Specimen Handling

In the clinical laboratory, every patient specimen - whether blood, urine, sputum, or tissue - must be treated as if it were potentially infectious. This core philosophy, known as Standard Precautions (formerly Universal Precautions), dictates that the infection status of the patient is irrelevant to the safety protocols employed. The laboratory scientist cannot “see” Hepatitis C or HIV in a tube; therefore, rigorous handling techniques are the primary defense against Laboratory Acquired Infections (LAIs). The two dominant vectors of transmission during specimen handling are aerosol generation (inhalation) and percutaneous/mucous membrane exposure (direct contact)

Aerosol Generation & Control

Aerosols are the “invisible enemy” in the laboratory. They are microscopic liquid or solid particles (< 5 micrometers) that can remain suspended in the air for long periods and be inhaled into the lungs. Larger droplets (> 5 micrometers) settle faster but can contaminate work surfaces, gloves, and mucous membranes

Common Sources of Aerosols

Many routine procedures generate significant aerosols that are often invisible to the naked eye:

• Centrifugation: The most potent source. If a tube breaks or leaks inside a spinning rotor, the high speed generates a massive cloud of infectious mist. If the centrifuge is opened immediately, this cloud is released directly into the user’s face
• Vortexing and Mixing: Agitating an open tube or a tube with a poorly sealed cap releases micro-droplets
• Opening Tubes: The “pop” heard when opening a snap-cap tube or a vacuum tube (vacutainer) is actually the release of internal pressure, which ejects a fine spray of specimen. This is a common transmission route for bloodborne pathogens to the eyes
• Pipetting: Blowing out the last drop from a pipette tip or dropping a sample onto a slide from a height creates splashback and aerosols
• Catalase Testing: performing the slide catalase test on a colony creates active bubbling (oxygen release), which aerosolizes the bacteria. This is a known risk factor for acquiring Meningitis (N. meningitidis) or Tularemia (F. tularensis) if done on an open bench

Mitigation Strategies

• Safety Cups: Always use centrifuge buckets with sealable safety caps. If a breakage is suspected (e.g., an imbalance or noise), the entire bucket should be moved to a Biological Safety Cabinet (BSC) before opening
• The BSC: Perform all procedures likely to generate aerosols (vortexing, grinding tissue, setting up mold cultures) inside a Class II BSC. The air curtain protects the user
• Technique
  • Open tubes pointing away from yourself and others
  • Use a gauze pad or alcohol wipe to cover the stopper of a vacutainer while twisting it off to catch the spray
  • Avoid “blowing out” pipettes unless the device requires it. Allow gravity to dispense the fluid gently against the side of the vessel

Handling High-Risk Specimens

While all specimens are potentially infectious, certain categories carry a significantly higher inoculum or harbor pathogens with low infectious doses/high mortality rates. These require enhanced precautions

Mycobacteriology (Tuberculosis) Specimens

• The Risk: Mycobacterium tuberculosis is a low-infectious-dose, airborne pathogen. Processing sputum (digestion/decontamination) involves vigorous chemical mixing and centrifugation, maximizing aerosol risk
• Protocol
  • All processing must occur in a dedicated BSL-3: (or BSL-2 with BSL-3 practices) negative-pressure room
  • Strict adherence to BSC use is mandatory. No open-bench work is permitted
  • Use of sealed centrifuge rotors is non-negotiable
  • Personnel must wear fit-tested N95 respirators or PAPRs

Blood Cultures & Positive Bottles

• The Risk: A positive blood culture bottle is a “bio-reactor” containing a massive concentration of organisms (often \(10^8\) to \(10^9\) CFU/mL) and gas under pressure. Venting these bottles or inserting a needle to aspirate fluid poses a high risk of spraying concentrated pathogen
• Protocol
  • Subculturing (Gram stains/plating) should be performed in a BSC
  • Use venting devices with safety shields or perform venting away from the face behind a plexiglass shield

Fungal Cultures (Mycology)

• The Risk: Filamentous molds (e.g., Coccidioides immitis, Histoplasma capsulatum) reproduce via microscopic spores (conidia) that are easily airborne. A single breath over an open mold plate can result in a severe systemic fungal infection
• Protocol
  • Never: sniff a fungal plate. This is an antiquated practice that has caused fatalities
  • All mold cultures must be taped shut (using shrink seal or gas-permeable tape) to prevent accidental opening
  • All examination of mold colonies must be done inside a BSC

Meningococcal/Brucella/Francisella Suspects

• The Risk: These organisms (Neisseria meningitidis, Brucella spp., Francisella tularensis) are the classic “Laboratory Acquired Infections.” They are highly infectious via aerosol and mucous membranes. They are often encountered unexpectedly in routine blood or wound cultures
• Protocol
  • Trigger: If a Gram stain reveals small Gram-negative coccobacilli (Brucella/Francisella) or Gram-negative diplococci (N. meningitidis), all further work (catalase, oxidase, spot indole) must immediately move to the BSC
  • Avoid automated identification systems (like MALDI-TOF or VITEK) until these agents are ruled out, as the preparation process can generate aerosols

Specimen Transport (Internal)

Moving specimens from the receiving window to the testing bench or between departments is a frequent point of failure

• The Container: Primary specimens must be in a leak-proof container with a secure lid
• Secondary Containment: Never carry tubes by hand (the “handful of tubes” method). Use racks placed inside a secondary leak-proof bin or tray with raised sides. This ensures that if a laboratory scientist trips, the spill is contained within the tray, not splashed across the hallway floor
• Requisition Separation: Paper requisitions must never be placed inside the bag with the specimen (unless there is a separate pouch). A leaking urine cup will contaminate the paper, which then contaminates the hands of the data entry clerk

Spill Response (Biological)

Despite best efforts, spills occur. The response depends on the volume and the location

• Spill Inside a BSC
  1. Leave the BSC on to maintain containment
  2. Cover the spill with absorbent towels
  3. Flood the towels with disinfectant (10% bleach) and let sit for contact time (e.g., 20 mins)
  4. Wipe up and dispose of as biohazard waste. If the spill flowed through the grilles into the catch pan, the pan must be drained and disinfected
• Spill Outside a BSC (Open Lab)
  1. Hold your breath and evacuate: Leave the immediate area to allow aerosols to settle (typically 30 minutes)
  2. Post Warning: Prevent others from entering
  3. Don PPE: Put on gloves, gown, and face protection (mask/goggles) before re-entering
  4. Contain and Disinfect: Cover with absorbents, pour disinfectant gently (from the outside in) to avoid splashing, wait for contact time, and clean. Do not pick up broken glass with hands - use forceps or a dustpan

Packaging & Shipping (External Transport)

Shipping specimens to reference laboratories is regulated by the Department of Transportation (DOT) and IATA. Biological substances are classified into two categories:

• Category A (UN 2814 or UN 2900): An infectious substance in a form that, when exposure to it occurs, is capable of causing permanent disability, life-threatening or fatal disease (e.g., Ebola, Anthrax cultures). Requires rigid triple packaging and specific dangerous goods documentation
• Category B (UN 3373): “Biological Substance, Category B.” This covers most diagnostic specimens (human or animal) being shipped for routine testing
  • Triple Packaging Requirement
    1. Primary Receptacle: Leak-proof, contains the specimen (e.g., the tube). Must be wrapped in cushioning
    2. Secondary Packaging: Leak-proof, contains the primary. Must contain enough absorbent material to soak up the entire liquid contents
    3. Outer Packaging: Rigid and strong (e.g., a fiberboard box) with the UN 3373 diamond label clearly displayed