Sterile Technique
Part of Vaccines
Preventing microbial contamination during vaccine preparation, culture work, and administration.
Why This Matters
Sterile technique is the discipline of preventing microbial contamination from entering sterile spaces, preparations, and equipment. In vaccine work, it is not one consideration among many — it is the foundation on which everything else rests. A vaccine that is contaminated with environmental bacteria can cause systemic infection when injected. Culture work contaminated with environmental organisms produces false results and wastes materials. A sterile field violated at the wrong moment can kill a patient who came for protection.
Sterile technique was developed in the 1870s-1880s by Lister, Koch, and Pasteur. Before it, surgical mortality from post-operative infection exceeded 50% in many hospitals. Within a decade of rigorous antiseptic and aseptic practice becoming standard, that rate dropped dramatically. The same transformation is available to any rebuilding society that adopts these principles.
Sterile technique is not magic. It is a disciplined habit of thought about where contamination comes from and how to interrupt every pathway by which it can travel from the environment to the sterile field.
Sources of Contamination
Understanding where contamination comes from allows systematic elimination:
Air: Bacteria and fungi float in air on dust particles, skin cells, and water droplets. Air currents carry them onto any exposed surface. The more air movement, the more contamination. Working in still air reduces airborne contamination significantly.
Skin: Human skin carries millions of bacteria per square centimeter. Hands are the most contaminated surface the practitioner controls. Every touch transfers organisms.
Non-sterile equipment: Any instrument, container, or surface that has not been sterilized carries organisms.
Non-sterile liquids: Water from environmental sources (rivers, wells) contains bacteria, fungi, and sometimes protozoa. Food-grade or drinking water is not sterile.
Coughing, talking, sneezing: Project droplets containing bacteria up to 1-2 meters. Talking over an open container can contaminate it.
Contaminated starting material: A culture intended as pure that contains mixed organisms.
Environmental Preparation
Before any sterile work:
Choose a dedicated space: Designate a specific area for sterile work. Do not use this area for food preparation, animal care, or other activities. The fewer activities in the space, the fewer organisms present.
Reduce air movement: Close windows and doors before beginning work. Allow disturbed air to settle for 15-30 minutes before working with open sterile containers. Avoid walking quickly or working near fans.
Clean work surfaces: Wipe all surfaces with 70% alcohol or dilute bleach (0.1%) and allow to dry. Clean from the outside in — not from a central clean area outward to the dirty periphery.
Prepare before starting: Lay out all equipment needed before opening any sterile materials. Opening and retrieving materials mid-procedure requires walking and disturbing air. Have everything ready: instruments, containers, media, labels.
Hand Preparation
Hands are the primary vector of contamination from practitioner to material.
Surgical hand scrub:
- Remove all rings and wrist jewelry (organisms shelter under them).
- Wet hands and forearms up to elbows with clean water.
- Apply soap; scrub with a clean brush or rough cloth for 3-5 minutes:
- Back of hands, palms, between each finger, fingertips, nails, wrists, forearms
- Pay special attention to fingernails — trim short and brush under edges
- Rinse thoroughly from fingertips to elbow (keep hands elevated above wrists).
- Dry with clean cloth or allow to air dry.
- Do not touch anything non-sterile after scrubbing.
For routine vaccine administration (not full sterile prep): Hand washing with soap and water for 20-30 seconds is sufficient. Use clean cloth to turn off faucet after washing (touching a contaminated faucet recontaminates hands).
Alcohol rub (when water unavailable): Apply 70% ethanol gel or solution (diluted from 95% alcohol if commercial gel unavailable) and rub hands until dry. Effective against most bacteria and viruses. Does not remove soil — if hands are visibly dirty, wash first.
Sterilizing Equipment
Heat sterilization — dry heat: Metal instruments, glass containers: bake at 180°C for 2 hours. Kills all organisms including bacterial spores. Also destroys endotoxins (very important for injectable preparation equipment). No water needed.
At lower temperatures:
- 160°C for 2 hours
- 170°C for 1 hour
Heat sterilization — moist heat (autoclaving/pressure steaming): 121°C for 15 minutes under steam pressure. More efficient than dry heat — moist heat penetrates better. Kills spores. Does not destroy endotoxins (higher temperature required for endotoxin destruction).
Improvised: sealed pressure vessel with small amount of water; heat until steam pressure builds (use pressure relief system); maintain for 15-20 minutes.
Boiling: 100°C for 20 minutes. Kills vegetative bacteria, most viruses, fungi. Does not reliably kill bacterial spores (Bacillus, Clostridium). Sufficient for most culture equipment and vaccine administration equipment.
Use boiling for:
- Reusable glass syringes
- Metal instruments
- Cloth covers
- Glass containers used in culture work
Flame sterilization: Metal loops, needles, knife edges: hold in flame until red-hot. Allow to cool before using (touching hot metal to biological material destroys it). Quick, reliable for small instruments.
Chemical sterilization (for heat-sensitive items): Instruments that cannot be heated (rubber, some plastics, heat-sensitive assembled devices):
- 70% ethanol: effective for skin preparation and surface treatment. Soak instruments for 30 minutes for surface sterilization.
- Glutaraldehyde 2% solution: 10-hour soak for full sterilization. Expensive to obtain; very effective.
- Formaldehyde vapor: enclose item in sealed container with formaldehyde source for 12 hours. Effective but requires ventilation afterward.
Maintaining Sterility During Work
Never reach over sterile field: Reach in from the side, not from above. Particles fall downward — reaching over the field rains contamination onto it.
Never put down a sterile instrument: Once sterile, hold the instrument until it is used. If you must set it down, place it on a sterile surface (boiled cloth, the sterile field itself). Never place it on an uncovered bench.
Open containers for minimum time: An open sterile container is being contaminated with every second of exposure to air. Work quickly, cover when not in active use.
Use sterile transfer: Moving material between containers requires sterile technique throughout: both the source container and destination container are open only during the transfer; the instrument used for transfer must be sterile; the material must not touch non-sterile surfaces during transfer.
Flame-and-cool loops: For bacteriological loop transfer: heat to red-hot, allow to cool in air 10-15 seconds before touching organisms (red-hot loop kills organisms; must cool first). After transfer, reflame to prevent cross-contamination.
Gravity away from sterile field: Tilt containers and use instruments so that if a drop falls, it falls away from the sterile area. Never pipette above an open sterile container.
Antiseptic Use for Injection Sites
Skin cannot be sterilized — organisms live within follicles and glands beyond surface access. The goal of skin preparation is to reduce surface organism count sufficiently that injection does not introduce significant numbers.
Alcohol preparation: Apply 70% ethanol (or isopropanol) to site; allow to evaporate fully before injection (approximately 30 seconds). Do not blow to speed drying — blowing introduces oral bacteria.
Do not apply alcohol to skin if administering a live virus vaccine by scarification — alcohol inactivates the vaccine at the site.
Iodine preparation (if alcohol unavailable): 2% iodine solution applied and allowed to dry. Allow to evaporate or wipe with sterile cloth after drying. Iodine staining shows where preparation was applied.
Plain water: In the absence of antiseptic, washing with clean water and soap immediately before injection is better than no preparation at all.
When Sterile Technique is Violated
Contamination happens. Recognizing it and responding correctly limits damage.
If instrument touches non-sterile surface: Resterilize. Do not continue with the compromised instrument.
If contamination falls into an open container: Discard the contents. The risk of proceeding with contaminated material outweighs the cost of the lost material.
If hand touches sterile field during procedure: For culture work, discard and restart. For injection: if the needle itself was touched, replace it; if the skin preparation site was touched, re-clean the site.
Document violations: In any critical work, note if and when sterile technique was violated. This allows review if cultures fail or adverse events occur.
The discipline of sterile technique is ultimately about respect for the stakes. When the preparation being made will enter someone’s body, or when the culture being grown will be used to save lives, the cost of contamination is measured in human health. That context should inform every decision made in the sterile field.