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Coronavirus Cases in India: What is Test Positivity Rate and Why is It Important?

Jun 24, 2020 11:54 AM 5 min read

As the number of coronavirus cases in India surges, we may want to ask ourselves: How do you reliably measure the severity of the COVID-19 pandemic in a country?

One option is by testing more and more people every day. We all know that “test, trace, isolate” is the most sure-shot way (aside from social distancing, face masks and keeping your hands clean) of controlling the pandemic until a vaccine is available.

But the number of tests can be an insufficient metric when it comes to large and diverse countries like India, where the extent of infection varies widely between cities, states and regions. The same goes for tests per million, which no doubt needs to be on the higher end, but may not shed enough light on the extent of the epidemic in a particular place.

Which brings us to Test Positivity Rate (TPR). This is the number of tests out of 100 (i.e., the percentage of tests conducted) that test positive for coronavirus. It measures the scale of the outbreak and indicates whether sufficient testing is being done, which is what makes it an important metric.

How Does Test Positivity Rate Work?

There’s more to TPR than meets the eye. Let’s look at Delhi. It is one of the worst-affected cities in India, with over 62,000 confirmed cases as of June 23rd. In the first two weeks of June, Delhi reported a TPR of nearly 30%. This sounds alarming, because you may assume from this that, on average, nearly one in every three people in Delhi is COVID-positive!

But the reality is more nuanced than that. TPR is dependent on how many are tested and, more importantly, who is tested.


The Two Ways to Test

India’s testing capacity is limited (meaning: there aren’t enough testing kits for everybody), so not everybody is tested. Tests are usually reserved for those who show COVID-19 symptoms (i.e., are symptomatic) or those with a higher risk of contracting the disease. This is reactive testing.

But countries like South Korea and Taiwan, which have successfully curbed their epidemics while avoiding a broad lockdown, did something different. They tested serious cases as well as those with milder symptoms + those without any symptoms. This allowed them to trace and isolate more positive cases so that those who tested negative could safely continue going to work. This is proactive testing.

Naturally, if you test mainly those more likely to have COVID-19 (either due to travel history, pre-existing conditions or contact with other positive cases), the positivity rate will be higher.


Why Proactive Testing is Crucial

Symptomatic cases are no doubt a danger, but they are relatively easy to test, trace and isolate so that they don’t spread the virus to others.

The real danger lies in the asymptomatic cases: those who have contracted the virus but don’t show any obvious symptoms. These cases may spread the infection far and wide before getting tested - if at all. This is particularly worrisome as India reopens after a long lockdown, increasing the risks of more infection.

Thus, it becomes imperative to not only test those vulnerable to the virus but also the general population - i.e. keep your testing criteria broad and test as many people as possible. And what happens when you test more people, even those who probably may not have the virus? The positivity rate automatically drops.


Here’s an Example to Explain TPR

Consider New York. In early April, the US state was conducting around 20,000 tests per day and its positivity rate was a staggering 50%. This didn’t mean half of all New Yorkers were infected but that testing was severely restricted to those likely to have COVID-19 (healthcare workers and patients requiring hospitalisation).

Now, however, the policy has changed to mass-testing. Upward of 50,000 tests per day are conducted in New York and positivity is less than 2%, a more realistic number and an indicator that enough tests are being conducted. Meanwhile, case numbers in the state have fallen considerably since April from a peak of more than 10,000 cases per day to around 600-700 per day.

Casting a wider net and testing those with milder symptoms or with no symptoms at all allows health officials to get one step ahead of the coronavirus. It enables the infection chain to be cut early before it can spread far and wide. Basically, lower TPR = good; higher TPR = we’re not doing enough.


What’s the Ideal Test Positivity Rate?

The World Health Organisation (WHO) has recommended a positivity rate of less than 5% for two weeks for allowing social restrictions to be gradually relaxed.


What is India’s Test Positivity Rate?

India’s TPR was 8% as of June 18th - well above WHO-recommended levels - and it has been consistently rising. But the data is complicated. Only a handful of states account for most of the increase in TPR since Unlock 1.0 - Delhi, Maharashtra, Tamil Nadu, Karnataka and Haryana, whose positivity rates more than doubled in recent weeks.

The overall picture is still worrisome. As of June 23rd, TPR in 12 states and Union Territories (UTs) is above 5%, with Maharashtra, Delhi and Telangana reporting rates above 20%.

Obviously, not enough people are being tested. And curbing TPR is imperative to control the epidemic.


What’s India’s Testing Capacity?

India’s testing policy is all-encompassing (i.e. It includes testing asymptomatic cases). But TPR continues to rise. This may indicate a spread of the epidemic as well as low testing rates.

To keep TPR low, experts say the country’s testing capacity has to be increased by a factor of 10. It is recommended that India conduct 1m tests daily. That number presently is around 1.5L. So, obviously, there’s a lot of work to be done.

Ramping up testing infrastructure will be the key to mass-testing across states and UTs, the best way to fight the virus. This would automatically bring down positivity rates and encourage businesses and offices to reopen with some degree of confidence and security.

One way to bring down TPR is by testing everybody: anybody who wants to get tested, symptomatic or not, can get tested whenever they want to. This would be ideal, but testing infrastructure is too limited for this to be realised.

Another route authorities could take is via proactive contact tracing: scale up testing and also contact everyone who has been in contact with positive cases of late and ask them to get tested or self-isolate. This is more doable, and indeed it’s what governments around the world, including India’s, have resorted to.

Whether these efforts will suffice remains to be seen. As of today at least, India’s COVID-19 peak still seems to be weeks away.

But if you’re looking for signs that the COVID-19 pandemic in India is finally losing steam, keep an eye on Test Positivity Rate. Until then, we’re going to have to get used to the fact that things are going to get worse before they get better.


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