1 SCIENTIFIC REPORTS | (2019) 9:17771 | https://doi.org/10.1038/s41598-019-54370-0 www.nature.com/scientificreports Respiratory tract infections among French Hajj pilgrims from 2014 to 2017 Van-Thuan Hoang 1,2,3 , Saliha Ali-Salem 1,2 , Khadidja Belhouchat 1,2 , Mohammed Meftah 1,2 , Doudou Sow 1,2,4 , Thi-Loi Dao 1,2,3 , Tran Duc Anh Ly 1,2 , Tassadit Drali 1,2 , Laetitia Ninove 5 , Saber Yezli 6 , Badriah Alotaibi 6 , Didier Raoult 2,7 , Philippe Parola 1,2 , Vincent Pommier de Santi 1,2,8 & Philippe Gautret 1,2* Respiratory tract infections (RTIs) are common among Hajj pilgrims, but risk factors for RTIs and respiratory pathogen acquisition during the Hajj are not clearly identifed. Based on previous studies, most frequent pathogens acquired by Hajj pilgrims were investigated: rhinovirus, human coronaviruses, infuenza viruses, Streptococcus pneumoniae, Staphylococcus aureus, Klebsiella pneumoniae and Haemophilus infuenzae. 485 pilgrims were included. 82.1% presented with RTIs. Respiratory chronic diseases were associated with cough, Infuenza-like illness (ILI) and the acquisition of H. infuenzae. Vaccination against invasive pneumococcal diseases (IPD) and infuenza 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. infuenzae-S. pneumoniae together were respectively twice and fve times more likely to have respiratory symptoms. Individual with H. infuenzae-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 confrm the efectiveness of infuenza and IPD vaccinations in reducing ILI symptoms and acquisition of S. pneumoniae carriage respectively. Te Hajj is one of the largest annual religious mass gatherings in the world. Each year, Saudi Arabia attracts over 2 million pilgrims from over 180 countries, including about 2,000 from Marseille, France 1 . Te Hajj presents major challenges in public health and infection control as the crowding conditions favor the acquisition, dissem- ination and transmission of pathogenic microorganisms 2 . Respiratory tract infections (RTIs) are particularly frequent during the pilgrimage and are responsible for most causes of hospitalization, with community-acquired pneumonia being a major cause of serious illness among pilgrims 3 . Many studies have been conducted among Hajj pilgrims over the last decade, demonstrating the high prevalence of respiratory symptoms and the frequent acquisition of respiratory pathogens 3–7 . Te viruses most commonly acquired afer the Hajj are human rhinovirus (HRV), human coronaviruses (HCoV) and infuenza A virus (IAV). Te most frequently acquired respiratory bacteria are Streptococcus pneumoniae (S. pneumoniae), Staphylococcus aureus (S. aureus) and Haemophilus infu- enzae (H. infuenzae) 3 . However, the etiology of RTIs at the Hajj is likely multifactorial and complex. Te poten- tial efects of vaccination against infuenza and pneumococcus 8,9 , of non-pharmaceutical preventive measures including face-mask use and hand hygiene practice 10–12 have been investigated, mostly based on clinical criteria, but results of studies are contradictory. So far, to our knowledge, risk factors for pathogen acquisition during the Hajj are not clearly identifed. Relationship between respiratory symptoms and carriage of respiratory pathogens at the Hajj also remain poorly understood making it difcult distinguishing between infection and colonization. We conducted this 1 Aix Marseille Univ, IRD, AP-HM, SSA, VITROME, Marseille, France. 2 IHU-Méditerranée Infection, Marseille, France. 3 Thai Binh University of Medicine and Pharmacy, Thai Binh, Viet Nam. 4 Service de Parasitologie-Mycologie, Faculté de médecine, Université Cheikh Anta Diop, Dakar, Senegal. 5 Unité des Virus Émergents (UVE: Aix-Marseille Univ – IRD 190 – Inserm 1207 – IHU Méditerranée Infection), Marseille, France. 6 The Global Centre for Mass Gatherings Medicine, Ministry of Health, Riyadh, Saudi Arabia. 7 Aix Marseille Univ, MEPHI, Marseille, France. 8 French Military Center for Epidemiology and Public Health, Marseille, France. *email: philippe.gautret@club-internet.fr OPEN