Indoor ventilation is underutilized for the control of exposure to infectious pathogens. Occupancy restrictions during the pandemic showed the acute need to control detailed airflow patterns, particularly in heavily occupied spaces, such as lecture halls or offices, and not just to focus on air changes. Displacement ventilation is increasingly considered a viable energy efficient approach. However, control of airflow patterns from displacement ventilation requires us to understand them first. The challenge in doing so is that, on the one hand, detailed numerical simulations – such as direct numerical simulations (DNSs) – enable the most accurate assessment of the flow, but they are computationally prohibitively costly, thus impractical. On the other hand, large eddy simulations (LES) use parametrizations instead of explicitly capturing small-scale flow processes critical to capturing the inhomogeneous mixing and fluid–boundary interactions. Moreover, their use for generalizable insights requires extensive validation against experiments or already validated gold-standard DNSs. In this study, we start to address this challenge by employing efficient monotonically integrated LES (MILES) to simulate airflows in large-scale geometries and benchmark against relevant gold-standard DNSs. We discuss the validity and limitations of MILES. Via its application to a lecture hall, we showcase its emerging potential as an assessment tool for indoor air mixing heterogeneity.

Toxoplasma gondii infections are acquired through the ingestion of oocysts present in the environment. However, there is no data about their occurrence in the air or about airborne transmission of these infections. In the present paper, we report on the identification of T. gondii using rapid molecular detection methods, supported by microscopic analysis, in environmental air samples. A total of 71 samples were collected, using gelatine filters, from kitchen gardens, recreational areas and sandpits located in northern and north-eastern Poland. Material recovered from the filters was analysed using real-time PCR and loop-mediated isothermal assays targeting the T. gondii B1 gene. Toxoplasma gondii DNA was found in two samples, as confirmed by both molecular assays. Genotyping at the SAG2 locus showed Toxoplasma SAG2 type I. Moreover, the presence of T. gondii oocysts was confirmed in one of the positive samples with the use of microscopy. The results showed that T. gondii may be present in environmental air samples and that respiratory tract infections may play a role in the high prevalence of toxoplasmosis in humans and animals. To the best of our knowledge, this is the first epidemiological evidence that oro-fecal and foodborne toxoplasmosis may be traceable to an airborne respiratory origin and that this may represent a new, previously unknown transmission route for this disease.

Unidentified open-air factors (OAFs) found to be adverse to the survival of microorganisms suspended on microthreads were investigated for their effect on realistic aerosols of Francisella tularensis in an open-air environment. This organism was chosen because it is probably the most infectious organism known to be capable of infecting both animals and man via the respiratory route, hence its potential use as a bioterrorist agent. A direct correlation was found between an open-air adverse effect on viability and virulence of airborne particles of <3 μm via the respiratory route in guinea pigs. One viable organism was sufficient to initiate an infection that resulted in a fatal tularaemia infection. The lethal effect of OAFs on F. tularensis was found to vary from day to day and was related to the source of the air in the UK. The adverse effect on viability was associated with an inverse effect according to the size of the airborne particle.

In an effort to minimize the probability of forward contamination of pristine extraterrestrial environments, the National Aeronautics and Space Administration requires that all US robotic spacecraft undergo assembly, testing and launch operations (ATLO) in controlled clean-room environments. This study examines the impact of ATLO activity on the microbial diversity and overall bioburden contained within the air of the clean-room facility in which the Mars Exploration Rovers (MERs) underwent final preparations for launch. Air samples were collected from several facility locations and traditional culture-based and molecular methodologies were used to measure microbial burden and diversity. Surprisingly, the greatest estimates of airborne bioburden, as derived from ATP content and cultivation assays, were observed prior to the commencement of MER ATLO activities. Furthermore, airborne microbial diversity gradually declined from the initiation of ATLO on through to launch. Proteobacterial sequences were common in 16S rDNA clone libraries. Conspicuously absent were members of the Firmicutes phylum, which includes the genus Bacillus. In previous studies, species of this genus were repeatedly isolated from the surfaces of spacecraft and clean-room assembly facilities. Increased cleaning and maintenance initiated immediately prior to the start of ATLO activity could explain the observed declines in both airborne bioburden and microbial diversity.