South Korea had just over 30 COVID-19 cases in the 28 days after it reported the first. But when contact-tracing was done for patient-31, a Pandora's box was opened. In the next 17 days, the number of cases crossed 6,000. Similarly, cases in Singapore would have been much lower if not for a dinner party. Infected persons in Kerala travelled to many places where people congregate before getting diagnosed. Essentially, all it took for the novel coronavirus to spread was one infected person who didn't maintain physical distance.
The Singapore clusters
As of March 23, Singapore has identified seven COVID-19 clusters responsible for 50% of its cases.
The graph plots cases in each such cluster. Each dot corresponds to a case. Close to 47 cases originated from a dinner party on February 15 at a restaurant in the Safra Jurong recreation club.
Which cluster in Singapore saw the most cases?
While some from the dinner party were declared as confirmed cases early (Cases 94 and 96), there were many who were declared much later (Cases 218 and 224). Some attendees of the dinner party (Cases 142 and 117) were confirmed as cases about 20 and 22 days after February 15 - the day it was organised.
Investigations are ongoing for cases which are not yet classified (the grey circles in the graph). New cases get added to a cluster almost every day.
Three new cases were added to the gym cluster and two more to the Bukit Timah cluster on March 20. So by the time the contact tracing ends, the share of cases from the clusters will exceed 50%
Leaking out of the clusters
Case 142, a 26-year-old male, visited two clusters, the dinner party and the gym. The virus spread from him to three others, Cases 211, 236 and 142, not connected to any clusters. So while only 50% of cases are directly connected to the clusters, there are many who indirectly contracted the virus from those who were part of such clusters.
The diagram plots cases which are linked to one another. Some of them are family members.
Cases outside clusters
Not all contacts are mapped to a cluster yet. Cases 311, 335 and 243 are linked but not in a cluster yet.
Also read: Spain’s COVID-19 toll surpasses that of China
Many such clusters similar to Singapore were identified in South Korea too. However, unlike Singapore where the source of such clusters was not known, South Korea was able to point to a female patient who was responsible for its biggest COVID-19 cluster.
South Korea's patient 31, a 61-year-old woman, despite "warnings from doctors", attended church at least twice and went for a buffet lunch with a friend ignoring the symptoms. The contacts she made at the church led to an exponential rise of COVID-19 cases in the country.
How patient 31 went about her business despite warnings
The South Korea clusters
Patient 31 came into contact with 1,160 people, by far the largest COVID-19 cluster in South Korea.
The graph traces the contact history of the first 31 cases. Isolated contacts are in red. For instance, Case 1 came into contact with 45 people, but none were isolated.
Which cluster in South Korea saw the most cases?
Just 6 days after patient 31 got hospitalised, cases multiplied quickly in Daegu city. Cases related to the church were then investigated.
As of March 24, S. Korea has mapped 80% of cases to some clusters. The Shincheonji cluster is responsible for 56% of the cases.
Victims from the Shincheonji cluster are not confined to Daegu. Out of the 17 regions in S. Korea, 15 have at least one case from the cluster.
A cluster of clusters
The Shincheonji cluster is responsible for 5,028 cases in South Korea as of March 20. There are many similar clusters. The second biggest cluster was made up of health workers and patients in the Cheongdo Daenam Hospital (119 cases).
According to a New York Times report, South Korean officials have learnt that Patient 31 visited Cheongdo too, in early February. Investigations to link the clusters are ongoing.
One massive cluster
Watch | A history of pandemics since the 20th century
A story closer to home
Kerala is one of the few States to publish activity trails of people who were identified as infected with the novel coronavirus. This was useful for contact-tracing purposes. An excerpt from one such actual activity trail of five patients from Pathanamthitta is presented below (images are representational and not of one person alone). Before their symptoms peaked, those infected visited a variety of places including hotels, post offices, banks, shopping centres and bus stops. Around the time the trail ended, only 11 people were under home isolation in Pathanamthitta. The number grew to 4,565 as of Monday, March 23, and many of whom could have been in contact with these patients. The more the infected persons travelled, the higher the risk of the spread.
Tracing the trails
All illustrations and graphics in the story are done by Kannan Sundar and J.A. Premkumar. With inputs from Sumant Sen
Source: South Korea data is sourced from Korea Centers for Disease Control & Prevention and Reuters. Singapore data is sourced from Ministry of Health, Singapore. Kerala data is sourced from State Health Minister's facebook account
