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. 2021 Feb:32:100717.
doi: 10.1016/j.eclinm.2020.100717. Epub 2021 Jan 6.

Descriptive epidemiology of SARS-CoV-2 infection in Karnataka state, South India: Transmission dynamics of symptomatic vs. asymptomatic infections

Narendra Kumar  1 , Shafeeq K Shahul Hameed  1 , Giridhara R Babu  2 , Manjunatha M Venkataswamy  1 , Prameela Dinesh  3 , Prakash Kumar Bg  3 , Daisy A John  2 , Anita Desai  1 , Vasanthapuram Ravi  1
Affiliations

Descriptive epidemiology of SARS-CoV-2 infection in Karnataka state, South India: Transmission dynamics of symptomatic vs. asymptomatic infections

Narendra Kumar et al. EClinicalMedicine.2021 Feb.

Abstract

Background: The huge surge in COVID-19 cases in Karnataka state, India, during early phase of the pandemic especially following return of residents from other states and countries required investigation with respect to transmission dynamics, clinical status, demographics, comorbidities and mortality. Knowledge on the role of symptomatic and asymptomatic cases in transmission of SARS-CoV-2 was not available.

Methods: The study included all the cases reported from March 8 - May 31, 2020. Individuals with a history of international or domestic travel from high burden states, Influenza-like Illness or Severe Acute Respiratory Illness and high-risk contacts of COVID-19 cases were included. Detailed analysis based on contact tracing data available from the line-list of state surveillance unit was performed using cluster network analysis software.

Findings: Amongst the 3404 COVID-19 positive cases, 3096 (91%) were asymptomatic while 308 (9%) were symptomatic. Majority of asymptomatic cases were in the age range of 16 and 45 years while symptomatic cases were between 31 and 65 years. Mortality rate was especially higher among middle-aged and elderly cases with co-morbidities, 34/38 (89·4%). Cluster network analysis of 822 cases indicated that the secondary attack rate, size of the cluster and superspreading events were higher when the source case was symptomatic as compared to an asymptomatic.

Interpretation: Our findings indicate that both asymptomatic and symptomatic SARS-CoV-2 cases transmit the infection, although symptomatic cases were the main driving force within the state during the beginning of the pandemic. Considering the large proportion of asymptomatic cases, their ability to spread infection cannot be overlooked. Notwithstanding the limitations and bias in identifying asymptomatic cases, the findings have major implications for testing policies. Active search, early testing and treatment of symptomatic elderly patients with comorbidities should be prioritized for containing the spread of COVID-19 and reducing mortality.

Funding: Intermediate Fellowship, Wellcome Trust-DBT India Alliance to Giridhara R Babu, Grant number: IA/CPHI/14/1/501499.

Keywords: COVID-19; Epidemiology; Karnataka; SARS-CoV-2 virus; Symptomatic vs asymptomatic.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1
Fig. 1
Distribution of case categories, number of cases and interventions undertaken. X axis depicts the timeline while Y axis depicts the number of COVID-19 positive cases. The date wise interventions undertaken by the state of Karnataka is described. The category of patients and the progression in numbers is depicted in various colors in a wave pattern.
Fig. 2
Fig. 2
Distribution of case categories and overall test positivity. X axis depicts the timeline, Y axis depicts the overall test positivity rate while the Z axis depicts the number of COVID-19 positive cases. Note there was a huge surge in the number of COVID-19 positive cases in the second half of May 2020.
Fig. 3
Fig. 3
Distribution and direction of transmission of COVID-19 cases in Karnataka State. Each dot represents a person with COVID-19. Primary cases are in red and secondary cases in blue. Blue colored dots connected to primary cases using lines. The dots not connected by lines represent independent introduction from elsewhere. Bengaluru city was the epicenter, had the highest density of COVID-19 cases, from where spread occurred to several districts in the state.
Fig. 4
Fig. 4
Cluster diagram depicting symptomatic and asymptomatic COVID-19 cases in the Karnataka state, March–May 2020. Each case is represented as a dot: red dot indicates a symptomatic case while yellow dots represent an asymptomatic case. The index case in each cluster is depicted as a larger dot and also indicated with the P number. The lesser the P number, the earlier the patient was detected either as a source or as a contact of a known source. Note there were 46 clusters with five or more cases. The index case of majority (32/46) of clusters was a symptomatic patient (red). Large open circles (depicted using interrupted lines) represent superspreading events (>6 cases originating from a source). Overall, among the 545 cases resulting from symptomatic source cases, 67.5% (368) cases were contributed by 12 SSEs originating from symptomatic cases. Whereas, two SSEs originating from asymptomatic cases contributed to 16.7% (19/114) cases.
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