Labs in quality control mode as positivity is in decimals

Nagpur: The unprecedented decline in test positivity rate at five public labs here has left officials baffled. As a large number of samples tested negative in the last two days, some of them started placing a known positive sample in the testing plate to ascertain if the PCR machines were working properly.
On Wednesday, none of the AIIMS, GMCH, IGGMCH, Neeri and RTMNU Covid testing labs reported more than five positive cases.
On Thursday, the highest number of samples processed were 1,198 by AIIMS. Of these, there were just 10 positive cases at the rate of 0.83%. Neeri had none positive from 93 samples, RTMNU had 8 from 323, IGGMCH 16 from 1057 and GMCH 36 from 1182 samples.
Lab officials said no positive case was detected from the samples processed till Thursday afternoon. These would be reported on Friday.
The first three labs processed over 1000-1200 samples and found 1, 2, 3, respectively, positive cases on Wednesday.
All the labs told TOI that the positive case numbers were incomplete yet they were under 15 from the same sample size. Civil surgeon Dr Devendra Paturkar didn’t respond to TOI’s queries regarding the data.
As cases began to spike, these labs were recording test positivity rate between 12% and 19% in mid-February. The percentage touched 52% during second wave peak and gradually started declining. However, in the last few days, the percentage plummeted below zero leaving lab officials perplexed.
An official from IGGMCH said such steep decline wasn’t reported before. “We had to cross check the result by inserting a known positive sample among the 94 samples in the plate. The known sample is from earlier testing and preserved for study. Our doubts were allayed only after the same sample tested positive while the rest were negative," the official said.
Dr Meena Mishra, professor and head of department of microbiology at AIIMS, said there is nothing to worry if large number of samples are testing negative. “At AIIMS, as part of quality control, we put one positive control, one negative control, and one positive sample of a day before. If labs are following this mechanism, I think there is nothing to worry,” she said.
Dr Mishra added the concentrated efforts for contact tracing, maximum number of samples processed by government and private labs have contributed in early detection, and timely intervention that has helped in the decline in positivity to a large extent.
“Movement relaxation in restricted phase is a good idea. The unlocking is happening after a good achievement. I don’t think we need to apprehend any resurgence if we continue to follow safety norms. Experts have also opined that the third wave may not be as severe as this one,” she said.