Pseudomonas aeruginosa (P. aeruginosa) is a pathogen that persistently colonizes the respiratory tract of patients with chronic lung diseases. The risk of acquiring a chronic P. aeruginosa infection can be minimized by rapidly detecting the pathogen in the patient's airways and promptly administrating adequate antibiotics. However, the rapid detection of P. aeruginosa in the lungs involves the analysis of sputum, which is a highly complex matrix that is not always available. Here, we propose an alternative diagnosis based on analyzing breath aerosols. In this approach, nanoparticle immunosensors identify bacteria adhered to the polypropylene layer of a surgical facemask that was previously worn by the patient. A polypropylene processing protocol was optimized to ensure the efficient capture and analysis of the target pathogen. The proposed analytical platform has a theoretical limit of detection of 105 CFU mL-1 in aerosolized mock samples, and a dynamic range between 105 and 108 CFU mL-1. When tested with facemasks worn by patients, the biosensors were able to detect chronic and acute P. aeruginosa lung infections, and to differentiate them from respiratory infections caused by other pathogens. The results shown here pave the way to diagnose Pseudomonas infections at the bedside, as well as to identify the progress from chronic to acute infection.