Objective To elucidate the role of phonation frequency (i.e., pitch) and intensity of speech on respiratory aerosol emissions during sustained phonations. Methods Respiratory aerosol emissions are measured in 40 (24 males and 16 females) healthy, non-trained singers phonating the phoneme /a/ at seven specific frequencies at varying vocal intensity levels. Results Increasing frequency of phonation was positively correlated with particle production ( r = 0.28, p < 0.001). Particle production rate was also positively correlated ( r = 0.37, p < 0.001) with the vocal intensity of phonation, confirming previously reported findings. The primary mode (particle diameter ~0.6 μm) and width of the particle number size distribution were independent of frequency and vocal intensity. Regression models of the particle production rate using frequency, vocal intensity, and the individual subject as predictor variables only produced goodness of fit of adjusted R 2 = 40% ( p < 0.001). Finally, it is proposed that superemitters be defined as statistical outliers, which resulted in the identification of one superemitter in the sample of 40 participants. Significance The results suggest there remain unexplored effects (e.g., biomechanical, environmental, behavioral, etc.) that contribute to the high variability in respiratory particle production rates, which ranged from 0.2 particles/s to 142 particles/s across all trials. This is evidenced as well by changes in the distribution of participant particle production that transitions to a more bimodal distribution (second mode at particle diameter ~2 μm) at higher frequencies and vocal intensity levels.

It was speculated that fewer COVID-19 infections may emerge in tropical countries due to their hot climate, but India emerged as one of the leading hotspot. There is no concrete answer on the influence of meteorological parameters on COVID-19 even after more than a year of outbreak. The present study examines the impacts of Meteorological parameters during the summer and monsoon season of 2020, in different Indian mega cities having distinct climate and geography. The results indicate the sign of association, but it varies from one climatic zone to another. The principal component analysis revealed that humidity is strongly correlated with COVID-19 infections in hillocky city Pune (R = 0.70), dry Delhi (R = 0.50) and coastal Mumbai (R = 0.46), but comparatively weak correlation is found in arid climatic city of Ahmedabad. As against the expectations, no discernible correlation is found with temperature in any of the cities. As the virus in 2020 in India largely travelled with droplets, the association with absolute humidity in the dry regions has serious implications. Clarity in understanding the impact of seasonality will greatly help epidemiological research and in making strategies to control the pandemic in India and other tropical countries around the world.

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Many respiratory viruses, including influenza and SARS-CoV-2, are transmitted via the emission and inhalation of infectious respiratory aerosols in indoor environments. Resuspended particles from indoor surfaces and clothing can be a major source of airborne microbiological contaminants in indoor environments; however, it is unknown whether resuspended viruses contribute substantially to disease transmission. In this study, we investigated the resuspension via human walking activity of influenza A virus H3N2 laboratory strain, which was generated through a nebulizer into a sealed, unventilated biosafety level 2 (BSL-2) laboratory. The mean airborne viral concentrations following the resuspension events (3.7×103 viral RNA copies m−3) were two orders of magnitude lower than those following direct emission via the nebulizer (1.1×105 viral RNA copies m−3). The calculated resuspension emission factor (normalized ratio of the airborne mass to mass available for resuspension on the surface) of 10−3 was similar to reported values for 1–2 μm particles. Thus, depending on the infectious dose and viability of the virus, resuspension of settled respiratory viruses could lead to transmission, but the risk appears to be much lower than for direct respiratory emissions. To our knowledge, this is the first full-scale experimental study designed to quantify virus resuspension.

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