by
Les May
IF WE are going to eliminate
the virus which causes Covid 19 the only way to do it is to break the
chain of transmission from one person to another. One effective way
of doing this is to interview every
infected person to find out who they have been in contact with,
trace all
the people named, contact them and determine if they are showing
signs of infection. If they are, they too
must be interviewed to
determine their contacts, and so on. If they are not showing signs
of infection they would be advised to ‘self
isolate’, a.k.a.
‘go into
quarantine’, and
monitored daily.
If they show symptoms during this period the business of contact
tracing must start all over again.
The
process of investigating identified cases and tracing contacts is
well shown
on the website of the
US Center
for Disease Control
website, but the basic procedure is applicable to any public health
system.
A
more detailed explanation is given at:
This
is what I call the ‘shoe leather’ approach to contact tracing.
It has both advantages and disadvantages. Its major advantages are
that it is ‘low tech’, a
pencil and notebook is all that is needed, proactive
in the sense that it is a public health initiative and does not rely
on the infected person to initiate it, and it is infinitely
adaptable, because the contact tracer can prompt the interviewee if
necessary.
Its
disadvantages are, it requires trained people to carry out the
interviews, hence it is expensive and difficult to implement if the
number of infections is high, it is relatively slow, the infected
person may not remember all their contacts or fail to mention, for
example, that they stood at a bus stop with other people.
It
is in order to mitigate these disadvantages that technological
solutions to the problem of contact tracing have been proposed.
These necessarily involve smartphones. At
which point one disadvantage of this approach becomes apparent, not
everyone owns, or
want to own,
a smartphone. Nor
would every smartphone owner want to allow it to be used in this way.
This
is not fatal to the enterprise; it only requires that about 60-70% of
a
population can or will allow this.
One
of the things which may make people reluctant to allow their
smartphone to be used for contact tracing is a concern for their
personal privacy. There are however a number of points which people
who have these concerns might like to consider. ‘Shoe
leather’
contact tracing also carries risks to personal privacy, remember
the pencil and notebook.
Owning and carrying a smartphone poses even greater privacy
risks.
Users may not switch off, or know how to switch off, the GPS
location
facility
on their phone. Even
if they do, smartphones regularly ‘ping’
nearby mobile phone masts. Both these can be used to obtain location
data for a mobile phone owner. Both
may be misused
for surveillance of individuals, but locations are too crude for
contact tracing.
So
called contact tracing ‘apps’
make use of Bluetooth
hardware which is available on most smartphones. This signal
is of much
lower
power which restricts the detection range
to other
smartphones in
the immediate vicinity, hence the term ‘proximity
tracing’.
Proximity
tracing applications send to, and collect from, other smartphones in
the vicinity very short ‘nonsense’
messages which
act as an identifier of the phone.
These
are changed frequently to prevent tracking by a third party. This
exchange only happens if the phones, and hence their owners, are
sufficiently close, say less than 2 metres, for a sufficient length
of time. This
assessment is carried out by the ‘app’,
not the phone owner, and
the
identifier of the nearby phone is then
logged.
It
is in measuring the strength of the Bluetooth signal and hence
estimating the distance between phones and their owners, that ‘apps’
seem to run into trouble.
At
this point all the logged data is on the user’s phone. To be
useful in alerting other
smartphone
users that they have been close enough, for long enough, to an
infected individual to be considered a contact, some means must be
found for bringing all logged identifiers together and alerting
potential contacts. It is at this point that the potential for
surveillance comes into play again.
The
extreme surveillance by the state in China
is well known, but other countries have implemented systems where
there is a high risk of exposure to surveillance. The TraceTogether
application used in Singapore
requires
users to share their contacts
information with
the authority
which
keeps
a database that links
identifiers to contact information.
When
a user tests positive, their phone
sends
all the identifiers it has logged
over the past two weeks.
The
authority looks up the
identifiers in its database, and contacts
by phone or e-mail the people who
may have been exposed to
infection.
This
places a lot of information in the hands of the government.
For
the potential for misuse of centralised information see:
For
the potential misuse in some other countries see;
Apple
and Google’s
proposal is a more decentralised system which uses a database
accessible to the public.
When
a user tests positive, they can upload their private identifiers
to
that public database.
The
database can
be hosted
by a health authority or on a peer-to-peer network; as long as
everyone can access it, the contact tracing system functions
effectively.
Peer
to peer networks do not have a centralised server. All users are
equally privileged.
How
the decentralised system works is here:
If
I used a smartphone I would probably find this system acceptable from
the privacy point of view if
the code were ‘open
source’
which would allow thousands of pairs of eyes all over the world to
check it for potential privacy violations.
So
far as I can ascertain the system which was
proposed initially
would
be
used in the UK was
in the second rank so far as privacy is concerned; better than many,
but still leaving something to be desired. Now
it seems to have been dropped altogether in favour of one using the
applications interface (appi)
proposed by Apple and Google, but
will it be ‘open
source’?
The
downside of relying on technology to alert us to something
that has already happened
to us is that we will be lulled into a false sense of security about
our present
behaviour. Rather
like the man who fell off the Empire State Building and as he passed
each window shouted “So
far so good”.
Meeting
as few people outside our own household and keeping at least two
metres away from those we do meet is still the best way of reducing
transmission and eliminating the virus.
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