Should we keep hope? Key 8 weeks - Spatiotemporal epidemic characteristics of COVID-19 in Sichuan Province and its comparative analysis with other provinces in China and global epidemic trend

Background: To compare the epidemiological characteristics of Sichuan other in by analyzing the prevalence and length of epidemic in order to provide a basis for responding to imported cases abroad and to formulate prevention and control strategies in areas that are still rapidly circulating. Methods: The number of confirmed cases, daily growth, incidence and the length of time from the first reported case to the end of local case(non-overseas imported cases) were compared by spatial and temporal (geographical, temporal) classification. Visualizing the development and changes of epidemic situation by layer through maps. Results: In the first wave, total of 539 cases were reported in Sichuan Province, with the incidence rate of 0.6462 / 100,000. The closer to Hubei, the heavier the epidemic. The peak of Sichuan Province came earlier and the value was lower. Eight weeks after Wuhan lockdown, all became better. The longest epidemic length in city level of China was 53 days, median 23 days. It was released quickly in the 1st month, and accelerated in the 2ed month (three times of 1st month). Most countries outside China began to rise rapidly 4 weeks after their first case. Some European countries was earlier than USA. Germany, Spain, Italy, and China cost 28, 29, 34, and 18 days to reached the peak of daily increment, after their daily increase up to 20 cases. Countries in African Region and South-East Asia Region were at the early stage, in Eastern Mediterranean Region and Region of the Americas were at rapid growth phase,in European presented an inflection point or at a plateau period but falling slowly. Conclusions: Adopting appropriate isolation and control measures is necessary to actively respond to the epidemic situation. If effective measures were implemented at the 8 key weeks, the peak value of the confirmed cases will be lower and decrease quickly. Some countries with improved epidemic situations also need to develop a continuous "local strategy at entry checkpoints" to respond to a possible second local epidemic.


Methods
To reflect the actual geographical distribution risk of confirmed cases in Sichuan Province, the current residential addresses of confirmed cases from the Sichuan COVID-19 Surveillance System were selected for distribution description. For comparison with neighboring provinces, the situation of confirmed cases reported by the National Health and Health Commission, 5 Hubei Province, 6 and other provinces Health and Health Commission, were analyzed using the address of reporting unit (usually hospital/ CDC). Data from various countries were from the WHO COVID-19 Daily Report published since January 21. 7 The case number in China before that first Report and the first case information of Thailand, Japan, Republic of Korea, and USA mentioned in the previous Report of WHO referred to their national government websites. [8][9][10][11] The population of various cities in Sichuan Province, and the number of counties and districts of the cities were from the Statistical Yearbook of Sichuan Province. 12 The characteristics of cumulative confirmed cases, daily new cases, morbidity, etc. were compared based on temporal and spatial factors; the length of time from the first case report to the end of the local case (nonforeign imported case) (abbreviated as "epidemic length") was analyzed to explore the influencing factors of prevention and control of the outbreaks. Setting key analysis time and units based on key time points of policy and disease incubation periods. Drawing the epidemic maps of Sichuan and China in different times and spaces by SAS software (SAS studio https://welcome.oda.sas.com/). Directly visually display the development and changes of the epidemic situation and explore the epidemic law by layers. Confirmed cases scatter plot, column diagram as well as line diagram were also used to display the the time trend.

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). 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. 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. 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.

Distribution of the epidemic length in each region
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 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.

Discussion
The eastern region of Sichuan Province is adjacent to Chongqing, and Hubei provinces. Many counties there have reported cases, which is related to the fact that imported cases were the main cases in our province in the early stage. Combined with the "Baidu Migration Data" analysis, 15 the national migration scale index 15 on January 23 and before was slightly higher than that of the same period last year (January 24 was the Chinese New Year's Eve), but after January 25, the national migration scale index fell slightly until March 12, which was lower than the same time of last year. On January 23, the proportion of migrants in cities across China (the ratio of the population moved to a city to the total population moved into kinds of cities in whole country), the top 3 were Chongqin, Chengdu, and Zhoukou city. Twelve of 100 cities were in Sichuan Province, all of which are located in the eastern part. Among them, Chengdu ranked first in the 26-30 days. The proportion of emigration place (the ratio of the emigration to a certain city to the total emigration of the whole country), 9 of the top 100 were in Sichuan Province,which were also located in the east. This result suggested that the population flow in eastern Sichuan was relatively large. In addition, the low incidence in western Sichuan was also associated with a lower population density in the western region than in the east. In a few of these areas the incidence was also high because of the an outbreak. 16 The first reports of kinds of cities in Sichuan Province were concentrated in the first week after Wuhan closed. This reflected a rapid response and quarantine nature of Sichuan Province. The number of cases increased significantly in the first 2 weeks (14 days), which was in line with the average incubation period of 14 days. 17,18 This suggested that the first two weeks after the occurrence of the first case was a critical stage for taking quarantine, prevention and control measures.
The spatiotemporal distribution of the country suggests that the virus spreads rapidly during the two incubation periods. The analysis of the length of the epidemic indicates that after China has adopted strong prevention and control measures, most regions can control the growth rate of the epidemic in approximately 3 weeks.The average and median of the epidemic length of county-level regional units are significantly lower than the epidemic length of city-state regional units. It is suggested that regional units of different levels can combine actual conditions to formulate prevention and control measures, duration of prevention and control, and resumption time. Especially for areas where there is no community outbreak in the local area, production can be resumed early to reduce economic losses. The doubling of cases in spatiotemporal distribution shows that under the Chinese national defense control model, the epidemic trend needs to go through two release stages. It was released rapidly in the first month after initiating prevention and control measures throughout China. The release was accelerated release in the second month and was three times that of the first month (approximately the regeneration index of COVID-19 reported in the recent research). It indicated that on March 12, the incidence of major countries in the world was still in the first stage, and from March 25, most countries entered the second stage of rising. After comparing and analyzing the morbidity, we found that the length from the first case to the rapid rise of cases varies in different countries.
Most countries entered the period of rapid growth after 4 weeks. The delayed entry of first confirmed cases in a few countries was related to the late launch of extensive testing. The effective control of the epidemic in China was also related to the reduction of direct contact of the money by using the mobile payment method. The popularity of foreign mobile payments was slightly lower than that in China, which increases the risk of prevention and control.
As COVID − 19 is a major public health emergency that has occurred in China since the founding of the People's Republic of China. In the early stage of the epidemic, due to the insufficient capacity of hospitals to receive treatment and the failure of a few medical institutions to timely connect with the disease prevention and control information system, hospitals were in overload operation and medical staff were busy with treatment, which objectively resulted in the phenomena of late report, missed report and false report. On March 18, the newly confirmed was reported zero growth in wuhan for the first time. Since then, the spread of the epidemic has been basically blocked, and the control of the passage from Wuhan to other city has been lifted, creating favorable conditions for the comprehensive and detailed verification and revision of the epidemic data. The revised types included reductions and additions. Among them, 217 cases were reduced after verification (some of the patients had been treated in different districts or in multiple hospitals, resulting in repeated card reporting); 542 cases were added (previous cases not reported in time due to late reporting and omission). The total confrimed cases number was revised from 50,008 to 50,333 in April 17 based on the principles of realism and transparency of data 19 . Although this part of the newly confirmed number accounted for a small proportion (0.6%) of the total confirmed number in wuhan, it was insufficient that this part of the revised number was not distributed to days by the reporting date, so this part of data was not included in the analysis in this study.

Conclusions
Combined with the history of the epidemic in China, it is suggested that if countries take effective and powerful measures the number of confirmed cases will increase rapidly in the recent month, which will inevitably challenge the medical resources and population health of countries. If no measures are taken, it is difficult to estimate the number of infections and the overall economic losses caused.
Combined with the severity and mortality rates, the health loss to the population is fatal.
In addition, with the period of entering into zero growth and gradual cure of local cases in China, high vigilance must be maintained. From February 26, 2020, the different provinces of China have begun to report imported cases abroad. With the change of epidemic situation in different countries and the different measures taken by governments, the import abroad of China has soared. A small number of overseas associated cases have appeared. In response, from March 28, 2020, entry of foreigners holding valid Chinese visas and residence permits will be suspended. Some countries with improved epidemic situations also need to quickly formulate a continuous "local strategy of entry checkpoints"      The comparison of average daily increment between Sichuan and other 6 Provinces *One unit of the abscissa was a week (7 days). It set the day when the first cases reported as the start point. .During the two weeks before Hubei lockdown, the top destinations of Hubei's emigration population was Henan Province.Sichuan Province ranked 7th. Taking the migration from Hubei at this stage as a possible high risk factor, this chart selected the provinces that rank close to Sichuan Province (4 to 10) for comparison. The peak time in Sichuan Province was earlier and the peak was lower. The fluctuation after the 8th week of each province was mainly imported cases abroad.   The analysis of average daily increment of 7-days round in different countries and regions *One unit of the abscissa was a week (7 days). It set the day when the new cases exceeded 20 as the start point. According to the regional division in WHO report, this  territory, city or area or of its authorities, or concerning the delimitation of its frontiers or