Featured image: A health worker takes swab samples for COVID-19 testing in Ghaziabad. Photo: PTI/Arun Sharma
New Delhi: The important role that testing and efficient contact tracing can play in containing the spread of the novel coronavirus was once again highlighted in a preliminary study conducted by scientists of the Indian Council for Medical Research (ICMR).
The study, released online on Monday in the Indian Journal of Medical Research, found that the funeral of the first COVID-19 casualty in eastern Uttar Pradesh turned into a ‘super-spreader’ event. By the time the man was tested for the viral infection and the result arrived, the virus spread to 16 other people.
Other findings of the study also reveal crucial insights into the way the disease is spreading, including that the infectivity may be much higher than admitted by the ICMR and that asymptomatic patients might be driving the pandemic.
The scientists said that their study focussed on one cluster of 17 cases, the source of which was a 25-year-old man (from here on, referred to as the index case) in Basti district of UP. The study was conducted to provide insights into the transmission chain and clinico-epidemiological characteristics of COVID-19 patients by scientists of the ICMR’s Regional Medical Research Centre in Gorakhpur.
The index case was the first laboratory-confirmed COVID-19 case in the eastern part of UP, which was reported on March 31, 2020. The man was admitted to the BRD Medical College in Gorakhpur on March 29, with acute respiratory distress syndrome (ARDS) with multiorgan dysfunction syndrome (MODS). He passed away the next day, during treatment. His sudden death prompted the doctors to collect nasal and oral swabs from the patient, which showed he had COVID-19.
Interestingly, even though the ICMR has refused to acknowledge that there is community spread of COVID-19 in the country, the scientists who conducted the study said that the source of the index case’s infection could not be determined. The man did not have a travel history outside of his district and neither did any of his family members.
The study states that by the time the confirmatory laboratory results were available on March 31, the family and relatives held the man’s funeral, which “turned out to be a super-spreader event”. A ‘super-spreader’ is a person who transmits an infectious disease to a significantly higher number of people than the average.
Medical authorities began containment procedure and found that the infection had already been transmitted to the index case’s family members and their close contacts.
Authorities found that the index case’s mother and two brothers were infected by the virus. In addition, the person who accompanied the index case to the hospital in Gorakhpur also had COVID-19. About 50 individuals attended the funeral of the index case and after active contact tracing, 39 individuals were quarantined and tested. Of these, seven persons tested positive for the infection. Three other family members of these seven persons also tested positive. In total, scientists were able to trace 16 persons in the cluster, apart from the index case.
Infectivity could be higher
The study also found that the infectivity of the novel coronavirus may be much higher than currently thought. The scientists found that transmission occurred at three levels: direct contact with the index case, which resulted in two secondary cases. “Second, at the household level, where four of seven susceptible contacts got infected, and the third was an event where 50 people participated and this resulted in seven positive individuals, in whom the infection was directly linked to a funeral gathering as there was no interaction after this,” the study says.
From this data, the scientists inferred that nearly half the person’s close contacts were infected. “The secondary attack rate [SAR] of 45.5% was found in the present cluster,” the study says. The Lancet defines SAR as “the probability that an infection occurs among susceptible people within a specific group (i.e, household or close contacts). SAR can provide an indication of how social interactions relate to transmission risk.”
Data provided by the ICMR says that on an average, the SAR in India is around 6% or that 94% of family members or close contacts of a COVID-19 patient did not contract the virus.
However, the scientists acknowledged that their study could not establish a “clear infector-infectee relationship” because all the households were linked by either vicinity or relation. “It was not clear that from whom or where the index case got infected… The present study being conducted on a small group of individuals and localised to a small geographical area, the findings cannot be generalised,” the study says.
High proportion of asymptomatic cases
Though 16 persons were infected, the scientists said that just two were symptomatic. The scientists observed that “asymptomatic cases can silently transmit infection”, a finding that is supported by other studies.
The scientists highlighted the impact of effective contact tracing and isolation in preventing and controlling the spread of an infectious disease. The study says that the less proportion of symptomatic individuals may be due to early diagnosis and isolation, absence of co-morbidities and relatively younger age, as compared to findings of other studies from different parts of the world.
“Testing, contact tracing, containment and strict adherence to social distancing, following hygienic practices, avoiding crowded places and wearing mask may play a key role in breaking the chain of transmission,” the study concludes.
The study reports that all 16 patients apart from the index case recovered clinically from the disease. Two of them had comorbidities (one patient with lung disease and one with liver disease) but also recovered fully. The study says that on average, the patients tested negative 12 days after testing positive for COVID-19.