Which statement best defines an outbreak (epidemic)?

• A. The occurrence of disease in excess of what is expected
• B. The disease is endemic in the population
• C. The outbreak requires no fieldwork
• D. The surveillance system cannot determine what is expected

Answer: (A)

An outbreak is defined by observing more cases of a disease than would be expected in a given population, over a specific time and place. This requires a baseline or expected number of cases, derived from historical data, seasonal patterns, and ongoing surveillance. When observed cases exceed that expected level, it signals an outbreak (often called an epidemic in broader terms). If the disease is usually present at a constant, background level, it is described as endemic, not an outbreak. Outbreak investigations typically involve fieldwork to confirm cases, explore exposures, and implement controls, so stating that no fieldwork is needed isn’t accurate. Surveillance systems are designed to help determine what’s expected, so the idea that they can’t determine an expected level isn’t correct.