Is random sampling of tests too random?

When Tamil Nadu received its first big alert of the Covid-19 pandemic in the state with the arrival of a contingent of Tablighi Jamaat (TJ) members from Delhi, the first instruction to district collectors was to test them and their contacts who showed symptoms. The TJ cluster constitutes a substantial number of people tested across the state. Subsequently, the new and expanding clusters in various parts of the state like Chennai, Coimbatore, Chengalpet and Tenkasi defined the new testing protocols in the state. But there seems to be very little method in the random sampling in districts where the number of Covid-19 positive cases is fewer. While Chennai leads in the number of community clusters and samples tested (more than 30,000) and the number of positive cases (1,458), Krishnagiri tested 2,086 samples and found, officially, none (the lone case from Nallur village, was shifted to Salem). There is some disparity in the number of samples tested and the number of positive cases among the various districts with the tests per million population (tpm) varying widely. medium75533358For instance, some northern districts like Chengalpet, Tiruvallur and Ranipet, besides Tenkasi and Erode, have recorded higher positive cases though the number of samples tested is lower. In contrast, districts like Dharmapuri, Perambalur and Tirupattur, where testing rates have been high, the number of positives has been low. Tamil Nadu Health minister C Vijayabaskar said the number of contacts is a criterion. “In some districts, the primary and secondary contacts would be low, so testing too would be low,” he told TOI. "Tamil Nadu has done 15% of the total tests in the country," he said. 75535516While the state government has laid down a testing protocol for district collectors to follow, the number of testing centres and incidence of infection also influence the testing pattern. “We are clocking 400 tests every day,” said Thanjavur collector M Govinda Rao. “After the first Tablighi Jamaat cluster, we were looking for SARI (severe acute respiratory illness) and ILI (Influenza like illness) in containment zones. We are now focused on people who are coming into the district from Koyembedu and other hotspots in Chennai. large75534262The number of testing labs in a district, too, matters. While Chennai has 34 labs and Coimbatore four, some others like Pudukottai have just one lab each. Pudukottai, which has tested around 1,500 samples, has recorded just one case. Trichy, which has one lab, has tested 928 samples and found 51 positive cases. The state’s priority now is frontline workers, including health staff and police besides pregnant women. “To create a method of random sampling outside containment zones, we are testing all pregnant women who get admitted for delivery. We also test anyone with flu or respiratory distress across all hospitals and primary health centres. We are considering testing all cancer patients too,” said Dr G Ramesh Kumar, Coimbatore deputy director of public health. large75534405Initially, the testing protocol was focused on targeted sampling, now the tests are on random samples. “Infectious diseases normally spread in geometric proportion. But Covid-19 has caught us unaware. The lockdown has beaten the geometry. But the infection rate is likely to spike after the lockdown is lifted,” said an ICMR consultant who did not want to be named. He said many cases in India are asymptomatic, and this may add to herd immunity.Krishnagiri trick: Why the green mattersEven as the admission of a 67-year-old Nallur resident of Krishnagiri district, who tested positive for Covid-19 on Saturday, to Salem government hospital set off speculations over the move, the 8,000-odd industrial units, both large and small, in the district are awaiting the directive from the district collector to resume operations from this week.While the admission of the Nallur resident at the Salem hospital has helped Krishnagiri district remain in the green zone, representatives of the industrial units in the region say it will not make a big difference – whether the district remains in green or orange zone -- as far as resuming industrial operations are concerned. However, they said the patient might have been transferred to the neighbouring district due to pressure from large industrial units. Remaining in the green zone helps such units to deploy 50% of workforce, they said. medium75533424“There is no correlation between zones and industries. The district did not have a single patient and this patient, despite being a native of Krishnagiri, is an import from Andhra Pradesh,” district collector S Prabhakar reiterated on Sunday. “The vehicle was intercepted at our district border and hence taken to Salem GH,” said Salem district collector S A Raman. “We are waiting for the directive from our collector to resume industrial activities in the district, especially in the industrial town of Hosur, with several units coming under the limits of the municipal corporation. We cannot take any chances. Hopefully, the directive will come by Monday and after getting the units ready on Tuesday, we can restart operations on Wednesday,” K Ramalingam, president, Hosur Small and Tiny Industries Association (Hostia) told TOI.According to him, the various industrial units in Krishnagiri together employ around four lakh people, with a sizeable number of them being guest workers. “Only if companies like TVS Motor resume operations, the smaller units will start getting new orders,” said Ramalingam. “I don’t think we are in a position to resume work on Monday. There has been no directive yet,” a TVS company official said, on condition of anonymity.“There is a large contingent of guest workers and the state government has hardly done anything to help them. While the administration is asking the respective villages to take care of the guest workers, they are suffering a lot. If at least the units resume operations, it could provide them some respite,” said K A Manoharan, a former Congress MLA .