Science of Spread of COVID-19 Infection

By: Prof Ghias Un Nabi Tayyab      Published: 07:49 PM, 20 Jun, 2020
Science of Spread of COVID-19 Infection
–File photo

Pakistan is going through a phase of rapid multiplication of patients suffering from COVID-19 infection. The pace of increase is frightening, mind baffling and is set to cause a huge catastrophe. Ever since the announcements by the World Health Authority, a slogan was adopted by health authorities in Pakistan which read “Corona sai darna nahee, larna hai’ and then strong mixed opinions on the impact of COVID-19 disease in local population have being aired by political figures, establishment and medical academicians leading to a false assurance for a possible resistance and less likely spread on number of accounts. It was mentioned that in subcontinent it is a mild disease, behavior is more like common flu, subcontinent people are protected by virtue of BCG vaccination and polio vaccination etc. There has been a common myth in the initial months that it is a disease of China and the Western areas only and it cannot affect Pakistani people. Another myth followed that only the affluent class is being affected. The notion that the problem is of big cities only and smaller towns and villages shall be spared still holds strong in the masses. While the countries with good governance were educating their masses on the preventive measures, setting rules of quarantine and building up resources to deal with complicated patients, we, in Pakistan, failed to generate adequate response to the upcoming menace though we had seen the best as well as worst scenarios of the disease in the rest of the world. 

COVID-19 infection pandemic in Pakistan can easily be divided in to three phases. In the initial phase, there were imported cases only. Later on we had a local spread from the patients who brought the disease from other countries and came back to their native town. Subsequently, we have gone in to community spread where the infection is spreading in high numbers from each other within a family, group of friends, office workers, professionals and innocent bystanders. The infectivity of the contagion is so high that if one member of the family acquires infection from a source and gets symptomatic, by the time he understands or attains confirmation of COVID-19 infection, he has already infected almost all of his family along with multiple members of his office and/or friends. This exponential spread of the infection is being seen due to the mass gatherings that occurred at the time of Iftaars, traveehs and other occasions during the recently concluded month of Ramadan and similarly, through family get-togethers during the Eid holidays. People travelled in planes, trains, buses and cars to get back to the place of origin while mixing up with each other during the course of travelling and having adequate exposure to get infected or carry the infection back to home during these Eid holidays. 

Since we, in Pakistan, missed the opportunity to educate our masses adequately, there have been extreme opinions on the presence and possibility of spread of the disease. Certain groups of people were and many still are in denial of the presence of the infection and labelled the whole pandemic as a hoax. Several groups of people underestimated the possible magnitude of impact as well as the morbidity and mortality it may cause. Then there have been people who thought that hospitalists are working in connivance with some external forces to kill the patients going there for management in the face of the severe disease. 

As people are heavily confused on the existence and magnitude of the problem, receptivity of the protective measures to control the disease is still limited. One can see politicians sitting in crowded press conferences without protective masks, officers sitting next to each other in disrespect to the widely advertised and recommended act of social distancing and general public going about their routine business in close and congested places without observing the protective and preventive strategies mentioned and advertised at various levels. 

Healthcare facilities have already been working at their capacity for almost four weeks now and high dependency units and intensive care beds are fully occupied in the public as well as private sector hospitals. Number of patients presenting to the family physicians (the first line of defence) are huge and mostly go untested and unnoticed while people with moderate to severe symptoms are going pillar to pillar to have the attention of the medics who are already over occupied and lack capacity to accommodate more patients. Since the disease is highly contagious, the medical staff is also contracting the infection in big numbers. Due to the absence of mandatory central testing and registry, the exact number of cases is unknown. Trace, Test & Treat strategy has been advised by WHO but with so many missing links, it has failed to give the desired results.

While it is understandable that the containment phase of this infection has past us, it is very important that we adopt a strategy to minimize the further spread of the infection in the community. For this reason, the science of the spread of COVID-19 infection needs a better understanding and requires elaboration. In the first instance, people should be made aware that an infected patient, who may be completely asymptomatic, in the community has the potential to spread the infection from the 2nd day to the 11th day after contracting the disease. In case the index person acquires the infection, he is likely to develop symptoms after 1-5 days of being exposed and his infectivity i.e. potential to spread the infection is at its peak 1 day prior to onset of infection to 4 days after the onset of the fever. As many as 40% of total new cases are catching infections from people who have the infection but are free of any symptom. Although chest symptoms are the most widely known manifestation of the disease, people may have very wide ranging presentations like loss of taste, smell or appetite, myalgia’s and bone pains, nausea, loose motions or impaired mentation. So, during this COVID time, any patient that comes in contact with the healthcare system should be considered as SARS – CoV 2 infected patient unless proven otherwise. After the presence of an infected patient, one needs to understand that the infection gets transferred through the transmission of infection down the respiratory system and not by ingestion or body contact and this transmission is via inhalation of a potentially contaminated air, application of a contaminated finger, tissue paper or cloth to the nose or possible inner lining of eye. If we eliminate the presence of an infected person or we are able to protect the nose and possibly the eyes as well, we shall be able to control the spread of infection. At the same time, it is worth remembering that the infective contagion of SARS-CoV 2 gets excreted in its potentially transmissible form though coughing, sneezing or talking and mere presence of the person in the vicinity is not a cause of spread of infection. A strong unified practice of isolating the infected person, putting mask to every person and a strict adherence to this simple two pronged approach can bring a halt to the escalating numbers in a period as brief as 2 weeks. 

How can we eliminate the presence of an infected person in our neighbourhood? This one million dollar question needs no heroic and out of box answering, firstly anybody who is actually suffering from a documented infection, possibly suffering from an infection or may be suffering from an infection must exercise voluntary isolation for at least 11 days from onset of symptoms. Since the contagion of SARS –CoV 2 gets excreted in its potentially transmissible form though coughing, sneezing or talking, hence for all other people in the community putting up a three ply surgical mask or 5 ply medical grade mask is enough, irrespective of their infection status for 2-4 weeks time in order to protect themselves and keep all others protected in case the infection is harboured in an asymptomatic patient. The air and secretions exuding out of the infected person contains enough SARS – CoV 2 viral particles to infect all others in a limited time span and the same suspended infective material starts settling down on the surfaces and cloths with their viability for a variable period of time. In addition to the suspended infected virus particles in a contaminated air, what are the other potential ways that the infection may get transferred? Touching the contaminated surfaces, for example an infected person’s face, hand during hand shake, body hug or contaminated surfaces exposed to the deposited material from the contaminated air, with fingers and then contaminating the nose or eyes mucosa is another potential way of transfer of infection

Now let us think of situations where we may come across an infected person or may expose ourselves to the infected material. Again there is no rocket science involved in to this. Closed spaces, damp places, public gatherings, mass congregations, hostels, hospitals, hotels, cafes, public offices, congested markets, public toilets and mass transport systems are the places where in the difficult summers of June and up coming months, viral transmission from an infected person to a healthy person can occur rapidly. The air in these places is capable of holding the contagion particles for long and may transfer a lethal dose. On the contrary, open parks, roadside shops and open markets like mandees with ensured social distancing are unlikely to contribute in the spread of infection. Hence avoidance of closed spaces, damp places, public gatherings, mass congregations, hostels, hospitals, hotels, cafes, public offices, congested markets and mass transport systems is another key step to control the spread of infection. In the aforementioned situations, certain areas may be unavoidable for example a sick person has to present himself to the hospitals and clinics for management of ailments, people have to attend office/shops for earning money to feed their children and similarly all other situations. Hence a mitigation plan is required and a cooperative approach is required between the service providers and serviced, employer and employee and the controlling establishment.  

We must understand that most people get infected in their own home. A household member contracts the virus in the community and brings it into the house where sustained contact between household members leads to infection. In order to get infected one needs to get exposed to an infectious dose of the virus; Based on an infectious dose like all other microbes, it appears that only small doses may be needed for infection to take hold in case of COVID-19. Some experts estimate that as few as 1000 SARS-CoV2 infectious viral particles are all that will be needed. Infection could occur, through 1000 infectious viral particles you receive in one breath or from one eye-rub, or 100 viral particles inhaled with each breath over 10 breaths, or 10 viral particles with 100 breaths.

Successful Infection = Exposure to Virus x Time

But where are people contracting the infection in the community? 

Each of the following situations can lead to an infection, as the amount of viral particles excreted, is variable and potentially still enough with prolonged exposure to ignite the infection. The situation and amount of potential presence of virus need a proper understanding. 

Toilets have a lot of high touch surfaces, door handles, faucets, stall doors, soap containers and etc. So fomite transfer risk in this environment can be high. Although an infected person releases infectious material and fragmented virus in faeces and an actual transmission through that may not be a realistic threat, but we do know that toilet flushing does aerosolize many droplets hence public toilets must be used with an extra caution (surface and air).

A single breath releases 50 - 5000 droplets. Most of these droplets are low velocity and fall to the ground quickly. There are even fewer droplets released through nosebreathing. Importantly, due to the lack of exhalation force with a breath, viral particles from the lower respiratory areas are not expelled. 

But with general breathing, 20 viral particles per minute into the environment, even if every virus ended up in the lungs, one would need 1000 viral particles divided by 20 per minute = 50 minutes to establish the infection.

 Speaking increases the release of respiratory droplets about 10 fold; ~200 virus particles per minute. Again, assuming every virus is inhaled, it would take ~5 minutes of speaking face-to-face to receive the required dose. 

A single cough releases about 3,000 droplets and droplets travels at 50 miles per hour. Most droplets are large, and fall quickly (gravity), but many do stay in the air and can travel across a room in a few seconds but rarely beyond 2 meters. Hence a strict observation of social distancing can go a long way in protecting one self.  

A single sneeze releases about 30,000 droplets, with droplets traveling at up to 200 MPH and most droplets are small and may travel great distances (easily across a room), hence a strict face cover with elbow bend, cloth or tissue paper is required to protect all others. If a person is infected, the droplets in a single cough or sneeze may contain as many as 200,000,000 (two hundred million) virus particles, which can all, be dispersed into the environment around them.

If a person coughs or sneezes, those 200,000,000 viral particles go everywhere. Some virus hangs in the air, some falls into surfaces, and most falls to the ground. So if you are face-to-face with a person, having a conversation, and that person sneezes or coughs straight at you, it is easy to see how it is possible to inhale 1,000 virus particles and become infected.

But even if that cough or sneeze was not directed at you, some infected droplets--the smallest of small--can hang in the air for a few minutes, filling every corner of a modest sized room with infectious viral particles. All you have to do is enter that room within a few minutes of the cough/sneeze and take a few breaths and you have potentially received enough viral particles to establish an infection

The exposure to virus x time formula is the basis of contact tracing. Anyone spending greater than 10 minutes with in a face-to-face situation is potentially infected. Anyone who shares a space with you (say an office, travel place, market or cafe) for an extended period is potentially infected. This is also why it is critical for people who are symptomatic to stay home. A sneeze and a bout of cough expel so many viruses that a whole room of people may get infected. 

What may be the mitigation plan? Let us get to the summary and identifying our personal roles to control the disease.

1.      Every body should be wearing a mask, irrespective whether he thinks that he is exposed, infected, non infected or non exposed and all times except for sleeping, bathing or eating.

2.      Covering of nose and mouth while coughing or sneezing with a piece of cloth, tissue paper or elbow bends.

3.      Voluntary isolation in case of symptoms as mentioned above.

4.      Avoidance of gatherings and crowded places. Do not participate in avoidable social functions. 

5.      Avoid face-to-face discussions.

6.      Maintain social distance, which is a minimum 2 meters.

7.      Work from home if possible.

8.      Maintain mental and physical health by positive thinking, walking in open and scheduling the activity to avoid crowding.

9.      Administration and law enforcing agencies should strictly implement Rule 144, mask in public places and social distancing.

10.  A cheap an easy provision of masks may be ensured.

11.  Trace, Test & Treat strategy should be implemented, monitored and audited with full vigour.

12.  A change in slogan “Corona sai darna nahee, larna hai’ is warranted to “Corona sai darna nahee, bachna hai aur bachna hai’

13.  Strong advocacy groups must be promoted by social media and civil administration

14.  A consensus policy framed by experts in public health, health economics, patient management, mass education and advocacy groups should be framed and pursued in coherence.

We can still control the spread of COVID 19 infection by understanding the science of spread of this infection and thus avoid the impending death dance likely to ensue out of further spread of this infection.

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