In an epidemic first to be done is -
Identity the cases
Confirm the diagnosis
Identify The prone people
Identify the causative factors
verification of diagnosis is the first step in the investigation of an epidemic.it is necessary to examine all cases before arriving at a diagnosis.a clinical examination of a sample of cases may suffice.laboratary investigations can also be employed in such way that it is not delaying any of the epidemiological investigations concerned. ref:park&;s textbook,ed22,pg no 123
Epidemiology