Large gatherings of people are erous because diseases can spread ( ) and ( ) . But doctors from around the world are ( ) their knowledge. Many pilgrims to the Hajj have had little ( ) care. So health officials first provide a health ( ) . There is a medical ( ) at the airport for pilgrims who are sick. The officials want to reduce the ( ) of diseases spreading. Saudi officials use ( ) to track the outbreak of diseases. They work with the World Health ( ) to use rapid testing. Health for mass gatherings is a new ( ) of medicine.