Experts question efficacy of sentinel surveillance study

Data from this exercise is at variance with actual picture

Public health experts have called into question why sentinel surveillance study, which should ideally provide early warning signals and trends about the probable course of COVID-19, has failed to give the State any advantage so far in combating the pandemic.

Three rounds of surveillance study from April-July, which tested exactly 1,18,554 (till July 31), and epidemiological samples later, the data garnered from this exercise is very much at variance with the actual picture of COVID-19 now unfolding in the State, with all districts reporting an average of 200 cases daily.

Sentinel surveillance studies are being done in specific chosen populations who are assessed to be at high risk of contracting COVID-19 in the community.

Between April and July, the test positivity (proportion of people who test positive amongst all tested) recorded by the sentinel survey ranged from 0.10 to 0.59. In June when the case graph of the State had really been climbing, only 38 out of the 17,079 samples from the high risk groups had tested positive. In July, just 205 out of the 35,038 samples tested positive.

“The huge variance in the data emerging out of the sentinel surveillance and the actual situation in the community begs the question whether this surveillance study is serving any purpose. The State’s current testing strategy focuses on testing all influenza like illness (ILI) cases in the community. It is a bit far-fetched that after testing 11,616 ILI samples in June-July, the sentinel survey picked up just 11 COVID-19 cases,” a public health expert said.

He also questioned why the official report of sentinel surveillance Round 3 has omitted the results of the samples tested from one of the groups (Group 6, epidemiological samples collected from community/hospital).

The sentinel surveillance should ideally have been an epidemiological exercise planned and executed at the district-level rather than a centralised plan, he said.

The official report concludes that “it is very evident that cases and positivity are more in clusters, whereas in the general population, the positivity still remains low.”

“Even when the credibility of the entire survey process is under fire, no questions are being raised about possible flaws in study design, implementation or data interpretation because it suits the political narrative that community transmission is not widespread in the State,” a senior epidemiologist said on condition of anonymity.