High exposure to virus in urban areas
NEW DELHI: Sero surveys conducted by the states to determine the extent of exposure to the Sarscov-2 virus that causes the coronavirus disease (Covid-19) have detected high antibody positivity rates among the population in cities such as Mumbai and Delhi and low rates in primarily rural states such as Bihar, Jharkhand and Chhattisgarh. The findings are good news for the cities because the high positivity rates signal a lower risk of reinfection, and conversely, they should worry the states in the hinterland where cases are beginning to spike.
In Mumbai, the positivity rate was 57% in three slums; it was 0.7% in six districts of Bihar and 0.5% in three districts of Chhattisgarh, according to state government officials.
Sero surveys are being conducted in select districts by the Indian Council for Medical Research (ICMR) and state governments to detect how many people have developed immunoglobulin (IGG) antibodies to the coronavirus disease and to gauge the extent of infection through random sampling.
Experts said a low sample size could be a reason for under and overestimation of the prevalence of antibodies. Higher antibody positivity rates indicate a lower possibility of reinfection. Lower rates shows that the possibility of Covid-19 spread is still high.
Delhi and Mumbai, the two major cities to have completed the sero surveys, have shown different results. While in Mumbai, 57% of the persons surveyed in three slums showed IGG antibodies, in Delhi it was 23.48%. To be sure, the Delhi survey was more comprehensive.
Delhi has conducted a second survey the results of which are expected in the coming week.
Of the total sample size of 6,936 persons, 4,232 were tested in the slums and 2,702 in non-slum residential areas. While in the slums, 57% of the individuals surveyed had once been infected with Covid-19, the proportion was only 16% in non-slum residential areas, the findings showed.
BIHAR, CHHATTISGARH, ODISHA
Bihar performed its first sero survey in six districts, each having a sample size of 400, between May 17 and May 20, when the number of Covid cases in the state was not high because of the low testing ratio of 1,500 per million population.
In Chhattisgarh, the survey was conducted in Bijapur, Kabirdham and Surguja districts in July with a sample size of about 400 people in each district. The results showed that the antibody positivity rate was 0.5%, which a health department official said could be because of a large number of false negatives.
In Odisha, the sero survey conducted in the Covid hotspot district of Ganjam found that 31% of 2,830 people tested had developed antibodies and in Bhubaneswar, it was 1.4% of the 951 tested.
NOT A HAPPY SITUATION
The Kerala health department started a sero survey with the help of the ICMR in three districts, Ernakulam, Thrissur and Palakkad, from the last week of May, but the results have not been declared as the findings are not as encouraging as Delhi’s, said a state health official.
State health minister KK Shailaja has warned that the daily cases may cross 15,000 by September from 45,000 now.
In Telangana, where the sero survey was conducted by the central government’s National Institute of Nutrition on May 30 and 31 with sample sizes of 600 in each of three districts (Jangaon, Kamareddy and Nalgonda), state health minister Eatala Rajender claimed the survey showed no community transmission. In other states such as Punjab, Madhya Pradesh and Haryana, sero surveys are under way in select districts and the results are expected by the end of August.