| Background Over the past few decades,China has made remarkable achievements in the prevention and control of infectious diseases,but infectious diseases are still a major public health problem threatening the lives and health of Chinese people.Over the past forty years since the reform and opening up,driven by various factors such as the reform of land system,the development of market economy,demographic changes,and the loosening of migration policies,the spatial mobility of China’s population has undergone a transformation from the state of “Rural China” with low population mobility to the state of “Migrating China” with large-scale and high-frequency population mobility.Population mobility is an important driver of infectious disease transmission and spread,while promoting the economic development,the large-scale inter-regional population movements has also brought challenges to the prevention and control of infectious diseases.However,there is still a lack of systematic and comprehensive research evidence on the flows of various infectious diseases lurking in the inter-regional population movements.By abstracting the real-world complex relations among entities into a network model consisting of nodes and edges,network analysis could effectively reveal the relation patterns among different parts of a complex system,and it would help us to understand the spatial characteristics and potential organizational patterns of the interregional population movements and flows of infectious diseases from a perspective of flow and network,so as to support for more efficient and targeted infectious disease control strategies in future.Objects To understand the current population mobility pattern,and the inter-regional flows of various infectious diseases in recent years in China.To identify the major types of infectious diseases with largest amounts of flow cases,and understand the demographic,temporal,and spatial characteristics of the infectious disease flows.To construct network models of the inter-city flows for the major types of notifiable infectious diseases,and analyze the spatial characteristics and potential organizational patterns of inter-regional flows of infectious diseases in China.Methods(1)Based on inter-city population mobility data among 337 major cities of mainland China collected from the AMAP open data platform,we constructed the intercity population mobility network model and used complex network analysis to characterize the inter-city population mobility pattern in China,in terms of node distribution,spatial connection,and community structure.(2)Based on the infectious diseases surveillance data collected from the notifiable infectious diseases reporting system during 2016 to 2020,we used descriptive statistical methods to describe and analyze the incidence of various infectious diseases with different transmission routes.(3)Based on the geographical location information of the residence and disease report in individual data of notifiable infectious diseases,we extracted the inter-city flow cases of infectious diseases,calculated the amounts of inter-city flow cases of various infectious diseases,and characterize the epidemiological features of these inter-city infectious diseases flows in terms of population,temporal,and spatial distribution.(4)Based on the inter-city flows of infectious diseases,we constructed network models of the inter-city flows for the major types of notifiable infectious diseases,respectively,and used complex network methods to analyze the spatial characteristics and potential organizational patterns of the infectious diseases’ inter-city flows in terms of node distribution,spatial connection,and community structure.Results The inter-city population mobility in China is dominated by short-distance flows,and it showed a spatial differentiation pattern of tight in southeast and sparse in northwest separated by the Hu line in general.Large amounts of population mobility were found in megacities like Beijing,Shanghai,Guangzhou,Shenzhen and other provincial capitals and formed a polycentric spatial pattern in the inter-city population mobility network.The community structure of the population mobility network was observed to be a certain coupled with the provincial administrative divisions,and was quite stable across different time periods including the travel restriction period of COVID-19 pandemic and travel rush period of the Spring Festival or official holidays.From 2016 to 2020,there were a total of 32,621,414 cases of the 44 types(including subtypes)of notifiable infectious diseases were reported in mainland China,with annual incidence of 463.07/100,000.The top five diseases with the highest incidence were HFMD(hand,foot,mouth disease),influenza,hepatitis B,tuberculosis,and syphilis,which accounted for 83.45% of the total reported incident cases.By transmission routes,respiratory infectious diseases had the highest incidence of 169.13/100,000,followed by directly transmitted/fecal-oral transmitted diseases(146.55/100,000)and blood-borne and sexually transmitted diseases(143.53/100,000),while zoonosis and vector-borne diseases had the lowest incidence of 5.23/100,000.From 2016 to 2020,there were a total of 2,674,892 inter-city flow cases reported in the notifiable infectious diseases reporting system,accounting for 8.20% of the total reported incident cases.The top five diseases with the largest amounts of inter-city flow cases were hepatitis B,tuberculosis,HFMD,syphilis and influenza,which accounted for79.23% of the total flow cases.The top five diseases with the largest proportion of flow cases in total reported cases were malaria,Kala-azar,plague,Japanese encephalitis and hydatid disease.The population distribution showed that there were more male than female and more preschool children and young adults than the school-age children and the elderly in the flow cases of infectious diseases,the temporal distribution showed that the trends of flow cases amounts were generally consistent with the seasonal patterns of local cases,and the spatial distribution showed that the inflow rates and inflow/outflow ratios were higher in provincial capital cities,while the outflow rates were higher in the Qinghai-Tibet Plateau region.The graph density of the networks of the 14 major types of infectious diseases was positively correlated with their amounts of flow cases(r=0.87,P<0.001),in which hepatitis B had the highest graph density of 0.279,followed by syphilis(0.236)and tuberculosis(0.196).Inter-city mobility of infectious diseases was dominant by shortdistance flows,with over 50% occurring within 400 kilometers.The cities with high inflow of infectious diseases cases were largely coincident with the provincial capital cities,which acted as the convergence centers in the network of infectious diseases flows.The inter-city flow networks of the major type of infectious diseases generally exhibited strong community characteristics,and the spatial distribution of community structure was also coupled with the provincial administrative divisions,similar to that of inter-city population mobility,formed 10 to 17 communities of dense internal connections,respectively,with modularity ranges from 0.515 to 0.795.Besides,there were strong connections between the cities in Southwest China and the Yangtze River Delta in the network of sexually-transmitted diseases such as HIV/AIDS and gonorrhea.Conclusions In this study,we used the complex network methods to analyze the spatial patterns of inter-city population mobility and infectious diseases flows in mainland China from the perspectives of flow and network,based on the inter-city population mobility data Internet location-based services and surveillance data of infectious diseases from the national notifiable infectious diseases reporting system.The results showed that:(1)China’s population mobility network held a polycentric structure with megacities and provincial capitals as cores,and the population mobility network could be generally divided into 11 communities,whose spatial structure was a certain coupled with the provincial administrative divisions and was generally stable across different times.(2)Under the large-scale population mobility,there were also frequent inter-city flows of various infectious diseases,accounting for 8.20% of the total reported cases of notifiable infectious diseases.The top five diseases with the largest amounts of inter-city flow cases were hepatitis B,pulmonary tuberculosis,HFMD,syphilis,and influenza,for which more efforts should be paid to their transmission risks with population movements.(3)The inter-city flows of infectious diseases was dominant by within-provincial short-distance flows.Most cities in the network were found centered around provincial capital cities,forming a spatial distribution pattern where surrounding cities converge around the provincial capitals.Therefore,it is necessary to establish integrated inter-regional infectious disease prevention and control strategies and information communication mechanism centered around the provincial capitals. |
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