1. Department of Medicine, Imam Abdulrahman Bin Faisal National Guard Hospital, Dammam, Saudi Arabia.
2. Department of Medicine, King Abdulaziz National Guard Hospital, Alhasa, Saudi Arabia.
3. Department of Medicine, King Abdulaziz National Guard Hospital, King Abdullah International Medical Research Center, Alhasa, Saudi Arabia.
4. Department of Medicine, King Abdulaziz Medical City, Riyadh, Saudi Arabia.
5. Biostatistics Unit, King Abdullah International Medical Research Center, Alhasa, Saudi Arabia.
6. Department of Medicine, Hamad Medical Corporation, Doha, Qatar.