There are different ways to assume someone was or is infected: Using
clinical symptoms, antibody tests or virus tests. PHOTO | AFP
Calls for Covid-19 testing are understandable. Many want to
know their status and realise that testing can not only slow
transmission but also help regain some normalcy if used to guide
reopening. And yet, there is widespread confusion around what tests are
available and their benefits. Oftentimes, just because one can get a
test, does not mean one should.
This
is an attempt to answer questions we get asked by people outside and
even within the health field as this is a specialised area and the
literature is not easy to navigate.
Some
facts help: First, Covid-19 symptoms mostly show around five-six days
after infection, but can take as long as two weeks. Second, those
carrying the virus (SARS-CoV-2) can infect others before and after
symptoms show. And lastly, antibodies are produced quite late in
infection — from the second week onwards and well after first symptoms
appear. There are different ways to assume someone was or is infected:
Using clinical symptoms (cough, fever etc.), antibody tests (which
detect the human response to infection) or virus tests (which detect
actual components of the virus circulating in the body).
Using
clinical symptoms is by far the most widespread method used to identify
Covid-19; this approach does not prove but assumes a diagnosis based on
symptoms typical for this disease. The drawbacks of this approach
include missing detecting infection in people with mild or few symptoms —
which could happen in as many as 80 per cent of cases. That said,
people with no or few symptoms are unlikely to consider getting a test
in any case.
Another problem with
detecting the virus through clinical symptoms, is that many
Covid-19-related symptoms are similar to those of other infections,
which means people could be diagnosed as having Covid-19 when in fact
they do not. The benefits, however, include that it’s free — anyone can
use the checklist of questions recommended to identify Covid-19
infections on themselves or others. A further benefit is that those who
use this method learn how to suspect infection in themselves and others
and get advice on steps to take; ranging from self-isolate at home if
symptoms are mild, or contact a doctor if symptoms are more serious or
coupled with additional health problems.
When
people are helped to diagnose themselves and take appropriate actions,
this helps the individual and health workers too. The other diagnostic
tests are in such short supply that very few individuals have had one.
These are tests for antibodies and for the virus.
Some antibody tests are regrettably,
unreliable although standards should improve with time. These usually
use a blood sample and are designed to pick up antibodies that recognise
the virus, but not the virus itself. As antibodies appear relatively
late in someone following infection, a positive antibody test
unfortunately is not much help with limiting infection spreading to
others. Antibody tests also do not predict whether or not someone is
immune, or, if even if they happen to be, how long their immunity might
last.
Until these tests improve,
people needing to be certain if they have been infected, would ideally
get a combination of antibody and/or viral tests. Antibody tests,
however, are useful in providing an indication of the extent of
infection in groups of people or by area; this information can help
guide efforts to relax or enforce lockdown measures and with
anticipating health care needs.
Tests
that detect components of the SARS-CoV-2 virus are definitive and tell
you if someone is infected. These are accurate; although they can fail
to detect those with low, levels of virus. Such tests generally use
nasal swabs, but will likely also soon include saliva, blood and
possibly stool samples, too. Unfortunately, the equipment and training
needs for these tests are sophisticated and costs are high.
When
these tests become more feasible, they will be particularly useful to
limit infection spread as they detect the virus early in infection in
people before symptoms show. Importantly, they also detect infection in
those without symptoms who may never otherwise suspect they are
infected. Finding out who is infected helps identify who should
self-isolate and thereby slow disease spread. These tests could also be
used to protect health workers and the highly vulnerable by reducing
their exposure to people who are infected. The limitation of these tests
is that they only capture whether or not someone has the virus at a
specific point in time. Someone negative today may have been infected
earlier, or may become infected tomorrow.
LATEST OPTIONS
When
tests become more widely available, people should review the latest
options. We recommend beginning with the latest national guidelines and
the World Health Organisation’s information on specific tests. It also
helps to know what to expect. Positive viral results have to be reported
to national authorities as part of global surveillance obligations and
will be coupled with contact tracing, too. Depending on the part of the
world and the contexts, those infected may be quarantined. There will be
many logistics as well as health and other issues to think through
around family and work arrangements. Certainly, no one should be tested
without their consent and pre and post-test counselling could be very
helpful.
Rasheed
is a programme and policy analyst with a medical research/immunology
background. Lalani is a professor working in laboratory and
translational medicine. He is the founding director of the Aga Khan
University Centre for Regenerative Medicine and Stem Cell Research.
Walraven is the director for Health of the Aga Khan Development Network
and general manager of the Aga Khan Health Services.
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