Epidemiological Triad of TB

The Epidemiologic Triad is a model used in the field of epidemiology to study diseases and how they are spread. It consists of a triangle with three vertices or corners. 

The three vertices for infectious diseases consist of:

1. Agent, or microbe that is the factor causing the disease.

2. Host, or organism harbouring the disease.

3. Environment, or those external factors that cause or allow disease transmission. 

In the Epidemiological Triad of TB (Figure), the agent is the TB causing bacteria Mycobacterium tuberculosis; the host refers to humans that are susceptible to TB. Susceptibility or the risk factors for acquiring TB can be:

• Close contact with a person having TB disease
• Nutritional status of the host
• Existing co-morbidities
• Low immunity.

Susceptibility of the host can also vary due to age, gender, genetic composition, race, ethnicity, etc. 

As TB is an airborne disease, environmental factors come into play for the transmission of TB. These include crowding, poor ventilation, bad sanitation, indoor air pollution, etc. 

The understanding between the interplay of agent, host and environment is essential to understanding the epidemiology of TB and taking measures to prevent and cure it. The risk of TB due to environmental factors can be reduced by practising airborne infection prevention measures like good ventilation, hand hygiene and cough etiquette. 

Figure: Epidemiological Triad of TB

Resources

• Understanding the Epidemiologic Triangle through Infectious Disease, CDC. 

• Epidemiological Triad of TB.

   

Assessment