'In a closed setting of similar nature as that on the cruise ship ‘Diamond Princess,’ one in 450 infected individuals to die,' reveals ICMR mathematical modelling study
New Delhi: The Indian Council of Medical Research (ICMR) on Monday warned that introduction of a community transmission of Covid-19 cases may take anywhere from a minimum of 20 days to a few months to be visible. In a mathematical modelling study published on Monday in the Indian Journal of Medical Research, the ICMR has highlighted that the control of epidemic would be difficult in “pessimist" scenarios in metropolitan cities such as Delhi, Mumbai, Kolkata, Bengaluru, Chennai, Hyderabad and Kochi, if people who have a travel history to infected countries or contact with the infect don’t isolate themselves.
The study results showed that symptomatic quarantine would identify and quarantine 50% of symptomatic individuals within three days of developing symptoms. In an optimistic scenario of the basic reproduction number (R0) being 1.5, and asymptomatic infections lacking any infectiousness, such measures would reduce the cumulative incidence by 62%, the study said. Reproduction number of an infection can be thought of as the expected number of cases directly generated by one case in a population where all individuals are susceptible to infection.
“In the pessimistic scenario of R0 =4, and asymptomatic infections being half as infectious as symptomatic, this projected impact falls to two per cent," the study warned adding that port-of-entry-based entry screening of travellers with suggestive clinical features and from Covid-19-affected countries, would achieve modest delays in the introduction of the virus into the community.
Acting alone, however, the study said such measures would be insufficient to delay the outbreak by weeks or longer. “Once the virus establishes transmission within the community, quarantine of symptomatics may have a meaningful impact on disease burden. As a public health measure, health system and community preparedness would be critical to control any impending spread of Covid-19 in the country," the study concluded.
The analysis was based on a simple Susceptible-Exposed-Infectious-Recovered (SEIR) model to capture the natural history of Covid-19 and its transmission dynamics. The study was jointly done by Translational Global Health Policy Research Cell (Department of Health Research), ICMR’s Division of Epidemiology & Communicable Diseases, School of Public Health, National Institute of Epidemiology, Chennai and Department of Infectious Disease Epidemiology, School of Public Health, Imperial College, St Mary’s Hospital, London.
The ICMR scientists have said that in order to have an appreciable effect on delaying the establishment of transmission of Covid-19 in India, airport arrival screening will need to have near-complete capture of incoming Covid-19 cases, including asymptomatic cases.
“Although not practically feasible using the currently available tools, our results provide a hypothetical illustration of the additional benefit of identifying asymptomatic cases: if they escape any containment effort, they would tend to negate the effects of that effort, by the onward transmission that they can cause," the study said.
Currently, there is no accurate, rapid test for Covid-19 to reach the required levels of detection among asymptomatic cases; the ICMR in the study said, the only way to reach 90% diagnosis among asymptomatic arrivals may be through isolation and quarantine of all arrivals from specified origin airports.
Resources may be better spent on the mitigation of infection in the community, the study pointed out. The scientists wanted to find out if it was possible to prevent, or delay, the local outbreaks of Covid-19 through restrictions on travel from abroad. As per a stochastic, worldwide, air transportation network dynamic model, India ranks 17th among the countries at the highest risk of importation of Covid-19 through air travel.
“The probability of an infected air traveller to come to India as the final destination was 0.209%, with the highest relative import risk in Delhi (0.064%) followed by Mumbai, Kolkata, Bengaluru, Chennai, Hyderabad and Kochi. This in the context of an epidemic that has already set in and travel from infected areas continues," the study said.
Various other studies across the world have established that travel screening would miss more than half of the infected travellers on account of being asymptomatic and being unaware of exposure, emphasizing the need for post-travel symptom tracking among them. “Our analysis shows that, even if symptomatic cases are comprehensively identified and quarantined, the delay in epidemic timing within India would be in days and not weeks," the study said.
“We also examined the potential impact of quarantine of symptomatics, in controlling transmission within India, with a focus on four major metropolitan areas. Our results suggest that it may be possible to interrupt the transmission of COVID-19 in India, but only in the most optimistic scenarios," it said.
Further, the ICMR in the study has said that the critical concerns are also the efficiency and timeliness of quarantine and isolation of patients. Further, the challenge is of detection of Covid-19 with symptoms similar to many other lower respiratory tract infections.
The study has projected that a continuous follow up of passengers returning from Covid-19-affected countries and their contact tracing for the emergence of suggestive symptoms would put a high strain on the healthcare system, more so in the eventuality of the introduction of community transmission.
“The increasing numbers would make it impractical to use laboratory testing to confirm each case, and therefore, use of symptomatic surveillance should become the primary public health strategy to detect and respond in the most effective and timely manner," the study said.
The study has also warned that with the evolving understanding of Covid-19 epidemiology, especially the proportion of asymptomatic infected cases, it is difficult to predict the number of beds required or ventilators necessary for COVID-19 cases at this stage.
“As per reports from other affected countries, we may expect eight to ten severe and 40-50 non-severe Covid-19 cases for every death. In a closed setting of similar nature as that on the cruise ship ‘Diamond Princess,’ we may expect 26% of the entire population to get infected and one in 450 infected individuals to die," the study said.
“We deduce that around five per cent of the infected patients will require intensive care and half of those admitted in the intensive care unit will require mechanical ventilation," the study said.
Considering the enormity of the evolving Covid-19 pandemic, the scientists have recommended that it is pertinent that frontline healthcare workers are identified and trained before the outbreak sets in. Health and life insurance should be announced for healthcare workers if they contract Covid-19.
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