Disease Transmission: How Infections Spread and Prevention Basics

Understanding transmission routes empowers prevention. Diseases spread via pathogens (bacteria, viruses, fungi, parasites) or, for chronic conditions, through shared risk behaviors.

Infectious Disease Transmission Routes

Route	Mechanism	Examples	Prevention
Direct Contact	Person-to-person touch	Skin infections (MRSA, herpes), STIs, scabies, lice	Barriers (condoms, gloves), hygiene, avoid contact with lesions
Respiratory Droplets	Cough/sneeze → large droplets → mucosa (short range)	Influenza, COVID-19, pertussis, meningococcal	Masking, distancing, ventilation, vaccination
Airborne (Aerosol)	Small particles suspend in air (long range/time)	Measles, TB, chickenpox, COVID-19 (aerosol component)	N95/KN95, HEPA filtration, UVGI, negative pressure
Fomite (Indirect Contact)	Contaminated surfaces/objects	Norovirus, C. diff, RSV, rhinovirus	Hand hygiene, surface disinfection, no face-touching
Vehicle (Food/Water)	Contaminated ingestion	Salmonella, E. coli, Hepatitis A, Cholera, Listeria	Safe food prep, water treatment, pasteurization
Vector-Borne	Arthropod bite	Malaria (mosquito), Lyme (tick), Dengue, Zika, Plague (flea)	Repellent, permethrin clothing, nets, vector control
Vertical (Mother-to-Child)	Prenatal, intrapartum, breastfeeding	HIV, Syphilis, HBV, HCV, CMV, Zika, HSV	Screening, treatment, C-section, avoid breastfeeding if indicated
Parenteral (Blood/Body Fluid)	Needlestick, transfusion, sharing injection equipment	HIV, HBV, HCV	Safe injection, screened blood, PEP/PrEP, harm reduction

Chronic Disease "Transmission"

Non-communicable diseases (heart disease, diabetes, cancer) aren't contagious but spread socially through:

• Shared obesogenic environments (food deserts, sedentary design).
• Cultural norms (diet, alcohol, tobacco).
• Intergenerational modeling (parenting behaviors).
• Structural determinants (poverty, racism, healthcare access).

Core Prevention Principles

1. Hand Hygiene: Soap/water 20 sec or ABHR 60%+ alcohol – #1 intervention.
2. Vaccination: Primary prevention for 20+ diseases.
3. Respiratory Etiquette: Cover cough/sneeze; mask when ill.
4. Safe Sex: Condoms, PrEP, vaccination, testing, communication.
5. Food Safety: Clean, separate, cook, chill.
6. Vector Protection: EPA-registered repellent; tick checks.
7. Environmental: Ventilation, sanitation, safe water.
8. Antimicrobial Stewardship: Use antibiotics only when needed, as prescribed.

If You Suspect You're Contagious

• Isolate; mask; test; notify contacts; follow public health guidance.
• Healthcare workers: Occupational health clearance before return.