Public Health Indoor Air Surveillance for Respiratory Pathogens: From Pilot to Citywide Implementation.
CONTEXT: Environmental surveillance has become an essential component of public health pathogen surveillance programs. Indoor air surveillance is a promising environmental surveillance method but has yet to be scaled citywide and incorporated into state and local public health programs. PROGRAM: The Chicago Department of Public Health established a citywide indoor air surveillance program to enhance monitoring of airborne pathogens and address gaps in existing surveillance. IMPLEMENTATION: The program began with a pilot phase from February to April 2023 at 5 sites, which informed expansion to 17 sites and 20 samplers across emergency departments (5), congregate (3), and community settings (15), across the city. Site staff conducted weekly cartridge exchanges for seven-day sample collection periods using AerosolSense and AirPrep Cub samplers, which were then processed at the Regional Innovative Public Health Laboratory for SARS-CoV-2, influenza, and respiratory syncytial virus. Samples were tested using quantitative polymerase chain reaction, and SARS-CoV-2-positive samples underwent whole genome sequencing to characterize circulating viral lineages. EVALUATION: From February 2023 to August 2025, 1246 samples were processed, with a mean compliance of 85% (SD = 0.149) for weekly cartridge exchanges and minimal operational disruption. The program data supported its use as a surveillance tool for respiratory pathogen detection and SARS-CoV-2 lineage monitoring, with 74% samples positive for at least 1 virus and 68% detecting SARS-CoV-2. DISCUSSION: The program successfully scaled to citywide coverage and was shown to be feasible and acceptable across sites. These results highlight the value of indoor air monitoring as a complementary surveillance tool and offer a framework for other jurisdictions seeking to enhance respiratory pathogen detection through establishing a citywide indoor air surveillance program. Facility-level sampling is aggregated across sites to capture citywide trends complementing clinical and wastewater surveillance, and provides insights into facility-level pathogen burden, not captured by other surveillance methods.