Respiratory infections: Proceedings of the Eighth Liverpool Tropical School Bayer Symposium of Microbial Disease held on 3 February 2001

Acute respiratory tract infections (ARI) are a major cause of morbidity and mortality world-wide. In a global survey of causes of mortality, respiratory tract disease was estimated to be the third commonest cause of death with 4.3 million deaths in 1990 [1]. The two major causes of death were ischaemic heart disease (6.3 million deaths) and cerebrovascular disease (4.4 million) [2]. However, it was also calculated that lower respiratory tract infections were responsible for 112.9 million disability-adjusted life year (DALYS) and as such were the major burden of premature death and disability world-wide, exceeding DALYS due to diarrhoeal disease (99.6 million) and perinatal disorders (92.3 million) [2]. As might be expected, the burden was significantly greater in the developing compared with the developed world [2]. ARI are estimated to be responsible for one third of all childhood deaths in developing countries [3]. It is estimated that the incidence of ARI, at 5–9 episodes/child/year in the first 5 years of life, is the same in developed and developing countries [4]. Although the incidence of ARI does not differ between developed and developing countries, the incidence of acute lower respiratory tract infection (ALRI) is over 12-fold greater in developing countries [5]. Risk factors for progression from ARI to ALRI include young age (0–11 months), gender (male), malnutrition (both macro- and micro-nutrients), lack of breast feeding, HIV infection and environmental factors such as crowding and indoor air pollution [6]. For ARI the major aetiological agents are viruses; in particular, respiratory syncytial virus (RSV) [7], influenza A, B and C virus, parainfluenza viruses and, in unvaccinated communities, measles virus are the most important. However, in 2001 a ‘new’ virus, human metapneumovirus was described [8]. It is a newly discovered rather than new virus and it appears to have similar epidemiological characteristics to RSV with most subjects having been infected by the age of 5 years. It has been detected in children in Canada [9], Australia [10] and Holland [8], as well as South Africa, Brazil and the UK (Hart et al., unpublished data).

Although RSV and, presumably, human metapneumovirus do cause pneumonia, bacteria such as Streptococcus pneumoniae and Haemophilus influenzae are also major pathogens [11]. Finally, the airways in cystic fibrosis pose a particular problem of infection with bacteria [12] not usually associated with community-acquired respiratory tract infection. We have attempted to address some of the aspects of the important topic of respiratory infection in the latest Liverpool Symposium on Microbial Disease.