Tracing the Sources and Comparing the Numbers of Confirmed Cases of 2019-nCoV in Singapore and Hong Kong

Both Hong Kong and Singapore found their first confirmed case of 2019-nCoV (Wuhan Coronavirus) on January 23. Since the two cities are of similar scale, comparable in the number of Chinese tourists, and the reported numbers of confirmed cases are also more credible, a comparison of the two cities can shed light on the actual spreading speed and the route of transmission.

  1. Comparing the Numbers of Confirmed Cases of 2019-nCoV

First of all, let’s try to compare the number of confirmed cases in the two cities, so as to let everyone know that the first three weeks of the outbreak are critical in containing the spread. Once the number of infections increases over the threshold, it is basically impossible to track the sources and/or implement an effective quarantine policy.

Figure 1 is a comparison of the numbers of confirmed cases of 2019-nCoV in Hong Kong and Singapore from January 23 to February 5, 2020 (the first 14 days after the first confirmed case). The blue line is the trend in Hong Kong and the orange line is that in Singapore. Singapore’s number of confirmed cases is increasing faster than in Hong Kong. There were 28 cases on the 14th day in Singapore in comparison with 21 cases in Hong Kong.

The gray line in Figure 1 is the number of cases in Wuhan in the first 3 weeks since December 9, 2019. It is just for reference only, as it is disclosed unofficially by scholars (Huang, C. et al., 2020). In fact, the Wuhan Mayor has officially acknowledged that they had concealed the release of data on this case and there were no official figures on the number of confirmed cases before December 31 last year.

According to the article written by the international experts (Huang et al., 2020), the earliest confirmed case in Wuhan occurred on December 1, 2019, and the second case was on December 10. The grey line in Figure 1 probably can remind us that if no effective quarantine measures are taken within the final golden period in the first three weeks of the outbreak, the result can become an epidemic like that in Wuhan.

2. Tracing the Sources of the Cases

Then, let’s trace the sources of the confirmed cases

2a. Tracing the sources in Wuhan
In the first 41 confirmed cases in Wuhan, the international expert team found that only 27 cases were related to the Huanan Seafood Market, and the sources of the remaining 14 cases are still unknown (blue bar in Figure 2).

It explains why closing the seafood market on Jan 1 still does not help contain the spread. It reflects the importance of tracing the sources for effective containment. Unfortunately, the tracking task was not only ignored, but the eight doctors who disclosed the epidemic situation were arrested, and the noise of the whistle blows was concealed. Without taking any quarantine measures in the early stage, and the citizens did not take any precautionary measures, it results in a thousand-time increase in the number of confirmed cases from 20 to 20,000 within two months!

2b. Tracing the sources in Singapore

On the contrary, in the first 28 cases in Singapore, all the sources have been basically found out. Of course, there may not be comprehensive or exhaustive, but it demonstrates the importance of tracking the sources and the relevance to the effectiveness of the quarantine measures.

Figure 3 shows the infection routes reported by the local media for these 28 cases. The first 16 cases were all directly from Wuhan or a Chinese who went to Singapore (# 1–14,16,18) and another 4 cases were evacuated Singaporeans returning home from Wuhan (# 15,17, 22, 23). In other words, a total of 20 cases were imported directly from China. The remaining 8 cases of local transmission can be roughly divided into two groups, all of which are related to the contact with tourists. The first transmission site was in Yong Thai Hong. Three confirmed cases were directly related to this. Two of them were salespersons (# 19,20), one was a tour guide (# 24), and the salesperson # 19 infected three family members at home (# 21,27,28); the tour guide # 24 also transmitted to her husband (# 25). (Two more cases on February 6. The 30th case was related to the Grand Hyatt Hotel, but the 29th case was a 41-year-old Singaporean man of unknown origin.)

2c. Tracing the sources in Hong Kong
There were 26 confirmed cases in Hong Kong as of February 7, 2020, of which only 8 were imported directly from Wuhan or Shenzhen (Figure 4 # 1,3,4,5,7,8,9,10), the proportion was only 30%. Another 1/3 are locals who have been infected either in Mainland China or overseas. The remaining 1/3 is probably via local community transmissions. The situation is very different from that in Singapore (detailed below), reflecting that the spread of the virus in Hong Kong would have more channels than that in Singapore.

Due to the integration of China and Hong Kong in the past two decades, a large number of Hong Kong citizens have frequently traveled to and from the Mainland of China to work, study, play and live. In this outbreak, up to 8 cases are Hong Kong people who have been in Mainland in the past few weeks (# 2, 6,12,13,14,22,25,26), that is, about 30%, compared with the less-than-15% in Singapore (all of them are one-time evacuees), it reflects the importance of not only prohibiting mainlanders from entering Hong Kong, but also quarantining the locals when returning Hong Kong from Mainland.

In addition, there were 9 cases in which the locals had no travel records in the recent weeks, and 4 of them were infected by family members (# 11,15,19,20), in other words, the sources of the remaining 5 cases were unknown (# 16,17,18,23,24). It brings great difficulties to the epidemic prevention work. If the number of confirmed patients continues to increase significantly, it will be difficult to track and quarantine those who have contacted the patients.

In contrast, the infection routes of the first 28 confirmed cases in Singapore were tracked successfully. 16 cases were imported directly from non-local China, accounting for almost 60%, and 4 cases were evacuees from Wuhan; 5 cases were probably infected via tourists, and the last 3 cases were transmitted at home.

3. Age of the Infected

It is also observed that no matter it is in Singapore or Hong Kong, the age of the infected is relatively high, especially those who came from Mainland China. There are 7 cases who are over the age of 55 in both cities, and the oldest are 73 years old. For the local group, the age of confirmed patients in Singapore is relatively young, but the average age in Hong Kong is still quite high. The highest age is an 80-year-old man, and the other two are a 75-year-old man and a 72-year-old women. It may reflect the fact that the elderly in Hong Kong is in lack of appropriate prevention measures, such as the face masks.



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