Coronavirus tests done by the Indian Council for Medical Research as part of its efforts to map the spread of the disease in India have found a significant proportion of people contracted the infection despite having no recent international travel history or contact with confirmed cases. The findings were published in the Indian Journal of Medical Research on Thursday.
ICMR labs tested 5,911 samples taken from patients with severe acute respiratory infections in 52 districts in 21 states and Union Territories between February 15 to April 2. In these tests, 104 samples, or 1.8% of the patients, tested positive for coronavirus.
Only one of positive samples came from a patient with recent international travel history, two from those who were in contact with a laboratory-confirmed case. Forty cases, or 39.2% of the dataset, did not have any travel or contact history. There was no data available for as many as 59 (58.7%) of the cases.
The council had initiated these tests as part of sentinel surveillance to detect community transmission of Covid-19 in India. Community transmission is said to take place when the source of infection for a large number of cases in an area cannot be traced: when individuals pick up the infection without having travelled to countries where the virus is circulating or having been in contact with known confirmed cases.
On March 19, the council said it had tested 829 samples of people with severe acute respiratory infection or influenza-like illnesses, and none of them tested positive.
Subsequently, ICMR declared that there was no community transmission of Covid-19 in India. “We did random sampling study of community transmission of about 820 samples from 50 sites,” said ICMR Director General Balram Bhargava. “They have come negative. According to this study, the community spread [of the virus] has not happened.”
The research paper published on Thursday was silent on whether the results of the 5,911 samples tested for Covid-19 confirmed community transmission. Experts were divided on this.
“One may not like to call it community transmission but this is in fact community transmission of Covid-19,” Dr T Jacob John, professor emeritus and former head of virology at the Christian Medical College, Vellore told The Hindustan Times.
Dr Shobha Broor, former head of the department of microbiology at the All India Institute of Medical Sciences, however, told the paper: “We can’t just jump to the conclusion that there is community transmission from these findings. These are from the laboratory and we haven’t started testing in the community yet. I think their case history hasn’t been analysed properly yet.”
The results also show a rising graph of positivity: from zero in the initial weeks to 2.6% in the 14th week. Among the 965 patients with severe acute respiratory infections tested retrospectively between February 15 to March 19, using stored samples in labs, just two (0.2%) were positive for Covid-19. “When the Covid testing strategy was expanded to include all SARI patients, a total of 4,946 samples yielded 102 (2.1%) cases,” the paper said.
However, the paper noted several limitations. One, “the data presented pertained to patients seeking care from selected sentinel hospitals that were predominantly in public sector in urban areas and hence might not be representative of the entire district, State or country.”
Another limitation was the testing method. The labs used RT-PCR or reverse transcription polymerase chain reaction tests, which detect the presence of the virus in genetic material. Such tests are effective only in a narrow window of time, when the infected person has a heavy concentration of the virus in their body. In contrast, antibodies stay in a person’s body for a much longer time than the virus. “Antibody-based testing among RT-PCR negative SARI patients could have increased the yield of COVID-19 cases in this group,” the paper said.
The paper concluded: “COVID-19 containment activities need to be targeted in districts reporting COVID-19 cases among SARI patients.”
Delhi has the highest percentage (5.1%) of positive samples among the patients with SARI tested for the virus. This is followed by Telangana at 4.2% and Maharashtra at 3.8%.
India has so far reported 6,412 cases of the coronavirus, of which 199 people have died and 503 have been cured, according to the Union Ministry of Health and Family Welfare.