Disease Outbreaks: Definitions, Steps, and Modes of Transmission

Posted on Jan 9, 2025 in Microbiology

Disease Detectives

Pandemic: A global disease outbreak.

Outbreak: A sudden occurrence of disease in a community.

Epidemic: A widespread occurrence of a disease in a community at a particular time.

Zoonosis: A disease that can be transmitted to humans from animals.


10 Steps to Investigate an Outbreak

  1. Prepare for field work
  2. Establish the existence of an outbreak
  3. Verify the diagnosis
  4. Construct a working case definition
  5. Find cases systematically and record information
  6. Develop Hypothesis
  7. Evaluate hypotheses
  8. Refine Hypothesis
  9. Implement Control and Preventive Measures
  10. Communicate Findings

5 Modes of Disease Transmission

  1. Air-borne transmission
  2. Contact transmission (direct and indirect)
  3. Vehicle transmission (Water, milk, food etc.)
  4. Vector-transmission
  5. Trans-placental transmission

W.H.O: World Health Organization

C.D.C: Centers for Disease Control

P.H.S: Public Health Surveillance.

Vector: An organism, typically a biting insect or tick, that transmits a disease or parasite from one animal or plant to another.

Fomite: Any object or substance capable of carrying infectious organisms.

Risk: The probability that one will become infected by an illness or injury within a specific period or time.

Cluster: An aggregation of cases over a particular period of time.

Reservoir: Any person, animal, plant, soil or substance in which an infectious agent normally lives and multiplies.

Morbidity: Illness

Mortality: The state of being subject to death

Parasite: An organism that lives in or on another organism (its host) and benefits by deriving nutrients at the host’s expense.

Pathogen: A bacterium, virus, or other microorganism that can cause disease.
Virus: A small infectious agent that can only replicate inside the cells of another organism.
Incubation period: The period between exposure to an infection and the appearance of the first symptoms.

Surveillance: The systematic collection, analysis, and interpretation of data

Epidemiological Calculations

A = The number of people who both had the exposure and developed the disease

B = The number of people who had the exposure but did not develop the disease

C = The number of people who did not have the exposure but did develop the disease

D = The number of people who neither had the exposure nor developed the disease

Specific Diseases

Zika: The most common symptoms of Zika are fever, rash, joint pain, red eyes, muscle pain, and headache. The illness is usually mild with symptoms lasting for several days to a week. Zika fever in pregnant women can cause abnormal brain development. Similar to a mild form of dengue fever. It is contagious. The mosquito that transmits Zika is aedes, the same that transmits dengue and yellow fever.

Ebola: An infectious and generally fatal disease marked by fever and severe internal bleeding, spread through contact with infected body fluids by a filovirus (Ebola virus), whose normal host species is unknown.


Salmonella: A bacterium that occurs mainly in the intestine, especially a stereotype causing food poisoning. Food poisoning caused by infection with salmonella bacterium.


E-Coli: A bacterium commonly found in the intestines of humans and other animals, where it usually causes no harm. Some strains can cause severe food poisoning, especially in old people and children.


MRSA: Methicillin-resistant Staphylococcus aureus is a bacterium responsible for several difficult-to-treat infections in humans. It is also called oxacillin-resistant Staphylococcus aureus.


Lime Disease: An inflammatory disease characterized at first by a rash, headache, fever, and chills, and later by possible arthritis and neurological and cardiac disorders, caused by bacteria that are transmitted by ticks.


Malaria: An intermittent and remittent fever caused by a protozoan parasite that invades the red blood cells. The parasite is transmitted by mosquitoes in many tropical and subtropical regions.