Covid-19 facts: Preventing and detecting the virus


  • Wellness
  • Wednesday, 04 Mar 2020

Primary school pupils put on face masks donated by a non-profit organisation in this filepic. Face masks are actually better at preventing an infected person from spreading the coronavirus, rather than preventing an infected person from catching the virus.

With the Covid-19 disease spreading to more and more countries, this first of a two-part article looks at what we know about how the virus spreads and how doctors detect it. For Part 2, go here: Covid-19 facts: The treatment and risk of death from the virus

Covid-19 is the name of the disease arising from the infection of a new (novel) coronavirus designated as SARS-CoV-2, also known as 2019-nCoV or the Wuhan virus.

It is the latest in a line of zoonotic diseases (or zoonoses) that has plagued humans ever since evolution begun. Zoonoses are diseases that are transmissible from a different species to humans.

Covid-19 is now certain to become a pandemic likely to affect not only people, but also the economic well-being of the planet.

The origins of the SARS-CoV-2 virus infecting humans is widely believed to be a wet market in Wuhan, China, which sold wildlife; although the exact original animal carrier is still unknown.

This is all not news by now to most people, so the first part of this article will focus on some other facts behind the reality that many humans will now be living under the shadow of Covid-19 until a cure or vaccine can be found.

Contamination

The known facts regarding the spread of coronaviruses are straightforward, and troubling at the same time.

Regarding the presence of SARS-CoV-2 in the environment, a paper from Germany, published in the Journal of Hospital Infection on Jan 31 (2020), analysed coronavirus persistence characteristics based on outcomes from other medical papers.

The data suggests that human coronaviruses can survive on inanimate surfaces (such as door handles, towels, clothing, plastics, etc) for up to nine days in general.

However, under the right conditions, it also noted that animal coronaviruses can survive for over 28 days. These conditions include damp surfaces and ambient temperatures of 4°C, such as those found in refrigerators.

The precise survival characteristics for SARS-CoV-2 are not known yet, although the virus is acknowledged to survive longer at room temperatures with 50% humidity, compared to 30% humidity.

Ambient air temperatures between 30°C to 40°C also appear to reduce the transmissibility of other coronaviruses.

The most common method of catching SARS-CoV-2 is via contact or inhalation of moisture/droplets from infected persons during person-to-person interactions (e.g. kissing, shaking hands, eating lunch together, etc).

This applies to all bodily fluids/moisture emanating from organs linked to the respiratory system of infected persons, such as exhaled air, mucus, saliva and sputum.

Perspiration is also a potential infection vector as the virus can contaminate and survive on moist skin.

Contamination with these liquids carries a probability of infection, which can exceed over 99%, depending on the exposure period and viral load transmitted.

The dangers linked to the persistence of SARS-CoV-2 in the environment and the potential of person-to-person transmission should not be underestimated.

For example, observational studies indicate that young adults touch their faces with their hands roughly 23 times per hour, on the skin, mouth, nose and eyes – all known entry points for SARS-CoV-2 infection.

Mitigation

The strongly infectious nature of SARS-CoV-2 means severe steps are needed to arrest widespread contagion once Covid-19 has taken a foothold in a community.

Despite the pervasive images of people wearing face masks in many towns, the reality is that face masks are more effective as a means to stop an infected person from spreading the coronavirus than preventing an uninfected wearer from acquiring the disease.

This is because an uninterrupted cough can expel around 3,000 fine droplets from the lungs at over 80 km/h, while a sneeze can disperse 100,000 droplets at a speed of over 160 km/h.

The radius of dispersal of a sneeze is roughly 0.8m, but dissipation by air currents can mean this radius may be increased by several factors.

A face mask would hinder the dissipation of such droplets.

Conversely, wearing a normal face mask only offers partial/limited protection against the inhalation of the coronavirus if present in the air.

Infectious droplets can also land on the unprotected eyes, and it is possible that face masks may give some users an unwarranted false sense of security.

The SARS-CoV-2 virus is only 125 nanometres in size and can squeeze through the gaps and sides of any ordinary/non-medical face mask (which are most of those being sold).

The probability of infection therefore depends on the viral load in the air inhaled and length of exposure.

However, N95 respirators can be effective at preventing the inhalation of droplets if one encounters an infected person; some training would be needed to use a N95 respirator properly.

The other infection vector, via contact with contaminated surfaces, can be mitigated by the use of disinfectants such as sodium hypochlorite (usually found in household bleach) at 0.1% concentration, and cleaning solutions containing 70%-80% ethanol or 75% 2-propanol.

With sodium hypochlorite, one should allow a period of one minute after cleaning before assuming the surface is safe.

The standard advice about washing/scrubbing hands thoroughly with soap for around 20 seconds should also be heeded, combined with subsequently drying the hands with clean towels or air dryers. Do not use towels that have been used by other people.

A very recent report suggests the virus may also be transmissible via urine and faeces.

If this proves to be true, it would be necessary to sanitise toilet seats, especially in public facilities, before use as wiping with tissues would have no effect in reducing the viral load.

Detection

Due to the speedy publication of the SARS-CoV-2 genome (by Fudan University, Shanghai, China, on Jan 10,2020), it was possible to very quickly develop several reverse transcriptase polymerase chain reaction (RT-PCR) test kits.

RT-PCR works by converting RNA (ribonucleic acid) into complementary DNA (deoxyribonucleic acid) strands, then amplifying the DNA via another PCR process to detect signatures and quantity of the target RNA via reagents, dyes and/or other chemicals.

However, due to the panic, there have been problems with rolling out test kits, as well as questions about their reliability.

Depending on which parts of the genome were targeted by the different test kits, it has been seen that some infected persons do not test positive for SARS-CoV-2 until after several previously-negative tests.

It may be that the viral loads in some people are too low for the tests to work, or in the case of the US Centres for Disease Control and Prevention (CDC), an incorrect reagent chemical was included in some kits.

At present, there are now several test kits available, including ones developed by China, Singapore and Hong Kong, and it is probably a matter of time before doctors standardise the use of a single reliable test.


Chris Chan works in advanced statistical and mathematical modelling of risks in large investment banks and often applies his analytical expertise to other fields such as chemistry and biochemistry. He also writes the Curious Cook column for StarLifestyle. For more information, email starhealth@thestar.com.my. The information provided is for educational purposes only and should not be considered as medical advice. The Star does not give any warranty on accuracy, completeness, functionality, usefulness or other assurances as to the content appearing in this column. The Star disclaims all responsibility for any losses, damage to property or personal injury suffered directly or indirectly from reliance on such information.

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