ICMR study finds evidence of community transmission

Published : May 01, 2020 07:00 IST

A recent research work published in the Indian Journal of Medical Research (IJMR), a journal of the Indian Council of Medical Research (ICMR), has found evidence for the community transmission (CT) of COVID-19 infection at least in some districts of India, even as Indian health officials and the ICMR spokesperson at the daily media briefing continue to deny the possibility.

The latest daily situation reports of the World Health Organisation (WHO) classify the Indian situation as “Clusters of Cases”, as they have done for countries such as China, South Korea, Japan and Australia. Transmission classification, according to the WHO, is based on a process of country/territory/area self-reporting.

There are, of course, countries such as the United States, Canada, Brazil, Iran and South Africa, whose situations have been classified as CT. There are also many other countries, the classification of whose situations is stated as “Pending”, such as the United Kingdom, Italy, Spain, France and Germany. The remaining WHO classification categories are: “No Cases” and “Sporadic Cases”.

The WHO’s current (as of April 9) definition of CT is:

“Countries/area/territories experiencing larger outbreaks of local transmission defined through an assessment of factors including, but not limited to:

* Large numbers of cases not linkable to transmission


* Large numbers of cases from sentinel lab surveillance

* Multiple unrelated clusters in several areas of the country/territory/area.”

The WHO’s definition for CT until April 9 (since this classification was started on February 28) essentially included the first two criteria mentioned above. The other categories until April 9 were: “Local Transmission”, “Imported Cases Only”, “Interrupted Transmission” and “Under Investigation”. India was classified as “Imported Cases Only” until March 4, when it was changed to “Local Transmission”, which remained the case until April 8.

What is interesting, however, is that until April 9, the WHO situation reports did not classify any country (including China, Italy, Spain or the U.S.A) in the CT category (even according to the old definition) even though it was known through studies in countries with rapidly escalating case load that CT was occurring. In India, too, epidemiologists have been saying at least since early March that CT must be occurring.

In a sentinel surveillance study among patients with Severe Acute Respiratory Illness (SARI)—a hallmark condition of COVID-19 in the context of the ongoing pandemic—initiated by the ICMR to identify the spread and extent of transmission of the disease, researchers have found that 40 among a total of 104 (over one-third) COVID-positive cases in a sample of 5,911 SARI patients had no history of international travel or contact with any known COVID-19 case.

The sampling was done from 41 sentinel surveillance sites across 52 districts in 20 States/Union Territories. The 40 cases with no apparent link to identifiable source of infection were from 36 districts in 15 States, and that is a large fraction (69 per cent) of the identified districts for surveillance. [Sentinel surveillance refers to a system covering selected sites (where good laboratory facilities and trained staff are available) with a high probability of seeing cases of the disease in question which the routine passive surveillance system may miss.] Even though the ICMR research paper does not explicitly state that this is evidence for CT (the reason for that is not clear), this clearly is evidence of that, and satisfies the second criterion in the WHO definition of the category, unless the ICMR considers the sample size of 104 COVID-19 patients as not “large”.

The first COVID-19 case in India was reported on January 30 in Kerala. The initial routine testing strategy adopted by the Government of India following the ICMR recommendation was only to test people with symptoms who had undertaken international travel, symptomatic contacts of confirmed cases of COVID-19 and symptomatic health care workers who were managing SARI patients. However, following WHO’s recommendation, stored samples of SARI patients who were hospitalised between February 15 and March 19 (965 in all) were tested for COVID-19 under the Virus Research and Diagnostic Laboratory Network (VRDLN) under ICMR. From March 20 onwards, the routine testing strategy was broadened to include all SARI patients as well from which set the study accessed data of 4,946 SARI patients.

The sentinel surveillance study thus analysed the data of SARI patients over a seven-week period between February 15 and April 2 from 104 SARI testing laboratories. In all, 5,911 (965+4,946) SARI patients were tested, of which 104 (1.8 per cent) tested positive for COVID-19.

While in the first set of samples up to March 19, only 2 (0.2 per cent) were found to be positive for COVID-19, in the latter set of 4,946 samples, 102 (2.1 per cent) were positive. The 40 cases that have no apparent identifiable causal link to COVID-19 source belong to the latter set (39.2 per cent). So the timeline also gives an idea of the progression of the disease in the country, and it would seem that CT may have set in at least around early March, if not earlier, if you allow for around a two-week period from the time of infection to development of severe symptoms in this set of 40 COVID-19 positive SARI patients.

The 36 districts (from 15 States) from where these 40 cases were identified should be prioritised to target COVID-19 testing, containment and mitigation efforts, say the authors of the study. However, an important limitation of the study pointed out by the authors is that the sentinel hospitals in the surveillance were all in the public sector and that too in urban areas. The data and the conclusions would therefore not truly be representative of the entire district.

Significantly, of the remaining 62 COVID-19 positive SARI patients, only two reported any contact with a confirmed COVID-19 case and one had a history of international travel, and data on exposure history for the rest 59 (57.8 per cent) is simply not there (Table). It is, therefore, eminently possible that a number of these 59 cases may well have no history of contact or international travel, and hence the spread would be due to CT. This only would mean a more widespread CT than the study concludes on the basis of hard data-based evidence alone.


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