Modular mouthpiece

A mouthpiece through which a user inhales and exhales when providing an exhaled breath sample, the mouthpiece including a mouth-engaging element about which a user places their mouth when using the mouthpiece;

• the mouthpiece including a housing having a housing wall, the housing wall defining a first aperture through the housing wall, the first aperture being linked by a conduit defining a first fluid flow path to the mouth-engaging element, and interposed therebetween a first directional valve, allowing air into the mouthpiece from atmosphere,
• a second conduit, defining a second fluid flow path from the mouth-engaging element, and directing exhaled air out of a second aperture of the mouthpiece, the second conduit housing a second directional valve housed within the second fluid flow path wherein a filter is interposed between the first aperture and the mouth-engaging element.