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| Edgar Alan Poe’s horror story, “the Masque of the Red Death”, is about a superspreader who spreads a contagion in an hour to an entire national aristocracy who thought they had escaped a deadly plague by holing up in a castle and partying. |
SUPERSPREADERS: How epidemics get started
SUMMARY:
As superspreaders create 80 per cent of the cases
in the early stages of epidemics, it is critical to be able
to locate them and curtail the numbers they unwittingly infect. Yet very little is known about
them, and no strategy seems to have been expressly tailored toward them.
The paper describes several key superspreader examples in SARS-2
and MERS coronavirus epidemics in Korea, adding to two other examples we have discussed.
Introduction
Epidemiology talks about epidemics as if they proceeded in a
constant expansion from their beginning according to R0 - the average
number of persons infected by a single person. But while R0 appears
through the law of averages once the epidemic gets rolling, the early
stages of an epidemic are not smooth at all, but lumpy. The survival or the
rapid expansion of an infective agent seems to depend not on one person infecting
two or three others, but on a few very active individuals infecting up to 60 others
in a short space of time.
According to what has become known as the ‘twenty-eighty
rule’ a small core group will do most of the infecting. It is not known why. As
early superspreading happens under the radar, infections from these patients can be
instrumental in allowing a virus to proliferate to the point it cannot
be stopped, before the first case is even noticed. It seems quite likely that without superspreaders, an epidemic would never get started, everyone would have time to detect and isolate.
Superspreading also speeds up the progress of the disease, when things would otherwise be very slow. W showed in an example that in 65 days, the numbers infected from COVID-19 would be four times as many (40 million) with a few superspreaders at the beginning than the disease slowly emerged according to R0.
Superspreading also speeds up the progress of the disease, when things would otherwise be very slow. W showed in an example that in 65 days, the numbers infected from COVID-19 would be four times as many (40 million) with a few superspreaders at the beginning than the disease slowly emerged according to R0.
Rules against mass gatherings during epidemics are aimed
largely at superspreaders. Coronaviruses seem to be particularly prone to
superspreading, along with typhoid, ebola and measles – which are some of the
most infectious diseases known.
We have already mentioned several examples of COVID-19
superspreaders in the USA.
The third British COVID-19 case, a man in his 50s who
attended a conference in Singapore was probably infected by a conference
attendee from Wuhan along with a number of others present, and went on to
infect eleven more people in a Swiss chalet.
A superspreader in South Korea infected
37 people at her church and possibly 52 more. She attended four services while ill
and refused to be tested. This church cluster turned out to be the most
difficult to eradicate in South Korea.
“We are deeply sorry that because of one of our members, who
thought of her condition as a cold because she had not traveled abroad, led to
many in our church being infected and thereby caused concern to the local
community," officials of the Shincheonji church said.
Middle East Respiratory Syndrome (MERS)
The dangerous coronavirus MERS is normally transmitted only
from camels to humans in the Middle East, or in a hospital care setting.
Because its progress occurs under clinical observation, the details of MERS spread are readily available.
The original case of MERS in Korea was a 68-year-old who ran
a commercial greenhouse business in Bahrain. He undertook a 10-day business
trip to Arabia and returned on 4 May 2015. On 15 May, after four days of
worsening illness, he was hospitalised with pneumonia at a regional hospital, and
after two days was moved to SMC in Seoul, where MERS was confirmed on 20 May.
A chain of 186 ‘nosocomial’ (hospital) transmissions began,
to 12 hospitals, four clinics and two ambulances, as patients were moved around.
145 of these transmissions were to other patients and visitors, but the other 40 were to hospital
employees, ranging from doctors and nurses to ambulance attendants, security
guards and IT workers. From the original index case 28 were infected, and then
130 in the next generation.
Most of the transmissions from Patient Zero occurred during the
two days he was at the regional hospital, when he was superspreading. None of the
infected shared a ward with Patient Zero, and it appears that some sort of long-range
airborne route was to blame.
A second superspreader was responsible for the second
generation spreads at SMC. He attended the ER on 27 May with pneumonia, eleven
days after being exposed to Patient zero. In a 58-hour stay at ER before being transferred to isolation,
some 675 patients, 683 visitors and 218 hospital staff were exposed. Of
these, 82 were soon confirmed with MERS.
Can superspreaders be identified?
The MERS cases did their superspreading during a few days in
ER in unprepared hospitals. They were already suffering from pneumonia. It was
not clear if they stopped superspreading because their infectivity subsided or because
they were removed to isolation facilities.
Compared with non-spreaders, the MERS superspreaders had:
- Higher temperature
- Chest infiltrates in more than three lung zones
- Somewhat higher viral counts
- More visitors
Conclusions
The traced examples are for a different but related disease MERS, which is considerably more deadly than SARS-2 but for some reason only superspreads in a hospital environment. Probably the difference is that it superspreads only from the very ill, whereas SARS-2 superspreads from the moderately ill. We do not yet know if SARS-2 spreads from the symptomless, as typhoid may.
There are many similarities. For all coronavirus epidemics, cluster sizes of 150 are not unexpected, originating in a single patient. In the early stages of an epidemic, the superspreaders are the most important to identify and isolate. This is not so easy as superspreading takes place ’under the radar’ so it is not known if the virus takes on a particular form at this time when it is more infectious.
There are many similarities. For all coronavirus epidemics, cluster sizes of 150 are not unexpected, originating in a single patient. In the early stages of an epidemic, the superspreaders are the most important to identify and isolate. This is not so easy as superspreading takes place ’under the radar’ so it is not known if the virus takes on a particular form at this time when it is more infectious.
Nor can any particular behaviour be associated with
superspreading, except the patients are ‘a bit more sick’. There appears to be no way to identify
superspreaders in advance.
Given that superspreading seems to occur in circumstances of
crowding and complete unpreparedness, social distancing in public and personal protection
equipment and isolation in hospitals and care facilities is probably effective against it.
The expectation for coronavirus superspreading
in less-affluent countries and poorer, more crowded and less prepared areas is high if coronavirus does become
established there, though so far this has not been the case.
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