Chart — Infection Control
Infection Transmission Precautions Chart
Understanding how pathogens spread determines which precautions to use and why they work. This chart covers the science of contact, droplet, and airborne transmission — particle sizes, travel distances, environmental survival, and the mechanistic rationale behind each precaution tier.
Educational use only. Based on CDC Guideline for Isolation Precautions (2007/2017). Transmission science continues to evolve — follow current institutional and public health guidance for specific pathogens. This material supports nursing education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional policy, or medical direction. Always follow facility protocols and current provider orders.
Transmission Route Quick Reference
| Route | Particle Size | Travel Distance | Primary Mechanism | Precaution Tier |
|---|---|---|---|---|
| Contact | N/A — surface or skin transfer | Direct touch; fomites (surfaces, equipment) | Physical transfer via hands, skin, or contaminated objects | Contact Precautions + Standard |
| Droplet | > 5 µm — heavy; fall quickly | < 3–6 feet; settles onto surfaces | Expelled during coughing, sneezing, talking, procedures | Droplet Precautions + Standard |
| Airborne | ≤ 5 µm (droplet nuclei) — light; remain suspended | > 3–6 feet; travels on air currents throughout room and beyond | Inhalation of suspended droplet nuclei carrying infectious load | Airborne Precautions + Standard (AIIR + N95) |
Transmission Mechanisms in Detail
Contact Transmission
Physical transfer of a pathogen from an infected source to a susceptible host — either directly (touching the patient) or indirectly via contaminated surfaces and equipment (fomites).
Not particle-based — pathogen transfers via skin contact or contaminated objects
No air travel — requires physical contact with source or contaminated environment
Hours to days on surfaces (MRSA: up to 9 days; VRE: weeks; C. diff spores: months; norovirus: days to weeks on hard surfaces)
Why the Precaution Works
Gown and gloves create a physical barrier between the nurse and the contaminated patient or environment. Removing and discarding PPE at the room door prevents carrying organisms out on clothing or hands. Dedicated equipment prevents fomite transfer to other patients via shared stethoscopes or BP cuffs.
Key Science
C. difficile forms spores that survive on surfaces for months and are resistant to alcohol — their spore coat has no outer lipid membrane for alcohol to disrupt. Only mechanical removal with soap and water, or sporicidal agents (bleach), interrupts C. diff spread. This is why ABHR alone is insufficient.
Droplet Transmission
Respiratory secretions expelled as large, heavy droplets during coughing, sneezing, talking, or procedures. Droplets travel short distances and fall quickly to surfaces under gravity due to their size.
> 5 µm — heavy enough to settle rapidly; do not remain suspended in air
< 3–6 feet before settling — cannot travel beyond the immediate patient environment under normal air currents
Land on mucous membranes (eyes, nose, mouth) of nearby persons, or settle on nearby surfaces where they can cause contact spread if touched
Why the Precaution Works
A surgical mask worn by the nurse intercepts large droplets before they reach the nasal or oral mucosa. Because droplets fall within 3–6 feet, spatial distancing also provides meaningful protection. Negative pressure rooms are not needed because droplets do not stay suspended — they fall out of the air before they could spread beyond the immediate space.
Key Science
The surgical mask versus N95 distinction is mechanistic: surgical masks filter large particles by blocking their physical path. N95 respirators use electrostatic filtration to capture particles as small as 0.3 µm. For droplet-only pathogens (> 5 µm particles), the fine filtration of N95 provides no additional benefit over a surgical mask — which is why N95 use is reserved for airborne pathogens and aerosol-generating procedures.
Airborne Transmission
Pathogen-containing particles small enough to remain suspended in the air for extended periods. These droplet nuclei form when large droplets evaporate, leaving behind a tiny, lightweight residue that drifts on air currents.
≤ 5 µm (droplet nuclei) — light enough to remain suspended indefinitely; can carry infectious viral or bacterial load
> 3–6 feet; can travel throughout a room, down corridors, and to adjacent spaces via ventilation systems
Remain viable and infectious suspended in air for hours (M. tuberculosis, measles virus, varicella-zoster virus); do not rely on surface contact for transmission
Why the Precaution Works
N95 respirators filter ≥ 95% of particles ≥ 0.3 µm using electrostatic mechanisms — sufficient to capture airborne droplet nuclei. Negative pressure rooms prevent contaminated air from escaping: air flows inward from the hallway, keeping contaminated room air contained. Keeping the door closed maintains the pressure differential — opening the door equalizes pressure and allows contaminated air to escape.
Key Science
Droplet nuclei form through droplet evaporation: a large droplet expelled during coughing loses water content as it travels, shrinking to a tiny particle that carries the infectious agent. This residue becomes so light it can remain airborne for hours and travel throughout a ventilated building. This is why standard masks and open rooms cannot protect against airborne pathogens — the particles bypass mechanical barriers and travel far beyond the immediate patient area.
Aerosol-Generating Procedures (AGPs)
Certain clinical procedures convert droplet-sized particles into airborne-sized aerosols. When an AGP is performed on a patient under droplet precautions, upgrade PPE to an N95 respirator — the procedure itself changes the transmission risk profile.
Common AGPs:
Endotracheal intubation, bronchoscopy, open airway suctioning, cardiopulmonary resuscitation, manual bag-mask ventilation, high-flow nasal oxygen (HFNO), non-invasive positive pressure ventilation (CPAP/BiPAP), nebulized medication administration, induced sputum collection.
The mechanism: high-velocity air movement during these procedures fragments respiratory secretions into particles small enough to remain airborne, regardless of the baseline transmission route of the target pathogen.
Pathogens With Multiple Transmission Routes
| Pathogen | Routes | Scientific Rationale | Combined Precautions |
|---|---|---|---|
| Varicella (VZV) | Airborne + Contact | Virus is aerosolized from respiratory secretions (airborne nuclei) AND transmitted via direct contact with vesicular fluid. Both routes are simultaneously active during active infection. | N95 + gown + gloves; AIIR required; non-immune staff should not enter |
| Disseminated herpes zoster | Airborne + Contact | Disseminated zoster generates airborne-sized particles from widespread skin lesions and respiratory shedding. Localized (dermatomal) zoster is contact/droplet only. | Same as varicella: N95 + gown + gloves; AIIR required |
| RSV | Contact + Droplet | RSV survives on hands and surfaces for several hours (contact fomite route) AND is expelled in large respiratory droplets that infect via nasal and ocular mucosae. Both routes are clinically relevant. | Gown + gloves + surgical mask |
| SARS-CoV-2 (COVID-19) | Droplet + Contact; airborne demonstrated in poorly ventilated indoor settings | Primarily spread via respiratory droplets. Studies demonstrated aerosol transmission in enclosed, poorly ventilated spaces at high viral loads. Transmission science evolved significantly during the pandemic. | Droplet + Contact (most settings); N95 for AGPs; follow current CDC/facility guidance |
NCLEX Science Pearls
5 µm: The Particle Size Dividing Line
Particles > 5 µm fall quickly (droplet precautions — surgical mask). Particles ≤ 5 µm remain suspended (airborne precautions — N95 + negative pressure room). The 5 µm threshold explains every difference in precaution requirements between droplet and airborne tiers.
Why C. diff Requires Soap and Water
Alcohol kills microorganisms by disrupting lipid membranes. Spores have no outer lipid membrane — they are physically resistant to alcohol. Only soap-and-water scrubbing (mechanical removal) or sporicidal bleach (chemical destruction) effectively addresses spores.
Why Negative Pressure Contains Airborne Pathogens
Air flows from high-pressure areas to low-pressure areas. Negative pressure rooms are lower pressure than hallways, so air always flows inward through gaps — hallway air flows into the room, contaminated room air cannot escape. The door must remain closed at all times to maintain this pressure differential.
Classic Airborne Three: TB, Measles, Varicella
These three share the key property: all generate infectious particles ≤ 5 µm that remain viable and airborne for extended periods. TB is bacterial; measles and varicella are viral — but the physics of their aerosols is identical, which is why all three require the same AIIR + N95 + door-closed protocol.
Related Resources
Standards & sources
Fact-checked Jun 21, 2026This page is written to align with CDC / HICPAC · Infectious Diseases Society of America (IDSA) / SHEA. It is an educational summary, not a citation of any single document — always verify specific doses, values, and protocols against current guidelines and your facility policy. How we source content →