Prevalence in Sichuan Province (non-foreign imported cases)
Geographical distribution Up to the March 4, Sichuan Province ended the increase in confirmed cases in the mainland (the first wave). Each city of Sichuan Province (in total 21) have reported the confirmed cases, with a total mainland case number of 539 and an incidence rate of 0.6462 / 100,000. Analysis of confirmed cases was based on their current address, with 48.33% in urban and 51.67% in rural areas. The top five cities with confirmed case numbers were Chengdu, Ganzi, Dazhou, Nanchong, and Guang'an. The top five incidencie cities were Ganzi Prefecture, Panzhihua, Guang'an City, Chengdu City, and Dazhou City (Table 1). The confirmed cases were distributed in 103 counties, accounting for 56.28% of Sichuan Province. Among them, there were 3 cities (in total 21 cities) found cases reported in all their counties. Geographically, the regions with the higher number of cases and counties are located in the eastern part of Sichuan Province, which is directly adjacent to Chongqing and closer to Hubei Province. Although the number of confirmed cases in the eastern counties is relatively high, a small number of counties in the western part also have a high incidence (Table 1, Fig. 1,Fig. 2).
Table 1
Number and incidence of COVID-19 in different cities of Sichuan Province
city | population | Number of counties | Comfirmed case number | Rank of case number | Incidence /100,000 | Rank of incidence |
Cheng Du | 1633 | 20 | 144 | 1 | 0.8818 | 4 |
Gan Zi | 119.6 | 18 | 78 | 2 | 6.5217 | 1 |
Da Zhou | 572 | 7 | 42 | 3 | 0.7343 | 5 |
Nan Chong | 644 | 9 | 39 | 4 | 0.6056 | 7 |
Guang An | 324.1 | 6 | 30 | 5 | 0.9256 | 3 |
Ba Zhong | 332.2 | 5 | 24 | 6 | 0.7225 | 6 |
Lu Zhou | 432.4 | 7 | 24 | 6 | 0.555 | 9 |
Nei Jiang | 369.9 | 5 | 22 | 8 | 0.5948 | 8 |
Mian Yang | 485.7 | 9 | 21 | 9 | 0.4324 | 12 |
De Yang | 354.5 | 6 | 19 | 10 | 0.536 | 10 |
Sui Ning | 320.2 | 5 | 17 | 11 | 0.5309 | 11 |
Pan Zhi Hua | 123.6 | 5 | 15 | 12 | 1.2136 | 2 |
Liang Shan | 490.8 | 17 | 15 | 13 | 0.3056 | 15 |
Yi Bin | 455.6 | 10 | 12 | 14 | 0.2634 | 17 |
Zi Gong | 292 | 6 | 9 | 15 | 0.3082 | 14 |
Mei Shan | 298.4 | 6 | 8 | 16 | 0.2681 | 16 |
Ya An | 154 | 8 | 6 | 17 | 0.3896 | 13 |
Guang Yuan | 266.7 | 7 | 6 | 17 | 0.225 | 18 |
Zi Yang | 251.2 | 3 | 4 | 19 | 0.1592 | 19 |
Le Shan | 326.7 | 11 | 3 | 20 | 0.0918 | 21 |
A Ba | 94.4 | 13 | 1 | 21 | 0.1059 | 20 |
Subtotal | 8341 | 183 | 539 | | 0.6462 | |
Overseas imported cases | | | 21 | | | |
Imported case after Wuhan unsealed | | | 1 | | | |
Total | | | 561 | | | |
*In Sichuan, up to March 4, a total of 21 cities has reported (covered all the city-level geographical unit), with a subtotal number of confirmed case 539, and a incidence 0.6432/100,000. The subtotal number was the first wave confirmed number. It did not contain 21 overseas imported cases reported from March 17 to April 6 and only one imported from Wuhan after Wuhan unsealed. Wuhan was unsealed on April 8 and this cases was reported on April 17. The 22 cases were discovered all in the observation period after they back to Chengdu and did not cause secondary transmission. |
Time distribution The time of the first confirmed case report in Sichuan Province was mainly concentrated in one week after Wuhan lockdown (January 24-January 31).13 At this stage, the current address of the first confirmed case was distributed in 70 counties, accounting for 68% of the counties (103) in Sichuan Province on March 4. The maximum number was the 3rd and 4th days after Wuhan lockdown (January 26–27). During the two days 28 counties (27%) reported their first case. The rapid increase in the confirmed number was concentrated in the four weeks after the closure of Wuhan (January 24-February 20), and the increase was particularly obvious in the first two weeks (Fig. 3).
Prevalence in neighboring provinces of Sichuan and other parts of the China
Spatiotemporal distribution On December 31, 2019, 27 cases were first reported on the official website of Hubei Province, all in Wuhan; on January 23, 2020, Hubei announced entered the Grade II response and Wuhan lockdown.14 Of the 835 cases reported nationwide (including 5 from Hong Kong, Macao, and Taiwan), 549 in Hubei (495 in Wuhan) and 267 in all provinces outside Hubei. A total of 15 cases in Sichuan Province were distributed in 7 cities (the first imported case was diagnosed on the January 21), ranking 9th in the China. The number of cases in Chongqing, adjacent in eastern of Sichuan, was the only neighboring province with more cases than Sichuan (cumulative cases 27). The epidemic situation in Yunnan, and Guizhou adjacent in the southern of Sichuan is relatively light. Twenty-eight days later, on February 20, a total of 75,993 cases (including Hong Kong, Macao, and Taiwan, 102 cases, the total number of which were corrected based on Hubei's revision) were reported, of which 63,088 were in Hubei (45,346 in Wuhan). The revision was originally made by the Hubei Health and Medical Commission website on February 21), a total of 12,905 cases (including Hong Kong, Macao, and Taiwan) in provinces outside Hubei. 525 cases in Sichuan Province were distributed in all cities (21 cities), ranking 11th in China, next to Chongqing. Fourteen days later, on March 5, a total of 80,710 cases (including Hong Kong, Macao, and Taiwan, 158 cases) were reported nationwide, including 67,592 cases in Hubei (49,797 in Wuhan), and a total of 13,118 cases (including Hong Kong, Macau, and Taiwan) in provinces outside Hubei. A total of 539 cases in Sichuan were distributed in all cities (21 cities),ranking 11th in China. The number of new cases nationwide fell below one hundred the next day.
The concentrated outbreak time of confirmed cases was the first 4 weeks after the implementation of the lockdown measures (Fig. 4). From December 31, only reports were reported in Wuhan. Later on January 19 the first confirmed case was reported outside Wuhan (reported in Shenzhen of Guangdong province). In the first three weeks from December 31 to January 23 (Wuhan lockdown, 118 cities reported cases), the confirmed cases turned 31 times. In the next four weeks, 90% of the cities nationwide were covered, and the number of cases increased by 91 times compared with January 23. In the 5th to 6th weeks, the number of newly confirmed cases and the number of reported areas slowed down significantly, with an increase of only 0.06 times (63 cities except Wuhan increased in total 473 cases, and the average daily increase was 0.53 cases / city). In the 7th week (March 5-March 12), there was only a small increase of 62 cases in 10 cities of China except for Wuhan.
Distribution of the epidemic length in each region In the seventh week after the closure of Wuhan (on March 12), all cities of China except Wuhan, Taiwan, and Hong Kong have ended the growth of cases. Based on statistics at the city level (according to the high population density of municipalities, the districts of municipalities were analyzed as a city unit), the length calculated by the information of occurrence and end of local cases in a total of 413 cities were used to analysis. The study shows that the largest date length from the first case confirmed to zero case in each city was 53 days, and an average and median length were 22 and 23 days, respectively. When the length was 21 days,the frequency of the cities was highest, approximately 26 Cities (6.3% in 413). Further analysis of the epidemic length at the county-level (regional unit) in Sichuan Province, included a total of 103 counties that had epidemics. The results showed that there was no local case increase after March 4. The largest date length from the first confirmed case to zero growth was 33 days, with a mean and median of 9 days. The highest city frequency of the date length was 1 day, approximately 31 cities (30% in 103) (Fig. 5). Taking the migration from Hubei during the two weeks before it lockdown as a possible high risk factor, this study compared the provinces of which the migration rank close to Sichuan Province and found the peak time in Sichuan Province was earlier and the peak value was lower (Fig. 6).
Global Situation During The Same Period
The earliest confirmed cases outside China were reported in Thailand on January 13 followed by Japan (January 15) and Republic of Korea (January 20), the USA (January 21), Singapore and Vietnam (January 23). On February 21, four weeks after the first reported case in Korea, the number of confirmed cases began to rise rapidly. In addition, Italy began to rise rapidly two weeks after the first case report and Iran increased quickly in the second week of the first case report. Furthermore, the USA (5 weeks after the first case) and other European countries such as Spain (3 weeks after the first case), France (5 weeks after the first case), Germany (4 weeks after the first case), and Switzerland (1 week after the first case) have begun to rise rapidly, and Many European countries slightly earlier than the USA into the rising period.The length of time from the first report to the period of rapid rise in different countries varied. Most of them entered the rapid growth phase were within 1 month (Fig. 7). The confirmed cases reported in USA increased sharply in the 8 to 9 week.
From the scatter plot of confirmed cases (top 10 countries), it was found that when the daily increase exceeded 20–30 cases, most countries entered a obvious increase stage (Fig. 8). From the time point of the first daily increase of 20 cases, Germany, Spain, and Italy reached the peak of daily increment after 28, 29, 34 days, and the daily increment showed a downward trend. The average daily increment of 7-days rolling also showed an inflection point in Italy. France, UK, USA appeared a peak in 36 days, 32 days, and 44 days respectively. According to the regional division in WHO report, many countries in African Region and South-East Asia Region were closer to the equator wtih slow growth or at the early stage. In Eastern Mediterranean Region and Region of the Americas, most countries were at rapid growth phase, as well as Russian in European Region. Most european countries as well as USA presented an inflection point or at a plateau period in the 4th to 5th weeks but falling slowly. The curve of China dropped fast after the 5th week (Fig. 9). China reached the peak of the daily increment of the epidemic in 18 days if do not take into account the clinical diagnosis cases and cost 27 days if take into account (Hubei province in China reported clinical diagnosis on February 13–15, and was counted in the 28th COVID-19 Situation Report by WHO which was only applicable to Hubei province). China was dominated by the imported cases since the 8th weeks with the basically disappearance of local cases and the rapid rise of epidemics in other countries abroad (Fig. 10). The overseas imported cases were first reported in Ningxia Province of China on Feb 26 and were cumulative to 1610 on April 21, 21 of which was reported by Sichuan Province.