Karnataka's Covid-19 survey may not yield true picture

A sentinel survey to gauge the prevalence of Covid-19 infection among people and take measures to prevent its spread is set to begin in Karnataka. But the exercise has been designed in such a way that its findings may be too broad and diluted.

The survey was approved by the government on August 20 but has been delayed due to a change in the nodal officer for the programme and a hold-up in the completion of a new mobile application by the National Informatics Centre (NIC).

While cities like Pune and Mumbai covered several heavily infected wards, Karnataka’s survey, set to start this week, will test high-risk zones across the state, including eight zones of the BBMP. Initially, it was only limited to Bengaluru Urban and Udupi.

For latest updates and live news on coronavirus, click here

In Mumbai’s sentinel survey, for example, 6,936 people living in slums and non-slums, across just three wards, were tested.

This yielded 57% of those in slums and 16% of those in non-slums showing that they had antibodies.

Officials declined to say how many tests would be done, although a source said the aim is to test a sample size of 432 people per 38 units per round. These “units” include all 30 districts of Karnataka and 8 zones of the BBMP. There are three rounds in total. That means, in Bengaluru, as many as 3,465 tests per round could be done.

There are 20 categories of high-risk people, mainly bus conductors, auto drivers, vegetable market vendors, healthcare workers, Asha workers, containment zone residents and pourakarmikas. Another focus is people who visit approximately 400 statewide hospitals for other medical issues, such as pregnant women.

Nevertheless, according to a source, transport workers, medical staff will be the focus because there are not enough staff to conduct a dense street-by-street survey of the type conducted at Mumbai.

Officials told DH that the point of the survey was to try to gauge the level of immunoglobulin G (IgG) antibodies within a sample population, which would indicate how many people had recovered from Covid-19 in the past, while revealing how many potential Covid-19 cases had been missed.

Noted virologist Dr T Jacob John, who designed Pune’s sentinel survey, which focused on several highly-infected areas, said that the central point of such a survey is to be able to project the findings on the larger population. “For example, by surveying transport workers, we can only make a projection and see how many missed cases there might be among the transport worker community,” he said.

He added that the scale of the exercise could potentially limit how much of the findings can be projected.

Dr Aurnab Ghose of Indian Institute of Science Education and Research (IISER), who was involved in the Pune survey told DH: “A study of high-risk professionals may be a good way to assess disease prevalence using these individuals as sentinels.”