19. Primary and secondary factors of epidemic process (virulence, source of infection, means of transmission, susceptible host)

Colonization?

An organism is replicating in a host but not causing disease

Sporadic case?

Case not connected to other cases

Endemic?

High occurrence of a disease within a given geographical are or population

- Malaria is endemic to Sub-saharan Africa

Epidemic?

Outbreak of a disease within a region in a country, or to multiple countries

Pandemic?

Global disease outbreak

- Covid-19

Levels of infection?

Colonization

- E.g. S.aureus in nasopharynx

Subclinical infection

- Before symptoms occur

- The disease may be contagious

Latent infection

- After initial symptoms has occured, but before they recur

- HSV-1 and 2 etc

Manifest (clinical) infection

Epidemic process?

The process of spreading of infectious diseases among people

Characteristics of infectious diseases:

- Sources of infection

- Possible route of transmission

- Susceptibility to humans

Primary (direct) factors?

- Sources of infection

- Possible routes of transmission

- Susceptible human persons

Secondary (indirect) factors?

- Natural factors

- Social factors

The source of infection - primary?

The reservoir is the habitat in which the infectious agent normally lives, multiplies and grows

- Can be human, nature or animals

Zoonosis: disease that is transmissible from vertebrae animals to human

Source: the location from which the infectious agent is immediately transmitted to the host

Environmental reservoir?

- Plant, soil, water

- Many fungal agents have reservoir in soil

- Legoinella pneumophila has reservoir in stale waters

Carriers?

A person with inapparent infection who can transmit the infectious agents to other

- Asymptomatic carrier

- Incubatory carrier

- Convalescent carrier

The route of transmission?

Direct transmission:

- Contact

- Sexually

- Transplacental

- Transplantation

- Respiratory droplets > 5µm

Indirect transmission?

Airborne

- Droplets < 5µm

- Suspended by air, can travel far

Waterborne

- Drinking water, bathwater

Foodborne

- Infected by improper handling

- Organisms can multiply in food

Soil

Personal objects

- Bed

- Clothes

- Door handle

Vector borne

- Ticks, fleas, mosquito

The susceptible population?

Susceptibility = a feature of a person that makes it possible for an infectious agent to cause illness

Individual: depends on the immune system of the individual

Population: depends on the proportion of susceptible and non-susceptible individuals

Secondary indirect factors of epidemic process?

Those factors that can help the spreading of infections and affect the spread and duration of epidemics

- Living and working environment

- Weather

- Nutritional status

- Social factors

- Status of health care in that region

Virulence?

Infectivity = out of 100 people exposed to a certain agent, how many will be infected?

Pathogenicity = how many that are infected will also be sick

- Measles = 100%

- Poliomyelitis = 1%

Lethality = how many who got the disease will die?