Section 2
Infectious
Diseases
I N F E C T I O U S
D I S E A S E S
Chain of Transmission
Individuals may have
traits that affect their
susceptibility and/or
severity of disease

Microorganisms
capable of causing
illness and/or disease
Place in which the
infectious organism
lives, grows and
reproduces




Ways in which the
infectious agent
leaves the reservoir

Ways in which the
infectious agent
enters the
susceptible host
Ways in which the
infectious agent is
spread from the
reservoir to the
susceptible host
Diagram adapted from: Ontario Agency for Health Protection and Promotion, Provincial Infectious Diseases Advisory Committee.
Routine practices and additional precautions in all health care settings. Toronto, ON: Queen’s Printer for Ontario; 2011
I N F E C T I O U S
D I S E A S E S
Modes of Transmission
Direct Contact
Involves contact between the infectious agent and a susceptible host.
E.g. Scabies, Chickenpox, Influenza, C. difficile, MRSA, VRE, etc.
Indirect Contact
Involves contact between a susceptible host and a contaminated object.
E.g. Scabies, Influenza, C. difficile, MRSA, VRE, etc.
Droplet
Contact of mucous membranes or conjunctivae with large infectious droplets
(>five microns) through face-to-face contact < two metres from an infectious person.
< 2 metres
Droplets do not remain suspended in the air.
E.g. Influenza, Streptococcus pneumoniae, Pertussis, Mumps, etc.
Airborne
Small droplets (five microns or less) remain suspended in the air for long periods of
time and can be carried by air currents.
E.g. Tuberculosis, Measles, Legionnaires’ Disease, etc.
Vectorborne
Transmission through the bite of an insect harbouring an infectious agent
E.g. West Nile virus, Malaria, Lyme Disease, etc.
Vehicle
Contaminated substances (e.g.: food, water) can transmit infectious agent when
consumed/ingested.
E.g. Salmonella, Hepatitis A
The more modes of transmission that an infectious agent has, the more easily it can spread from one
person to another.
Adapted from: Public Health Agency of Canada. Canada Communicable Disease Report: Routine Practices and Transmission of
Infection in Health Care
I N F E C T I O U S
D I S E A S E S
Breaking the Chain of Transmission
Transmission of an infectious agent can be broken anywhere in the chain by implementing
appropriate measures and precautions.
Diagram from: Ontario Agency for Health Protection and Promotion, Provincial Infectious Diseases Advisory Committee. Routine
practices and additional precautions in all health care settings. Toronto, ON: Queen’s Printer for Ontario; 2011
I N F E C T I O U S
D I S E A S E S
Preventing Transmission of Infection
Prevention is the key to protecting Emergency Service Workers against potential exposures to blood
and/or body fluids. Although it may be impossible to completely avoid exposures to infectious agents
due to the nature of the emergency services environment, following best practice guidelines can greatly
reduce transmission risks.
In order to prevent the transmission of infectious diseases, ESWs and Designated Officers should have a
basic knowledge and understanding of:
• Disease categories and specific diseases
• Exposure Risks
• Transmission Risks
• Routine Practices and Additional Precautions (see Section 3 in this guide)
Disease Categories
Blood-Borne Infections (BBI) are infections that are spread through exposure to blood through needle
stick injury or other sharp related injury, mucous membrane, broken skin and high risk behaviours.
Examples of these diseases are Hepatitis B, Hepatitis C and HIV infection.
Gastroenteritis Infections can be caused by bacteria, viruses, or parasites. Symptoms of an infection
are vomiting, diarrhea, headache and lethargy. Gastroenteritis can be contracted through the
consumption of contaminated foods or beverages and through contaminated items or infected persons.
Some infections, like Norovirus can also be spread aerosolized particles (through vomitus). Examples are
Norovirus, Giardia, and Campylobacter.
Respiratory Infections are infections that can affect the upper or lower respiratory tracts. These
infections cause a variety of symptoms such as runny nose, sore throat, fever, cough and shortness of
breath. Respiratory infections are spread through direct or indirect contact. Examples of respiratory
infection are Influenza (flu), Rhinovirus and Coronavirus.
Vaccine Preventable Diseases (VPD) are diseases that can be prevented through one or a series of
immunizations throughout one’s lifetime. The goal with any immunization is the elimination of the
vaccine preventable disease. Some examples of VPD are measles, mumps, rubella, Hepatitis B, Tetanus.
Antibiotic Resistant Organisms (AROs) have been around for many years but are becoming more
common. These bacteria have developed resistance to several antimicrobial agents (antibiotics) and thus
cannot be killed with the usual antibiotic medications. As a result, they are a threat to the treatment of
infectious diseases. ARO’s are most commonly found in hospitals and long-term care facilities, as well as
in the community. Examples of AROs include Methicillin Resistant Staphylococcus aureus (MRSA),
Vancomycin Resistant Enterococci (VRE), Carbapenem Resistant Enterobacteriacae (CRE) and Extended
Spectrum Beta-Lactamase producing bacteria (ESBL).
*Fact Sheets about specific AROs are located in the Valuable Resource Section of this manual *
AROs are NOT part of the Designated Officer program: information is for general reference only.
I N F E C T I O U S
D I S E A S E S
Exposure Risks
In general, the risk of contracting an infectious disease following an exposure is dependent upon
several factors including:
• Type of exposure
• Amount of blood/body fluid involved
• Risk factors related to the source
• Factors related to the ability of the infectious pathogen to survive in the environment
Survival of Pathogens on Environmental Surfaces
> 1 week
Hepatitis C virus
4 weeks
Human Immunodeficiency virus HIV
> 7 days
Clostridium difficile (spores)
5 months
Escherichia coli
1.5 hours – 16 months
Hepatitis A virus (also a VPD)
2 hours – 60 days
Listeria
1 day – months
Norovirus
8 hours – 7 days
Rotavirus
6 – 60 days
Vibrio cholera
1 – 7 days
Coronavirus
3 hours
Haemophilus influenza (also a VPD)
12 days
Influenza virus (also a VPD)
1 – 2 days
Mycobacterium tuberculosis
1 day – 4 months
Respiratory Syncytial virus RSV
up to 6 hours
Rhinovirus
2 hours – 7 days
SARS associated virus
72 – 96 hours
Streptococcus pyogenes (iGAS)
3 days – 6.5 months
Staphylococcus aureus, including MRSA
7 days – 7 months
Vancomycin-Resistant Enterococci VRE
5 days – 4 months
Adenovirus
7 days – 3 months
Cytomegalovirus
8 hours
Herpes simplex virus ( type 1 and 2)
4.5 hours – 8 weeks
Acinetobacter
3 days – 5 months
Other
AROs
Respiratory
Hepatitis B virus (also a VPD)
BBIs
Length of Time
Gastrointestinal (GI)
Pathogen
Source: Kramer, A., Schwebke, I. & Kampf, G. (2006). How long do nosocomial pathogens persist on inanimate surfaces? A systematic
review. BMC Infectious Diseases, 6:130.
I N F E C T I O U S
D I S E A S E S
Transmission Risks
The following chart outlines the estimated transmission rates associated with Blood Borne Infections
that ESWs may come into contact with during the line of duty.
Estimated Blood-Borne Infection Transmission Rates
Disease
Exposure
Transmission Rate
Needle-stick injury with HIV infected blood
Approximately 0.1 – 0.3%
Mucous membrane exposure
Approximately 0.09%
Human bite involving blood-tinged saliva
Rare, few documented cases
Hepatitis B
Needle-stick injury with HBV infected blood
Ranges from 6-60%
Hepatitis C
Needle-stick injury with HCV infected blood
Approximately 2%
HIV
World Health Organization (2011). International Travel and Health Guide – Chapter 8: Exposure to Blood or Other Body Fluids.
Public Health Agency of Canada. Prevention and control of occupational infections in health care. CCDR 2002; 28S1.