Sample collection and handling
Armpit sweat samples were collected following the same standard protocol for all volunteers and using the same media across all locations. The volunteers were asked to hold an inert polymer tube (3.6 cm length, 0.8 cm thickness) commonly used for adsorbing VOCs for explosive, drug, or criminology detection (Getxent, Neuchâtel, Switzerland) simultaneously under each armpit for 20 min. Each individual polymer tube was immediately placed in a sealed envelope, bearing the subject's ID. The samples were then shipped while refrigerated (+ 4 to + 8 °C) to the laboratory of the dog training/testing centre, in separate packaging for cases and controls, and kept stored at a temperature of 4 °C. The choice to work with sweat samples was made, in accordance with what reported by Grandjean et al.