Human-induced resuspension of floor dust is a dynamic process that can serve as a major indoor source of biological particulate matter (bioPM). Inhalation exposure to the microbial and allergenic content of indoor dust is associated with adverse and protective health effects. This study evaluates infant and adult inhalation exposures and respiratory tract deposited dose rates of resuspended bioPM from carpets. Chamber experiments were conducted with a robotic crawling infant and an adult performing a walking sequence. Breathing zone (BZ) size distributions of resuspended fluorescent biological aerosol particles (FBAPs), a bioPM proxy, were monitored in real-time. FBAP exposures were highly transient during periods of locomotion. Both crawling and walking delivered a significant number of resuspended FBAPs to the BZ, with concentrations ranging from 0.5 to 2 cm (mass range: ∼50 to 600 μg/m). Infants and adults are primarily exposed to a unimodal FBAP size distribution between 2 and 6 μm, with infants receiving greater exposures to super-10 μm FBAPs. In just 1 min of crawling or walking, 10-10 resuspended FBAPs can deposit in the respiratory tract, with an infant receiving much of their respiratory tract deposited dose in their lower airways. Per kg body mass, an infant will receive a nearly four times greater respiratory tract deposited dose of resuspended FBAPs compared to an adult.

BackgroundFloor dust is commonly used for microbial determinations in epidemiological studies to estimate early-life indoor microbial exposures. Resuspension of floor dust and its impact on infant microbial exposure is, however, little explored. The aim of our study was to investigate how floor dust resuspension induced by an infant’s crawling motion and an adult walking affects infant inhalation exposure to microbes.ResultsWe conducted controlled chamber experiments with a simplified mechanical crawling infant robot and an adult volunteer walking over carpeted flooring. We applied bacterial 16S rRNA gene sequencing and quantitative PCR to monitor the infant breathing zone microbial content and compared that to the adult breathing zone and the carpet dust as the source. During crawling, fungal and bacterial levels were, on average, 8- to 21-fold higher in the infant breathing zone compared to measurements from the adult breathing zone. During walking experiments, the increase in microbial levels in the infant breathing zone was far less pronounced. The correlation in rank orders of microbial levels in the carpet dust and the corresponding infant breathing zone sample varied between different microbial groups but was mostly moderate. The relative abundance of bacterial taxa was characteristically distinct in carpet dust and infant and adult breathing zones during the infant crawling experiments. Bacterial diversity in carpet dust and the infant breathing zone did not correlate significantly.ConclusionsThe microbiota in the infant breathing zone differ in absolute quantitative and compositional terms from that of the adult breathing zone and of floor dust. Crawling induces resuspension of floor dust from carpeted flooring, creating a concentrated and localized cloud of microbial content around the infant. Thus, the microbial exposure of infants following dust resuspension is difficult to predict based on common house dust or bulk air measurements. Improved approaches for the assessment of infant microbial exposure, such as sampling at the infant breathing zone level, are needed.Electronic supplementary materialThe online version of this article (10.1186/s40168-018-0405-8) contains supplementary material, which is available to authorized users.

Objectives: Good ventilation is more important in hospitals than in many other buildings. The objective of this study was to evaluate the effect of the condition, performance and modernity of ventilation systems on the perceived indoor air quality (IAQ) and the indoor air-related symptoms of hospital personnel. Materials and Methods: An inspection and evaluation graded on a 1 to 3 scale of the condition, performance, and modernity of the ventilation systems was carried out in ten central hospitals in Finland. The perceived IAQ and the related symptoms were collected by means of an indoor air questionnaire survey among the workers in these hospitals. Results: The condition, performance and modernity of the ventilation systems were good in 40% of the hospitals included in the research and poor in another 40% of them. In hospitals where the majority of the ventilation systems were assessed to be good, the prevalence of the indoor air-related complaints and symptoms was lower than in hospitals where the majority of the ventilation systems were assessed as needing extensive repairs. Conclusions: The condition and performance of the ventilation systems in hospitals had a significant impact on the perceived IAQ and the symptoms observed among the employees in Finnish hospitals. Therefore, it is important that hospital ventilation systems are maintained properly and regularly. Furthermore, they should be renovated, at the latest when their technical lifespan expires.

This paper reports the comparison of three measuring methods for quantifying the amount of dust on the inner surface of ventilation ducts: 1) a vacuum test method; 2) a gravimetric tape method; and 3) an optical method. Thirteen recently constructed buildings were selected for the field test in the Helsinki metropolitan area. The dust samples in each method were all taken from the same location in the duct. Most of the ducts sampled had no residual oil originating from the manufacturing process. The mean amount of dust measured with the vacuum test method was 1.3 g/m2 and the range was < 0.1-8.4 g/m2. The mean surface dust level measured using the gravimetric tape method was slightly lower, i.e. 1.2 g/m2 (< 0.1-5.0 g/m2). The mean cleanliness level of the ducts was 15% (2-41%) using the optical method. The wide variations and differences in the results of the different methods were caused by the unequal distribution of dust on the duct surfaces.

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