Tuberculosis (TB) has been of interest to human researchers for a long time; with writings mentioning the disease dating as far back as three millennia. In 2019, TB affected 10 million people globally, causing the deaths of around 1.2 million HIV-negative people and an additional 208 000 deaths in HIV-positive persons. The disease has a predilection for the male population, accounting for 56% of the cases, in males over the age of 15.
Comorbid conditions that increase vulnerability to TB include communicable diseases, such as HIV and noncommunicable diseases, such as diabetes, rheumatoid arthritis, silicosis, and other biological factors affecting the immune system. Socioeconomic factors such as poor housing, malnutrition and lack of access to healthcare, all increase the risk of a TB infection.
Although TB is a global phenomenon, the region most affected is South-East Asia (44%), followed by Africa (25%), and the Western Pacific (18%). The top eight high-burden countries make up two-thirds of the global share. The high-burden countries include India, Indonesia, China, the Philippines, Pakistan, Nigeria, Bangladesh, and South Africa.
Continuous research on TB plays a vital role in mapping progress, making informed decisions, and devising new strategies to combat the disease. Bibliometrics aims to analyze the contributions of different regions, countries, institutions, authors, and their impact on research. Thus, it identifies the gaps and points toward areas where improvement is needed. Moreover, it helps identify new trends and opportunities for collaborative efforts to reach a goal. Bibliometric studies significantly contribute to furthering valuable academic knowledge, which is essential to global economic and social welfare. They look at volume, constituency, and collaboration of research in a specific field and are used to justify the work of a researcher. In recent decades, many bibliometric studies have explored different healthcare issues and public health problems, such as the trends of infectious diseases in general, and more specifically, HIV/AIDS, hepatitis, and recently, the coronavirus disease.
Although a few studies have explored TB in this context, literature on global TB research trends in the last decade is still limited. The study by Nafade et al., in 2018 analyzed global trends of research before 2016, and the analysis by Igwaran and Edoamodu only targeted Africa; another by Morishita et al., targeted the Western Pacific. A study with a global aspect was, therefore, necessary. This study aimed to perform a bibliometric analysis of TB research from 2011 to 2020 to discover research performance and trends from a global perspective.
Materials and Methods
The databases available to researchers include Scopus, PubMed, Embase, ScienceDirect, and The Cochrane Library, to name just a few. For our study, we used the Web of Science (WoS), as it has been mostly used for bibliometric analysis by researchers and is more standardized than other databases. WoS, a Clarivate analytics division (Formerly Thomson Reuters), contains over 75 million records and is one of the oldest citation indexes for sciences, without which the development of bibliometrics would have been hindered. Bibliometric techniques are used to discern trends of data output and provide quantitative measures for the contribution of countries, authors, institutions, funding agencies, collaborations, and more. Ethical approval was not applicable in this research since the study had no direct involvement of human subjects.
In this study, we planned to describe global TB research trends from 2011 to 2020. For this, we accessed the King Abdulaziz University (KAU) online library and digital resources to retrieve the information. We performed the advanced search on WoS using the following search strategy TI = (TB OR Tuberculosis), from 2011 to 2020 only, document types restricted to article only, and only articles in English. We retrieved 33,088 records. Figure 1 shows the detailed search strategy.
Title (TI) rather than the Topic (TS) was used in the search strategy to be more specific to prevent irrelevant results since TS contains, Title (TI), Abstract (AB), Keywords (AP), and Keywords plus (KP). Similar search strategies containing TI had been used by other studies, thus supporting our choice. To avoid bias resulting from frequent database renewal, all the records were retrieved on the same day (November 3, 2021).
After the records were extracted in a plain text format, two reviewers independently screened them manually by title to eliminate any that fell outside the scope of the study and resolved any conflicts. Irrelevant articles (2627) beyond the study scope were excluded from detailed analysis, such as articles with “TB” used in the context as an acronym for the element terbium or as unit of data known as terabyte. Using R-Bibliometrix on the remaining 30,461 articles, a detailed analysis of various bibliometric matrices such as journal, publication year, authors, citations, institutes, countries, sources, and more was done. Collaboration networks of authors, institutions, countries, and top keywords were also observed. Finally, two reviewers independently extracted and rechecked the information to verify the process.
A total of 30,461 articles from 3260 sources were analyzed [Figure 1]. Around 91,862 authors originated from 145 countries, led by the United States of America (USA), China, India, the United Kingdom, and South Africa. Table 1 gives the summary of relevant information.
The number of articles increased from 2246 articles in 2011 to 3899 in 2020, a 73.6 % increase in yearly production [Figure 2]. The top three funding sources, the United States Department of Health Human Services, the National Institutes of Health (NIH) USA, and the National Institute of Allergy Infectious Diseases, contributed approximately one-third of the funding.
Table 2 shows the 20 most productive authors, led by Zhang Y with 205 articles, and he was the only author with more than 200 articles to his name. Dheda K had the highest share of corresponding author contributions (58%), while Gupta A was the highest contributor as the first author (32%). Barry CE led with the highest h-index (45) and had 6421 total citations. Seventeen out of the 20 authors had h-index ≥20, and 8 of the 20 authors had total citations >3000. Only three authors had Articles Fractionalized (AF) more than 20. Two authors, Barry CE and Gagneux S, did not contribute as the first authors.
The authors’ collaboration network showed that 18 of the top 20 authors collaborated, the most being between Zhan Y and Wang J. Two authors, namely Zhang X and Wang C, did not collaborate with any others or each other.
Five countries, including the USA, China, India, the United Kingdom, and South Africa, made 52% of the corresponding author’s contribution [Table 3]. The USA led with more than twice as many citations as China, which was in the second place. Switzerland (0.67), the Netherlands (0.65), and the United Kingdom (0.60) had the highest multicountry publication (MCP) ratio, while Turkey had the lowest MCP ratio (0.07) out of the top 20 countries with corresponding authors [Table 3].
The collaboration world map for countries with ten or more international collaborations showed hotspots in the USA and Europe. Within the top 20 collaborations, the USA collaborated with 12 other countries, making it the most collaborative country. The United Kingdom collaborated with seven countries and South Africa with three countries, placing them second and third, respectively, in terms of collaboration. Among bilateral collaborations, the USA and South Africa were leading with 1203 instances.
As shown in Figure 3, the collaboration of institutions shows the largest collaboration cluster (red) dominated by institutions in South Africa. The USA institutional affiliations dominated the other two clusters (blue and green).
The top 10 most frequent affiliations comprised 28.1% (8569) of the total number of articles. The University of Cape Town showed the most frequent affiliation with 1893 articles, followed by the Stellenbosch University with 1117 articles and the London School of Hygiene and Tropical Medicine with 1010 articles. Overall, 14 institutions had more than 500 articles each. Out of the top 20 affiliations, seven belonged to the USA, four to South Africa, and two to China.
The Sankey diagram for the top 20 countries, affiliations, and sources shows that the USA had the largest share in articles and had connections with most of the affiliations. South Africa showed a significant number of affiliation with the University of Cape Town. PLOS ONE was the largest source showing connections to articles from almost all countries [Figure 4].
Ten of the 20 highly cited articles were five articles each from The Lancet associated Journals and The New England Journal of Medicine with citations in 2011. Bochme CC, 2011 (Lancet) had the most Internal Citations (IC) at 403 and the most global citations (GC) cited 685 times. All the top 20 highly cited articles had an IC/GC ratio ≥50%, with Demay C, 2012; Infect Genet Evol had the highest IC/GC Ratio.
TB was the most frequently used keyword with over 9000 occurrences over the last decade, followed by Mycobacterium tuberculosis, with approximately 3500 total occurrences. The remaining keywords, such as HIV, pulmonary TB, and the diagnosis had <1000 total occurrences.
Some important keywords plus (ID) were “M. tuberculosis,” “infection,” and “pulmonary TB,” each of which occurred over 2000 times.
Yearly growth of the most abundant sources showed “PLOS ONE” in the lead with more than 2,200 articles in the last decade, followed closely by the “International Journal of TB and Lung Disease” with 1600 articles, and “BMC infectious disease” with 753. The yearly increase of PLOS ONE peaked in 2013 with over 300 annual occurrences, but then descended into a decreasing trend to <200 annual occurrences in 2020. The top two sources (PLOS ONE and the International Journal of TB and Lung Disease) have shown a decreasing trend in the last 5 years.
This study evaluates the TB-related research performance and trends in the past decade to provide an outline for evidence-based future research. In 2015, The WHO sustainable development goals (SDGs) and End TB strategy set targets for 2030 and 2035, respectively, to fulfill a vision; “zero deaths, disease, and suffering due to TB.”
The general trend showed an increase in the last decade, with the most significant jump in the number of articles published from 2014 to 2015. The production which plateaued from 2015 to 2018, as shown by the almost horizontal blue line in Figure 2, is ironic because the SDGs set in 2015 warranted more TB research than a plateau. However, the pace of research resumed an upward trend after 2018. Another interesting finding is the decrease in the annual growth rate from 7.3% in 2007–2016 to 6.3% in 2011–2020. When global TB research production should have been increasing or at least been constant, it decreased, which is worrisome. Furthermore, the global COVID-19 pandemic had a highly negative short-term impact on the progress of SDG 3 (which pertains to TB), as stated by the SDG report. This further underscores the importance of this paper, as the world looks to bounce back and resume TB research with a road map.
Interestingly, the world’s Top 30 high-burden countries make up 86% of the total cases, and approximately 60% of the contribution to research articles. As attention shifted toward the COVID-19 pandemic, the number of people diagnosed with TB in India, the Philippines, Indonesia, and South Africa decreased, threatening to unravel previous work. Furthermore, these four countries make up 44% of the global TB burden, but only two of them are in the top 20 countries with corresponding authors’ lists. This finding suggests that Indonesia and the Philippines need to step up or expand TB research.
The top three funding sources were from the USA, the fourth from China and the fifth from Europe. The UN had proposed increasing funding to 2 billion $ annually from 2018 to 2022, of which not even half was met. This shows there is a need to increase funding globally to meet targets.
Most of the top-cited articles were published in high-impact factor (IF) journals, such as The Lancet and the New England Journal of Medicine; thus, these articles may have higher citations not necessarily because they were of high quality, but rather because they were published in high IF journals. Twelve of the 20 top-cited articles were on the prevention, diagnosis, and treatment of TB. This shows that articles targeting the management of TB are highly sought after.
Rather unusual is the fact that, none of the first authors of the top 20 most cited articles were in the top 20 productive authors list. Zhan Y and Wang J from the USA were two of the most prominent hotspots on the author collaboration network and had worked with each other significantly. The third-most prolific author Wang Y was from the UK, which may be why there was no significant collaboration with the top 2. Another interesting finding was that the top 20 authors had contributed almost 8% of the total TB research in the last decade.
The USA led TB research globally, as seen in the previous bibliometric analyses, but its share decreased from 24.1% in 1997–2006 to 18.4% in 2007–2016 to 16% in 2011–2020. The top five most productive countries make up almost half of the global production of TB articles [Table 3] and share almost 38.5% of the global TB burden. However, out of the top 20 countries with corresponding authors, only seven were from high-burden countries. The high-burden countries present in the top corresponding author list make up 48% of the global TB burden and 42% of the contribution to articles. India led with 26.4% burden, and 12% global contribution, China with 8.3% of global burden and 15% of contribution, Pakistan with 5.7% of burden and 2% of contribution, South Africa with 3.6% of the burden and 4% of contribution, Brazil with 0.96% of burden and 4% of contribution, Korea with 1.32% of burden and 3% of contribution, and Ethiopia with 1.57% of contribution and 2% production. This shows that Pakistan and India have a greater burden than their contribution to research and, therefore, need to put in more effort. Furthermore, much work is required from other high-burden countries, especially Indonesia, Philippines, Bangladesh, and Nigeria, as these countries are in the top eight highly burdened countries, but are not in the top 20 corresponding authors list.
China and India showed more SCP, which was almost five times more than MCP. In comparison, the USA and the United Kingdom had SCP almost equal to MCP. Only five out of the top 20 countries had MCP more than SCP. This shows that there is still room for improvement in global collaboration to increase MCPs, especially from India and China.
The University of Cape Town was the most frequent affiliation worldwide, leading TB Research globally. It was also ranked number 13 in infectious diseases by the US News and World Report Best Global Universities Rankings for Subjects 2021. The third-most common affiliation, London School of Hygiene and Tropical Medicine, was fourth in infectious diseases. This shows that these institutions not only focus on TB but also other infectious diseases.
Furthermore, a study by Igwaran and Edoamodu, on research trends in Africa also showed the University of Cape Town as the most common affiliation, thus supporting our findings. Of the top eight high-burden countries, only South Africa, China, and India were present in the top 20 institutional affiliations. The remaining high-burden countries need to conduct more TB research in their institutions.
Only five of the top 30 high-burden countries, namely, South Africa, India, China, Brazil, and Uganda, had ten or more international collaborations. This further shows that more global collaboration is required, especially from the top eight high burdens that did not make the list, such as Pakistan, Bangladesh, Philippines, Indonesia, and Nigeria. The institutional collaboration cluster showed that two clusters were dominated by the USA institutions and one by South Africa [Figure 3] and only 6 out of the top 20 institutions belonged to the high-burden countries.
To the best of our knowledge, this is the only study that has tracked global TB research in the last decade. We made a comprehensive trends analysis, listed the top corresponding authors, country-wise contributions, frequent affiliations, and top-cited articles.
The limitations of our study were that we only included articles in English and used only WoS database. Newer, higher quality articles would not have been cited as much, so their analysis may not be representative of their quality. Using corresponding author affiliation as the source country of research production is also not always accurate as the corresponding author may be from a country different from where the research is being conducted.
More such global and regional bibliometric studies on TB and other infectious diseases along with further in-depth exploration can be beneficial. Besides, as TB affects every continent, a collaborative research effort is very necessary.
More importantly, we recommend more research output and collaboration by high-burden countries with more corresponding authors from those countries.
This bibliometric analysis describes salient trends in global TB research from 2011 to 2020. There has been an increasing trend in article production over the last decade. High-income, low-burden countries, such as the USA and the UK have led the global output, but what is gratifying is that high-burden countries such as South Africa, China, and India were also in the top five involved in TB research. However, of the top 20 corresponding authors, only seven were from high-burden countries, suggesting that most of the high-burden countries still need to be supported to contribute more. Furthermore, only five high-burden countries were present in the top 30 collaborations.
The findings of this study are critical in progress toward the SDGs and the WHO End TB strategy.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
The authors would like to thank “Clarivate Analytics-WoS” and “KAU, Saudi Arabia” for this research-related data access and support.
1. Cave AJ, Demonstrator A The evidence for the incidence of tuberculosis in ancient Egypt Br J Tuberc 1939 33 142 52
2. Brown L The story of clinical pulmonary tuberculosis Radiology 1941 37 108 9 Available from: https://pubs.rsna.org/doi/10.1148/37.1.108g
Last accessed on 2022 Apr 09
3. Global Tuberculosis Report; 2020 Available from: https://www.who.int/publications-detail-redirect/9789240013131
Last accessed on 2022 Apr 09
4. Marais BJ, Lönnroth K, Lawn SD, Migliori GB, Mwaba P, Glaziou P, et al. Tuberculosis comorbidity with communicable and non-communicable diseases: Integrating health services and control efforts Lancet Infect Dis 2013 13 436 48
5. Duarte R, Lönnroth K, Carvalho C, Lima F, Carvalho AC, Muñoz-Torrico M, et al. Tuberculosis, social determinants and co-morbidities (including HIV) Pulmonology 2018 24 115 9
6. Moreira AD, Kritski AL, Carvalho AC Social determinants of health and catastrophic costs associated with the diagnosis and treatment of tuberculosis J Bras Pneumol 2020 46 e20200015
7. Ellegaard O, Wallin JA The bibliometric analysis of scholarly production: How great is the impact? Scientometrics 2015 105 1809 31
8. Moed HF New developments in the use of citation analysis in research evaluation Arch Immunol Ther Exp (Warsz) 2009 57 13 8
9. Shang G, Saladin B, Fry T, Donohue J Twenty-six years of operations management research (1985 – 2010): Authorship patterns and research constituents in eleven top rated journals Int J Prod Res 2015 53 6161 97
10. Cooper ID Bibliometrics basics J Med Libr Assoc 2015 103 217 8
11. Malik AA, Mahmood H, Butt NS, Baig M, Humayun A A bibliometric study of infectious diseases research in Pakistan (2000-2020): A call for increased productivity Ann King Edward Med Univ 2020 26 206 13
12. Yang W, Zhang J, Ma R The prediction of infectious diseases: A bibliometric analysis Int J Environ Res Public Health 2020 17 6218
13. Fajardo-Ortiz D, Lopez-Cervantes M, Duran L, Dumontier M, Lara M, Ochoa H, et al. The emergence and evolution of the research fronts in HIV/AIDS research PLoS One 2017 12 e0178293
14. Sweileh WM Global research output on HIV/AIDS-related medication adherence from 1980 to 2017 BMC Health Serv Res 2018 18 765
15. Rezaee Zavareh MS, Alavian SM Ten-year analysis of hepatitis-related papers in the Middle East: A web of science
-based scientometric study Turk J Gastroenterol 2017 28 20 5
16. Zhou Y, Chen L Twenty-year span of global coronavirus research trends: A bibliometric analysis Int J Environ Res Public Health 2020 17 3082
17. Lou J, Tian SJ, Niu SM, Kang XQ, Lian HX, Zhang LX, et al. Coronavirus disease 2019: A bibliometric analysis and review Eur Rev Med Pharmacol Sci 2020 24 3411 21
18. Mao X, Guo L, Fu P, Xiang C The status and trends of coronavirus research: A global bibliometric and visualized analysis Medicine (Baltimore) 2020 99 e20137
19. Igwaran A, Edoamodu CE Bibliometric analysis on tuberculosis and tuberculosis-related research trends in Africa: A decade-long study Antibiotics (Basel) 2021 10 423
20. Morishita F, Yamanaka T, Islam T Intensified research on tuberculosis in the Western Pacific Region: A bibliometric analysis, 2000-2019 Western Pac Surveill Response J 2020 11 24 31
21. Nafade V, Nash M, Huddart S, Pande T, Gebreselassie N, Lienhardt C, et al. Abibliometric analysis of tuberculosis research, 2007-2016 PLoS One 2018 13 e0199706
22. AlRyalat SAS, Malkawi LW, Momani SM Comparing Bibliometric Analysis Using PubMed, Scopus, and Web of Science
Databases J Vis Exp JoVE 2019 152
23. Yu D, Xu Z, Pedrycz W, Wang W Information sciences 1968– 2016: A retrospective analysis with text mining and bibliometric Inf Sci 2017 418-419 619 34
24. Merigó JM, Yang JB A bibliometric analysis of operations research and management science Omega 2017 73 37 48
25. Bettencourt LM, Kaur J Evolution and structure of sustainability science Proc Natl Acad Sci U S A 2011 108 19540 5
26. Birkle C, Pendlebury DA, Schnell J, Adams J Web of Science
as a data source for research on scientific and scholarly activity Quant Sci Stud. 2020 1 363 76
27. Yu D, Xu Z, Fujita H Bibliometric analysis on the evolution of applied intelligence Appl Intell 2019 49 449 62
28. Liu W, Hu G, Tang L Missing author address information in web of science
– An explorative study J Informetr 2018 12 985 97
29. Web of Science
Core Collection Help Available from: https://images.webofknowledge.com/images/help/WOS/hs_advanced_fieldtags.html
Last accessed on 2022 Apr 09
30. Gao Y, Wang Y, Zhai X, He Y, Chen R, Zhou J, et al. Publication trends of research on diabetes mellitus and T cells (1997-2016): A 20-year bibliometric study PLoS One 2017 12 e0184869
31. Aria M, Cuccurullo C Bibliometrix: An R-tool for comprehensive science mapping analysis J Informetr 2017 11 959 75
32. Floyd K, Glaziou P, Houben RM, Sumner T, White RG, Raviglione M Global tuberculosis targets and milestones set for 2016-2035: Definition and rationale Int J Tuberc Lung Dis 2018 22 723 30
33. Sachs J, Kroll C, Lafortune G, Fuller G, Woelm F Sustainable Development Report 2021 Cambridge: Cambridge University Press; 2021
34. Ramos JM, Padilla S, Masiá M, Gutiérrez F A bibliometric analysis of tuberculosis research indexed in PubMed, 1997-2006 Int J Tuberc Lung Dis 2008 12 1461 8
35. Top Infectious Diseases Schools in the World – US News Education Available from: https://www.usnews.com/education/best-global-universities/infectious-diseases
Last accessed on 2022 Apr 09