There is a significant knowledge gap in understanding and assessing the risk of outdoor pathogens in air. In order to complete the transmission pathway and set up regulation, control and prevention measures, we need to better understand and identify pathogens at their source, identify the aerosolisation mechanisms and dispersal plume, have adequate qualitative and quantitative techniques to detect the pathogens in different media, and understand the deposition process and required dose for infection. As in Skyes et al.'s analysis, a risk assessment framework was used to assess the potential health risks from bioaerosols from composting [10] . Current knowledge of pathogen risk assessment in air is far from complete; without knowing the infectious dose and actual risk to society, there is little motivation on the part of governments or manufacturers to research methods of control.