Why is test data important?
No country knows the total number and traffic of people infected with COVID-19. All we know is the infectious status of those tested. This means that the number of confirmed cases of the disease depends on how many tests actually are in the country. No data available without testing. Testing is our window into the pandemic and how it spreads. Without data on who is infected with the virus, we will not be able to understand the pandemic. Without this data, we cannot know which countries are doing well, and which are simply underreported on cases of illness and death. To interpret any data on confirmed cases, we need to know how many COVID-19 tests each country actually does.
Positive indicator: An important indicator for understanding the pandemic.
A positive score is a good indicator of how adequately countries are testing, as it indicates the level of testing in relation to the size of the outbreak. To be able to properly track and control the spread of the virus, countries with more widespread outbreaks need additional testing. According to criteria published by WHO in May 2020, a positive rate of less than 5% is one indicator that the country’s epidemic is under control. Since limited testing increases the likelihood that many cases will be missed, a positive test can also help us understand the spread of the virus. In countries with high positive rates, the number of confirmed cases is likely to represent only a small fraction of the true number of infections. And if a country rises in positive numbers, it could indicate that the virus is actually spreading faster than the growth seen in confirmed cases.
How many tests are performed each day?
The number of tests is not the same in every country – one difference is that some countries report the number of people tested, while others report the number of tests performed (which can be higher if the same person is tested more than once). And other countries report their test data in a way that makes it unclear exactly what the test counter refers to.
Tests for a confirmed case
Another way to look at the degree of testing versus the scale of the outbreak is to ask: How many tests does a country conduct to identify one case of COVID-19? Countries that conduct very few tests for every confirmed case are unlikely to test extensively enough to identify all cases. WHO has proposed about 10-30 tests per confirmed case as a general criterion for adequate testing.
Different types of tests for COVID-19
There are many technologies for testing COVID-19, some of which are currently available and some are still in development:
- Those that check for a virus to determine if a person is currently infected. The most common way to perform the first test is a PCR (polymerase chain reaction) test. 6 Rapid antigen tests have also become widely used in many countries, especially for mass testing purposes.
- Those that test for antibodies to determine if a person has been infected at some point in the past.
We need to understand what the published testing numbers mean.
Different countries publish their test data according to different definitions. To make meaningful comparisons between countries and over time, the numbers need to be interpreted along with an understanding of these differences. This means that, in addition to the numbers, detailed descriptions are needed to clarify what exactly the numbers mean.
What testing technologies are used?
There are many different technologies for testing COVID-19, some of which have already been implemented, some are currently available but not yet implemented, and some are still in development. It is very important that governments provide a detailed and clear report on the technologies that are being deployed as they are deployed, with appropriate breakdowns of test results. For citizens to trust and understand the published data, and for epidemiologists to use the data in models used in public policy, it is imperative that each country provides test data in a clearly documented form.
Around the world, researchers and policymakers are looking to confirmed cases and deaths to understand and compare the spread of the COVID-19 pandemic. However, data on cases of illness and death can only be interpreted in conjunction with an accurate understanding of the scope and distribution of virus testing.