Abstract

Purpose

Population mobility significantly contributes to the spread and prevalence of infectious diseases, posing a serious threat to public health safety and sustainable development across the globe. Understanding the impact of population mobility on the prevention and control of infectious diseases holds profound significance.

Methods

In this study, we collected the data on the incidence of notifiable infectious diseases in mainland China from 2013 to 2019, and analyzed the characteristics of notifiable infectious diseases, as well as their correlation with transportation passenger traffic.

Results

Among 29 common notifiable infectious diseases, the incidence rate of intestinal diseases per 100,000 people was the highest (256.35 cases), while the mortality rate was the lowest (0.017 cases). The mortality rate per 100,000 people due to sexually transmitted and bloodborne diseases was the highest (1.154 cases). A significant linear correlation was noted between commercial passenger traffic and the number of cases of tuberculosis (r = 0.83, P = 0.022), hepatitis A (r = 0.87, P = 0.012), bacillary and amebic dysentery (r = 0.90, P = 0.006), typhoid/paratyphoid (r = 0.94, P = 0.002), leptospirosis (r = 0.90, P = 0.005), AIDS(r=-0.90, P = 0.006), gonorrhea (r=-0.79, P = 0.035) and scarlet fever (r=-0.85, P = 0.016). A significant linear correlation was noted between public transportation passenger traffic and the number of cases of measles (r = 0.94, P = 0.002), hepatitis A (r = 0.96, P = 0.001), parasitic and vector-borne diseases (r = 0.96, P = 0.001), brucellosis (r = 0.95, P = 0.001), leptospirosis (r = 0.88, P = 0.008), other infectious diarrhea (r = 0.86, P = 0.013) and gonorrhea (r = 0.84, P = 0.018).

Conclusion

The results of this study indicated that transportation passenger traffic significantly affected the incidence of infectious diseases, and reasonable management of passenger traffic was a potentially important means of prevention and control of infectious diseases.

Background

Societal development frequently coincides with accelerated population mobility, which facilitates communication and heightens the risk of infectious disease transmission, particularly in areas characterized by close social interaction such as crowded transportation vehicles [1,2,3]. Beyond speed, efficiency, accessibility, and volume of human travel, convenient transportation also creates conditions conducive to the spread of infectious diseases [4, 5]. For example, at the onset of the global coronavirus disease 2019 (COVID-19) pandemic, population migration significantly expedited the spread of the epidemic [6,7,8]. The Chinese government was able to effectively mitigate the spread of the epidemic through a range of emergency interventions, including traffic restrictions and localized isolation, thereby underscoring the significance of population mobility and disease transmission [9, 10].

Population mobility encompasses both long-distance and short-distance travel. Long-distance travel, which involves crossing urban areas, provinces, or even countries via trains, planes, ships, etc., is characterized by extended contact durations between individuals and a larger number of people in contact. On the other hand, short-distance migrations are more frequent and can be facilitated through modes such as buses, subways, and taxis [11]. Both forms of population mobility have the potential to influence the spread of infectious diseases. However, there is a lack of data evaluating the evolving characteristics of population mobility and its complex, diverse patterns [12].

China, with its large population and expansive territory, is burdened by high incidence rates and mortality of various infectious diseases. The country accounts for 9% of the global new cases of tuberculosis, ranking second only to India (27%) [13]. Furthermore, China has the highest mortality rate from viral hepatitis worldwide [14], a situation that poses significant threats to public health, social development, and national security. Consequently, understanding the relationship between passenger traffic in public transportation and the incidence of infectious diseases is crucial. However, most existing research on the impact of population mobility on infectious diseases focuses on respiratory infections, neglecting the potential influence of transportation passenger traffic on the spread of other infective diseases.

In this study, we collected incidence data for 29 prevalent notifiable infectious diseases in mainland China from 2013 to 2019. The aim was to evaluate the fundamental characteristics of infectious disease onsets. Furthermore, we investigated the correlation between the number of new infectious disease cases and the volume of national transportation passenger traffic. This analysis provides a valuable reference for public health supervision, prevention, and control of infectious diseases in China.

Methods

Data sources

Data on the number of new cases and deaths due to notifiable infectious diseases were obtained from the official website of the National Health Commission of the People’s Republic of China (). This study collected nationwide data, excluding Hong Kong and Macao Special Administrative Regions and Taiwan, on 29 common notifiable infectious diseases from 2013 to 2019. The diseases encompassed 21 Class B infectious diseases, which include acquired immune deficiency syndrome (AIDS), hepatitis A, B, C, and E, measles, epidemic hemorrhagic fever, rabies, epidemic encephalitis B, dengue fever, bacillary and amebic dysentery, tuberculosis, typhoid/paratyphoid, pertussis, scarlet fever, brucellosis, gonorrhea, syphilis, leptospirosis, schistosomiasis, malaria. Additionally, the study included 8 Class C infectious diseases such as influenza, mumps, rubella, acute hemorrhagic conjunctivitis (AHC), kala-azar, echinococcosis, other infectious diarrhea, and hand-foot-and-mouth disease (HFMD).

The data pertaining to nationwide passenger traffic, excluding Hong Kong and Macao Special Administrative Region and Taiwan, were sourced from the annual analysis report from the Ministry of Transport of the People’s Republic of China (). The data analyzed comprised of commercial passenger traffic and public transportation passenger traffic. Commercial passenger traffic encompassed the aggregate passenger traffic across various modes of transport, including railways, highways, waterways, and aviation. On the other hand, highway passenger traffic specifically referred to traditional chartered and shuttle bus passenger traffic. Public transportation passenger traffic, on the other hand, included the total passenger traffic for buses, trams, and urban rail transit.

Case definition

Infectious diseases were diagnosed using the standard diagnostic methods outlined in the 2013 revised version of the Infectious Disease Prevention and Control Law of the People’s Republic of China (). Passenger traffic was assessed on a per-person basis, irrespective of the distance traveled or fare paid. Each passenger was counted as one individual per trip. Discounted tickets and those issued to children were also considered as one person.

Statistical analysis

The data was statistically evaluated utilizing SPSS 24.0 software. The correlation between passenger traffic and the incidence of infectious diseases was assessed using Pearson bivariate correlation. For data exhibiting a significant correlation, additional linear regression analysis was conducted to ascertain the influence of passenger traffic on the number of infectious disease cases. A two-tailed P < 0.05 denoted the statistical significance of the findings.

• 1. Annual average number of new cases = total number of new cases from 2013 to 2019/7.

• 2. Annual average number of new deaths = total number of new deaths from 2013 to 2019/7.

• 3. Annual average incidence rate = (total number of new cases from 2013 to 2019/7)/(total population from 2013 to 2019/7) *100,000.

• 4. Annual average mortality rate = (total number of new deaths from 2013 to 2019/7)/(total population from 2013 to 2019/7) * 100,000.

• 5. Annual increase rate = (total number of new cases in the current year/total number of new cases in the previous year − 1) * 100%.

Results

An overview of the incidence of common notifiable infectious diseases from 2013 to 2019

Between 2013 and 2019, a total of 55,913,973 cases of common notifiable infectious diseases were reported nationwide, resulting in 133,811 deaths. The estimated annual average incidence rate was 577.75 cases/100,000 people, and the annual average mortality was 1.38 cases/100,000 people. Based on the estimated transmission route, the incidence rate was highest for intestinal diseases (256.35 cases/100,000 people), followed by respiratory diseases (165.88 cases/100,000 people), the lowest was for parasitic and vector-borne diseases (6.86 cases/100,000 people). The highest mortality rate per 100,000 people was observed for sexually transmitted and bloodborne diseases (1.154 cases), and the lowest for intestinal diseases (0.017 cases).

The top five ranking diseases per 100,000 people with the reported annual average incidence rate were HFMD (159.50 cases), hepatitis B (83.06 cases), tuberculosis (83.01 cases), other infectious diarrhea (80.33 cases), influenza (57.03 cases), accounting for 80.22% of all diseases. The three top-ranking diseases per 100,000 people with annual average mortality reported were AIDS (1.107 cases), tuberculosis (0.142 cases), and rabies (0.047 cases), accounting for 93.91% of the total deaths (TableÌý1).

Table 1 Incidence and mortality data of 29 notifiable infectious diseases nationwide from 2013 to 2019

The change trend of common notifiable infectious diseases and transportation passenger traffic

From 2013 to 2019, there was an average annual increase rate of 19% for respiratory diseases. However, when influenza was excluded, the total number of respiratory diseases only decreased marginally by -3.6%. A slow upward trend was observed from influenza, from 2013 to 2018, with a sharp rise in 2019, resulting in a 356.51% increase in cases. The average annual increase in tuberculosis cases was − 3.9%, showing a slow downward trend. Measles cases have been on a downward trajectory since 2015, with a significant drop of -75.54% in 2017. The cases of pertussis and scarlet fever showed a wave-like upward trend, with a 113.11% increase in pertussis cases in 2018. Mumps and rubella showed a decreasing trend first and then increased, and the cases of rubella increased by 677.40% in 2019.

Compared with other diseases, the smallest fluctuation was seen in sexually transmitted and bloodborne diseases. In general, AIDS, hepatitis B, hepatitis C, and syphilis showed an increasing trend, at the rates of 1.64%, 5.78%, 0.04%, 2.53%, and 4.47%, respectively. Gonorrhea exhibited volatility, with a peak growth rate of 20.95% in 2017 and a decrease of 11.28% in 2019.

The increased rates of total intestinal diseases and HFMD fluctuated at nearly 0, and the number of cases tended to stabilize. The number of cases for both bacillary and amebic dysentery demonstrated an annual decline of 12.54%. There was also a marginal decrease in hepatitis A cases by 2.53%, while other infectious diarrhea cases saw a slight increase of 6.56%. There was no significant increase or decrease in the number of cases of hepatitis E, typhoid/paratyphoid, and AHC that tended to stabilize.

Relative to infectious diseases transmitted through other channels, the cases of parasitic and vector-borne diseases exhibited the largest fluctuation. The total number of cases increased to its highest level in 2014 (61.89% increase), followed by a downward trend. Among these, rabies showed a decreasing trend annually (-19.66%), while the incidence of leptospirosis cases decreased by 95.55% in 2013 and subsequently remained at a relatively low level. The incidence of dengue fever peaked in 2014 with a 910.7% increase in cases, then remained at a relatively low level and increased again at a 334.01% rate in 2019. The cases of schistosomiasis reached its peak in 2015, with an 871.39% increase in cases and gradually decreasing thereafter. The range of fluctuation in cases of Japanese encephalitis was relatively large, with a 76.55% decrease in cases from 2013 to 2015 and an increase of 115.75% in 2016. The range of fluctuation of brucellosis, malaria, and echinococcosis was relatively small compared to that of other parasitic and vector-borne diseases.

The trend of changes from 2013 to 2019 in commercial and public transportation passenger traffic were similar, peaking in 2014 and then showing a downward trend. However, while commercial passenger traffic continued to decline in 2019, public transportation passenger traffic showed an upward trend (Fig.Ìý1).

Fig. 1

The change trend of annual increase rates of notifiable infectious diseases and transportation passenger traffic from 2013 to 2019. (A) Respiratory diseases; (B) Sexually transmitted and bloodborne diseases; (C) Intestinal diseases; (D) Parasitic and vector-borne diseases; (E) Transportation passenger traffic

Pearson correlation analysis

Among sexually transmitted and bloodborne diseases, we noted a significant negative correlation of commercial passenger traffic with the number of cases of AIDS, hepatitis B, hepatitis C, gonorrhea and syphilis (P < 0.05). The public transportation passenger traffic exhibited a significantly negative correlation with the cases of hepatitis B and gonorrhea (P < 0.05), but not with AIDS, hepatitis C and syphilis.

Among respiratory diseases, we observed a significant positive correlation of commercial passenger traffic with the cases of measles and tuberculosis (P < 0.05), and a significant negative correlation with the cases of pertussis, scarlet fever, and influenza (P < 0.05), but has no significant correlation with mumps and rubella. The study found a significant positive correlation between public transportation passenger traffic and the incidence of total respiratory diseases (excluding influenza) and measles (P < 0.05). However, no significant correlation was observed with the incidence of tuberculosis, pertussis, scarlet fever, influenza, mumps, and rubella.

Among intestinal diseases, commercial passenger traffic was significantly positively correlated (P < 0.05) with the cases of hepatitis A, bacillary and amebic dysentery, typhoid/ paratyphoid, and significantly negatively correlated (P < 0.05) with the cases of other infectious diarrhea, but the correlation with the cases of hepatitis E, AHC and HFMD was not significant. Likewise, public transportation passenger traffic was significantly positively correlated with the cases of hepatitis A (P < 0.05), and significantly negatively correlated with the cases of hepatitis E and other infectious diarrhea (P < 0.05), but exhibited no significant correlation with the cases of bacillary and amebic dysentery, typhoid/paratyphoid, AHC, and HFMD.

Among parasitic and vector-borne diseases, commercial passenger traffic was significantly positively correlated with the cases of rabies and leptospirosis (P < 0.05), but the correlation with epidemic hemorrhagic fever, Japanese encephalitis, dengue, brucellosis, schistosomiasis, malaria, black fever and echinococcosis was not significant. Public transportation passenger traffic showed a significant positive correlation with the cases of total parasitic and vector-borne diseases, brucellosis, and leptospirosis (P < 0.05), but had no significant correlation with the cases of epidemic hemorrhagic fever, rabies, Japanese encephalitis, dengue, schistosomiasis, malaria, black fever and echinococcosis (TableÌý2).

Table 2 Pearson correlation analysis between the number of new cases of notifiable infectious diseases and transportation passenger traffic

Linear regression analysis

A linear regression analysis was conducted on the correlated passenger traffic and infectious diseases using passenger traffic as the independent variable and the cases of infectious diseases as the dependent variable (TableÌý3). The results of the linear regression analysis showed a linear regression relationship of commercial passenger traffic with tuberculosis, hepatitis A, bacillary and amebic dysentery, typhoid/paratyphoid, leptospirosis, AIDS, gonorrhea, and scarlet fever (P < 0.05). The cases of tuberculosis, hepatitis A, bacillary and amebic dysentery, typhoid/paratyphoid, and leptospirosis increased with the increase in commercial passenger traffic and decreased with the decrease in traffic, while the cases of AIDS, gonorrhea and scarlet fever increased with reduced commercial passenger traffic.

Table 3 Univariate and binary linear regression analysis between the number of new cases of notifiable infectious diseases and transportation passenger traffic

A linear regression relationship was observed between public transportation passenger traffic and the cases of gonorrhea, measles, hepatitis A, other infectious diarrhea, total parasitic and vector-borne diseases, brucellosis and leptospirosis (P < 0.05). The cases of measles, hepatitis A, total parasitic and vector-borne diseases, brucellosis and leptospirosis increased with the increase in public transportation passenger traffic and decreased with reduced traffic, while the cases of gonorrhea and other infectious diarrhea was inversely correlated with the decrease in public transportation passenger traffic.

The binary linear regression analysis showed a linear regression relationship of commercial passenger traffic and public transportation passenger traffic with measles, hepatitis A and other infectious diarrhea (P < 0.05). The cases of hepatitis A and measles were directly correlated with commercial and public transportation passenger traffic and increased or decreased accordingly, while the cases of other infectious diarrhea was inversely correlated with the increase in commercial and public transportation passenger traffic (Fig.Ìý2).

Fig. 2

Correlation regression analysis between the number of new cases of notifiable infectious diseases and transportation passenger traffic

Discussion

Transportation vehicles have the potential to transmit diseases through human contact and may also serve as vectors for transmission, such as Aedes mosquitoes and ticks [15]. Pathogen-carrying individuals or vectors can disseminate diseases to others during travel or upon arrival at their destination. In some instances, passengers may even contract a local disease upon reaching their destination. During migration, these individuals act as either infected or asymptomatic carriers, subsequently introducing the disease to new locations. This process significantly accelerates the transmission of infectious diseases and broadens their geographical distribution, leading to outbreaks and epidemics [16]. Given the complexity associated with population mobility and the multiple modes of disease transmission, it is imperative that passenger transportation be more rigorously controlled to prevent the global spread of infectious diseases once they occur.

Despite significant improvements in the hygiene conditions of global public spaces, there remains a notable deficiency in attention to infectious disease incidents within transportation hubs [17, 18]. Furthermore, no dedicated network system currently exists to monitor and track the influence of population mobility patterns on the incidence of infectious diseases. For instance, integrating preventative measures for infectious diseases with the transportation network system could be beneficial. This could involve constructing a population mobility positioning system, enhancing screening procedures for infectious diseases [19], and equipping transportation hubs with standard temperature detectors. For patients or asymptomatic carriers of infectious diseases, it is imperative that care-taking staff supervise them to ensure they wear masks, wash their hands frequently, improve indoor ventilation, and arrange for them to sit at the window to minimize close contact with other passengers [20,21,22].

In this study, although we observed an annual decline in the incidence of tuberculosis, the incidence and mortality rates of tuberculosis were the highest among respiratory diseases, consistent with the study of Dong Z et al. [23]. Screening of high-risk groups should be strengthened in the prevention and control of tuberculosis, considering the global challenges of multidrug-resistant tuberculosis [24]. Unlike tuberculosis, the infection symptoms of other respiratory diseases were relatively mild. In addition, although the overall symptoms of intestinal diseases were relatively mild, the incidence rate in terms of the number of cases, was the highest, inconsistent with the research of Zhu Y et al. [25]. In our study, the incidence rate of HFMD was the highest among all infectious diseases [26]. Although the incidence rate of AIDS was low, the mortality rate was the highest, even higher than that due to rabies. Therefore, to prevent and control infectious diseases, the health department needs to increase efforts to improve the public health environment, and cooperate with the education department to improve the public’s self-protection consciousness and capabilities.

This study showed a significant negative correlation between commercial passenger traffic and the number of cases of sexually transmitted and bloodborne diseases (AIDS, hepatitis B, hepatitis C, gonorrhea, and syphilis). The cases of gonorrhea decreased with the increase in commercial passenger traffic and public transport passenger traffic, consistent with the increase in the number of cases of sexually transmitted and bloodborne diseases during the COVID-19 pandemic [27, 28]. This may be because non- pharmacological interventions result in longer indoor activities, also increasing the risk of unsafe sexual behavior [27, 29]. Therefore, during the lockdown period amidst the outbreaks of infectious diseases, besides strengthening epidemic prevention and control, it is crucial to enhance publicity and education on safe sexual behavior. Enhancing the public’s health awareness and self-protection abilities is an important means of preventing the spread of infectious diseases. Healthcare professionals should strengthen health education, popularize knowledge about the prevention and control of infectious diseases.

Respiratory diseases are more amenable to spread during travel. This study found a significant positive correlation between commercial passenger traffic and the number of cases of measles and tuberculosis. Likewise, public transportation passenger traffic was also significantly positively correlated with the number of cases of total respiratory diseases (except for influenza) and measles. With the increase in commercial passenger traffic, the cases of tuberculosis also increased, while that of scarlet fever decreased, which may be attributed to the decline in the birth population [30]. The cases of measles also increased with the increase in public transportation passenger traffic. Population migration has been found to increase the risk of tuberculosis and measles transmission [31,32,33], consistent with the results of this study. This necessitates that healthcare professionals bolster their surveillance and early warning mechanisms for infectious diseases to promptly identify outbreaks and implement effective interventions. Concurrently, they must devise efficient strategies to address these outbreaks, encompassing traffic management, passenger transport coordination, and ensuring the timely delivery of emergency supplies, all with the aim of mitigating the public health repercussions of such events. While some studies have found that air travel cannot spread tuberculosis, possibly due to the good ventilation of the aircraft, and the number of passengers is less than that in land transportation vehicles such as trains and high-speed railways. In this study, a significant negative correlation was noted between commercial passenger traffic and the cases of pertussis, scarlet fever, and influenza, in contrast to the research results of Ndeh NT et al. [34]. However, one survey of the incidence of infectious diseases in China reported increased incidence rate of influenza in 2020 [35], consistent with the results of this study.

Among intestinal and parasitic and vector-borne diseases, the number of cases of hepatitis A, bacillary and amebic dysentery, typhoid/paratyphoid, and leptospirosis were related directly to commercial passenger traffic. Concurrently, the cases of hepatitis A and parasitic and vector-borne diseases directly correlated with the increase or decrease in public transportation passenger traffic, consistent with the results reported by Bai BK et al. [36], but the number of cases of other infectious diarrhea increased with the decrease of public transportation passenger traffic. The prevention and control of infectious diseases should consider the means of transportation, and any places where people are in close contact with each other, such as schools, hospitals , shopping malls, the infectious diseases may spread in any places with large populations. Public intervention measures may have varying impacts on different infectious diseases, and these should be comprehensively considered and supervised. Healthcare professionals are tasked with the development and refinement of pertinent policies and regulations, taking into account the unique characteristics and trends of infectious disease transmission. This provides a legal framework and policy support for epidemic response, thereby ensuring that such efforts are conducted in an orderly and systematic manner.

There may be some possible limitations in this study. Firstly, this study only analyzed the correlation between passenger traffic in transportation and common notifiable infectious diseases in China from 2013 to 2019, and it is necessary to extend the time span of analysis in future research. Secondly, the passenger traffic volume calculated in this study does not represent all population migration; other modes of transportation such as private cars and taxis also contribute to population movement, which should be further considered in future studies.

Conclusion

To summarize, commercial and public transportation passenger traffic impact the incidence of various notifiable infectious diseases in mainland China. Therefore, to prevent, manage, and control infectious diseases, it is necessary to examine population mobility, strengthen global public health awareness, and foster the participation of society in resisting the spread of infectious diseases.