Possibility and implications of Airborne Spread of COVID19

April 8, 2020

By – Dr. Rajesh B Iyer
(Vikram Hospital)

COVID-19 is spreading easily, aggressively and sustainably in the community. We have just crossed 1000 positive cases in India. This is likely an under estimation because the number of tests conducted is low and the present protocol of testing by real time polymerase chain reaction test from throat swab specimens can detect only about 1/3rd of patients who actually have the disease1.

Persons infected with SARS-CoV-2 shed and transmit the virus while beingasymptomatic2 and early in the course of infection3. So, almost2/3rd of people who have thedisease do not test positive by this method, but still transmit the disease. They could bemajor contributors towards rapid and sustained disease spread.

So far, we have heard that COVID 19 spreads through fomites, that is objects and surfaces contaminated with the virus and through larger droplets in close proximities. There has generally been a reluctance to accept that the SARS-CoV-2 can be airborne as aerosols and is therefore considered unlikely to spread through the air like measles or chickenpox virus. Is the SARS-CoV-2 airborne? If so, our present strategies against the pandemic maybe inadequate.

In the usual respiratory infections, depending on the force of cough or sneeze and the volume of secretions, the droplets travel a variable distance. Larger ones tend to settle down quickly in the vicinity whereas smaller ones tend to travel further. The settled droplets can subsequently generate “droplet nuclei” containing the pathogen, which is much smaller in size and can get carried away by the air to far off places, thus propagating infection.
Particles < 10 μm size easily reach below the glottis. Smaller particles like droplet nuclei, typically < 5 μm easily reach the terminal airways and alveoli of the lungs.4

Studies on previous coronaviral outbreaks provide valuable information.The SARSCoV-1 caused outbreaks in 2003 and MERS-CoV (Middle East respiratory syndrome) in 2012. Full-length genome sequences show that SARS-CoV-2 shares 79.6 % sequence identity to SARS-CoV-15.In both SARS and MERS, lower respiratory tract (LRT) samples provided best diagnostic yield, often in the absence of any detectable virus in upper respiratory tract (URT) samples. ymptomatic patients developed severe LRT infections rather than URT disease, suggesting direct entry into LRT. Moreover, the human URT seems noncongenial for MERS-CoV replication, indicating that successful infection can only result by
smaller droplet-nuclei like particles directly reaching the LRT4.These data strongly support transmission by an airborne droplet-nuclei mechanism of these coronaviruses. The analysis of a SARS superspread event at Amoy Gardens apartment complex in Hong Kong during the SARS-CoV-1 epidemic in 2003 provides further support for airborne transmission of SARSCoV-1 as the primary mechanism of rapid transmission6.

The SARS‐CoV‐2 seems to have similar airborne transmissibility. Like the other SARS viruses, broncho-alveolar lavage rather than throat or nasal swab specimens in COVID 19 patients yielded the highest (93%) positive rates 1.This suggests prominent LRT involvement, similar to SARS‐CoV-1, indicating droplet nuclei seeding by airborne viral particles. Asymptomatic and preclinical patients with SARS‐CoV‐2 have CT scan findings of pneumonia, again suggesting direct entry of virus to the LRT by small droplet nuclei7 .Moreover, rapid spread with superspreading ability indicates effective airborne transmission.

Therefore, this calls for more effective strategies than what is being recommended now. The present standard of practice advocated includes social distancing and hand wash for everyone and PPE or N95 masks for health care workers depending on the clinical circumstances. The way social distancing is practiced today in India and elsewhere may not be adequate to stop the rapid spread of the infection. We see people going out for walking
and jogging, often without maintaining a safe distance, and sometimes in groups, especially in apartment complexes. It is not uncommon to see people adjacent to each other at groceries and medical shops. For social distancing, an interpersonal distance of 3-6 feet would seem sufficient to prevent transmission by large droplets. But when there are airborne viral particles, then this distance becomes irrelevant. For example, a walker might be passing
through the same path as somebody else, who could be asymptomatic but shedding the virus. Similarly, standing in queues at a distance of 1-2 meters may still not prevent airborne infection. Even if we assume that ideal social distancing is practiced by one and all, it may not effectively protect from airborne transmission.

So, what are the options we have?

  1. Universal use of effective respiratory barriers like a good quality mask (N95 and above) clubbed with proper hand wash techniques
  2. Implementation of social distancing in true spirit and adopt more effective practices. These could include “staying sheltered at home” which means to step out of one’s place if and only if absolutely essential and limiting travel and time spent outside one’s residence to the minimum. Go out only with a mask! The combination of the above two should be very effective
  3. A large part of our people stay in small crowded residences and slums where space for maintaining a safe distance will not be available. Again, masks and handwashing along with health education should help
  4. Self quarantine will be another effective method.
  5. Self isolation, if somebody has high risk of exposure or suspicious symptoms.

To succeed, we need every human being to act responsibly and honestly in social distancing and in using respiratory barriers. If governmental agencies and other organizations provide effective respiratory barriers like N95/N99 masks to all, we may win the war sooner!. Hopefully, if these measures are thought about and implemented, it can help to dampen and wishfully stop the pandemic.

Disclaimer: I am a neurologist and not a virologist or respiratory medicine specialist. These are my personal views, arrived at, after observations from the present pandemic and review of relevant scientific medical literature pertaining to the previous SARS outbreaks and COVID19. The references are listed below.

Dr Rajesh B Iyer
Consultant Neurologist & Epileptologist,
Vikram Hospital, Bengaluru
31-03-2020/ Bengaluru

  1. Wang W, Xu Y, Gao R, et al. Detection of SARS-CoV-2 in Different Types of Clinical Specimens. JAMA. 2020; e203786. doi:10.1001/jama.2020.3786
  2. Rothe C, Schunk M, Sothmann P, et al. Transmission of 2019-nCoV infection from an asymptomatic contact in Germany. N Engl J Med 2020;382:970-971. doi: 10.1056/NEJMc2001468.
  3. Zou L, Ruan F, Huang M, et al. SARS-CoV-2 viral load in upper respiratory specimens of infected patients. N Engl J Med. doi: 10.1056/NEJMc2001737.
  4. Tellier R, Li Y, Cowling BJ, Tang JW. Recognition of aerosol transmission of infectious agents: a commentary. BMC Infect Dis. 2019;19(1):101 doi:10.1186/s12879-019-3707-y
  5. Zhou P, Yang XL, Wang XG, et al. A pneumonia outbreak associated with a new coronavirus of probable bat origin. Nature. 2020; 579(7798):270–273. doi:10.1038/s41586-020-2012-7
  6. Yu IT, Li Y, Wong TW, et al. Evidence of airborne transmission of the severe acute espiratory syndrome virus. N Engl J Med. 2004;350(17):1731–1739. doi: 10.1056/NEJMoa032867.
  7. Shi H, Han X, Jiang N, et al. Radiological findings from 81 patients with COVID-19 pneumonia in Wuhan, China: a descriptive study. Lancet Infect Dis. 2020;20(4):425–434. doi:10.1016/S1473-3099(20)30086-4.

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