In the highly sensitive environment of a health care facility, where both infectious patients and those highly susceptible to infection receive treatment, it is essential to minimize the possibility of infection and disease transmission.

In fact, it's safe to say that any facility that may be visited by infected members of the general public could stand to benefit from minimizing disease transmission. Public buildings with regularly changing populations are at risk. Health care facilities, however, tend to have larger populations of people known to carry infectious disease.

One potential transmitter of infection that must be managed is the air circulating within the building. Failure to correctly monitor and manage indoor air quality (IAQ) can add cost in health care facilities due to increased lengths of stay, expose the institution to liability, and expose patients and staff to unnecessary risk.

Airborne particle counters provide vital information for maintaining indoor air quality in health care facilities.


In an effective IAQ program, HVAC contractors, engineers, and facility staff need a variety of diagnostic weapons in their arsenal: pressure and airflow testers, particle traps, lab analysis, and particle counters. The latter item can provide facility managers with the data they need to detect IAQ problems, identify and address root causes, and verify when conditions have returned to acceptable levels.

Specifically, a particle counter enables the facility manager to:

  • Document baseline particle counts within a specific space.

  • Detect when airborne particulate levels diverge from baseline (normal) levels.

  • Gain early warning of underlying issues, such as changes in operating procedures, equipment malfunctions, maintenance shortcomings, or failure to separate construction zones from patient areas.

  • Test particle levels after changes have been made, to ensure that remedies have been effective.

    The use of handheld test instruments has received endorsement at the highest levels. According to infection control guidelines published by the U.S. Centers for Disease Control (CDC) in 2003, "the use of handheld, calibrated equipment that can provide a numerical reading on a daily basis is preferred for engineering purposes" to ensure the proper and safe operation of HVAC systems.

    It must be clearly stated, however, that the particle counter is not designed to determine what particles consist of or whether the particles counted pose a threat of infection. Those judgments must be based on laboratory analysis of collected particle samples.


    The spread of infection through indoor air is a serious potential problem in health care facilities. Such infections can stem from two sources:

    1. Infectious agents - such as Tuberculosis, Rubella (measles), and influenza - produced by people inside the facility.

    2. Agents normally present in the human environment that can endanger patients who have compromised immune systems. Such organisms include Aspergillus fumigatus (a common species of mold) and others.

    Other airborne particulates, such as inorganic materials and allergens, are capable of causing health problems. These contaminants, however, pose a lesser threat to patients and will not be addressed in this article, even though the air filtration and air pressure balancing techniques that help control biological pathogens can also control odors, dust, and other nonviable air pollutants.

    To control the movement and spread of infectious agents, facility designers and managers establish special-purpose spaces called Airborne Infection Isolation (AII) or patient isolation rooms, and Protective Environment (PE) facilities. In both of these special ventilation spaces, air pressures are regulated to move air from clean to dirty areas.

    The AII room would house a patient judged to be a source of airborne infection, such as Mycobacterium tuberculosis or measles virus. Vents draw air from the room and exhaust it outside the building. High-efficiency particulate air (HEPA) filters may be used to help remove particles from the air. Makeup air flowing into the room is balanced so that the room remains under negative air pressure. Thus, the direction of airflow under the door or when the door is opened is into the space, rather than out, helping contain infectious particles.

    The PE facility is designed to keep infectious agents out and protect immunosuppressant patients and others, such as bone marrow and organ transplant patients and premature infants, who are especially vulnerable to opportunistic infectious agents. The CDC recommends that PE facilities be maintained under positive air pressure, with directional airflow (from one side of the room, across the patient to the exhaust), and with 12 or more air changes per hour. Clean air is supplied through HEPA filters. Point-of-use HEPA filters may also be used. Air flowing through an open door or leak moves out of the space, not in.


    AII and PE facilities provide a framework for limiting the spread of infectious agents, but they are not foolproof. Building design, inconsistent or inadequate operating procedures, poor maintenance, and facilities construction and renovation projects all have the potential to cause problems. In any case, protective facilities are not used for all patients.

    Even the best air filtration and airflow design can be defeated by inadequate maintenance or incorrect operation. A slipping fan belt on a ventilation supply fan, for instance, could alter the air balance in a PE facility, allowing particle-laden air from the hallway outside to flow in. Failure to correctly seal off and ventilate a construction area can send a cloud of construction dust and Aspergillus spores into areas where patients are housed. Failure to fix a leaking sink can turn the cabinet below into a nursery for potentially hazardous mold.

    Andrew Streifel, a hospital environment specialist at the University of Minnesota, recalled what happened when cost-conscious hospital administrators turned off the fan ventilating the space over a dropped ceiling in an intensive care unit (ICU). "That allowed humidity to stagnate," he recalled.

    "When humidity reached extremely high levels in the Minnesota summer, it started raining in the ICU. The water was coming through the ceiling grid and dripping on the patients. They stopped using four or five of the intensive care rooms, and diverted patients."

    The larger concern, Streifel said, was the possibility that the high humidity would permit mold growth. Raising the room temperature above the dew point provided a temporary fix; at least it stopped the "rain."

    Building construction and renovation can pose particular challenges. Disruption to the building's envelope, generation of large amounts of construction dust and debris, and the movement of workers and equipment in and out of containment zones all present contamination threats beyond the norm for a health care facility.

    According to the CDC, "a recent aspergillosis outbreak among oncology patients was attributed to depressurization of the building housing the HSCT [Hematopoietic Stem Cell Transplant] unit while construction was underway in an adjacent building. Unfiltered outdoor air flowed into the building through doors and windows, exposing patients in the HSCT unit to fungal spores."

    When such problems occur, an airborne particle counter can help hospital staff and industrial hygienists detect increased particle levels, identify the sources, and verify the effectiveness of remedial action.

    One such tool, the Fluke 983 particle counter, operates by pumping an air sample of known volume (generally 1 liter) past a laser beam. As dust particles in the airstream pass through the beam, each one reflects or scatters the laser light.

    A photodetector senses the scattered light and generates an analog electrical signal. Larger particles scatter more light and create higher-voltage electronic hits. Onboard electronics track the hits and count the particles in six size categories, ranging from 0.3 to 10 microns. Particles larger than 10 microns generally settle out of the air.

    According to the CDC, "Particulate sampling (total numbers and size range of particulates) is a practical method for evaluating the infection-control performance of the HVAC system, with an emphasis on filter efficiency in removing respirational particles (<5 µm in diameter) or larger particles from the air."

    Particle counters help health care facility managers document baseline particle counts, detect deviations from baseline levels, gain early warning of underlying issues, and test particle levels after work has been done.


  • Baseline testing: To know when the "abnormal" occurs, it's necessary to document normal levels of particles. According to Streifel, it's not reasonable to expect clean room conditions in a health care setting. When staff rushes into a room to intervene in a patient emergency, for instance, there's no time to worry about air quality. Particle counts will soar with the presence of multiple people (human beings shed some 500,000 particles/minute).

    Medical procedures also can contaminate the air. Later, however, counts should return to normal or baseline levels. Best practice calls for baseline particulate levels to be documented, both within spaces and in the supply air flowing into the space.

  • Maintenance testing: Once baseline particle levels are determined, follow-up tests should be performed and documented periodically. These tests can provide early warnings of developing anomalies and enable the facility manager to intervene before anyone gets sick.

  • Filter testing: Used to test for particle levels in the air upstream and downstream from filter media, the Fluke 983 can verify that filters are performing as they should. Testing the level of particles in incoming filtered air at the diffuser (air grate) - air that should be the cleanest in the room - provides an additional check on the performance of filtration systems.

  • Locating particle sources: The right particle counter can help identify areas where particle counts are elevated and, ultimately, lead the user to the source. A leaking air duct could be sending unfiltered air into a room, for instance; work above a suspended ceiling could be disturbing accumulated dust.

  • Verifying the effectiveness of remediation: Once the causes of higher particle counts have been addressed, posttesting will show whether the fixes have really worked at bringing particulate levels down.

    Eric Hudson manages Indoor Air Diagnostics products and applications for Fluke Corp. He may be reached at or 425-446-5334.

    Publication date: 01/16/2006