Chain of Infection: Six Components and Strategies for Breaking the Chain
1. Causative agent: Biological, physical, or chemical agent capable of causing disease.
a.
2.
3.
4.
5.
6.
Examples of biological agents would include:
i. Viruses
ii. Fungi
iii. Bacteria
iv. Protozoa
v. Helminthes
b. Strategies for breaking this link:
i. Remove or reduce the number of microbes through hand washing
ii. Eliminate and destroy microbes using sterilization techniques
iii. Use antibiotics and antimicrobials prudently
Reservoir: location where an infectious agent can survive, but may or may not multiply. Microbes causing nosocomial
infections can be found in patients, health care workers, equipment, or health care facilities.
a. Strategies for breaking this link
i. Eliminate contaminated equipment through thorough sterilization or the use of disposable supplies
ii. Isolate infectious patients when appropriate
iii. Relieve infected health care workers from duty until non-contagious
Portal of exit: pathway by which an infectious agent exits or leaves the reservoir, such as via the respiratory or
gastrointestinal tract or the blood
a. Strategies for breaking this link:
i. Contain infectious microbe, for example, cover the mouth and nose when coughing or sneezing
ii. Use gloves when in contact with high risk body fluids
Mode of transmission: the medium or mechanism through which an infectious agent moves from a reservoir to a
susceptible host. Transmission of a disease may be through contact (direct, such as per to person or indirect through
contaminated instruments, linens, or dressing), common vehicle (contaminated food), airborne (TB) or vector borne
(malaria).
a. Strategies of breaking this link:
i. Disrupt direct contact transmission by washing hands after patient contact
ii. Interrupt indirect contact by using bags/covered containers for isolating contaminated material
iii. Prevent contamination of common vehicles, such as adequately refrigerating food in hospitals’
eliminate vectors through public health measures, such as pesticides and water drainage in
malaria ridden areas.
Portal of entry: pathway by which the infectious agent enters the susceptible host: examples include the respiratory
and genitourinary tracts, broken skin, or placenta.
a. Strategies for breaking link:
i. Wearing gloves when touching high risk body fluids
ii. Use masks when caring for patients with MDR-TB
Susceptible host: person (or animal) who lacks sufficient resistance to a specific pathogenic organism. Factors
influencing susceptibility include age, gender, ethnicity, occupation, nutritional status, current medications, concomitant
disease, genetics, socioeconomic status, and lifestyle.
a. Strategies for breaking link:
i. Use vaccines, such as the hepatitis B vaccine for health care workers
ii. Employ vaccines for high risk population such as influenza inoculation for the elderly and those
with respiratory conditions.
iii. Screen health care workers, including periodic TB test
iv. Support public health interventions that address such areas as nutrition, potable water, and vector
control.