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Coronavirus (COVID-19) information

 

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SARS-CoV-2 (the virus) and COVID-19 (the Disease)  

SARS = Severe Acute Respiratory Syndrome. COVID-19 = Coronavirus Disease 2019

 

This is an enveloped RNA virus of the coronaviridae family. Some members of this family cause the common cold while others have caused SARS (2002/3 outbreak in humans – this came from horseshoe bats via a civet cat intermediary. A lesser known coronavirus caused MERS (Middle Eastern Respiratory Syndrome) in 2011 – this most likely also came from bats via camels. The current SARS-CoV-2 which causes COVID-19 has undergone a series of mutations that have eventually allowed human to human transmission not occur easily. MERS and SARS outbreaks had case fatality rates (CFR) approaching 10% while the CFR for COVID-19 appears to be 0.2% - 1%. Diligent contact tracing meant both SARS and MERS were contained. If there were no intervention in the current pandemic, then the R0 (reproduction number) would be at least 2.2 - 2.6, meaning one person on average could transmit to 2.4 others. Current efforts need to reduce this to below 1.

 

Evidence shows that this infection is transmitted by muco/salivary droplets containing sufficient viral numbers reaching the nasopharynx and overcoming a susceptible host’s defences. This is most likely to occur over a period of sustained contact e.g. 15 minutes face to face or 2 hours in the same room. Large droplets from coughing / sneezing / talking are able to transmit sufficient virus to the upper respiratory tract of susceptible others within a couple of metres, possibly further. Smaller droplets that dry off and remain suspended for 30-60 minutes may not contain sufficient virus to cause infection when inhaled. Remaining 1.5-2 metres from others reduces risk to you and them in case you are infectious – of course isolating yourself when you have any symptoms remains the greatest means of reducing transmission. Consider even the mildest of symptoms such as a scratchy throat or dry cough to be enough to ensure you have a swab done and remain at home and away from others in your household until the results are known and you have recovered.
   
In the 24-48 hours before symptoms develop (the pre-symptomatic phase), viral shedding gradually increases. All viral illnesses have some pre-symptomatic/asymptomatic phase but given there is no coughing, they tend to be less efficient at transmission. The greater risk is from those with mild symptoms who do not isolate. Physical distancing is an effort to reduce infection from this group and from those in the late presymptomatic phase.

 

Frequent hand hygiene reduces the risk of sufficient virus reaching your nose/mouth from surfaces you have touched. Handwashing with soap essentially washes off organic matter / soil that contains the virus while alcohol based hand rub disrupts the viral envelope and prevents the virus from attaching to your cells. Hand hygiene is more effective in reducing risk when more important measures such as remaining at home when symptomatic or in quarantine remain and keeping up physical distancing.

 

Regular cleaning of frequently touched surfaces such as handles, buttons etc will reduce the amount of virus on a surface but it is unknown to what extent transmission via surfaces occurs. This is not a difficult virus to inactivate and most commonly used household disinfectants are effective at achieving an acceptable 4 log reduction i.e. reducing infective virus from 10,000 particles to 1 as long as:

      • 1. The surface is cleaned first with detergent (this is often all that is required)
      • 2. The required concentration is used
      • 3. Wet contact is maintained for the specified time (usually a minute)

       

How long a surface remains infective varies with the surface itself. Humidity, whether sufficient virus remains or whether its infectivity is hampered are other factors. It appears virus can remain able to infect cells for hours only on fibre/paper but possibly a couple of days on smooth surfaces such as plastic and metal. Much is still unknown.

 

The sample required is a single oropharyngeal swab followed by a nasopharyngeal swab taken from a symptomatic person. However, newer studies have validated a patient taking his/her own nose and throat swab. The test performed detects SARS-CoV-2 viral RNA and is called a RT-PCR (reverse transcriptase polymerase chain reaction) test. It is extremely sensitive and specific. Rapid tests on swabs taking an hour are expensive but becoming available to targeted groups. Studies are being conducted to determine a reliable antibody blood test to show who has had the infection. However, the imperative at present is to detect current infection.

 

Over the 18 months ie until late 2021 that this pandemic is likely to run, second and third waves of infection are likely when virus is reintroduced e.g. by travel or when precautions are relaxed.