Abstract: Breath sample systems for use with ventilators are disclosed herein. An example device can include a housing that contains a breath capture module that collects a breath sample from a patient, an input in fluid communication with an expiratory limb of a ventilator and the breath capture module, the input receiving a breath of the patient, an output in fluid communication with the expiratory limb of a ventilator to return the breath to the ventilator, a pump, and a controller that controls the pump to obtain the breath sample by drawing the breath into the input, across the breath capture module, and out of the output.