Acute respiratory infections among returning Hajj pilgrims-Jordan, 2014

Respiratory viral infections during Hajj seasons

Respiratory viral infections pose a public health concern during mass gathering (MG) events. Sustainable and continuous surveillance of respiratory viruses remains a priority to early identify and prevent potential outbreaks. This article reviews recent literature addressed the prevalence and diversity of circulating respiratory viruses during Hajj pilgrimage, one of the largest planned religious MG events held annually in Saudi Arabia. The variation between studies with respect to study design, sample size, time of sample collection (pre-, during, and pos-Hajj), type of participants (e.g., symptomatic vs. a symptomatic pilgrims), and laboratory procedure was highlighted. The majority of these studies were conducted on the 2019 Hajj season or earlier, prior to the emergence of COVID-19 which had significant impact on the past three Hajj seasons (2020, 2021, and 2022). A summary about key aspects related to organization of Hajj during COVID-19 pandemic and the implementation of exceptional infection control strategies is provided.

Middle East Respiratory Syndrome Coronavirus (MERS-CoV) is Not Circulating Among Hajj Pilgrims

Since the emergence of the middle east respiratory syndrome coronavirus (MERS-CoV) 2012, the virus had caused multiple healthcare-associated outbreaks. The initial 2012 Hajj season started few weeks after the first case of MERS-CoV, but there were no reported cases among pilgrims in 2012. Since then, there had been multiple studies examining the prevalence of MERS-CoV among Hajj pilgrims. Subsequently, multiple studies utilized screening of pilgrims for MERS-CoV and > 10,000 pilgrims were screened with no identifiable cases of MERS.

Epidemiological Differences in Hajj-Acquired Airborne Infections in Pilgrims Arriving from Low and Middle-Income versus High-Income Countries: A Systematised Review

This systematised review aims to compare the epidemiological patterns of Hajj-acquired airborne infections among pilgrims from low and middle-income countries (LMIC) versus those from high-income countries (HIC). A PubMed search was carried out for all published articles before February 2023, using a combination of MeSH terms and text words. The Newcastle-Ottawa Scale (NOS) was used to assess data quality. From a total of 453 titles identified, 58 studies were included in the review (LMIC = 32, and HIC = 26). In the pooled sample, there were 27,799 pilgrims aged 2 days to 105 years (male: female = 1.3:1) from LMIC and 70,865 pilgrims aged 2 months to 95 years (male: female = 1:1) from HIC. Pilgrims from both HIC and LMIC had viral and bacterial infections, but pilgrims from HIC tended to have higher attack rates of viral infections than their LMIC counterparts. However, the attack rates of bacterial infections were variable: for instance, pilgrims from LMIC seemed to have higher rates of meningococcal infections (0.015-82% in LMIC vs. 0.002-40% in HIC) based on the study population, but not Mycobacterium tuberculosis (0.7-20.3% in LMIC vs. 38% in HIC). Targeted measures are needed to prevent the spread of airborne infections at Hajj.

COVID-19 and other respiratory tract infections at mass gathering religious and sporting events

PURPOSE OF REVIEW

Mass gathering (MG) religious events provide ideal conditions for transmission and globalization of respiratory tract infections (RTIs). We review recent literature on COVID-19 and other RTIs at recurring international annual MG religious and sporting events.

RECENT FINDINGS

Due to the COVID-19 pandemic organizers of MG religious and sporting events introduced risk-based infection control measures that limited transmission of RTIs. The 2020 and 2021 Hajj were conducted with limited numbers of pilgrims compared to the annual millions of pilgrims. The Tokyo 2020 Olympic and Paralympic Games were cancelled and held in 2021. The success of the COVID-19 countermeasures at the 2021 Hajj and 2021 Tokyo Olympics was based on implementing good public health and social measures alongside a comprehensive testing strategy.

SUMMARY

MG events are associated with transmission of a range of bacterial and viral RTIs. Introducing risk based a multitude of public health interventions can reduce transmission of SARS-CoV-2 and other RTIs.

Novel Respiratory Viruses in the Context of Mass-Gathering Events: A Systematic Review to Inform Event Planning from a Health Perspective

BACKGROUND

Mass-gathering events (MGEs) occur regularly throughout the world. As people congregate at MGEs, there is an increased risk of transmission of communicable diseases. Novel respiratory viruses, such as Severe Acute Respiratory Syndrome Coronavirus-1 (SARS-CoV-1), Influenza A Virus Subtype H1N1 Strain 2009 (H1N1pdm09), Middle East Respiratory Syndrome Coronavirus (MERS-CoV), and Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2), or Coronavirus Disease 2019 (COVID-19), may require specific infection prevention and control strategies to minimize the risk of transmission when planning MGEs. This literature review aimed to identify and analyze papers relating to novel respiratory viruses with pandemic potential and to inform MGE planning.

METHOD

This paper used a systematic literature review method. Various health care databases were searched using keywords relating to MGEs and novel respiratory viruses. Information was extracted from identified papers into various tables for analysis. The analysis identified infection prevention and control strategies used at MGEs to inform planning before, during, and following events.

RESULTS

In total, 27 papers met the criteria for inclusion. No papers were identified regarding SARS-CoV-1, while the remainder reported on H1N1pdm09 (n = 9), MERS-CoV (n = 15), and SARS-CoV-2 (n = 3). Various before, during, and after event mitigation strategies were identified that can be implemented for future events.

CONCLUSIONS

This literature review provided an overview of the novel respiratory virus epidemiology at MGEs alongside related public health mitigation strategies that have been implemented at these events. This paper also discusses the health security of event participants and host communities in the context of cancelling, postponing, and modifying events due to a novel respiratory virus. In particular, ways to recommence events incorporating various mitigation strategies are outlined.

Prevalence of Influenza Among Hajj Pilgrims: A Systematic Review and Meta-Analysis

OBJECTIVES

Respiratory transmission, especially in mass gatherings, is considered one of the main ways of influenza transmission. The Hajj ceremony, as one of the largest gatherings worldwide, can increase the distribution of influenza infection. Thus, the present study aimed to evaluate the incidence of influenza among Hajj pilgrims.

METHODS

In this present systematic review and meta-analysis, all English studies published by 2019 were extracted from several databases such as the Web of Science, PubMed, Scopus, Cochrane Library, Science Direct, and Google Scholar. Finally, the data were extracted using a pre-prepared checklist and then analyzed by fixed and random effects model tests in the meta-analysis, Cochran, meta-regression, and Begg's test.

RESULTS

Eighteen studies with a sample size of 62 431 were entered into the meta-analysis process. The overall prevalence of influenza, in addition to the prevalence of types A, B, and C influenza, was estimated at 5.9 (95% CI: 4.3-8.0), 3.6 (95% CI: 2.6-4.9), 2.9 (95% CI: 2.8-3.1), and 0.9% (95% CI: 0.5-1.5), respectively.

CONCLUSIONS

In general, influenza remains widespread regardless of vaccinating pilgrims and following health protocols. Therefore, it is recommended that comprehensive management and educational approaches be used to reduce the prevalence of influenza and its adverse consequences among the pilgrims.

Pattern of Respiratory Viruses among Pilgrims during 2019 Hajj Season Who Sought Healthcare Due to Severe Respiratory Symptoms

The aim of our study was to define the spectrum of viral infections in pilgrims with acute respiratory tract illnesses presenting to healthcare facilities around the holy places in Makkah, Saudi Arabia during the 2019 Hajj pilgrimage. During the five days of Hajj, a total of 185 pilgrims were enrolled in the study. Nasopharyngeal swabs (NPSs) of 126/185 patients (68.11%) tested positive for one or more respiratory viruses by PCR. Among the 126 pilgrims whose NPS were PCR positive: (a) there were 93/126 (74%) with a single virus infection, (b) 33/126 (26%) with coinfection with more than one virus (up to four viruses): of these, 25/33 cases had coinfection with two viruses; 6/33 were infected with three viruses, while the remaining 2/33 patients had infection with four viruses. Human rhinovirus (HRV) was the most common detected viruses with 53 cases (42.06%), followed by 27 (21.43%) cases of influenza A (H1N1), and 23 (18.25%) cases of influenza A other than H1N1. Twenty-five cases of CoV-229E (19.84%) were detected more than other coronavirus members (5 CoV-OC43 (3.97%), 4 CoV-HKU1 (3.17%), and 1 CoV-NL63 (0.79%)). PIV-3 was detected in 8 cases (6.35%). A single case (0.79%) of PIV-1 and PIV-4 were found. HMPV represented 5 (3.97%), RSV and influenza B 4 (3.17%) for each, and Parechovirus 1 (0.79%). Enterovirus, Bocavirus, and M. pneumoniae were not detected. Whether identification of viral nucleic acid represents nasopharyngeal carriage or specific causal etiology of RTI remains to be defined. Large controlled cohort studies (pre-Hajj, during Hajj, and post-Hajj) are required to define the carriage rates and the specific etiology and causal roles of specific individual viruses or combination of viruses in the pathogenesis of respiratory tract infections in pilgrims participating in the annual Hajj. Studies of the specific microbial etiology of respiratory track infections (RTIs) at mass gathering religious events remain a priority, especially in light of the novel SARS-CoV-2 pandemic.

Bat-Borne Coronaviruses in Jordan and Saudi Arabia: A Threat to Public Health?

Emerging infectious diseases are of great concern to public health, as highlighted by the ongoing coronavirus disease 2019 (COVID-19) pandemic. Such diseases are of particular danger during mass gathering and mass influx events, as large crowds of people in close proximity to each other creates optimal opportunities for disease transmission. The Hashemite Kingdom of Jordan and the Kingdom of Saudi Arabia are two countries that have witnessed mass gatherings due to the arrival of Syrian refugees and the annual Hajj season. The mass migration of people not only brings exotic diseases to these regions but also brings new diseases back to their own countries, e.g., the outbreak of MERS in South Korea. Many emerging pathogens originate in bats, and more than 30 bat species have been identified in these two countries. Some of those bat species are known to carry viruses that cause deadly diseases in other parts of the world, such as the rabies virus and coronaviruses. However, little is known about bats and the pathogens they carry in Jordan and Saudi Arabia. Here, the importance of enhanced surveillance of bat-borne infections in Jordan and Saudi Arabia is emphasized, promoting the awareness of bat-borne diseases among the general public and building up infrastructure and capability to fill the gaps in public health preparedness to prevent future pandemics.

Health Education Intervention as an Effective Means for Prevention of Respiratory Infections Among Hajj Pilgrims: A Review

The prevalence of respiratory illness has continued to surge among Hajj pilgrims from different countries despite having some practices of preventive measures. Respiratory illnesses during Hajj could be due to many reasons and many factors that promote disease spread. These factors include overcrowding, cigarette smoking, and direct contact with infectious agents particularly viruses promote the spread of respiratory infections. However, due to the longer duration of the pilgrimage, there are high chances of pilgrims contracting various respiratory illnesses due to exposure to respiratory pathogens. Hajj pilgrims' knowledge, attitudes, and practices toward respiratory tract infections are used as the determinant of the effectiveness of the health education interventions. Knowledge and application of basic hygiene principles, use of face masks, following cough etiquettes, engaging in social distancing, and engaging in other measures are highly important. In this paper, we reviewed the various effective intervention strategies implemented to help prevent respiratory tract infections during Hajj.

Development and validation of knowledge, attitude and practice questionnaire for prevention of respiratory tract infections among Malaysian Hajj pilgrims

Background

Hajj pilgrimage faces numerous challenges including a high prevalence of respiratory tract infection as well as its prevention strategies. The aim of this study was to develop and validate a questionnaire to evaluate knowledge, attitude and practice (KAP) towards respiratory tract infections (RTIs) prevention among Malaysian Hajj pilgrims.

Methods

This study was conducted among Malaysian Umrah pilgrims in Malaysia from Kuala Lumpur and Kelantan. The questionnaire then underwent a series of validation process that included content, face validity and exploratory part. Item response theory (IRT) analysis was utilized for the validation of the knowledge domain. The attitude and practice were validated using the exploratory factor analysis (EFA).

Results

The validation process resulted in a questionnaire that comprised of four main sections: demography, knowledge, attitude, and practice. Following IRT analysis of the knowledge domain, all items analyzed were within the acceptable range of difficulty and discrimination. The Kaiser-Meyer-Olkin measure of sampling adequacy (KMO) was 0.72 and 0.84 for attitude and practice domain respectively and Bartlett’s test of Sphericity for both domains were highly significant (P < 0.001). The factor analysis resulted in two factors with total of 12 items in attitude domain, and 2 factors with total of 13 items in the practice domain with satisfactory factor loading (> 0.3). The Cronbach’s alpha for reliability of the knowledge, attitude and practice domains all showed acceptable values of > 0.6 (0.92, 0.77 and 0.85).

Conclusion

The findings of this validation and reliability study showed that the developed questionnaire had a satisfactory psychometric property for measuring KAP of Malaysian Hajj pilgrims.

Preventive Efficacy of Dried Lime (Citrus aurantifulia) in Common Cold Among Hajj Pilgrims: A Randomized, Double-Blinded, Placebo-Controlled Clinical Trial

Background

Dried lime (Citrus aurantifulia) is one of the herbal preparations used especially by Iranian pilgrims as a preventative agent and self-remedy for respiratory tracts symptoms in folklore medicine. Therefore, we evaluated the preventive efficacy of dried lime preparation in common cold among Iranian pilgrims.

Materials and Methods

In this randomized, double-blinded, clinical trial patients in the drug group received dried lime capsules, 500 mg in a single dose per day for four weeks. In the placebo group, the patients received placebo capsules using the same method. The primary outcome measure in this trial was the severity of cold symptoms assessed by a self-administered questionnaire.

Results

There were no significant differences between the two groups in terms of the trend of cold symptoms severity during the study period. However, in the second week, the severity of all the cold symptoms in the drug group was less, compared to the placebo, but at the end of the study, comparison of the two groups revealed no significant difference in any of the investigated options.

Conclusion

The findings revealed that although the severity of all the cold symptoms in the drug group was less as compared to the placebo group, the dried lime capsule showed no statistically significant effect on the control of these symptoms in Iranian pilgrims.

Respiratory tract infections among French Hajj pilgrims from 2014 to 2017

Respiratory tract infections (RTIs) are common among Hajj pilgrims, but risk factors for RTIs and respiratory pathogen acquisition during the Hajj are not clearly identified. Based on previous studies, most frequent pathogens acquired by Hajj pilgrims were investigated: rhinovirus, human coronaviruses, influenza viruses, Streptococcus pneumoniae, Staphylococcus aureus, Klebsiella pneumoniae and Haemophilus influenzae. 485 pilgrims were included. 82.1% presented with RTIs. Respiratory chronic diseases were associated with cough, Influenza-like illness (ILI) and the acquisition of H. influenzae. Vaccination against invasive pneumococcal diseases (IPD) and influenza was associated with a decrease in the acquisition of S. pneumoniae and prevalence of ILI (aRR = 0.53, 95%CI [0.39-0.73] and aRR = 0.69, 95%CI [0.52-0.92] respectively). Individuals carrying rhinovirus and H. influenzae-S. pneumoniae together were respectively twice and five times more likely to have respiratory symptoms. Individual with H. influenzae-K. pneumoniae carriage were twice (p = 0.04) as likely to develop a cough. The use of disposable handkerchiefs was associated with a decrease in the acquisition of S. aureus (aRR = 0.75, 95%CI [0.57-0.97]). Results could be used to identify pilgrims at increased risk of RTIs and acquisition of respiratory pathogens. Results also confirm the effectiveness of influenza and IPD vaccinations in reducing ILI symptoms and acquisition of S. pneumoniae carriage respectively.

Epidemiology of respiratory viruses in Saudi Arabia: toward a complete picture

Acute lower respiratory tract infection is a major health problem that affects more than 15% of the total population of Saudi Arabia each year. Epidemiological studies conducted over the last three decades have indicated that viruses are responsible for the majority of these infections. The epidemiology of respiratory viruses in Saudi Arabia is proposed to be affected mainly by the presence and mobility of large numbers of foreign workers and the gathering of millions of Muslims in Mecca during the Hajj and Umrah seasons. Knowledge concerning the epidemiology, circulation pattern, and evolutionary kinetics of respiratory viruses in Saudi Arabia are scant, with the available literature being inconsistent. This review summarizes the available data on the epidemiology and evolution of respiratory viruses. The demographic features associated with Middle East respiratory syndrome-related coronavirus infections are specifically analyzed for a better understanding of the epidemiology of this virus. The data support the view that continuous entry and exit of pilgrims and foreign workers with different ethnicities and socioeconomic backgrounds in Saudi Arabia is the most likely vehicle for global dissemination of respiratory viruses and for the emergence of new viruses (or virus variants) capable of greater dissemination.

Acquisition of respiratory viruses and presence of respiratory symptoms in French pilgrims during the 2016 Hajj: A prospective cohort study

BACKGROUND

Viral respiratory tract infections are frequent among Hajj pilgrims. However, it is still not known whether viruses are responsible for the symptoms observed in sick pilgrims or whether they only colonize sick and asymptomatic pilgrims.

PATIENTS AND METHODS

A prospective cohort study was conducted among French Hajj pilgrims in 2016. Medical follow-up and systematic nasal swabbing were performed pre- and post-Hajj. Additional samples were obtained per-Hajj, at symptom onset in ill pilgrims. Viruses were identified using the BioFire FilmArray^® Respiratory multiplex qualitative PCR panel.

RESULTS

109 pilgrims were included. 83.5% presented respiratory symptoms during Hajj and 39.5% were still symptomatic on return. 5.5% of pre-Hajj, 95.2% of per-Hajj (at symptom onset) and 46.5% of post-Hajj samples tested positive (p < 0.0001). Acquisition rates of rhinovirus/enterovirus, coronavirus 229E and influenza A virus were respectively 38.6%, 19.8% and 2.0%. Although rhinovirus/enterovirus, coronavirus 229E and influenza A clearance were respectively 70.6%, 71.4% and 100% on return, overall virus carriage proportion on return was 75.0% in pilgrims with influenza-like illness and 44.0% in those who have never experienced this symptoms or resolved it (OR = 4.05, 95% CI [1.02-16.02]).

CONCLUSIONS

Viruses likely play some role in the pathogenesis of the respiratory tract infections at the Hajj. Point of care-rapid multiplex PCR assays are valuable diagnosis tools in this context when used at respiratory symptom onset or soon after.

MERS-CoV, influenza and other respiratory viruses among symptomatic pilgrims during 2014 Hajj season

More than two million Muslims visit Makkah, Saudi Arabia, annually to perform the religious rituals of Hajj where the risk of spreading respiratory infections is very common. The aim here was to screen symptomatic pilgrims for Middle East respiratory syndrome coronavirus (MERS-CoV) and other viral etiologies. Thus, 132 nasopharyngeal samples were collected from pilgrims presenting with acute respiratory symptoms at the healthcare facilities in the holy sites during the 5 days of the 2014 Hajj season. Samples were tested using real-time reverse transcription polymerase chain reactions and microarray. Demographic data including age, sex, and country of origin were obtained for all participants. While we did not detect MERS-CoV in any of the samples, several other viruses were detected in 50.8% of the cases. Among the detected viruses, 64.2% of the cases were due to a single-virus infection and 35.8% were due to the coinfections with up to four viruses. The most common respiratory virus was influenza A, followed by non-MERS human coronaviruses, rhinoviruses, and influenza B. Together, we found that it was not MERS-CoV but other respiratory viruses that caused acute respiratory symptoms among pilgrims. The observed high prevalence of influenza viruses underscores the need for more effective surveillance during the Hajj and adoption of stringent vaccination requirements from all pilgrims.

Asymptomatic Middle East Respiratory Syndrome Coronavirus (MERS-CoV) infection: Extent and implications for infection control: A systematic review

Background

The Middle East Respiratory Syndrome Coronavirus (MERS-CoV) emerged in 2012 and attracted an international attention as the virus caused multiple healthcare associated outbreaks. There are reports of the role of asymptomatic individuals in the transmission of MERS-CoV, however, the exact role is not known.

Method

The MEDLINE/PubMed and Scopus databases were searched for relevant papers published till August 2018 describing asymptomatic MERS-CoV infection.

Results

A total of 10 papers were retrieved and included in the final analysis and review. The extent of asymptomatic MERS infection had increased with change in the policy of testing asymptomatic contacts. In early cases in April 2012–October 2013, 12.5% were asymptomatic among 144 PCR laboratory-confirmed MERS-CoV cases while in 2014 the proportion rose to 25.1% among 255 confirmed cases. The proportion of asymptomatic cases reported among pediatric confirmed MERS-CoV cases were higher (41.9%–81.8%). Overall, the detection rate of MERS infection among asymptomatic contacts was 1-3.9% in studies included in this review. Asymptomatic individuals were less likely to have underlying condition compared to fatal cases. Of particular interest is that most of the identified pediatric cases were asymptomatic with no clear explanation.

Conclusions

The proportion of asymptomatic MERS cases were detected with increasing frequency as the disease progressed overtime. Those patients were less likely to have comorbid disease and may contribute to the transmission of the virus.

MERS: Progress on the global response, remaining challenges and the way forward

This article summarizes progress in research on Middle East Respiratory Syndrome (MERS) since a FAO-OIE-WHO Global Technical Meeting held at WHO Headquarters in Geneva on 25-27 September 2017. The meeting reviewed the latest scientific findings and identified and prioritized the global activities necessary to prevent, manage and control the disease. Critical needs for research and technical guidance identified during the meeting have been used to update the WHO R&D MERS-CoV Roadmap for diagnostics, therapeutics and vaccines and a broader public health research agenda. Since the 2017 meeting, progress has been made on several key actions in animal populations, at the animal/human interface and in human populations. This report also summarizes the latest scientific studies on MERS since 2017, including data from more than 50 research studies examining the presence of MERS-CoV infection in dromedary camels.

Infectious Diseases and Mass Gatherings

Purpose of Review

Mass gatherings (MGs) are characterized by a high concentration of people at a specific time and location. Infectious diseases are of particular concern at MGs. The aim of this review was to summarize findings in the field of infectious diseases with a variety of pathogens associated with international MGs in the last 5 years.

Recent Findings

In the context of Hajj, one of the largest religious MGs at Mecca, Saudi Arabia, respiratory tract infections are the leading cause of infectious diseases in pilgrims with a prevalence of 50–93%. The most commonly acquired respiratory viruses were human rhinovirus, followed by human coronaviruses and influenza A virus, in decreasing order. Haemophilus influenzae, Staphylococcus aureus, and Streptococcus pneumoniae were the predominant bacteria. The prevalence of Hajj-related diarrhea ranged from 1.1 to 23.3% and etiologies included Salmonella spp., and Escherichia coli, with evidence of acquisition of antimicrobial-resistant bacteria. In other MGs such as Muslim, Christian, and Hindu religious events, sports events, and large-scale open-air festivals, outbreaks have been reported less frequently. The most common outbreaks at these events involved diseases preventable by vaccination, notably measles and influenza. Gastrointestinal infections caused by a variety of pathogens were also recorded.

Summary

Because social distancing and contact avoidance are difficult measures to implement in the context of many MGs, individual preventive measures including vaccination, use of face mask, disposable handkerchief and hand hygiene may be recommended. Nevertheless, the effectiveness of these measures has been poorly investigated in the context of MGs.

A systematic review of emerging respiratory viruses at the Hajj and possible coinfection with Streptococcus pneumoniae

Background

The annual Hajj to the Kingdom of Saudi Arabia attracts millions of pilgrims from around the world. International health community's attention goes towards this mass gathering and the possibility of the development of any respiratory tract infections due to the high risk of acquisition of respiratory viruses.

Method

We searched MEDLINE/PubMed and Scopus databases for relevant papers describing the prevalence of respiratory viruses among Hajj pilgrims.

Results

The retrieved articles were summarized based on the methodology of testing for these viruses. A total of 31 studies were included in the quantitative/qualitative analyses. The main methods used for the diagnosis of most common respiratory viruses were polymerase chain reaction (PCR), culture and enzyme-linked immunosorbent assay (ELISA). Influenza, rhinovirus and parainfluenza were the most common viruses detected among pilgrims. Coronaviruses other than MERS-CoV were also detected among pilgrims. The acquisition of MERS-CoV remains very limited and systematic screening of pilgrims showed no infections.

Conclusions

Well conducted multinational follow-up studies using the same methodology of testing are necessary for accurate surveillance of respiratory viral infections among Hajj pilgrims. Post-Hajj cohort studies would further evaluate the impact of the Hajj on the acquisition of respiratory viruses.

Multiple Sources of Genetic Diversity of Influenza A Viruses during the Hajj

Outbreaks of respiratory virus infection at mass gatherings pose significant health risks to attendees, host communities, and ultimately the global population if they help facilitate viral emergence. However, little is known about the genetic diversity, evolution, and patterns of viral transmission during mass gatherings, particularly how much diversity is generated by in situ transmission compared to that imported from other locations. Here, we describe the genome-scale evolution of influenza A viruses sampled from the Hajj pilgrimages at Makkah during 2013 to 2015. Phylogenetic analysis revealed that the diversity of influenza viruses at the Hajj pilgrimages was shaped by multiple introduction events, comprising multiple cocirculating lineages in each year, including those that have circulated in the Middle East and those whose origins likely lie on different continents. At the scale of individual hosts, the majority of minor variants resulted from de novo mutation, with only limited evidence of minor variant transmission or minor variants circulating at subconsensus level despite the likely identification of multiple transmission clusters. Together, these data highlight the complexity of influenza virus infection at the Hajj pilgrimages, reflecting a mix of global genetic diversity drawn from multiple sources combined with local transmission, and reemphasize the need for vigilant surveillance at mass gatherings.IMPORTANCE Large population sizes and densities at mass gatherings such as the Hajj (Makkah, Saudi Arabia) can contribute to outbreaks of respiratory virus infection by providing local hot spots for transmission followed by spread to other localities. Using a genome-scale analysis, we show that the genetic diversity of influenza A viruses at the Hajj gatherings during 2013 to 2015 was largely shaped by the introduction of multiple viruses from diverse geographic regions, including the Middle East, with only little evidence of interhost virus transmission at the Hajj and seemingly limited spread of subconsensus mutational variants. The diversity of viruses at the Hajj pilgrimages highlights the potential for lineage cocirculation during mass gatherings, in turn fuelling segment reassortment and the emergence of novel variants, such that the continued surveillance of respiratory pathogens at mass gatherings should be a public health priority.