Airborne Escherichia coli (E. coli) in the poultry environment can migrate inside and outside houses through air movement. The airborne E. coli, after settling on surfaces, could be re-aerosolized or picked up by vectors (e.g., caretakers, rodents, transport trucks) for further transmission. To assess the impacts of airborne E. coli transmission among poultry farms, understanding the survivability of the bacteria is necessary. The objective of this study is to determine the survivability of airborne E. coli, settled E. coli, and E. coli in poultry litter under laboratory environmental conditions (22–28 °C with relative humidity of 54–63%). To determine the survivability of airborne E. coli, an AGI-30 bioaerosol sampler (AGI-30) was used to collect the E. coli at 0 and 20 min after the aerosolization. The half-life time of airborne E. coli was then determined by comparing the number of colony-forming units (CFUs) of the two samplings. To determine the survivability of settled E. coli, four sterile Petri dishes were placed on the chamber floor right after the aerosolization to collect settled E. coli. The Petri dishes were then divided into two groups, with each group being quantified for culturable E. coli concentrations and dust particle weight at 24-h intervals. The survivability of settled E. coli was then determined by comparing the number of viable E. coli per milligram settled dust collected in the Petri dishes in the two groups. The survivability of E. coli in the poultry litter sample (for aerosolization) was also determined. Results show that the half-life time of airborne E. coli was 5.7 ± 1.2 min. The survivability of E. coli in poultry litter and settled E. coli were much longer with the half-life time of 15.9 ± 1.3 h and 9.6 ± 1.6 h, respectively. In addition, the size distribution of airborne E. coli attached to dust particles and the size distribution of airborne dust particles were measured by using an Andersen impactor and a dust concentration monitor (DustTrak). Results show that most airborne E. coli (98.89% of total E. coli) were carried by the dust particles with aerodynamic diameter larger than 2.1 µm. The findings of this study may help better understand the fate of E. coli transmitted through the air and settled on surfaces and evaluate the impact of airborne transmission in poultry production.

Highlights The study demonstrated a methodology to evaluate bioaerosol samplers on collecting Escherichia coli (E. coli) carried by airborne dust. A dry-base aerosolization system was developed for the study. The sampling efficiency of Andersen six-stage impactor and AGI-30 outperformed that of ACD-200 Bobcat. Airborne E. coli might be preferentially aggregated on large particles (> 7.0 µm). Abstract. Pathogenic Escherichia coli (E. coli) are frequently recovered in poultry litter and may be transmitted through the air after bird activities create airborne dust. To assess risks of airborne transmission of E. coli carried by dust, efficient bioaerosol samplers under dry aerosolization conditions are required. The objective of this study was to compare the performance of three commonly used bioaerosol samplers, which included an Andersen six-stage impactor, an all-glass impinger (AGI-30), and an ACD-200 Bobcat (Bobcat), for collecting the airborne E. coli carried by dust particles under dry aerosolization condition in a bio-safety chamber. A dry aerosolization system was designed to generate dry bioaerosols for the study. Under the same airborne E. coli concentration with stable environmental conditions including temperature and relative humidity (RH), the E. coli concentrations determined by the three samplers were 5.05±2.08 log10 colony-forming units (CFU) m-3, 5.69±1.92 log10 CFU m-3, and 2.69±0.81 log10 CFU m-3 for Andersen six-stage impactor, AGI-30, and Bobcat, respectively. The results showed that there is no significant difference between Andersen six-stage impactor and AGI-30, while there was a sizeable decrease in the bacteria concentration determined by the Bobcat sampler. The results also showed that airborne E. coli were preferentially aggregated on large particles (> 7.0 µm). This study demonstrated a methodology to evaluate bioaerosol sampler efficiency using dry-base carriers of biological agents which are predominant in poultry houses. The optimal sampler can be used to determine the airborne E. coli loading in commercial poultry houses. Keywords: Airborne transmission, Bioaerosol samplers, Dry aerosolization, E. coli, Poultry.

The pathogenic Escherichia coli (E. coli) has been frequently recovered in poultry litter and may be transmitted through the air once bioaerosols are generated by the foraging behavior of birds. To quantify the airborne E. coli for risk assessment of transmission, efficient bioaerosol samplers are required. The objective of this study was to compare the performances of three bioaerosol samplers, which include an Andersen six-stage impactor, an all-glass impinger (AGI-30), and an ACD-200 BOBCAT (BOBCAT), for collecting the airborne E. coli attached to dust particles in an aerosolization chamber. The Andersen six-stage impactor separately collects airborne microorganisms attached to dust particles of different sizes. The AGI-30 is an affordable sampler that collects microorganisms in liquid medium. The BOBCAT is a high-volume sampler designed for collecting microorganisms at low concentrations. Under the same airborne E. coli concentration with stable environmental conditions including temperature and relative humidity (RH), the E. coli concentration determined by the three samplers were 5.05±2.08 log₁₀ CFU m^-3 for Andersen six-stage, 5.69±1.92 log₁₀ CFU m^-3 for AGI-30 and 2.94±0.81 log₁₀ CFU m^-3 for BOBCAT. The results show there is no significant difference between Andersen six-stage and AGI-30, while there was a sizeable decrease in the bacteria concentration determined in the BOBCAT sampler. This study also demonstrated a methodology to evaluate bioaerosol sampler efficiency using dry-base carriers of biological agents which are predominant. The optimal sampler can be used to accurately determine the airborne E. coli loading in commercial poultry houses.

Airborne Escherichia coli (E. coli) originating in poultry houses can be transmitted outside poultry farms through the air, posing risks of barn-to-barn infection through airborne transmission. The objective of this study is to examine the effect of ultraviolet (UV) light on the inactivation of airborne E. coli carried by poultry dust particles under laboratory conditions. A system containing two chambers that were connected by a UV scrubber was designed in the study. In the upstream chamber of the system, airborne E. coli attached to dust particles were aerosolized by a dry aerosolization-based system. Two sets of air samplers were placed in the two chambers to collect the viable airborne E. coli. By comparing the concentration of airborne E. coli in the two chambers, the inactivation rates were calculated. The airborne E. coli inactivation rates were tested at different contact times with the aid of a vacuum pump (from 5.62 to 0.23 s of contact time) and different UV irradiance levels (of 1707 µW cm⁻² and 3422 µW cm⁻²). The inactivation rates varied from over 99.87% and 99.95% at 5.62 s of contact time with 1707 µW cm⁻² and 3422 µW cm⁻² of UV irradiance to 72.90% and 86.60% at 0.23 s of contact time with 1707 µW cm⁻² and 3422 µW cm⁻² of UV irradiance. The designed system was able to create the average UV irradiation of 1707 µW cm⁻² and 3422 µW cm⁻² for one UV lamp and two UV lamps, respectively. The findings of this study may provide an understanding of the effect of UV light on the inactivation of airborne E. coli carried by dust particles and help to design an affordable mitigation system for poultry houses.

Airborne transmission is a major route of influenza virus spread, yet how environmental conditions shape the persistence and downrange transport of infectious exhaled virions is not fully understood. Using a physiologically relevant swine model infected with A/California/04/2009 (H1N1), we investigated how temperature and relative humidity (T/RH) influence airborne influenza emission, persistence, and transmission under two environmental conditions: 20°C/50% RH (ambient indoor), and 7°C/73% RH (cold/high-humidity). Donor pigs shed comparable nasal viral loads across conditions, but naïve sentinel pigs housed 4 m away became infected 1 day earlier under ambient conditions. Breath and environmental air sampling showed that cold/high-humidity conditions transiently increased viral RNA in exhaled aerosols at 1 day post-infection (dpi), whereas ambient conditions supported greater and more persistent airborne viral burdens at 2–3 dpi, particularly at downrange locations. Controlled aerosol generation experiments further showed that ambient conditions enabled substantially greater recovery of infectious virus with distance, even though RNA-containing particles were transported under both T/RH states. Together, these results demonstrate that, under the tested environmental conditions, infectious influenza aerosols persisted longer and transmitted farther under the ambient indoor environment than in the cold/high-humidity environment. These findings establish that environmental temperature-humidity conditions shape post-emission aerosol fate, and thereby constrain the airborne transmission range of the influenza virus. IMPORTANCE: Influenza viruses spread efficiently through the air, yet the environmental conditions that determine whether exhaled virions remain infectious long enough to initiate new infections remain poorly defined. Using a swine model that closely replicates human expiratory aerosol output, we identify environmental temperature-humidity conditions as a critical determinant of airborne infectious range. Cold/high-humidity conditions increased early viral RNA levels near the host but failed to sustain infectious particles at a distance. In contrast, ambient conditions supported prolonged airborne suspension and rapid transmission to distant recipients. Controlled aerosolization experiments showed that infectious virus is transported far more effectively under ambient indoor conditions than in cold/high-humidity air despite similar RNA dispersal. These results reveal post-emission aerosol fate as the critical bottleneck in determining airborne influenza transmissibility. This mechanistic insight is essential for refining predictive models of influenza spread and developing environmental and public health strategies that more effectively limit airborne infection.