Circulation of respiratory pathogens at mass gatherings, with special focus on the Hajj pilgrimage

A major public health concern in relation to mass gatherings is the international circulation of infectious diseases, and the spread between participants and to the population of the nation hosting the event. Transmission of respiratory pathogens at the Hajj Muslim pilgrimage in the Kingdom of Saudi Arabia is highly frequent, resulting in high acquisition rates of virus and bacteria carriage. The Hajj may, therefore, contribute to the globalization of common respiratory pathogens resulting from the cross-contamination of participants harboring pathogens that easily spread among pilgrims. A wide range of viral and bacterial clinical infections of the upper and lower respiratory tract can occur during the Hajj, leading to a high number of outpatient consultations and hospitalization in Saudi hospitals. Although outbreaks are less frequently reported in or after mass gatherings, they do sometimes occur, resulting in the international spread of measles, influenza, and mumps.