Millions of people die each year from infectious diseases caused by germs like viruses, bacteria and parasites. These germs spread through a variety of ways including sexual transmission, direct contact (e.g., touching or breathing infected blood), or through the environment such as contaminated food or water, poor hygiene, or unsanitary conditions. These factors allow disease outbreaks to grow rapidly resulting in epidemics and pandemics.
A disease outbreak occurs when a number of cases is greater than expected and occurs in a geographical area or specific subpopulation and time frame. It may also include a single case that is linked to another case or multiple cases that occur over a prolonged period of time and share similar characteristics.
Viruses, such as Ebola and Marburg, and some bacteria, such as Legionella, are unique in that they can spread directly from human to human. Fungal diseases, on the other hand, are often spread through disruption of the environment. This can occur on a small scale, such as during construction or excavation projects, or on a large scale, such as in relation to natural disasters.
A well-conducted outbreak investigation involves a systematic approach to identifying and evaluating evidence about the cause, transmission, and epidemiology of a disease in order to inform public health response to it. This includes confirming the diagnosis, writing an investigative report, and taking action to control the outbreak by changing public health policies and/or providing preventive measures such as vaccination, improved hygiene, removing patients from the infectious source, interruption of animate or inanimate environmental transmission, and treatment of infected persons.