General characteristics of the retrieved documents

The search strategy retrieved 509 documents related to religious mass gatherings of Muslims. The retrieved documents were of seven types, mainly research articles (n = 346, 68.0%). Other types of retrieved documents are shown in Table 1. The retrieved documents have 2811 author names, an average of 5.5 authors per document. Of the retrieved documents, 290 (57.0%) were published in open access journals. Of the 509 documents, 503 (98.8%) were published in English. The remaining documents (n = 6, 1.2%) were published in a non-English language. The retrieved documents received 8504 citations, an average of 16.7 citations per document. Of the 509 retrieved documents, 472 (92.7%) had the keyword “Hajj” in the title.

Table 1 Types of documents on religious mass gatherings of Muslims

Growth trajectories of publications and citations

Figure 1 shows the growth trajectory of publications which can be organized into three distinct phases: an emergence phase (≤1998), a fermentation phase (1999–2008), and a take-off phase (2009–2020). The growth of citations during the study period showed a gradual increase that ultimately coincided with that of the number of publications.

Fig. 1

Growth of publications and citations on religious mass gatherings of Muslims

Core journals

The retrieved documents were published in 181 peer-reviewed scientific journals. The Travel Medicine and Infectious Disease journal (n = 57, 11.2%) ranked first in the number of publications. Table 2 shows the ten core journals. The Lancet journal ranked fifth in the core list. The majority of the journals in the core list were in the field of infectious diseases or public health or both.

Table 2 Core journals in publishing documents on religious mass gatherings of Muslims

Leading authors

In total, 2811 authors participated in publishing the retrieved documents. Memish, Z.A. (Saudi Arabia) ranked first (n = 107, 21.0%) in the number of publications. Table 3 shows the ten core researchers in the field. The core researchers were from Saudi Arabia, France, and Australia.

Table 3 Core countries in publishing documents on religious mass gatherings of Muslims

Leading countries

Authors from 61 different countries participated in publishing the retrieved documents. Saudi Arabia was the indisputable leader in this field, publishing more than half (n = 278, 54.6%) of the retrieved documents. Table 4 shows the ten core countries in the number of publications. The list of core countries included the US, France, the UK, Australia, Canada, and India with large Muslim communities. At the institutional level, the Ministry of Health of Saudi Arabia ranked first in the number of publications with 146 (28.7%) documents.

Table 4 Core researchers in publishing documents on religious mass gatherings of Muslims

Networks of author collaboration

Figure 2 is a network visualization map of authors with a minimum of 10 publications. The map included 27 authors. The red cluster included 11 authors and represented Saudi researchers led by Memish, Z.A. The Saudi cluster existed in the center with collaborative ties with the two remaining clusters. The blue cluster represented French researchers while the green cluster represented Australian researchers.

Fig. 2

Collaborative research networks between researchers with a minimum number of publications of 10 documents. The number of researchers on the map was 27. The map has three clusters with three different colors. Each cluster represents a group of closely related researchers

Networks of international research collaboration

Figure 3 is a network visualization map of countries with a minimum of 10 publications (n = 14). The map shows Saudi Arabia in the center of the map with collaborative ties with most countries on the map. The strongest international research collaboration was between Saudi Arabia and the US, followed by Saudi Arabia and France, Saudi Arabia and Australia, and Saudi Arabia and the UK.

Fig. 3

Collaborative research networks between countries with 10 or more publications. Only countries that exist in research networks were mapped. The thickness of the connecting line between two countries is proportional to the strength of research collaboration

Co-occurrence analysis of author keywords (important topics)

Figure 4 shows a co-occurrence analysis of author keywords with a minimum occurrence of five. The analysis excluded keywords related to “mass gatherings”. Important keywords in the map included vaccination, respiratory tract infections, influenza, coronavirus, prevention, and knowledge.

Fig. 4

Network visualization map of author keywords with a minimum of five or more. Keywords such as “mass gatherings” and Hajj were excluded to expose other keywords. The map has 24 keywords. The size of the node is proportional to the number of occurrences in the retrieved documents and represents an important topic

Most frequent terms in titles/abstracts (major research themes)

Network visualization map of terms in titles and abstracts with a minimum occurrence of five were mapped resulting in four clusters (research themes) (Fig. 5). The clusters were as follows:

  1. 1.

    The yellow cluster represents surveys and questionnaire-based studies on knowledge, attitude, and practices of pilgrims to Mecca/Makkah

  2. 2.

    The green cluster represents studies on vaccine-preventable outbreaks of meningitis, pneumonia, and other infections

  3. 3.

    The red cluster represents studies on etiology and epidemiology of hospital admission among pilgrims in Mecca/Makkah

  4. 4.

    The blue cluster represents studies on prevention, symptoms, and epidemiology of various viral infectious diseases

Fig. 5

Network visualization map of terms in the titles/abstracts with a minimum occurrence of five or more. Nodes having similar color are closely related and represent a separate cluster. Each cluster represents a general research theme present in the retrieved documents

Disciplines underlying the foundations of the field

Figure 6 is a co-citation analysis of journals with a minimum citation of 10 (n = 105 journals). The node size represents journals that were most commonly co-cited by journals having similar node colors. The subject area(s) of the journals with the largest node size represents disciplines underlying the field. In the current study, the field of mass gatherings of Muslims was formulated by general medicine (The Lancet, Saudi Medical Journal), infectious diseases/public health (Vaccine, Journal of Travel Medicine, Travel Medicine and Infectious Diseases), and infectious diseases (International Journal of Infectious Diseases, Emerging Infectious Diseases).

Fig. 6

A map of journal co-citation analysis (n = 105 journals). A node with a large size represents journals that are most frequently co-cited by other journals with the same node color. The subject area of the largest nodes are the underlying fields of the retrieved documents (religious mass gatherings of Muslims)

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