Infection Control Today - 10/2002: Environmental Services

Infectious Reservoirs in the Physical Plant

By Kathy Dix

Microorganisms seem to take every opportunity to hide, and your facility is full of crevices where they can go underground. There are other places besides nooks and crannies where they take up residence -- namely inside your physical plant. Airborne and waterborne organisms can make themselves at home in your facility's heating and cooling system or in your ventilation system. They are perfectly capable of loitering in forgotten reservoirs of water or in intake and exhaust ducts.

But many outbreaks of nosocomial infections could be controlled just by awareness of the potential source of such infections and preventing their growth in those sources.1

Certain areas of the hospital are particularly in need of good waterborne and airborne infection control. These areas include operating rooms, special procedure rooms, delivery rooms, airborne communicable disease isolation rooms, protective isolation rooms, laboratories and sterile supply rooms.2

Airborne Microorganisms

Indoor air quality is a definite environmental health problem, according to the Environmental Protection Agency (EPA). And although most people may not be bothered by normal levels of fungus or other "natural" irritants in the air, immunocompromised patients or people with severe allergies could be at serious risk from even naturally-occurring airborne microorganisms. However, airborne contaminants can be controlled with properly maintained pressure relationships, air exchanges, filtration systems, local exhaust and dilution ventilation.2

These recommendations are intended to control not only fungi, viruses and bacteria, but also biological agents, gases, fumes and dust. However, control necessitates clean filtration systems, correct balances and filter efficiencies. Preventative maintenance, surveillance surveys and environmental rounds should be part of the regularly scheduled infection control procedures.

Accurate records should be kept of these procedures, and of the solutions to any problems that arise during regular maintenance. Copies of these records should be kept by infection control personnel as well as facility managers and leadership.

Waterborne Microorganisms

You should pay particular attention to these water systems, which may be good sources of pathogens: cooling towers, aerosolizing systems and domestic hot water.

The growth of Legionella pneumophila, for example, can be intensified by water stagnation and sediment buildup -- which can be caused by alterations in the plumbing of intricate distribution systems found in some hospital hot-water systems. Proper maintenance could remove or at least control the sediment accumulation.1

Cooling towers spray water onto a packing material through which there is a countercurrent flow of air -- easily producing fine droplets of water. Such towers are often the source of outbreaks and should thus be cleaned and disinfected on a regular basis.

According to the American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (ASHRAE), to avoid Legionellosis specifically, avoid piping that is capped and has no flow (dead legs); keep water temperatures below 25 degrees Centigrade and above 55 degrees C; apply biocides appropriately; and limit available niches for microbiata.3

ASHRAE specifies, "More emphasis should be placed on clean equipment in excellent repair than on periodic testing with concurrent system neglect," and stresses that periodic or routine monitoring is never effective if done without adequate maintenance.

To curtail colonization and multiplication of bacteria in water systems, water should be circulated and not allowed to stagnate. Inspection, cleaning and disinfecting should be part of the regular maintenance schedule for storage tanks and calorifiers. Remove "dead legs" from plumbing systems, avoid washers and gaskets made of natural rubber, replace heavily-scaled faucets and showerheads (which can distribute contaminated water droplets) and avoid shock absorbers and pipe materials that are not copper or plastic.1, 3

Fungi can breed in the drain pan under cooling coils or in the cooling coils themselves. Water pans for humidifiers are also a potential site. Although HEPA filters are a reasonable means of filtering out organisms from the air we breathe, they should be tightly installed and well-maintained -- and they should be monitored to ensure the filters themselves do not harbor fungus growth.4

Ductwork is also a possible hiding place for moisture and microorganisms. Clean ductwork with a disinfectant after inspecting it for fungus. Insulation can also harbor moisture and fungus.

But fungi don't necessarily need moisture to get into your facility. If water is not available, they can reduce to spore form and become even easier to transmit by air.

JCAHO Recommendations

The Joint Commission on the Accreditation of Healthcare Organizations (JCAHO) recommends that at least once a year, facilities choose one high-risk process and assess the risk and how a failure of the system can occur. Three steps are involved in this risk assessment: failure mode, effect on other components or systems, and criticality analysis.2

One proactive risk reduction activity might be to study the safety of the hospital's water system. Staff members from multiple departments -- engineering, maintenance, infection control and clinical areas -- could identify any ways in which the water system could fail, and how notice of those failures could be relayed to the hospital.

The facility would then assess how the users would be affected, how often the failure might occur, how severe the failure's effect would be, and whether it could be discovered before adverse effects arose.

Some other potential reservoirs include fireproofing material, damp wood, and bird droppings in air ducts. Aspergillus sp. has been found in these sites.5

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