Background
Tuberculosis (TB), caused by the mycobacterium Tuberculosis complex, is a longstanding global health challenge. Its origins can be traced back 9,000 years through the detection of TB in ancient human remains [
1]. TB primarily spreads through respiratory droplets released during activities such as coughing, sneezing, and talking, allowing the inhalation of Mycobacterium Tuberculosis particles by others. Additionally, the infection can occur through the mouth, intestines, and skin [
2]. With approximately 25% of the global population infected with Mycobacterium Tuberculosis, new infections occur in about 1% of the population annually [
3]. To combat the TB epidemic, several global strategies have been implemented. In 2018, the United Nations held a high-level meeting on TB, prioritising discussions on the pandemic and eradication strategies to the level of heads of state and government [
4]. All UN member nations have pledged to strengthen efforts and eliminate TB by 2030 [
5,
6]. Countries like China, India, and the United States have developed national programs and policies to prevent and control TB [
4,
7,
8].
Individuals with active TB can transmit the disease to approximately 10–15 people each year through close contact [
9]. Despite a net reduction of around 10% in TB incidence between 2015 and 2021, it remains a significant public health challenge globally. Worryingly, there has been a 3.9% increase in the incidence of TB between 2020 and 2021, reversing the downward trend observed for the majority of the past two decades [
10]. Additionally, the emergence of drug-resistant TB, exacerbated by the misuse of antibiotics, further complicates the fight against the TB epidemic. Furthermore, the disruption of health services due to the COVID-19 pandemic has contributed to an increase in TB-related deaths worldwide between 2019 and 2021 [
10,
11]. Although TB may frequently be remedied with the correct treatment plan, a significant reduction in its burden is still a distant goal for many countries [
12].
The spatial distribution of TB incidence exhibits significant regional variations. Southeast Asia and Africa account for nearly 70% of all global TB cases, with the majority of high-incidence countries situated in these regions [
13,
14]. Moreover, the decline in the global burden of TB has varied considerably across countries and regions. For instance, the annual percentage decline in TB incidence among HIV-negative individuals between 2006 and 2016 ranged from 6.2% in Kazakhstan to 1.2% in the Philippines [
15].
The incidence of TB is influenced by various risk factors. Diabetes is a significant risk factor for active TB, with diabetic patients having a three-fold higher risk of acquiring TB compared to those without diabetes [
16]. Undernourishment is also a crucial risk factor, associated with increased TB incidence, severity, poorer treatment outcomes, and higher mortality rates [
17‐
19]. Workplace exposure to PM2.5 has been linked to smear-positive TB, as it may increase the risk of Mycobacterium TB transmission [
20]. Additionally, social and economic factors, such as low socio-economic status and limited literacy, contribute to the risk of TB [
21,
22]. Age is another important risk factor, with TB prevalence rates increasing significantly beyond the age of 65 [
23,
24]. Besides, the incidence of TB is substantially higher in males compared to females [
25‐
27]. Tuberculosis is also a social disease with medical aspects, it is closely related to the social factors of a country or region [
28,
29].
Understanding the spatial distribution characteristics of TB incidence and the associated risk factors is essential for effective prevention and control strategies [
30]. Spatial analysis can optimize resource allocation and aid in early diagnosis, transmission reduction. Consequently, this study aims to spatially investigate the global, regional and national trends in Tuberculosis incidence and the key underlying risk factors over time, thus from 2000 to 2021. This will contribute to the implementation of evidence-based and targeted tuberculosis prevention and control measures by policymakers in different countries and regions, thus assisting in achieving the global goal of ending the TB epidemic.
Discussion
The prime focus of this study was to investigate the global trend of TB incidence and underlying risk factors between 2000 and 2021. This study found that there was a trend of clustering in the spatial distribution of tuberculosis incidence, but that the trend of clustering was decreasing from year to year. There are differences in TB incidence across countries and regions with different income levels, this finding is in line with previous research, which has revealed that a vast majority of individuals with TB are concentrated in low- and middle-income countries (LMICs), underscoring the strong association between TB and poverty, as well as other socioeconomic risk factors [
45]. This may also be linked to the truth that people in LMICs do not have enough money to choose better health care services. The most important finding of this study is that the risk factors for tuberculosis vary across countries and regions, with literacy rate being the risk factor with the relatively widest and deepest impact. Based on the results of the projections, with the present trends, the World Health Organization’s goal of ending the tuberculosis pandemic by 2030 is unlikely to be achieved, which is worthy of our attention.
Studies have shown that there is a higher incidence of TB not being diagnosed in a timely manner in LMICs, as a significant number of TB patients in LMICs seek primary treatment from private medical institutions, drug suppliers and lower-level public health institutions that do not have access to TB diagnostic services, which contributes to the this has led to the further spread of the epidemic [
46,
47]. At the same time, health care professionals in LMICs are at an increased risk of TB infection, which can contribute to the epidemic’s spread [
48,
49]. However, although the incidence of TB in LMICs is at a higher level compared to high-income countries, it is also generally declining, suggesting that previous TB control strategies in LMICs have been effective.
This study found a high geographic spatial autocorrelation in the spatial distribution of TB incidence even though the incidence was declining, suggesting that TB patients may be more clustered in specific areas. In previous studies, Africa (particularly sub-Saharan Africa) and Southeast Asia have generally been considered to be the regions with the most severe TB epidemics [
13]. In this study, we can see that in addition to the high incidence areas in Africa and Southeast Asia, most of South Asia and Mongolia in East Asia are also areas of high TB incidence, which is a slight departure from the previous view. These countries and regions not only have a high TB burden of their own, but also tend to spread to surrounding countries or regions and should be given priority attention. On the other hand, significant geographical inequalities in TB incidence have been observed, with the majority of countries with high concentrations being low- and middle-income countries, and economic polarization contributing to clustering of TB incidence. Studies have shown that one-third of people diagnosed with TB in the Republic of South Africa do not start treatment or are not informed of their disease, while the rising proportion of extensively drug-resistant TB may also be contributing to the spread of the TB epidemic in South Africa [
50,
51]. In addition, the number of cases of TB in South Asia is staggering yet has been under-appreciated. With a large, chaotic and unregulated private health sector, South Asia is also vulnerable to natural disasters and political disruption. When disaster inevitably strikes, emergency measures can greatly reduce the opportunistic spread of diseases such as TB [
52].
In contrast, 19 countries in low-high cluster areas, which are surrounded by high prevalence areas but have managed to maintain low prevalence rates themselves, have TB control strategies that deserve further study and replication. In previous studies, Sudan has often been considered a country with a high TB burden [
53]. However, this study shows that Sudan is in a low-high cluster area with a lower incidence of TB than the surrounding countries, suggesting that its TB control strategies are achieving some success. Of course, it is also argued that this is due to a lack of data management and higher levels of surveillance due to the conflict that has erupted in Sudan in recent years [
54]. Rwanda, a low-high cluster country in Africa, on the other hand, has an effective TB surveillance system with precise, comprehensive, and both inside and outside consistent data that provides an excellent summary of the country, and TB control strategies developed through this system have been effective in decreasing the incidence of TB in Rwanda [
55].
It is worth noting that although the incidence of TB in Oceania is still below the world average, and Fiji and Vanuatu are among the low-high cluster areas, the growing trend in the overall incidence of TB in Oceania is not negligible and requires attention [
56]. The low-low cluster areas are mostly high-income countries and territories in Europe and the USA, which are most likely to be the first to achieve the 2030 complete elimination plan but should also be aware of the TB risks associated with migration from high-incidence countries [
57].
Countries and regions with identical leading risk factors, comparable cultural affinities, and geographic proximity may opt for analogous TB control strategies. It is noteworthy that several neighboring countries in Central Africa have a population ages 65 and above as the leading risk factor for TB. This phenomenon can be attributed to the fact that although the degree of population aging in Africa is relatively low, this is due to a comparatively young age structure, high rates of fertility and death in the African population. However, elderly individuals in the African region generally experience a higher burden of chronic diseases and infectious diseases due to healthcare conditions, nutritional status, and other factors. This view is supported by relevant research, which indicates that immune function decreases with age, and the disease burden of elderly individuals in Africa is increasing [
58].
In high-income and low TB incidence areas such as Europe and North America, low literacy rates have become a leading risk factor for TB incidence [
59]. Low literacy rates may lead to low health literacy, which is detrimental to public access to health education. Europe and the United States have received a large influx of immigrants, whose health literacy is relatively poor, and who have also brought new burdens of TB [
60,
61]. Therefore, it is necessary to implement TB interventions targeted at immigrants [
62‐
66].
From the perspective of the second leading risk factor, there is low similarity among neighboring countries and regions. However, countries that share the same leading risk factor and second leading risk factors can be regarded as homogeneous countries and adopt similar TB prevention and control measures. Considering the third leading risk factor, our study found that many countries and regions have multiple risk factors, especially those with a high incidence of TB, such as Africa and Southeast Asia. This suggests that the incidence of TB in these areas is a complex issue, influenced not only by a single factor but by multiple factors.
In these areas with a high incidence of TB, comprehensive interventions need to be developed, including improving people’s health literacy, improving the living environment and strengthening health services. In particular, interventions targeting these risk factors are necessary [
67]. For example, for areas with a high proportion of men, we need to strengthen health promotion and education for men and encourage them to undergo health screening and preventive measures [
68]. There is the need for regular screening and treatment in the community and appropriate medical services and support. In addition, we need to further strengthen disease surveillance and data collection in order to better understand and control the spread of TB in different areas and groups.
This study demonstrates that low literacy rates are one of the most common risk factors for the occurrence of TB. Literacy rates are closely related to education level. There is a significant link between education and health, and low levels of education may exacerbate health problems [
69,
70]. Therefore, enhancing education plays an important role in improving public health and preventing TB transmission. Governments should increase investment in education and health to raise the standard of public health and decrease the occurrence and spread of TB [
71]. The study also found that diabetes prevalence is the second most common risk factor for the occurrence of TB. Previous research has shown that diabetes increases susceptibility to TB [
72].
In addition, the study also points out that the 65 years and older age group is the third most common risk factor for the occurrence of TB. This is because the immune system of older people declines and their body’s resistance weakens, making them more susceptible to various diseases. Furthermore, aged persons are more likely to have other chronic conditions, which raises the chance of TB infection [
73,
74]. Therefore, the elderly should also pay attention to TB prevention, exercise regularly, maintain a healthy diet, and improve their body’s immunity. These risk factors have a widespread impact and should receive more attention from relevant authorities.
Limitations of the study
This study has some limitations that should be acknowledged. Firstly, the data used in the study are not exhaustive, and several risk factors were not included in the analysis. Moreover, some of the data used in this study have a high number of missing values, which could potentially bias the results. In addition, although the data used in this study are from official sources and we believe that they reflect the real situation, some countries may also have some errors in their official data due to their more backward level of development, which may have an impact on the results. Additionally, it is important to note that TB incidence rates often exhibit spatial variations within countries and regions, with notable differences between rural and urban areas. To obtain more comprehensive and accurate results, it is essential to incorporate more detailed data that capture these spatially aggregated trends.
Furthermore, it should be recognized that TB in many countries and regions is influenced by a multitude of risk factors, and these factors can interact with each other, potentially leading to complexities and inaccuracies in the results. Future studies should aim to address this issue by utilizing more comprehensive data sets and further reducing the effect of multicollinearity.
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.