Viral load of SARS-CoV-2 in droplets and bioaerosols directly captured during breathing, speaking and coughing

Abstract

Determining the viral load and infectivity of SARS-CoV-2 in macroscopic respiratory droplets, bioaerosols, and other bodily fluids and secretions is important for identifying transmission modes, assessing risks and informing public health guidelines. Here we show that viral load of SARS-CoV-2 Ribonucleic Acid (RNA) in participants’ naso-pharyngeal (NP) swabs positively correlated with RNA viral load they emitted in both droplets >10 $$\upmu \hbox {m}$$ μ m and bioaerosols <10 $$\upmu \hbox {m}$$ μ m directly captured during the combined expiratory activities of breathing, speaking and coughing using a standardized protocol, although the NP swabs had $$\approx$$ ≈ 10$$^3\times$$ 3 × more RNA on average. By identifying highly-infectious individuals (maximum of 18,000 PFU/mL in NP), we retrieved higher numbers of SARS-CoV-2 RNA gene copies in bioaerosol samples (maximum of 4.8$${\times }10^{5}$$ × 10 5 gene copies/mL and minimum cycle threshold of 26.2) relative to other studies. However, all attempts to identify infectious virus in size-segregated droplets and bioaerosols were negative by plaque assay (0 of 58). This outcome is partly attributed to the insufficient amount of viral material in each sample (as indicated by SARS-CoV-2 gene copies) or may indicate no infectious virus was present in such samples, although other possible factors are identified.

Rapid SARS-CoV-2 disinfection on distant surfaces with UV-C: The inactivation is affected by the type of material

“…For virus inactivation experiments we added 10 5 PFUs of SARS-CoV-2 diluted in 0.5 ml of infection medium (MEM with 0.2% bovine serum albumin, 2mM glutamine and 20mM Hepes) to sterile polystyrene 100 mm culture dishes (Corning, Corning, NY). The virus concentration used for drying (2 × 10 5 PFU/ml) was approximately 10-fold higher than that present in droplets from highly-infectious individuals, for whom a maximum of 1.8 × 10 4 PFU/ml of SARS-CoV-2 was detected in nasopharingeal swabs [16] . We spreaded the virus inoculum on each plate using a spatula and let it dry inside a biosafety hood for 30 min.…”

Stability and transmissibility of SARS‐CoV‐2 in the environment

“…Studies found that the viral load in patients' nasopharyngeal swabs is positively correlated with viral loads emitted in both droplets and aerosols, and with environmental contamination. 21 , 22 , 23 Multivariate analyses have identified that viral load (viral RNA) larger than 10 7 copies/ml (OR = 14.7) is independently associated with isolation of infectious virus from respiratory tract samples. 13 Numerous studies have demonstrated that higher SARS‐CoV‐2 viral load in the upper airway of an infected person is associated their increased infectivity.…”

A Novel Framework for Modeling Person-to-Person Transmission of Respiratory Diseases

“…The first step in developing a model of respiratory particle emission is to physically characterize the particles. Respiratory particles are heterogeneous and vary in number, size, chemical composition, and viral content depending on the generation mechanism, the stage of infection, as well as inter- and intra-subject variability [ 32 , 36 , 69 , 70 ]. Accounting for this heterogeneity is an important step in quantifying the potential uncertainty in particle emission from an infected individual.…”

“…For the indoor environment, a value of 0 m/s can be assumed for wind speed, resulting in an inhalable fraction of ~0 for 100-micron particles. To determine likelihood of infection from an exposure environment, the model first accounts for how many particles are inhaled, the location of deposition, and the particle composition; this is determined by considering particle-size dependent inhalability [ 57 ], particle size-dependent deposition site [ 78 ] (which would also account for hygroscopic growth of a particle as it enters the humid respiratory tract [ 20 ]), and the viral content of particles [ 70 ]. The severity and course of illness of the disease then could depend solely on demographic factors, immune response, deposited dose, or a combination of factors.…”

“…growth of a particle as it enters the humid respiratory tract [20]), and the viral content of particles [70]. The severity and course of illness of the disease then could depend solely on demographic factors, immune response, deposited dose, or a combination of factors.…”