Outbreak describes an occurrence of disease greater than would otherwise be expected at a particular time and place. OUTBREAK may affect a small and localized group or impact thousands of people across an entire continent or large region. Two linked cases of a rare infectious disease can be considered sufficient to declare an outbreak.



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Epidemic is the rapid spread of infectious disease to a large number of persons in a given population within a short period of time -- usually two weeks or less.

Pandemic is an epidemic of infectious disease that spreads through human populations across a large region, multiple continents, or worldwide.

Endemic describes infectious disease that is maintained in the population in a steady state.

Transmission refers to transfer of microorganisms from a vector (another organism, such as a mosquito), intermediate host (e.g., pig with tapeworm), or directly from one person to another by one or more of the following:

droplet contact – coughing or sneezing on another person

direct physical contact – touching an infected person, including sexual contact

indirect physical contact (casual) – usually by touching soil contamination or a contaminated surface (fomite)

airborne transmission – microorganism in aerosol when it remains viable in the air for long periods

fecal-oral transmission – usually from contaminated food or water sources

Infectious disease is the presence and growth of pathogenic biological agents in an individual host organism with invasion of body tissues by disease-causing agents, the hosting of the biological agent's multiplication, and the resulting reaction of host tissues to these organisms and the toxins they produce which cause clinically evident illness.

Contagious disease is a subset category of transmissible diseases (transmit from person to person) involving infections or some non-infection diseases, which are transmitted to other persons, either by physical contact (as in contact = contagious) with the person suffering the disease, or by casual contact with their secretions or objects touched by them or airborne route among other routes

Non-contagious infections and diseases usually require a special mode of transmission between persons or hosts, such as by an intermediate vector species (mosquitoes that cause Malaria or West Nile Virus) or by non-casual transfer of bodily fluid (such as transfusions, needle sharing or sexual contact). Non-contagious can also be inherited from parents or caused by environmental or behavioral factors.