Non-droplet routes of SARS-CoV-2 transmission

In a recent review article published in the Science of The Total Environment journal, a group of Polish researchers discussed the different transmission routes of the severe acute respiratory coronavirus 2 (SARS-CoV-2), the virus responsible for the coronavirus disease 2019 (COVID-19). In their work, the researchers focused on the extent of SARS-CoV-2 survival in the environment, particularly in sewages and contaminated surfaces.

Introduction

As of May 26, 2021, SARS-CoV-2 has infected over 167 million individuals, which has led to almost 3.5 million deaths worldwide. It is generally thought that the incubation period of SARS-CoV-2 lasts from 2 to 12 days, with an average of 5.1 days.

Because of its high transmissibility, which primarily occurs in aerosols, public health officials and medical professionals worldwide are highly interested in better understanding all possible modes of SARS-CoV-2 transmission. Expanding the knowledge on the survivability of the virus on various surfaces and discharges and identifying effective disinfection procedures remain crucial to adequately reducing the transmission of this coronavirus.

The Science of The Total Environment review article summarizes the current knowledge on SARS-CoV-2 transmission and survival, particularly via non-droplet routes. The authors of this paper emphasized the need for a thorough investigation of the COVID-19 patient's environment.

"This article aimed to review the available data on the non-droplet routes of the spread of SARS-CoV-2 and related coronaviruses (including SARS-CoV-1, MERS) such as wastewater, soil, and surface, and methods of their elimination."

A review of SARS-CoV-2 transmission sources

In their review, the authors used relevant keywords and performed a manual search of electronic databases such as Pubmed, Google Scholar, Web of Science, and the medRxiv preprint server for primary articles and abstracts that were published between July 1, 2020, and October 17, 2020. They selected 128 peer-reviewed articles, review articles, and other relevant documents published in 2020, as well as 60 relevant articles published before 2020.

SARS-CoV-2 in aerosols

After reviewing these published pieces, the authors discussed the presence of SARS-CoV-2 in the air and on surfaces, as well as documented cases of SARS-CoV-2 detected in water, sewage, and soil.

When COVID-19 patients speak, cough, or sneeze, they disperse aerosols containing infectious viral particles to their surrounding environment. Overall, the spread of these droplets is considered to be the main transmission route for SARS-CoV-2.

When present in an aerosol, the half-life of SARS-Cov-2 is about 3 hours. This half-life represents the amount of time required for half of the viral genetic material to die. Although SARS-CoV-2 can persist in the environment for clearly extensive periods, in particular closed environments like a hospital, the authors found that stringent disinfection procedures successfully eliminate the genetic material of SARS-CoV-2 in these closed environments.

SARS-CoV-2 on various surfaces

In addition to aerosols, several other modes of viral transmission may add to a rapid increase in infection rates over a short period of time. Various surfaces touched by infected persons, as well as the contamination of water, sewage, garbage, or soil, are all likely routes of SARS-CoV-2 transmission.

The duration of SARS-CoV-2 on different surfaces varies significantly, depending on the surface. A latex glove that has been contaminated with SARS-CoV-2, for example, will have viable viral genetic material remaining on its surface for a maximum of 8 hours. This is comparable to the duration of SARS-CoV-2 on wood, metal, and paper surfaces, which is between 4 and 5 days.

In addition to these surfaces, SARS-CoV-2 also remains on everyday items such as mobile phones, desktop computers, keyboards, printers, remote controls for televisions, elevator buttons, and much more. The authors also found that the persistence of SARS-CoV-2 in the hospital environment, particularly areas that are often touched by both patients and healthcare professionals, is a significant problem.

SARS-CoV-2 in water, sewage, and soil

The RNA of SARS-CoV-2, as well as several live viruses, have been detected in stool and urine samples of infected individuals, thus indicating their potential as open transmission routes.

"It is particularly relevant in areas where people have contact with feces or sewage containing virus particles, i.e., contaminated water reservoirs with raw discharges," noted the authors.

A recent study showed that the lowest observed percentage of SARS-CoV-2 positive samples was for toilets (8.70%), followed by shower traps (18.75%) and sink traps (19.23%).

"Guaranteeing drinking water safety, sewage collection, and maintaining effective hygiene during the COVID-19 pandemic, play a key role in ensuring public health safety."

While there is no data for developing countries, the genetic material of SARS-CoV-2 was not present in wastewater rivers that were tested in Japan. Contrastingly, SARS-CoV-2 RNA was found in river samples obtained from Quito, Ecuador.

In a 2003 report on SARS-CoV-1 in Hong Kong, the virus was found to spread among residents from a sewer pipe leakage in an apartment, which contributed to the aerosolization of water droplets containing virus particles. "It can be assumed that a similar situation can apply to SARS-CoV-2," observed the authors of the current study.

Taken together, the presence of SARS-CoV-2 in untreated sewage or waters is suggestive of possible soil penetration with its particles.

"Soil, a matrix rich in organic substances that can protect various viruses, can probably act as a reservoir for SARS-CoV-2, being a secondary element in aerosol-mediated dispersion."

Appropriate disinfection methods

To control and contain the transmission of SARS-CoV-2, it is imperative to implement effective decontamination methods for these environments. The effective elimination of SARS-CoV-2 from surfaces can be achieved through the use of 65–70% ethanol, 0.5% hydrogen peroxide, or 0.1% sodium hypochlorite.

Within the air, frequent ventilation with 6 to 12 changes per hour is recommended. Additionally, certain air purification technologies, such as that which is offered by ActivePure Technologies LLC, have been found to inactive airborne SARS-CoV-2 by up to 99.9%.

Despite its persistence in wastewaters, several disinfection methods have the potential to mitigate the risk of spreading SARS-CoV-2. These include chemical disinfection through the use of chlorine solutions like sodium hypochlorite and chlorine dioxide and physical disinfection via ultraviolet (UV) and gamma radiation and thermal inactivation. Notably, mechanical disinfection methods, such as micro-and ultrafiltration, cannot mitigate the spread of any viruses, including SARS-CoV-2.

This review collates the information that is currently available on how SARS-CoV-2 is spread. Moreover, this article raises important questions on the non-droplet spreading routes within the environment that require public attention in the global fight against this pandemic.

Written by

Dr. Ramya Dwivedi

Ramya has a Ph.D. in Biotechnology from the National Chemical Laboratories (CSIR-NCL), in Pune. Her work consisted of functionalizing nanoparticles with different molecules of biological interest, studying the reaction system and establishing useful applications.