CMAAO
CORONA FACTS and MYTH BUSTER 42
Dr K K Aggarwal
President Confederation of Medical
Associations of Asia and Oceania
375: Viral
load
Dr Edward Parker of the London School of Hygiene and
Tropical Medicine explains how a high viral load can impact humans.
He said: “After we are infected with a virus, it
replicates in our body’s cells. The total amount of virus a person has inside
them is referred to as their ‘viral load’. For Covid-19, early reports from
China suggest the viral load is higher in patients with more severe disease,
which is also the case for Sars and influenza.
376: Infectious dose
The amount of virus we are exposed to at the start of an
infection is referred to as the ‘infectious dose’. For influenza, we know that
that initial exposure to more virus — or a higher infectious dose — appears to
increase the chance of infection and illness.
377:
Can repeated small doses be more infectious
Studies in mice have also shown that repeated exposure
to low doses may be just as infectious as a single high dose.
So, all in all, it is crucial for us to limit all
possible exposures to Covid-19, whether these are to highly symptomatic
individuals coughing up large quantities of virus or to asymptomatic
individuals shedding small quantities. And if we are feeling unwell, we need to
observe strict self-isolation measures to limit our chance of infecting others.
378: What is the similia between load and dose
Viral load, on the other
hand, relates to the number of viral particles being carried by an infected
individual and shed into their environment. “The viral load is a measure of how
bright the fire is burning in an individual, whereas the infectious dose is the
spark that gets that fire going,” says Edward Parker at the London School of
Hygiene and Tropical Medicine.
379:
Infectious dose and health care workers
Professor Wendy Barclay, the head of the Department of
Infectious Disease at Imperial College London, said existing knowledge of viral
load means healthcare workers can be at greater risk of infection.
In general, with respiratory viruses, the outcome of
infection — whether you get severely ill or only get a mild cold — can sometimes
be determined by how much virus actually got into your body and started the
infection off. It’s all about the size
of the armies on each side of the battle, a very large virus army is difficult
for our immune systems army to fight off.
So, standing further away from someone when they
breathe or cough out virus likely means fewer virus particles reach you and
then you get infected with a lower dose and get less ill. Doctors who have to get very close to
patients to take samples from them or to intubate them are at higher risk so
need to wear masks.
380:
What is minimum infectious dose of COVID 19
Dr Michael Skinner, Reader in Virology, Imperial
College London, said: Viruses are not poisons, within the cell they are
self-replicating. That means an infection can start with just a small number of
articles (the ‘dose’). The actual minimum number varies between different viruses
and we don’t yet know what that ‘minimum infectious dose’ is for COVID-19, but
we might presume it’s around a hundred virus particles.
381:
How many cells are infected to start with
When that dose reaches our respiratory tract, one or
two cells will be infected and will be re-programmed to produce many new
viruses within 12-24 hours (for COVID-19, we don’t yet know how many or over
how long). The new viruses will infect many more nearby cells (which can
include cells of our immune defence system too, possibly compromising it) and
the whole process goes around again, and again, and again.
382:
What is inmate and acquired immune responses
At some time quite early in infection, our ‘innate
immune system’ detects there’s a virus infection and mounts an innate immune
response. This is not the virus-specific, ‘acquired immune response’ with
which people are generally familiar (i.e. antibodies) but rather a broad,
non-specific, anti-viral response (characterised by interferon and cytokines,
small proteins that have the side effect of causing many of the symptoms:
fever, headaches, muscle pain).
This response serves two purposes: to slow down the
replication and spread of the virus, keeping us alive until the ‘acquired
immune response’ kicks in (which, for a virus we haven’t seen, is about 2 to 3
weeks) and to call-up and commission the ‘acquired immune response’
which will stop and finally clear the infection, as well as laying-down immune
memory to allow a faster response if we are infected again in the future (this
is the basis of the expected immunity in survivors and of vaccination).
With COVID-19, these two arms of the immune system
(innate and acquired) obviously work well for 80% of the population who recover
from more or less mild influenza-like illness.
383:
What happens in older people
In older people, or people with immunodeficiencies,
the activation of the acquired immune system may be delayed. This means that
the virus can carry on replicating and spreading in the body, causing chaos and
damage as it does, but there’s another consequence.
Another job of the acquired immune system is to
stand-down the innate immune system; until that’s done the innate immune
response will keep increasing as the virus replicates and spreads.
Part of the innate immune response is to cause
‘inflammation’. That is useful in containing the virus early in an infection
but can result in widespread damage of uninfected tissue (we call this a
‘bystander effect’) if it becomes too large and uncontrolled, a situation named
‘cytokine storm’ when it was first seen with SARS and avian influenza H5N1. It
is difficult to manage clinically, requiring intensive care and treatment and
carries with it high risk of death.
384:
What following infection with ‘normal’ doses of virus
The scenarios described above describe what happens
following infection with ‘normal’ doses of virus, both in those who make a
recovery, those who require intensive care and those (mainly elderly and/or
immunosuppressed) who might succumb. Those with other comorbidities probably
succumb due to additional stress of their already compromised essential systems
by virus and/or cytokine storm.
385:
Does getting exposed to multiple COVID positive patients matter
It is unlikely that higher doses that would be
acquired by being exposed to multiple infected sources would make much
difference to the course of disease or the outcome.
It’s hard to see how the dose would vary by more than
10 fold. (Although differences have been seen in lab animal infections with
some viruses, those animals are inbred (genetically similar to respond in the
same way).
386:
What about a massive viral dose inhalation
Under such circumstances the virus receives a massive
jump start, leading to a massive innate immune response, which will struggle to
control the virus to allow time for acquired immunity to kick-in while at the
same time leading to considerable inflammation and a cytokine storm.
For most of us, it’s hard to see how we could receive
such a high dose; it’s going to be a rare event.
In the COVID-19 clinic, the purpose of PPE is to
prevent such large exposures leading to high dose infection. Situations we
should be concerned about are potential high dose exposure of clinical staff
conducting procedures on patients who are not known to be infected.
There is a Chinese description of an early stage
COVID-19 infection of the lung, which only came about because lung cancer
patients (not known to be infected) had lobectemies. There have been
suggestions that such situations contributed to the deaths of medics in Wuhan,
who were conducting normal procedures (including some that could generate
aerosols of infected fluids) before the spread and risk had been appreciated.
388:
What is the link between army and viral load
Prof Wendy Barclay, Action Medical Research Chair
Virology, and Head of Department of Infectious Disease, Imperial College
London, said: “In general with respiratory viruses, the outcome of infection –
whether you get severely ill or only get a mild cold – can sometimes be
determined by how much virus actually got into your body and started the
infection off. It’s all about the size
of the armies on each side of the battle, a very large virus army is difficult
for our immune systems army to fight off.
389:
What is the difference between doctors and patients viral dose
Standing further away from someone when they breathe
or cough out virus likely means fewer virus particles reach you and then you
get infected with a lower dose and get less ill. Doctors who have to get very close to
patients to take samples from them or to intubate them are at higher risk so
need to wear masks.
The fewer people in the room, the less likely it is
than one person is coughing or breathing out infectious virus at any one time,
so mixing with as few people as possible is the safest way.
390:
Can two persons with same covid disease stay in one place
“But there is no evidence for any suggestion that if
everyone in a family is already sick they can they reinfect each other with
more and more virus. In fact for other
viruses once you are infected it’s quite hard to get infected with the same
virus on top.”
391:
What is minimal infective dose
Professor Willem van Schaik, Professor in Microbiology
and Infection at the University of Birmingham, said: “The minimal infective
dose is defined as the lowest number of viral particles that cause an infection
in 50% of individuals (or ‘the average person’). For many bacterial and viral
pathogens we have a general idea of the minimal infective dose but because
SARS-CoV-2 is a new pathogen we lack data. For SARS, the infective dose in
mouse models was only a few hundred viral particles. It thus seems likely that we
need to breathe in something like a few hundred or thousands of SARS-CoV-2
particles to develop symptoms. This would be a relatively low infective dose
and could explain why the virus is spreading relatively efficiently.
392:
What about the crowd
It seems unlikely that people can pick up small
numbers of viruses from others (e.g. in a crowd) and that will tip the
infection over the edge to become symptomatic as that must happen around the
same time.
In the lockdown situation this seems even less likely
as gatherings of more than two individuals are banned.
Because the infectious dose is probably quite low, it
is more likely that you will be infected by a single source rather than from
multiple sources. Transmission can take place through small droplets in the air
(like the ones that are produced after sneezing and which stay in the air for a
few seconds). You can breathe in these droplets or they can land on surfaces.
Unfortunately, SARS-CoV-2 survives reasonably well on most surfaces, so if
somebody touches these and then touches their mouth or nose, there is a very
real risk that they will be infected with the viruses. This is the main reason
why hand washing is promoted as a precautionary measure.
393: Why
does the amount of virus shed matter?
“The inoculum, i.e. the infecting dose of virus is
more likely to lead to infection in the “recipient” the higher the amount of
the virus there is in the excreta.
The virus will survive and remain infectious outside
the body, as viruses do; BUT infectivity will fall away with time. How quickly
this fall occurs is measured as the time taken for virus infectivity to reduce
by half. This is termed ‘half life’ or T1/2 and for this virus is measured in
hours. In fact this is best thought of as ‘rate of decay’.
The rate of decay is fastest on copper with a T1/2
around 1 hour, in air as an aerosol T1/2 is also around 1 hour, cardboard is 3
and 1/2 hours, plastic and steel T1/2 is around 6 hours.
“For example, if one million viruses were placed on
various surfaces it would require 20 half lives to become undetectable and
non-infectious, so 20 hours if in an aerosol, 20 hours on copper, 60-70 hours
on cardboard and finally 120-130 hours on plastic and steel.
“Of course, when one deals with infectivity rather
than detectability, extinguishing infectivity is far quicker. Studies with cultured virus starting at
relatively high levels have shown loss of infectivity within around 12-15 hours
on copper, under 10 hours on cardboard, around 50 hours on steel and 70 hours
on plastic. The data for infectivity in aerosols were not comparable and were
of a different time course.”
394: COVID Care Center (CCC)
· The
COVID Care Centers shall offer care only for cases that have been clinically
assigned as mild or very mild cases or COVID suspect cases.
· The
COVID Care Centers are makeshift facilities. These may be set up in hostels,
hotels, schools, stadiums, lodges etc., both public and private. If need be,
existing quarantine facilities could also be converted into COVID Care Centers.
Functional hospitals like CHCs, etc, which may be handling regular, non-COVID
cases should be designated as COVID Care Centers as a last resort. This is
important as essential non COVID Medical services like those for pregnant
women, newborns etc, are to be maintained.
· Wherever
a COVID Care Center is designated for admitting both the confirmed and the
suspected cases, these facilities must have separate areas for suspected and
confirmed cases with preferably separate entry and exit. Suspect and confirmed
cases must not be allowed to mix under any circumstances.
· As
far as possible, wherever suspect cases are admitted in the COVID Care Center,
preferably individual rooms should be assigned for such cases.
· Every
Dedicated COVID Care Centre must necessarily be mapped to one or more Dedicated
COVID Health Centres and at least one Dedicated COVID Hospital for referral
purpose (details given below).
· Every
Dedicated COVID Care Centre must also have a dedicated Basic Life Support
Ambulance (BLSA) equipped with sufficient oxygen support on 24x7 basis, for
ensuring safe transport of a case to Dedicated higher facilities if the
symptoms progress from mild to moderate or severe.
· The
human resource to man these Care Centre facilities may also be drawn from AYUSH
doctors. Training protocols developed by AIIMS is uploaded on MoHFW website.
Ministry of AYUSH has also carried out training sessions. The State AYUSH
Secretary/ Director should be involved in this deployment. State wise details
of trained AYUSH doctors has been shared with the States. Their work can be
guided by an Allopathic doctor.
395: Dedicated COVID Health Centre (DCHC)
· The
Dedicated COVID Health Centre are hospitals that shall offer care for all cases
that have been clinically assigned as moderate.
· These
should either be a full hospital or a separate block in a hospital with
preferably separate entry\exit/zoning.
· Private
hospitals may also be designated as COVID Dedicated Health Centres.
· Wherever
a Dedicated COVID Health Center is designated for admitting both the confirmed
and the suspect cases with moderate symptoms, these hospitals must have
separate areas for suspect and confirmed cases. Suspect and confirmed cases
must not be allowed to mix under any circumstances.
· These
hospitals would have beds with assured Oxygen support.
· Every
Dedicated COVID Health Centre must necessarily be mapped to one or more
Dedicated COVID Hospitals.
· Every
DCHC must also have a dedicated Basic Life Support Ambulance (BLSA) equipped
with sufficient oxygen support for ensuring safe transport of a case to a
Dedicated COVID Hospital if the symptoms progress from moderate to severe.
396: Dedicated COVID Hospital (DCH)
· The
Dedicated COVID Hospitals are hospitals that shall offer comprehensive care
primarily for those who have been clinically assigned as severe.
· The
Dedicated COVID Hospitals should either be a full hospital or a separate block
in a hospital with preferably separate entry\exit.
· Private
hospitals may also be designated as COVID Dedicated Hospitals.
· These
hospitals would have fully equipped ICUs, Ventilators and beds with assured
Oxygen support.
· These
hospitals will have separate areas for suspect and confirmed cases. Suspect and
confirmed cases should not be allowed to mix under any circumstances.
· The
Dedicated COVID Hospitals would also be referral centers for the Dedicated
COVID Health Centers and the COVID Care Centers.
(Source: Guidance document on appropriate management of
suspect/confirmed cases of COVID-19.
Ministry of Health & Family Welfare, Directorate General of Health
Services, EMR Division, 7th April, 2020)
397: What is Joshua
Santarpia study
The report cited several studies it said supported the idea that
SARS-CoV-2 is airborne. One study (still
in preprint and not yet peer reviewed) by Joshua Santarpia, PhD, and colleagues
at the University of Nebraska Medical Center in Omaha, has gotten a lot of
attention. The researchers collected air and surface samples from 11 rooms of
patients with COVID-19, and found viral RNA in the air both inside and outside
the rooms and on ventilation grates.
398: how safe are
toilets in hospitals
Another study in
preprint looking at hospitals and public areas in Wuhan found that the highest
concentrations of virus were in toilet facilities and in PPE removal rooms. Doffing
of the PPE may potentially have aerosolized the virus, the researchers
hypothesized.
Fineberg and colleagues,
however, approached the finding with caution, stating that "it may be
difficult to re-suspend particles of a respirable size." More likely,
"fomites could be transmitted to hands, mouth, nose, or eyes without
requiring direct respiration into the lungs," they write.
399: What is a covid
puff
The report did not cite a recent overview in
the Journal of the American Medical
Association by Lydia Bourouiba, PhD, of the Massachusetts Institute
of Technology in Cambridge. The report noted that recent research has found
that "exhalations, sneezes, and coughs not only consist of mucosalivary
droplets following short-range semiballistic emission trajectories but,
importantly, are primarily made of a multiphase turbulent gas (a puff) cloud
that entrains ambient air and traps and carries within it clusters of droplets
with a continuum of droplet sizes."
400:
Can smoker covid positive patient shed more viruses ar morer diatsnce
There is no study as yet.
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