To address the airborne transmission mode of SARS-CoV-2 air samples were collected in the largest hospital in Iran. • Our results indicated that all collected samples were negative in terms of the viral RNA. • We did not detect any positive readings 2 m from the patients' beds.

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The viability of airborne respiratory viruses varies with ambient relative humidity (RH). Numerous contrasting reports spanning several viruses have failed to identify the mechanism underlying this dependence. We hypothesized that an "efflorescence/ deliquescence divergent infectivity" (EDDI) model accurately predicts the RH-dependent survival of airborne human rhinovirus-16 (HRV-16). We measured the efflorescence and deliquescence RH (RH E and RH D , respectively) of aerosols nebulized from a protein-enriched saline carrier fluid simulating the human respiratory fluid and found the RH range of the aerosols' hygroscopic hysteresis zone (RH E−D ) to be 38− 68%, which encompasses the preferred RH for indoor air (40−60%). The carrier fluid containing HRV-16 was nebulized into the subhysteresis zone (RH D ) air, to set the aerosols to the effloresced/solid or deliquesced/liquid state before transitioning the RH into the intermediate hysteresis zone. The surviving fractions (SFs) of the virus were then measured 15 min post nebulization. SFs were also measured for aerosols introduced directly into the RH D zones without transition. SFs for transitioned aerosols in the hysteresis zone were higher for effloresced (0.17 ± 0.02) than for deliquesced (0.005 ± 0.005) aerosols. SFs for nontransitioned aerosols in the RH D zones were 0.18 ± 0.06, 0.05 ± 0.02, and 0.20 ± 0.05, respectively, revealing a V-shaped SF/RH dependence. The EDDI model's prediction of enhanced survival in the hysteresis zone for effloresced carrier aerosols was confirmed.

Relative humidity (RH) can affect influenza A virus (IAV) survival. However, the mechanism driving this relationship is unknown. We hypothesized that the RH-dependent survival of airborne IAV could be predicted by the efflorescence/deliquescence divergent infectivity (EDDI) hypothesis. We determined three distinct RH response zones based on the hygroscopic growth factor of carrier aerosols. These zones were classified as the super-deliquescence zone (RH > 75%), the hysteresis zone (43% < RH < 75%), and the sub-efflorescence zone (RH < 43%). We added IAV (H3N2) to protein-enriched saline and aerosolized it into sub-efflorescence or superdeliquescence zone air, yielding aerosols in the effloresced or noneffloresced state, respectively. We then adjusted the RH to an ergonomically comfortable RH (60%). Fifteen minutes post-aerosolization, the surviving fractions (arithmetic means ± standard errors) of virus were higher in effloresced aerosols (9.5 ± 0.5%) than in non-effloresced aerosols (0.40 ± 0.05%). A virus suspension was also aerosolized directly into air within the super-deliquescence, hysteresis, and sub-efflorescence zones to assess the impact of the sudden change in RH from an initial 100% saturated RH to these zonal ranges. Fifteen minutes post-aerosolization, the surviving fractions were 3 ± 0.4%, 2 ± 0.1%, and 12 ± 2%, respectively. Survival following gradual adaptation to the hysteresis zone RH range was sustained in effloresced and reduced in the non-effloresced aerosols. The EDDI model predicted the survival of IAV under seasonal conditions, offering strategies for controlling indoor air infection.

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