epidemics

An epidemic is a rapid increase in the number of cases of an infectious disease in a defined population over a short period, exceeding what is normally expected. Epidemics are localized in space or group and can occur when transmission rises or a pathogen becomes more virulent. They differ from outbreaks (smaller or shorter spikes) and from endemic diseases (constant presence). If spread is global, the event may be termed a pandemic.

Epidemics are caused by infectious agents such as viruses, bacteria, parasites, or fungi. Transmission can occur by contact, droplets, airborne routes, vectors, or contaminated water or food. The potential for spread is described by the reproduction number, R0, which estimates the average secondary cases caused by a single case in a wholly susceptible population. When Rt exceeds 1, transmission grows.

Public health surveillance detects unusual increases in illness and uses case definitions, laboratory confirmation, and reporting to classify events. Data analysis, contact tracing, and laboratory work support outbreak investigation. Timely communication among clinicians, laboratories, and health authorities helps identify transmission chains and direct interventions.

Control and prevention combine medical treatment and non-pharmaceutical measures. Vaccination reduces susceptibility and transmission; therapies can lessen severity and duration. Non-pharmaceutical measures include isolation, quarantine, hygiene, masking, social distancing, and vector control. Improvements in water, sanitation, and access to care also reduce risk.

Epidemics influence public health policy and research, driving advances in surveillance, vaccines, and health infrastructure. Notable examples include influenza outbreaks, SARS, Ebola, and other disease surges. Effective response relies on timely data, scientific guidance, and coordinated action across communities and governments.