Research Article

Epidemiology and transmission dynamics of COVID-19 in two Indian states

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Science  06 Nov 2020:
Vol. 370, Issue 6517, pp. 691-697
DOI: 10.1126/science.abd7672

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  • Children and SARS-CoV-2: Key to spread?
    • Volker Strenger, Associate Professor for Pediatrics, Division of Pediatric Pulmonology and Allergology, Department of Pediatrics and Adolescent Medicine, Medical University Graz, Au
    • Other Contributors:
      • Florian Götzinger, Pediatrician, Department of Paediatric and Adolescent Medicine, National Reference Centre for Childhood Tuberculosis, Klinik Ottakring, Vienna

    We read with great interest the study by Laxminarayan et al. analyzing 84,965 SARS-CoV-2 infected cases captured in two Indian states and their 575,071 traced contacts. The authors suggest that children transmit the virus to a greater extent to their same-aged contacts than adults, based on a high secondary attack rate (SAR) for same-aged contacts of 26% for children aged 0-4 years (23 same-aged contacts out of only 89 contacts in this age group; table S8). However, the SAR for same-aged contacts in older children and adolescents (5-17 years) was only 11% (390/3419) and, therefore, identical to the median SAR for same-aged contacts in the adult age groups (range 7-71, Table S8) (1).
    Furthermore, analysis of detailed data provided in Table S8, showed similar overall SAR in children/adolescents (7.6%) and adults (7.2%), but SAR affecting secondary cases >65 years (being at higher risk for severe infections) turned out to be much lower for index cases <18 years (6.1%) compared to adult index cases (11.8%) (1).
    As reported by many other studies (2-5), children and adolescents were much less often afflicted by SARS-CoV-2 in the analyzed cohort. Consequently, secondary infections were traced back to adult index cases in 92.3% (33.966 infected contacts), while only 7.7% (2.825 infected contacts) of secondary infections have been transmitted by children or adolescents (1).
    Despite this, the lead author emphasized the epidemiological role of children and the...

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    Competing Interests: None declared.
  • Children and adolescents play a minor role in the transmission of SARS-CoV-2
    • Marc Tebruegge, Honorary Associate Professor of Paediatric Infectious Diseases, Department of Infection, Immunity & Inflammation, UCL Great Ormond Street Institute of Child Health, University College London.
    • Other Contributors:
      • Nigel Curtis, Professor of Paediatric Infectious Diseases, Department of Paediatrics, The University of Melbourne.

    We read with interest Laxminarayan et al.’s study of COVID-19 cases and their contacts in two Indian states (1).

    The authors highlight the significant role of children in transmission. However, this conflicts with the data presented (Table S8). The study included only 37,322 index cases aged below 18 years, but 241,613 middle-aged adults (30-49 years of age). The proportion of contacts of children and adolescents found to be SARS-CoV-2-infected was 7.6% (2,825/37,322), which is similar to the 7.3% (7,683/241,613) transmission rate observed in middle-aged adults [two-tailed Fisher’s exact test: p=0.09; relative risk: 1.03 (95%CI: 0.99-1.07)]. These figures show that children: (i) contributed little to transmission of SARS-CoV-2; and (ii) were not transmitting SARS-CoV-2 more ‘efficiently’ than middle-aged adults.

    There are also substantial limitations to the study that warrant consideration. Importantly, it is likely a significant proportion of contacts were falsely classified as ‘uninfected’. Firstly, some contacts were tested within 5 days post-exposure, well within the average incubation period of SARS-CoV-2 infection (2); consequently, a substantial proportion will have developed COVID-19 subsequently. Secondly, most PCR-based SARS-CoV-2 assays have a sensitivity of only 80-90% (3), meaning up to 1 in 5 contacts would have had false-negative test results. Thirdly, no information is provided about the assays or associated quality control measures used fo...

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    Competing Interests: None declared.
  • RE: Time varying basic reproductive number computed during COVID-19, especially during lockdowns could be questionable
    • Arni S.R. Srinivasa Rao, Professor, Medical College of Georgia, Augusta University, Georgia, U.S.A
    • Other Contributors:
      • Steven G. Krantz, Professor, Washington University in St. Louis, Campus Box 1146, One Brookings Drive, St. Louis, Missouri 63130, U.S.A.
      • Michael B. Bonsall, Professor, University of Oxford, OX1 3PS, U.K.
      • Thomas Kurien, Professor, Pondicherry institute of Medical Sciences, Puducherry 605014, India
      • Siddappa N. Byrareddy, Associate Professor, University of Nebraska Medical Center, Omaha, NE 68198, U.S.A
      • David Swanson, Edward A. Dickson Emeritus Professor, University of California Riverside Riverside, CA U.S.A 92521, Affiliated Faculty Center for Studies in Demography & Ecology University of Washington Seattle, WA USA 981955
      • Ramesh Bhat, Professor, NMIMS University, Mumbai, India
      • Sudhakar Kurapati, Senior Health Advisor (Retd), formerly with CDC, World Bank, and USAID

    While the epidemiological conclusions found in by Laxminarayan et al. [1] are supported by their data, the estimates of time-varying basic reproductive numbers raise some methodological issues that need further discussion. Limitations associated with computing time-varying basic reproductive rates are generally unavoidable, however, inappropriate interpretations, especially during lockdowns in the ongoing COVID-19 pandemic, have key implications for controlling the epidemic.
    Suppose a certain number of infections at a time generate secondary infections, and these secondary infections could be treated as primary infections which in turn generate further secondary infections and so on. At each stage of the infection process, the number of individuals tested through contact tracing or through other criteria for testing individuals may not capture all the infected individuals that could arise under-reporting due to undiagnosed infections [2, 3, 4]. This leads to under-reporting of the true level of infections. Lockdowns add further difficulties in contact tracing and testing. The degree of under-reporting due to mis-diagnosis could also be varying over a lockdown period. Such limitations also apply to Laxminarayan et al. [1] study. Moreover, the authors also noted that “Expansions in testing over this period are likely to bias in computing time-varying basic reproductive rates…” Thus, it also is important to realize that heterogeneity may exist in the data that could hav...

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    Competing Interests: None declared.
  • Secondary infection rate in COVID-19 contacts depends on testing policy used

    Article by Laxminarayana R et al (1) has brought out important aspects related to epidemiology and transmission of COVID-19 in two south Indian states. Authors have also compared secondary infection rates between high risk and low risk contacts. However, I would like to bring out that this comparison has a major limitation which authors have not mentioned in their paper i.e. different testing policy for high risk and low risk contacts in India. All high risk contacts (symptomatic as well as asymptomatic) were being tested while only symptomatic individuals were tested among low risk contacts, as per Government of India's policy (2).

    Secondary attack rate of diseases which have significant proportion of asymptomatic infections depend on strategy being employed to identify secondary cases. Hence, difference in testing strategy used in India to identify secondary cases among high risk and low risk contacts of COVID-19 cases could have brought significant bias in this comparison.

    Secondly, data of less than 2% of contacts tested in Tamil Nadu state was available for analysis (1). Hence, these limitations of the study should also be considered while understanding the dynamics of COVID-19 transmission from this study.

    1. Ramanan Laxminarayan, Brian Wahl, Shankar Reddy Dudala, K. Gopal, Chandra Mohan, S. Neelima, K. S. Jawahar Reddy, J. Radhakrishnan, Joseph A. Lewnard. Epidemiology and transmission dynamics of COVID-19 in two Indian...

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    Competing Interests: None declared.
  • RE: : 452 Doctors Fighting COVID-19 already Dead In India till 30 september 2020

    COVID-19 disease appears to have been associated with significant mortality amongst doctors and health care workers globally. I in this article tries to explore the various risk factors associated with this occupational risk of medical faternity , especially focusing on India. The novel Coronavirus SARS-CoV-2 outbreak has created a significant impact on the daily life and health care systems across the world including India [[1], [2], [3]]. COVID-19 has caused a huge burden and loss to the world where doctors bearing the brunt of physical burnout, mental stress, occupational risks of getting themselves infected with increased risk of morbidity and mortality, being the most front-line workers with little recognition from government,,laws, society in respect to compensation, free treatment , lodging in rental home and neighbourhood . Currently India is the third worst affected country in the world with more than 6,312,584 confirmed cases and above 98,708 deaths attributed to COVID-19 till 30th September 2020[4]. It has been observed that COVID-19 related mortality in the general population has been slightly lower in the South Asian subcontinent [5]. Concerns have been raised since nearly 452 doctors have succumbed to COVID-19 so far with a significant number of healthcare professionals affected as well not counted. The mortality of these doctors has made a dent in an already compromised health care system due to poor doctor patient ratio. The Indian Medical Association...

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    Competing Interests: None declared.
  • RE: Why super spreaders spread the way they do?
    • Emmanuel Bhaskar, Professor of Medicine, Sri Ramachandra Medical College and Research Institute,Porur,Chennai-600116,India

    This largest contact tracing study has confirmed the possibility that a small number of severe acute corona virus 2 ( SARS-CoV-2) infected persons lead the transmission cycle and children play a vital part in disease transmission. (1) A small review of reports on secondary attack rate observed a rate as high as 35% among individuals exposed in superspreading events. ( 2) Super spreaders increase the transmission of illness not due to change in the behavior of virus they are carrying, but due to the living environment ( household and community) and their social behavior during pre-symptomatic and early symptomatic phase of their illness. Having observed the dynamics of transmission in Chennai (Tamilnadu) among contacts of SARS-CoV-2 patients at hospital and community setting during the same period as the study, I put forward few case examples. In May and June 2020, the illness was more prevalent in two locations in Chennai ( Tondiarpet and Royapuram) where substantial number of people live as joint family ( of at least 5 people) in house smaller than 300 square feet with shared toilet for about 3 families.(3) We have seen multiple instances when the index case visited around 5 neighboring houses ( each with around 5 persons) per day during the pre-symptomatic period and during first or second day of illness. Since most were staying at home due to lockdown restrictions in May and June 2020, the contact time of persons with index case was longer and occurred at poorl...

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    Competing Interests: None declared.

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