Participants discussed four main areas that are known to contribute pathogens to the outdoor air and have proved to be linked with human health -1. Natural environments 2. Engineering environments 3. Agriculture and 4. Waste treatment ( Figure 1 ). As shown in Figure 1 , air pathogens from environmental sources are diverse in terms of type of source and aerosolisation factors, and it is moreover possible that some pathogens are under-reported because a number of them cause similar respiratory symptoms, e.g. coughing and sneezing [2, 3] . Because there are numerous types of pathogens released to the outdoors and given the publishing constraints, the list of pathogens from different sources can be found in the cited references in Figure  1 . In addition, although many environmental pathogens are restricted to limited geographic areas, it may be naïve to assume that pathogens previously restricted to specific locations will not shift with impending global climate change; or we may find that our current knowledge is based on inadequate data and we have yet to discover the actual distribution of a number of these pathogens [2, 4] . The pathogens cited in the references may not yet be relevant to the UK, but could pose a future threat due, for example, to climate change. Moreover, various pathogens can potentially be released from waste treatment facilities; how will the mounting levels of composted green waste, food waste and other traditional landfill materials, as well as increasing bio-solid applications to land, impact on the pathogens in air?