Comparative Mask Protection against Inhaling Wildfire Smoke, Allergenic Bioaerosols, and Infectious Particles.

This work compares relative mask inhalation protection against a range of airborne particle sizes that the general public may encounter, including infectious particles, wildfire smoke and ash, and allergenic fungal and plant particles. Several mask types available to the public were modeled with respirable fraction deposition. Best-case collection efficiencies for cloth, surgical, and respirator masks were predicted to be lowest (0.3, 0.6, and 0.8, respectively) for particle types with dominant sub-micrometer modes (wildfire smoke and human-emitted bronchial particles). Conversely, all mask types were predicted to achieve good collection efficiency (up to ~1.0) for the largest-sized particle types, including pollen grains, some fungal spores, and wildfire ash. Polydisperse infectious particles were predicted to be captured by masks with efficiencies of 0.3-1.0 depending on the pathogen size distribution and the type of mask used. Viruses aerosolized orally are predicted to be captured efficiently by all mask types, while those aerosolized from bronchiolar or laryngeal-tracheal sites are captured with much lower efficiency by surgical and cloth masks. The predicted efficiencies changed very little when extrathoracic deposition was included (inhalable rather than respirable fraction) or when very large (100 µm) particles were neglected. Actual mask fit and usage will determine protection levels in practice, but the relative comparisons in this work can inform mask guidance for different inhalation hazards, including particles generated by yard work, wildfires, and infections.

Modeling the impacts of physical distancing and other exposure determinants on aerosol transmission.

Minimization of airborne virus transmission has become increasingly important due to pandemic and endemic infectious respiratory diseases. Physical distancing is a frequently advocated control measure, but the proximity-based transmission it is intended to control is challenging to incorporate into generalized, ventilation-based models. We utilize a size-dependent aerosol release model with turbulent dispersion to assess the impact of direct, near-field transport in conjunction with changes in ventilation, exposure duration, exhalation/inhalation rates, and masks. We demonstrate this model on indoor and outdoor scenarios to estimate the relative impacts on infection risk. The model can be expressed as a product of six multiplicative factors that may be used to identify opportunities for risk reduction. The additive nature of the short-range (proximity) and long-range (background) transmission components of the aerosol transport factor implies that they must be minimized simultaneously. Indoor simulations showed that close physical distances attenuated the impact of most other risk reduction factors. Increasing ventilation resulted in a 17-fold risk decrease at further physical distances but only a 6-fold decrease at shorter distances. Distance, emission rate, and duration also had large impacts on risk (11-65-fold), while air direction and inhalation rate had lower risk impacts (3-4-fold range). Surgical mask and respirator models predicted higher maximum risk impacts (33- and 280-fold, respectively) than cloth masks (4-fold). Most simulations showed decreasing risk at distances > 1-2 m (3-6 ft). The risk benefit of maintaining 2-m distance vs. 1 m depended substantially on the environmental turbulence and ventilation rate. Outdoors, long-range transmission was negligible and short-range transmission was the primary determinant of risk. Temporary passing events increased risk by up to 50 times at very slow walking speeds and close passing distances, but the relative risks outdoors were still much lower than indoors. The current model assumes turbulent dispersion typical of a given room size and ventilation rate. However, calm environments or confined airflows may increase transmission risks beyond levels predicted with this turbulent model.

Raman microspectroscopy-based identification of individual fungal spores as potential indicators of indoor contamination and moisture-related building damage.

We present an application of Raman microspectroscopy (RMS) for the rapid characterization and identification of individual spores from several species of microfungi. The RMS-based methodology requires minimal sample preparation and small sample volumes for analyses. Hence, it is suitable for preserving sample integrity while providing micrometer-scale spatial resolution required for the characterization of individual cells. We present the acquisition of unique Raman spectral signatures from intact fungal spores dispersed on commercially available aluminum foil substrate. The RMS-based method has been used to compile a reference library of Raman spectra from several species of microfungi typically associated with damp indoor environments. The acquired reference spectral library has subsequently been used to identify individual microfungal spores through direct comparison of the spore Raman spectra with the reference spectral signatures in the library. Moreover, the distinct peak structures of Raman spectra provide detailed insight into the overall chemical composition of spores. We anticipate potential application of this methodology in the fields of public health, forensic sciences, and environmental microbiology.

Field evaluation of a personal, bioaerosol cyclone sampler.

A personal cyclone sampler (cyclone) was operated continuously alongside a 25-mm filter sampler (filter), a slit impactor (Burkard slide), and a high-volume cyclone sampler (Burkard cyclone) at an outdoor location with abundant naturally occurring fungi (N = 30; sampling time: 12.5 +/- 2.3 hr). Air concentrations (spore m(-3)) of 28 fungal groups were determined for all samplers by microscopy. Cyclone performance was judged using various indices to determine if it agreed with the other samplers in determination of the frequencies with which the fungal groups were observed, as well as their proportions of the total air concentration. Fungal diversity estimates were similar for all samplers and in the range of what has been reported nationally, i.e., observation of 9-11 equal groups per sample, but spore concentration dominated by 2-3 groups. Plots of paired cyclone:comparison sampler ratios against average concentrations identified biases. For example, ratios were correlated with concentration and there was greater uncertainty at lower concentrations. Mean ratios for cyclone:filter comparisons were not significantly different from one for ascospores, Aspergillus-Penicillium spp., basidiospores, Cladosporium spp., or total spore m(-3). However, agreement was less consistent with the Burkard slide (0.74, 1.12, 0.91, 1.09, and 0.92, respectively) and the Burkard cyclone (2.31, 1.62, 1.43, 1.91, and 1.33, respectively). Concentrations of cell equivalent m(-3) also were determined for the filter and two cyclone samples by polymerase chain reaction. Cell equivalents for Aspergillus fumigatus and Penicillium brevicompactum were compared with Aspergillus-Penicillium spp. spores, and Cladosporium cladosporioides and Cladosporium herbarum cell equivalents were compared with Cladosporium spp. spores. Cell equivalent:spore ratios below one for A. fumigatus and P. brevicompactum indicated that these species comprised smaller factions of total spores or were collected less efficiently than the larger C. cladosporioides and C. herbarum spores. The personal cyclone was shown to be suitable for collection of ambient airborne fungal spores and for analysis by microscopy and polymerase chain reaction.

Chamber evaluation of a personal, bioaerosol cyclone sampler.

A personal cyclone sampler (cyclone) was operated in a 0.9-m3 chamber, side by side with a 25-mm filter sampler (filter) and either a slit impactor (Air-O-Cell) or a single-stage, multiple-hole, agar impactor (N6). Aerosols of two fungal spores were collected for 5 min to 5 hr-Aspergillus versicolor: 10, 20, 40, 80, 160, and 320 min; concentration: 10(2)-10(5) spore m(-3); Scopulariopsis brevicaulis: 5, 10, 15, 20, 25, and 30-min; concentration: 10(3)-10(5) spore m(-3) (six replicates for each sampling time). For each fungus, air concentrations were determined by a 15-channel optical particle counter (particle m(-3); N = 36), microscopy (spore m(-3); cyclone and filter, N = 36; Air-O-Cell, N = 18), culture (colony forming unit m(-3); cyclone and filter, N = 36; N6, N = 18), and polymerase chain reaction (cell equivalent m(-3); cyclone and filter, N = 36). Samplers were significantly correlated with each other as were the three analyses (correlation coefficients = 0.79-1.00 and 0.87-0.98, respectively). Ratios were calculated for simultaneous measurements with the cyclone and comparison samplers and for paired colony:spore, colony:cell equivalent, and cell equivalent:spore measurements for the cyclone and filter samples. The cyclone equaled or underestimated the other samplers for both fungi and all analyses (mean ratio: 0.75-1.04). A. versicolor colony and cell equivalent measurements exceeded spore measurements although microscopy should detect all spores not just culturable ones, perhaps due to difficulty observing the smaller spores or detection of DNA in cell fragments in addition to intact spores. Plots of the ratios of paired measurements against their averages identified biases between samplers and analyses. For example, ratios were correlated with spore concentration, and there was greater uncertainty at lower concentrations. These chamber tests have shown that the cyclone is suitable for collection of airborne fungal spores over a wide concentration range and time period and for analysis by microscopy, culture, and polymerase chain reaction.

Association of housing disrepair indicators with cockroach and rodent infestations in a cohort of pregnant Latina women and their children.

Health burdens associated with poor housing and indoor pest infestations are likely to affect young children in particular, who spend most of their time indoors at home. We completed environmental assessments in 644 homes of pregnant Latina women and their children living in the Salinas Valley, California. High residential densities were common, with 39% of homes housing > 1.5 persons per room. Housing disrepair was also common: 58% of homes had peeling paint, 43% had mold, 25% had water damage, and 11% had rotting wood. Evidence of cockroaches and rodents was present in 60% and 32% of homes, respectively. Compared with representative national survey data from the U.S. Department of Housing and Urban Development, homes in our sample were more likely to have rodents, peeling paint, leaks under sinks, and much higher residential densities. The odds of rodent infestations in homes increased in the presence of peeling paint [odds ratio (OR) 2.1; 95% confidence interval (CI), 1.5-3.1], water damage (OR 1.9; 95% CI, 1.2-2.7), and mold (OR 1.5; 95% CI, 1.0-2.1). The odds of cockroach infestation increased in the presence of peeling paint (OR 3.8; 95% CI, 2.7-5.6), water damage (OR 1.9; 95% CI, 1.2-2.9), or high residential density (OR 2.1; 95% CI, 1.2-3.8). Homes that were less clean than average were more prone to both types of infestations. Pesticides were stored or used in 51% of households, partly to control roach and rodent infestations. These data indicate that adverse housing conditions are common in this community and increase the likelihood of pest infestations and home pesticide use. Interventions to improve housing and promote children's health and safety in this population are needed.

Comparison of a passive aerosol sampler to size-selective pump samplers in indoor environments.

The objective of this work was to investigate the ability of the Wagner-Leith passive aerosol sampler to measure indoor exposures over periods of 24 hours to 2 weeks. An automated analysis technique was developed so that lower aerosol concentrations could be sampled over shorter time periods. A test of the new analytical method against a manual method showed good agreement. The passive sampler was tested alongside three pump-operated, size-selective samplers in indoor environments. Generally, good correlation with the active samplers was observed. Correlation with a personal impactor with uncoated substrates was not statistically significant, but the cyclone, MS&T impactor, and overall correlations had R(2) values of 0.73-0.88. Combining these data with a previous study produced an R(2) of 0.96 between passive and active results. Large discrepancies (up to 147%) between passive and personal impactor results were observed and were attributed to particle bounce in the impactor, passive sampler imprecision due to few collected fine particles, and problems with detection of organic particles in the passive sampler. The Wagner-Leith sampler has now been tested over five orders of magnitude in mass concentration, in which it has proved useful for obtaining aerosol size distributions, mass fractions, qualitative elemental analysis, and morphology of individual particles. The sampler has several limitations, including increased sensitivity to contamination when fewer particles are collected, uncertainties in sampling semi-volatile particles, and the need for some expertise and expense to analyze the passive samples.