Mass gatherings, including sporting events like the Olympics or FIFA World Cup attract millions of visitors from all over the world.
Every year, over 2 million Muslims make the sacred pilgrimage to The Hajj in Mecca, Saudi Arabia which is the largest mass gathering in the world.
Large numbers of people in close quarters increases the risk of contagious diseases, including respiratory illnesses and infectious diarrhea. Heat exhaustion and dehydration are also common.
All pilgrims to The Hajj are required to have a meningitis vaccine in order to get a travel Visa. Routine immunizations should be up-to-date and Hepatitis A and B and typhoid vaccines are recommended.