DH Deciphers | How will serosurvey help in Karnataka's fight against Covid?

The consensus among experts is that the survey is necessary because of the need to discover the extent of community transmission

For some time now, the state government has been considering conducting a sentinel survey to help evaluate earlier estimates of how many Covid-19 cases can be expected in the future while determining if there were any unknown sources of transmission. The survey (also known as a serosurvey) is a key tool used by epidemiologists to determine the prevalence of a disease in a population.

It will help determine how much of the target population has generated antibodies, which is an indicator of how many people had contracted the disease at some point. A similar survey conducted in Delhi last month discovered that 23% of the residents had antibodies for Covid-19.

The final results of that survey are expected soon. In Karnataka, the State Covid Task Force had proposed a pilot sentinel survey in Bengaluru and Udupi in June. Although the survey was supposed to start on July 15, it appears to have stalled. Why is this kind of survey so important and why has it not gone into effect so far?

Why do we need a serosurvey in Karnataka?

The consensus among several experts and officials is that the survey is necessary because of the need to discover the extent of the community transmission of Covid-19 in the state. In Karnataka, according to the proposal made by an expert committee, the survey is to cover specific sample sizes across three categories: high-risk, moderate-risk and low-risk groups. Following the conclusion of the pilot programme (if it ever gets started) in Bengaluru and Udupi, the plan is to expand it to the whole state.

What goes into the survey and where will it be carried out?

The primary focus of sentinel surveys is their employment in "reporting sites", in this case, hospitals, explained noted epidemiologist, Dr Giridhar Babu, who was involved in proposing the survey to the government. "Once the hospitals are recruited, whoever comes to the hospital will be asked if they are willing to be part of the study. Upon informed consent, they will be made a part of the study," he said. Also considered will be an external "moderate-risk group” made up of various occupations outside the hospital setting, with a high chance of contact with other humans. These are people such as vegetable vendors, BMTC drivers and conductors.

Is the sentinel or serosurvey the same thing as a sentinel or a sero-surveillance?

While these terms are sometimes used interchangeably by the media and people, they are not the same, according to Dr Babu. For one, the survey which has been proposed will be limited to three rounds, but a surveillance indicates that it is always happening.

What are the specific professions that will fall under the testing criteria?

Some 20 occupations make up the three "risk" categories, including bus conductors and auto drivers, vendors at vegetable markets, healthcare workers such as doctors, opticians, laboratory technicians, radiographers, attendants at hospitals, veterinarians, medical practitioners, ambulance staff, paramedics, auxiliary nurse midwives, ASHA workers, nurses, pharmacists and hospital receptionists. Other professions include those employed in markets, malls, retail stores, bus stops, railway stations, pourakarmikas and other waste collectors. Individuals living in containment zones are also included.

What sort of testing will be carried out during the survey?

The survey involves using a special antibody test (not to be confused with the Rapid Antigen Test kits) to test the blood serum (sero means relating to serum) of individuals to check for the prevalence of antibodies against the coronavirus infection. According to the experts, the proposal is to procure 16,000 such kits to kick-start the pilot survey.

So what is the problem? Why hasn't testing begun yet?

Well, for one, the antibody test kits have not been procured. The government appears to be hesitant to invest the Rs 59 lakh needed to procure the initial batch of 16,000 antibody kits.