A super spreader is an individual who is more likely to infect others compared with a typical patient (pictured). An example is the doctor who treated early SARS-CoV patients in China, traveled to a hotel in Hong Kong, and infected 10 others who then went on bring the virus to multiple countries. Superspreaders of SARS-CoV-2 have been thought to be involved in transmission of the virus and the results of a recent study confirm their substantial role in the pandemic.
Analysis of superspreaders was done by examining 1,038 confirmed cases in Hong Kong up to 28 April. Over half of these infections were associated with at least one of 137 clusters (two or more confirmed cases). The median size of a cluster was 2 cases and the largest had 106 cases. Some 41% of the cluster cases were initiated locally, and 16% were initiated by an imported case. However, most clusters (63%) were initiated overseas. Of the 505 cases that were not linked to clusters, over 90% were acquired overseas. Transmission in social settings (bars, weddings) was linked to more secondary cases than households. Parenthetically, 19% of all cases in Hong Kong were asymptomatic at confirmation.
The largest cluster (106 cases) was traced to four bars in Hong Kong and was spread in part by musicians traveling between the venues. This cluster contained one or more superspreader events. The second largest cluster (22 cases) was linked to two superspreader events at a wedding and a preceding social event. The third largest cluster (19 cases) was linked to attendance at a temple with 12 cases part of a superspreader event. An asymptomatic monk who worked at the temple was likely the source of 11 temple cases.
These data were used to calculate the reproduction number R. The basic R0 of SARS-CoV-2, calculated early during the outbreak in Wuhan, is 2-3. The reproductive number calculated from the Hong Kong data is 0.62, a reflection of quarantine and isolation measures put in place during the outbreak. The dispersion coefficient was determined to be 0.35. The latter number indicates that 19% of cases were responsible for 80% of all SARS-CoV-2 transmission. Remarkably, 69% of cases did not transmit to anyone. These conclusions are in line with observations made in other countries.
Those conclusions need to be repeated: 19% of cases were responsible for 80% of all SARS-CoV-2 transmission, and 69% of cases did not transmit to anyone.
Wouldn’t it be great if we could identify the superspreaders, quarantine them, and stop 80% of all transmission? Right now we can’t. But what we can do is isolate confirmed cases very quickly. In Hong Kong, the median time from onset of symptoms to lab confirmation was 6 days for transmitters. That’s too long: onward transmission has likely already occurred in 6 days. Confirmation and isolation has to occur VERY quickly.
Based on these data, the authors suggest the following disease control measures:
•Rapid tracing and quarantine of confirmed contacts
•Closure or reduced capacity measures of high risk social settings (bars, weddings, religious sites, restaurants)
America, do you understand, or will some of you continue to ignore reality?