Covid-19: where does testing help?

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Many want to know their status and realise that ‘testing’ cannot only slow transmission but also help regain some normality if used to guide ‘reopening’.  — AFP/File
Many want to know their status and realise that ‘testing’ cannot only slow transmission but also help regain some normality if used to guide ‘reopening’. — AFP/File

CALLS for ‘testing’ are understandable. Many want to know their status and realise that ‘testing’ cannot only slow transmission but also help regain some normality if used to guide ‘reopening’. And yet, there is widespread confusion around what tests are available and their benefits.

Just because one can get a test, it does not mean one should invariably go for it.

This is an attempt to answer questions we are asked by people outside and even within the health sector 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 to 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 after infection --- from the second week onwards and well after the 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 inability to detect infection among people with mild or few symptoms. This could happen in as many as 80 per cent of the 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 as well as others and get advice on steps to take; ranging from self-isolation 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 action, 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 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, 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 or not, would ideally get a combination of antibody and viral tests (see below).

Antibody tests, however, are useful in providing an indication of the extent of infection among groups of people or by area; this information can help guide efforts to relax or enforce lockdown measures and with anticipating healthcare needs.

Tests that detect components of the SARS-CoV-2 virus are definitive and tell you if someone is infected. Although they can fail to detect those with low levels of virus, they are nevertheless accurate.

Such tests generally use nasal swabs, but will likely 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 at an early stage and before symptoms show.

Importantly, they also detect infection in those who are without symptoms and who might 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.

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.

Fawzia Rasheed is a policy analyst and has oversight responsibilities for health and development operations across Asia and Africa. A professor, El-Nasir Lalani is the founding director of the Aga Khan University Centre for Regenerative Medicine. Gijs Walraven is the director for health of the Aga Khan Development Network. He has authored `Health and Poverty: Global Health Problems and Solutions’

Published in Dawn, June 15th, 2020