n

• Stage 1 or imported and sporadic cases: When only those who have travelled to virus-hit countries test positive.
• Stage 2 or local transmission: When the source of the transmission is known and can be located, usually with ones close to the patient such as family or people s/he have come in contact with.
• Stage 3 or community transmission: When the source of the infection cannot be located. This happens when a patient tests positive despite no exposure to an infected person nor any history of travelling to an infected country.
• Stage 4: When the disease is termed an epidemic, or an outbreak so severe with no clear end point for the ongoing transmission.