Infectious Disease Transmission

• Infectious diseases, caused by microorganisms like bacteria, viruses, fungi, and parasites, present global health challenges
• Understanding how infectious diseases spread among hosts and environments informs public health policies and personal practices
• Disease transmission routes include direct contact, droplet spread, vector-borne means, and contaminated surfaces
• Population density, sanitation, human behavior, and healthcare practices significantly influence spread

Modes of Infectious Disease Transmission

• Modes of transmission define how infectious diseases spread from one host to another
• The 3 main modes of transmission are contact, droplet, and airborne, each with distinct characteristics
• Contact transmission involves direct or indirect transfer of an infectious agent

Direct Contact

• Requires physical interaction someone infected and a susceptible host
• Kissing, touching, and sexual contact can spread diseases like influenza, herpes, and the common cold

Indirect Contact

• Involves transmission through an intermediary object or surface (fomite)
• Touching a contaminated surface like a doorknob can spread pathogens like norovirus and MRSA

Droplet Transmission

• Involves the spread of agents through respiratory droplets when someone coughs, sneezes, talks, or breathes
• Droplets are relatively large (greater than 5 micrometers)
• They only travel 3 to 6 feet from the infected person and contain influenza, COVID-19, and pertussis
• Droplets do not remain suspended in the air but settle on surfaces or are inhaled nearby
• Preventive measures include masks, physical distancing, and hygiene

Airborne Transmission

• Occurs when agents are carried by dust particles or droplet nuclei suspended in the air
• Transmission is typically beyond 6 feet.
• Pathogens spread in enclosed or poorly ventilated spaces
• Tuberculosis, measles, and chickenpox exhibit significant airborne transmission
• Ventilation, air filtration, and isolation protocols help control spread
• Vaccination may also be recommended

Food and Water Transmission

• Diseases spread through contaminated food and water
• Food and water safety are critical components of public health

Food Transmission

• Occurs when infectious agents are ingested, which can happen at any point from production to consumption
• Pathogens contaminate surfaces during farming, processing, transportation, and cooking, like salmonella, E. coli, Norovirus and Giardia
• Unsafe food handling, like inadequate cooking or improper storage, increases the risk of foodborne illnesses causing foodborne outbreaks
• Meat not cooked correctly can carry bacteria.
• Fruits and vegetables washed with contaminated water can carry pathogens.

Water Transmission

• Occurs through contaminated water sources
• Poses health risks, especially in areas lacking adequate sanitation or water treatment via contaminated water supply
• Pathogens enter the water supply through waste, industrial effluents, and runoff
• Cholera, dysentery, and typhoid fever are often linked to contact with unclean water
• Poor hygiene when not washing hands can transmit pathogens through contaminated water
• inadequate sanitation facilities exacerbate spread, causing waterborne outbreaks
• Water quality monitoring and sanitation are crucial

Antimicrobial Resistance (AMR)

• A challenge characterized by the ability of microorganisms to defy medications
• Can lead to treatment failure, increased costs, longer stays, and higher mortality
• Microorganisms build resistance via the following mechanisms

Genetic Mutations

• Spontaneous mutations can occur, changing target sites and rendering drugs ineffective

Acquisition of Resistance Genes

• Bacteria gain resistance genes from other organisms through horizontal gene transfer

Biofilm Formation

• Biofilms exhibit reduced susceptibility to treatment

Efflux Pumps

• Bacteria expel antimicrobial agents before they exert effects

Causes of Antimicrobial Resistance

• Include overuse and misuse of antimicrobials, which can encourage the development of resistant strains
• Agricultural practices can contribute to AMR, transferring resistant bacteria from animals to humans via livestock
• Can also occur by Inadequate infection prevention and control
• Can also occur by global travel and trade
• Inadequate hygiene, sanitation and infection control facilitate resistant pathogen spread

Consequences of Antimicrobial Resistance

• AMR leads to treatment failure and increased complications
• The more severe and prolonged infections from AMR can result in high rates of hospitalization and mortality, straining healthcare systems
• There is also a significant economic impact