and pandemics such as plague in medieval Europe, and conclude that it is important to better understand the social conditions that facilitate the appearance of diseases outbreaks in order to determine why and how societies react to outbreaks and their impact on different population groups.