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Build Simul ; 16(5): 781-794, 2023.
Article in English | MEDLINE | ID: covidwho-2286268


Origin of differently sized respiratory droplets is fundamental for clarifying their viral loads and the sequential transmission mechanism of SARS-CoV-2 in indoor environments. Transient talking activities characterized by low (0.2 L/s), medium (0.9 L/s), and high (1.6 L/s) airflow rates of monosyllabic and successive syllabic vocalizations were investigated by computational fluid dynamics (CFD) simulations based on a real human airway model. SST k-ω model was chosen to predict the airflow field, and the discrete phase model (DPM) was used to calculate the trajectories of droplets within the respiratory tract. The results showed that flow field in the respiratory tract during speech is characterized by a significant laryngeal jet, and bronchi, larynx, and pharynx-larynx junction were main deposition sites for droplets released from the lower respiratory tract or around the vocal cords, and among which, over 90% of droplets over 5 µm released from vocal cords deposited at the larynx and pharynx-larynx junction. Generally, droplets' deposition fraction increased with their size, and the maximum size of droplets that were able to escape into external environment decreased with the airflow rate. This threshold size for droplets released from the vocal folds was 10-20 µm, while that for droplets released from the bronchi was 5-20 µm under various airflow rates. Besides, successive syllables pronounced at low airflow rates promoted the escape of small droplets, but do not significantly affect the droplet threshold diameter. This study indicates that droplets larger than 20 µm may entirely originate from the oral cavity, where viral loads are lower; it provides a reference for evaluating the relative importance of large-droplet spray and airborne transmission route of COVID-19 and other respiratory infections.

Psychiatr Serv ; : appips20220345, 2022 Nov 29.
Article in English | MEDLINE | ID: covidwho-2138394


OBJECTIVE: The authors aimed to evaluate changes in use of government-subsidized primary mental health services, through the Medicare Benefits Schedule (MBS), by young people during the first year of the COVID-19 pandemic in Australia and whether changes were associated with age, sex, socioeconomic status, and residence in particular geographical areas. METHODS: Interrupted time-series analyses were conducted by using quarterly mental health MBS service data (all young people ages 12-25 years, 2015-2020) for individual Statistical Area Level 3 areas across Australia. The data captured >22.4 million service records. Meta-analysis and meta-regression models estimated the pandemic interruption effect at the national level and delineated factors influencing these estimates. RESULTS: Compared with expected prepandemic trends, a 6.2% (95% CI=5.3%-7.2%) increase was noted for all young people in use of MBS mental health services in 2020. Substantial differences were found between age and sex subgroups, with a higher increase among females and young people ages 18-25. A decreasing trend was observed for males ages 18-25 (3.5% reduction, 95% CI=2.5%-4.5%). The interruption effect was strongly associated with socioeconomic status. Service uptake increased in areas of high socioeconomic status, with smaller or limited uptake in areas of low socioeconomic status. CONCLUSIONS: During 2020, young people's use of primary mental health services increased overall. However, increases were inequitably distributed and relatively low, compared with increases in population-level mental health burden. Policy makers should address barriers to primary care access for young people, particularly for young males and those from socioeconomically disadvantaged backgrounds.