Disease outbreaks are usually caused by an infection, transmitted through person-to-person contact, animal-to-person contact, or from the environment or other media.
Outbreaks may also occur following exposure to chemicals or to radioactive materials. For example, Minamata disease is caused by exposure to mercury.
Occasionally the cause of an outbreak is unknown, even after thorough investigation.
Communicable disease outbreaks
Environmental factors influencing the spread of communicable diseases
Water, sanitation, food and air quality are vital elements in the transmission of communicable diseases and in the spread of diseases prone to cause epidemics.
A number of environmental factors influence the spread of communicable diseases that are prone to cause epidemics. The most important of these are:
- water supply
- sanitation facilities
- food
- climate.
A lack of safe water, inadequate excreta disposal facilities, poor hygiene, poor living conditions and unsafe food can all cause diarrhoeal diseases. These diseases are a major cause of suffering and death in an emergency situation.
Climate can affect disease transmission in a variety of ways. The distribution and population size of disease vectors can be heavily affected by local climate. Flooding after heavy rains can result in sewage overflow and widespread water contamination. In addition, there is some evidence to suggest that pathogens can be spread from one region to another along air streams or by wind.
WHO’s response to communicable disease outbreaks is led by the Epidemic and Pandemic Alert and Response Department.
