A screening device intended to be installed in a reusable gas sampling line or gas measuring instrument to remove and retain bacterial pathogens, and sometimes moisture, from the gas. It is designed to prevent a measuring instrument [e.g., a carbon dioxide (CO2) or multi-gas analyser, bedside respiration monitor] and the system it is connected to (e.g., a breathing circuit) from becoming contaminated to reduce the risk of patient cross-contamination. Some types function as a water trap to help minimize damage to the measuring instrument from gas condensation. This is a reusable device.