Haryana’s test positivity rate is low, but it isn’t declining, shows data

Of all samples tested for Covid-19 in Haryana (42,472 in all), just 1.47% are positive (as of May 7), according to government data. This is less than the national

Of all samples tested for Covid-19 in Haryana (42,472 in all), just 1.47% are positive (as of May 7), according to government data. This is less than the national average of about 3.9%. Officials said this indicates that the spread of Covid-19 in Haryana has slowed, thanks to the lockdown and public health interventions.

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To support this claim, officials referred to a metric known as ‘Covid-19 positive rate’, a cumulative rate that has featured in the state’s daily epidemic bulletin since April 22. At the time, only 250 out of 13,647 tested samples (or 1.83%, the Covid-19 positive rate) came back positive. Despite testing numbers having increased since then, this rate has declined. As of Thursday, Haryana had conducted close to 42,500 tests, yielding 611 positive cases.

Public health experts have, however, cautioned against using this metric to infer the severity of its outbreak. They said positivity rates are valuable only when compared on a daily basis, unlike the cumulative figure presented by the state.

Experts pointed out that when analysed daily, Haryana’s positivity rate has not been declining.

WHAT IS TEST POSITIVITY RATE (TPR)?

A senior official in Haryana’s Integrated Disease Surveillance Program (IDSP), seeking anonymity, explained, “Covid-19 positive rate is the same as ‘test positivity rate’, or TPR. A decreasing TPR could indicate that the prevalence of Covid-19 in Haryana is lower, in comparison to other states which have a higher TPR, like Delhi.”

This view was seconded by Dr. Dhruv Chaudhury, a nodal officer for Covid-19 at PGIMS Rohtak, one of the state’s accredited testing labs. Haryana’s lower TPR becomes all the more significant, he said, given that testing numbers have grown along with the widening of testing criteria.

“Since March 14, Haryana has focused on testing only high-risk subjects, such as people in confirmed contact with Covid-19 patients, health workers, and residents in containment zones. This is known as public health testing. However, we have also started doing ‘health care testing’, where the focus is on patients hospitalised with symptoms of severe acute respiratory infection (SARI) or influenza-like illnesses (ILI). So we are testing more high-risk subjects, while the percentage of them testing positive is decreasing,” Chaudhury added.

Dr. Ram Prakash, district epidemiologist, Gurugram, said, “Going by the TPR, we assume that the prevalence of Covid-19 in Haryana is not as serious as it is in some other states.”

HOW SHOULD TPR BE CALCULATED?

Other experts, on the other hand, cautioned against this ‘narrow interpretation’ of data.

Dr. Rajib Dasgupta, a public health expert at the Centre of Social Medicine and Community Health, Jawaharlal Nehru University, said, “The trend of infected cases is a function of the number of people tested, and this trend must be compared daily. A cumulative total is akin to a cricket team’s score, say at the fall of the sixth wicket. This doesn’t tell us how each wicket partnership scored.”

For example, when calculated on a daily basis—i.e. the percentage of new positive cases among new tests conducted—Haryana’s TPR on May 4 was 3.76% (the highest since testing numbers were ramped up in mid-April), as opposed to the 1.48% net positive rate mentioned in the state bulletin. On May 6, the state bulletin showed a cumulative TPR of 1.52%, which doesn’t reveal that 3.5% of new samples tested that day came back positive. “Haryana’s test positivity rate is relatively low, but it has not been declining as the official state bulletin seems to suggest,” Dasgupta said.

Responding to this, Rajeev Arora, additional chief secretary (health), Haryana, said, “Even the government of India is calculating test positivity ratio this way (using cumulative numbers). However, we are also calculating the TPR daily, and it is still quite low in percentage terms,” Arora said.

WHAT DOES A LOWER TPR MEAN?

According to Dr Prabhakaran Dorairaj, epidemiologist and vice president of research and policy at the Public Health Foundation of India (PHFI), a low TPR is desirable when accompanied by an increase in testing, especially in healthcare testing. “If this is the case in Haryana, then it may be a good sign,” he said.

However, Dorairaj and other experts repeatedly emphasised that Haryana’s low TPR should not be taken as an indicator of the prevalence of Covid-19 among the population, given that many asymptomatic/mildly symptomatic cases are going undetected. In fact, a low TPR could also mean that tests are not being administered widely enough.

“A low TPR could indicate a decreased transmission of the virus, or it could mean that you are testing the wrong people,” T Jacob John, a virologist and former chief of the Indian Council for Medical Research (ICMR), said.

If a state is testing subjects only through contact tracing, and finding an overwhelming majority of them to be negative, the subjects are not “truly real contacts”, John explained, advocating for an increase in health care testing over contact tracing. “Efficiency requires finding a higher percentage of positive cases. That means: increase health care testing and decrease in public health testing,” he added.

Dasgupta echoed this view, saying, “TPR in the context of Covid-19 cannot tell us how severe the outbreak is. For that, one might look at the disease’s prevalence or mortality rates. But TPR can tell us a lot about the quality and strategy of public health surveillance. The daily test positivity rate for Haryana remained stable throughout mid-April, but has now begun showing increases. So the picture could look very different two weeks down the line.”

BOX:

1. The government data shows the test positivity rate (TPR) in Haryana has declined despite an increase in testing (1.48% on May 4, as opposed to 1.63% on April 22), leading them to believe that the spread of the coronavirus disease (Covid-19) is declining in the state

2. However, experts say that the government is using the cumulative number of administered tests to calculate the TPR, whereas the TPR must be calculated based on the number of daily tests. When calculated in this manner, the TPR in Haryana is found to have actually increased (3.76% on May 4, as opposed to 0.78% on April 22)

3. Experts also emphasise that Haryana’s low TPR should not be taken as an indicator of the prevalence of Covid-19 among the population, given that many asymptomatic/mildly symptomatic cases are going undetected. In fact, a low TPR could also mean that tests are not being administered widely enough.

4. According to experts, just the TPR cannot tell us how severe the outbreak is. For that, one must look at the disease’s prevalence or mortality rates.

TEST POSITIVITY RATE IN HARYANA

(CUMULATIVE, AS PER STATE BULLETIN, SHOWS DECLINE)

Apr 22: 1.63%

Apr 23: 1.54%

Apr 24: 1.51%

Apr 25: 1.44%

Apr 26: 1.37%

Apr 27: 1.29%

Apr 28: 1.20%

Apr 29: 1.24%

Apr 30: 1.29%

May 1: 1.27%

May 2: 1.25%

May 3: 1.34

May 4: 1.48%

May 5: 1.47%

May 6: 1.52%

May 7: 1.47%

TEST POSITIVITY RATE IN HARYANA

(ANALYSED DAILY, SHOWS VARIATION)

Apr 22: 0.78%

Apr 23: 0.29 %

Apr 24: 0.42 %

Apr 25: 1.04%

Apr 26: 0.62%

Apr 27: 0.34%

Apr 28: 0.37%

Apr 29: 0.17%

Apr 30: 1.76%

May 1: 0.96%

May 2: 0.95%

May 3: 2.28%

May 4: 3.76% [largest single day jump, 75 new cases]

May 5: 1.08%

May 6: 3.55%

May 7: 0.94%