SARS-CoV-2 Droplet and Airborne Transmission Heterogeneity

Abstract

The spread dynamics of the SARS-CoV-2 virus have not yet been fully understood after two years of the pandemic. The virus’s global spread represented a unique scenario for advancing infectious disease research. Consequently, mechanistic epidemiological theories were quickly dismissed, and more attention was paid to other approaches that considered heterogeneity in the spread. One of the most critical advances in aerial pathogens transmission was the global acceptance of the airborne model, where the airway is presented as the epicenter of the spread of the disease. Although the aerodynamics and persistence of the SARS-CoV-2 virus in the air have been extensively studied, the actual probability of contagion is still unknown. In this work, the individual heterogeneity in the transmission of 22 patients infected with COVID-19 was analyzed by close contact (cough samples) and air (environmental samples). Viral RNA was detected in 2/19 cough samples from patient subgroups, with a mean Ct (Cycle Threshold in Quantitative Polymerase Chain Reaction analysis) of 25.7 ± 7.0. Nevertheless, viral RNA was only detected in air samples from 1/8 patients, with an average Ct of 25.0 ± 4.0. Viral load in cough samples ranged from 7.3 × 105 to 8.7 × 108 copies/mL among patients, while concentrations between 1.1–4.8 copies/m3 were found in air, consistent with other reports in the literature. In patients undergoing follow-up, no viral load was found (neither in coughs nor in the air) after the third day of symptoms, which could help define quarantine periods in infected individuals. In addition, it was found that the patient’s Ct should not be considered an indicator of infectiousness, since it could not be correlated with the viral load disseminated. The results of this work are in line with proposed hypotheses of superspreaders, which can attribute part of the heterogeneity of the spread to the oversized emission of a small percentage of infected people.

Epidemiology of Covid-19

“…The patient's Ct should not be considered as an indicator of infectiousness, since it could not be correlated with the disseminated viral load [22]. However this result is based on a small sample size (n=22; no viral load was found, in coughs or air after the third day of symptoms) and is consistent with the proposed hypotheses of superspreaders.…”

COVID-19: An overview on possible transmission ways, sampling matrices and diagnosis

“…But it is necessary to pay attention to the fact that the spread speed of this virus is not always the same but changes periodically. 26 The negative result of SARS-CoV-2 air sample tests is due to one of the following reasons. 27 i) The amount of virus released is small, ii) Viruses are inactivated by disinfectant, and iii) The sample air is diluted by fresh air flow.…”

Identify the Virus-like Models for COVID-19 as Bio-Threats: Combining Phage Display, Spectral Detection and Algorithms Analysis

“…And it could be the most severe threat for generations due to its dangerousness and unpredictability [ 1 ]. Great efforts have been made to understand and discover SARS-CoV-2, including its viral structure [ 2 , 3 , 4 ], spread process [ 5 , 6 , 7 , 8 ], pathogenesis mechanism [ 9 , 10 ], diagnostic approach [ 8 ], variants [ 11 , 12 , 13 ], and vaccine immunity [ 13 , 14 , 15 ]. However, there are still significant challenges in the detection of this virus despite all kinds of positive scientific progress have been achieved.…”