High exposure to Covid-19 in urban areas, find sero surveys
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.Updated: Aug 17, 2020, 08:25 IST
Sero surveys conducted by the states to determine the extent of exposure to the Sars-CoV-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.
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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.
“This is suggestive of infection during mid-June, and since then, we have seen a decent increase in the number of cases. That means more people are exposed to the virus, and the disease prevalence could be higher,” said Dr Jugal Kishore, head of the community medicine department of Safdarjung Hospital in New Delhi.
Delhi has conducted a second survey the results of which are expected in the coming week.
On July 28, the Brihanmumbai Municipal Corporation (BMC), along with the government think tank NITI Aayog and Tata Institute of Fundamental Research (TIFR), published the results of the survey conducted in three wards—M-West (Tilaknagar and Chembur), F-North (Matunga, Sion and Wadala) and R-North (Dahisar and Mandapeshwar) -- of Mumbai.
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
“The prevalence of the virus in slums is high due to the densely populated areas. In non-slums, there is better social distancing and maintenance of hygiene which helped to stop the spread of the virus to a larger number of people,” said Suresh Kakani, additional commissioner, BMC.
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. “The reliability of the test is said to be about 60%, meaning there is a high chance of false negativity in 40% cases. So unless mass testing is done in a very short time, we are not giving priority to this test,” said a Chhattisgarh health official, requesting anonymity.
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. Puri had zero positivity. The survey was conducted in July in four districts. “It’s a good sign as 31% people in Ganjam did not show symptoms and have recovered. In case of Bhubaneswar, the numbers would be higher if the Sero survey is done by the end of this month as the cases are shooting up in Bhubaneswar now,” said Dr TM Mohapatra, a microbiologist and former advisor to ICMR.
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.
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.
Director of Public Health G Srinivasa Rao said the sero-prevalence survey showed four positive cases out of 1,200 samples in rural areas and 15 positive cases out of 500 samples in the Greater Hyderabad Municipal Corporation (GHMC) limits, indicating that there was no community transmission.
Jharkhand’s sero surveym conducted in 10 high Covid-19 districts in June, showed an antibody positivity rate of 0.63%. The sample size in each district was a little over 400, which included health workers.
Planning health interventions
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.
In Pune, a Covid hotspot in Maharashtra, the first sero survey on 1,550 people was conducted by Indian Institute of Science Education and Research (IISER) with the Savitribai Phule Pune University (SPPU). The results of the survey are expected this week. Two other sero surveys by the government-run Sassoon Hospital and the National Institute of Virology (NIV) are expected to start soon.
Results of the ICMR sero survey of a few districts in West Bengal and Assam conducted in May are yet to be announced. Some states such as Uttarakhand, Himachal Pradesh and Sikkim have not conducted any sero surveys.
After completing a pilot sero survey around mid-May, to check the level of exposure to the Sars-CoV-2 virus,ICMR on May 31 sent an advisory to all states to perform periodical sero surveys.
ICMR’s sero survey results have shown a disease prevalence rate of 0.73% across India, but that was in May. India ended that month with 190,000 cases; it currently has over 2.5 million.