Biological Hazards in the Workplace: Legionella, Mould and Bloodborne Pathogens

Biological agents — bacteria, viruses, fungi, parasites and biological toxins — are increasingly recognised as significant occupational health hazards across a range of industries and settings. The model WHS Act and Regulations include biological hazards within the general hazard management obligations, and several specific biological hazards have dedicated regulatory frameworks. This guide addresses three of the most significant biological workplace hazards in Australia: Legionella in water and cooling systems, mould in water-damaged buildings, and bloodborne pathogens in healthcare and emergency response settings.

Legionella in Cooling Towers and Water Systems

The Hazard

Legionella pneumophila is a gram-negative bacterium that colonises warm water systems — particularly cooling towers, evaporative condensers, hot water services, hydrotherapy pools and decorative fountains. When contaminated water is aerosolised (cooling tower drift, shower spray, fountain mist), small droplets (<5 µm) can be inhaled deeply into the lungs and cause Legionnaires’ disease — a severe, potentially fatal pneumonia — or Pontiac fever, a milder febrile illness.

Risk Factors

Conditions favouring Legionella proliferation: water temperatures 25–45°C; stagnant water (dead legs in pipework, infrequently used outlets); sediment and biofilm providing nutrient; scale and corrosion in heat exchangers; inadequate biocide maintenance; and failure to maintain adequate disinfectant residuals.

Australian Regulatory Framework

States and territories have mandatory Legionella risk management requirements for high-risk water systems. AS/NZS 3666 series (Air-handling and water systems — maintenance and operation) provides the technical standard. Requirements typically include:

• A written risk management plan prepared by a competent person
• Quarterly microbiological testing of cooling towers for Legionella (target <10 CFU/mL; action level ≥1,000 CFU/mL for immediate decontamination)
• Monthly physical and chemical testing (pH, conductivity, biocide levels, turbidity)
• Notification to state health authorities when Legionella counts exceed action thresholds
• Emergency decontamination procedures for cooling towers linked to Legionnaires’ disease cases

Control Measures

Physical, chemical and operational controls prevent Legionella colonisation:

• Maintain cold water at <20°C and hot water at ≥60°C at the storage vessel; deliver to outlets at ≥55°C
• Regular biocide dosing (oxidising biocides: chlorine, bromine, chlorine dioxide; non-oxidising biocides: DBNPA, isothiazolinones)
• Eliminate dead legs and infrequently used outlets through regular flushing or system redesign
• Annual cleaning and inspection of cooling towers with mechanical descaling
• Drift eliminators on cooling towers to minimise aerosol release

Mould in Water-Damaged Buildings

Health Effects

Indoor mould colonisation following water intrusion, flooding or sustained elevated humidity can produce significant airborne fungal spore concentrations. Health effects include: upper respiratory irritation; hypersensitivity pneumonitis (from sustained high-level exposure to certain mould species); exacerbation of asthma; and sensitisation in atopic individuals. Stachybotrys chartarum (“toxic black mould”) has attracted disproportionate media attention; most health effects from building-related mould are from more common genera (Aspergillus, Penicillium, Cladosporium) at high total spore loads.

Assessment

Mould assessment involves: visual inspection for water damage signs; moisture mapping using calibrated pin and non-destructive moisture meters; air sampling (spore trap or culturable methods) comparing indoor to outdoor spore concentrations and species diversity; surface sampling where source identification is needed. AIOH’s “Guide to Mould Investigation and Management” provides the Australian assessment framework.

Remediation

Mould remediation requires source control (repairing water intrusion) before surface remediation — cleaning mould without fixing the water source is temporary at best. During remediation:

• Containment with plastic sheeting and negative pressure HEPA air units
• P2 (small areas) to P3 (large-scale remediation) respirators for remediators
• HEPA vacuum and damp wipe methods — no dry brushing
• Post-remediation air testing to verify return to background spore levels

Bloodborne Pathogens in Healthcare

Healthcare workers, laboratory workers, first responders and others exposed to blood and body fluids face risk of transmission of bloodborne pathogens — primarily Hepatitis B (HBV), Hepatitis C (HCV) and HIV. The primary exposure route is percutaneous injury (needlestick, sharps injury) or mucous membrane/broken skin contact.

Exposure Control Plan

Under WHS obligations and healthcare accreditation standards, healthcare PCBUs must have a written exposure control plan addressing:

• Universal precautions — treating all blood and body fluids as potentially infectious regardless of known patient status
• Standard and additional precautions (contact, droplet, airborne) appropriate to the clinical situation
• Engineering controls: safety-engineered sharps devices (needles with retractable sheaths), sharps containers at point of use, needle-free IV systems
• HBV vaccination programme for all at-risk workers
• Post-exposure prophylaxis (PEP) availability for HIV (within 72 hours of exposure) and immediate hepatitis B immunoglobulin for unvaccinated workers following exposure
• Incident reporting and case management for all blood and body fluid exposure incidents