Measuring What Matters: A New Index for Reducing Exposure Risks on Hospital Surfaces

An EVS worker wiping down a handrail on a hospital bed.

(Adobe Stock 1612822382 by evgenia_lo)

Hospitals are designed to heal, but they can also serve as environments where patients, staff, and visitors are exposed to infectious agents. Reducing the risk of illness in health care settings requires moving beyond traditional cleaning metrics and adopting frameworks that directly link environmental hygiene practices to health outcomes. A new concept in development, the Bioload Exposure Metric Index (BEMI), aims to do just that: quantify the relationship between environmental surface cleaning and the probability of illness.

The formula at the core of this work is deceptively simple:

Risk = Hazard × Exposure + Vulnerability.

In this model, hazards are pathogens, exposure is where people and pathogens meet, and vulnerability is individual resistance to infection. While pathogens can never be fully eliminated, and vulnerability cannot be controlled, exposure levels can be measured and managed.

Building a New Metric

The Indoor Exposure Index, a nonprofit (501c3 status pending), is collaborating with Charles Gerba, PhD, of the University of Arizona to establish BEMI. Their shared vision is to create a quantitative approach to infection prevention, allowing statements such as: “This cleaning method reduces the chances of becoming ill by ‘x’ percent.”

This shift is powered by Quantitative Microbial Risk Assessment (QMRA), paired with adenosine triphosphate (ATP) sampling, a long-standing method of measuring organic soils on surfaces. Together, QMRA and ATP provide the foundation for BEMI, reframing the conversation from cleaning as a compliance activity to cleaning as a measurable health intervention.

Why Exposure Matters

Pathogens on hospital surfaces cannot be eradicated entirely, and patient vulnerability varies widely, but exposure is a controllable factor. Reducing the bioload, which is the accumulation of soils such as pathogens, organic material, chemical residues, and particulates, directly lowers the probability of illness.

“Cleaning for Health” emphasizes this concept: by reducing exposure, hospitals not only reduce infection risk but also cut down on absenteeism, presenteeism, and overall health care costs. BEMI builds on this philosophy, offering a more accessible way for infection preventionists (IPs), environmental services leaders, and hospital administrators to see how cleaning impacts patient outcomes.

How BEMI Works

At its core, BEMI translates ATP test results into a simple 1-to-10 scale:

90% Reduction in ATP (best)

80% Reduction in ATP

70% Reduction in ATP

60% Reduction in ATP

50% Reduction in ATP

40% Reduction in ATP

30% Reduction in ATP

20% Reduction in ATP

10% Reduction in ATP

0% Reduction in ATP (worst)

Since ATP meters vary across manufacturers and platforms, the reduction percentage before and after—not the absolute numbers—matters most. BEMI levels therefore reflect actual improvements in cleanliness, regardless of the tools used.

By capturing these reductions, BEMI provides hospitals with an index score that not only reflects hygienic conditions but also helps identify areas for process improvement.

Applications in Health Care

BEMI’s potential applications extend across healthcare environments:

• EVS performance evaluation: Hospitals can measure cleaning effectiveness in real time and provide targeted staff feedback.
• Process optimization: Facilities can identify which cleaning methods, products, or technologies (such as EPA-registered disinfectants or UVC) deliver the best measurable outcomes.
• Resource justification: Administrators can use quantifiable return- on-investment data when deciding on staffing, training, or technology investments.
• Accreditation and compliance: While not yet a regulatory standard, BEMI could help facilities demonstrate a proactive commitment to infection prevention during surveys or audits.

By linking environmental cleaning directly to exposure reduction, BEMI encourages minimally intensive yet maximally effective disinfection regimens.

• Strengths and Limitations
• BEMI offers several advantages:
• Provides a common language that is more intuitive than raw ATP numbers.
• Functions as a proxy for a wide range of contaminants, not just microbial.
• Supports the broader movement toward evidence-based cleaning for health.

However, important caveats remain. The BEMI is still under development and not yet a universally recognized standard. Its scores must be interpreted within the context of each facility, and further validation research is required. As with any metric, BEMI should be viewed as a tool to guide continuous improvement, not as an absolute measure of safety.

Looking Forward

The development of the BEMI represents a significant step toward aligning environmental hygiene with patient safety outcomes. By translating ATP reductions into a simple index, BEMI promises to bring clarity to a space often clouded by technical jargon and inconsistent practices.

In the words of its developers, the goal is to empower infection prevention and EVS leaders to say with confidence: “This cleaning approach doesn’t just look clean, it measurably reduces the chance of infection.”

As research continues, BEMI could provide health care facilities with the first widely applicable metric that connects cleaning processes directly to quantifiable health outcomes. For IPs, this represents an opportunity to move beyond assumptions and toward measurable, evidence-based environmental hygiene strategies.