What public-health action is reasonable in light of this new evidence? The situation might seem to resemble the classical example of cholera in a population using a particular pumped water source in 19th century London.5 Then preventive action could be taken even though the causative agent had not been discovered. However, there is one fundamental difference; the excess risk near the landfills is much lower than it was for the Broad Street pump, and bias could explain associations of the magnitude quoted by Dolk et al. Overall the evidence is very limited, and the results clearly point to the need for further studies, focusing on exposure measurements as well as on specific exposure-response relations.