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ASSESSING
THE HEALTH RISKS, Dr. Malcolm
Slifkin - Director of Microbiology Legionella Generally, people in industrialized nations spend about 90 percent of their time indoors, where natural ventilation has been replaced by self-controlled environments with HVAC systems. Such indoor air is not necessarily any cleaner than outdoor polluted air. In fact, this restricted environment may concentrate indoor air pollutants and create health concerns for exposed persons. Major problems in system design, building construction and operational mechanisms that lead to excessive moisture and elevated relative humidity promote bacterial and fungal growth. Outdoor pollutants may also be introduced into a building through open windows, ventilation system air intakes, water-damaged roofs, drainage leaks from septic systems, and cracks in building walls, floors, and ceilings. Indoor air contains many microorganisms that can cause infectious diseases, allergies, mycotoxicosis, and mucous membrane and skin irritations. Indoor air quality (IAQ) concerns are associated with sick building syndrome and building related illness. Sick building syndrome generally indicates the existence of persistent nonspecific factors that dissipate once inhabitants leave a building. In contrast, building-related illness refers to clinically diagnosed diseases(s) in a building's occupants that occur from exposure to indoor air pollutants. Individuals suffering from a building-related illness often require prolonged recovery times after leaving the suspected environment. Removal of this illness requires elimination of exposure to the causative agent(s). Over the past two decades, medical advances have dramatically improved diagnostic and therapeutic regimens for a variety of diseases. However, aggressive therapies involving the use of invasive surgical techniques and prosthetic materials as well as chemotherapeutic agents that induce severe immunosuppression (e.g., management of cancer and organ transplantation) increase a person's susceptibility to an expanding array of bacteria and fungi. The indoor environment offers ecological niches for the proliferation of infective particles. The primary route of bioaerosol exposure to patients in a hospital is through inhalation of the infective particle. The greatest retention is in the alveoli of the lung associated with 1-2 mm particles, which is the size of many bacterial cells and fungal spores. Nosocomial infections may be spread by contaminated food, water, medications, medical devices, or the hands of the medical personnel. In addition, environmental sources such as contaminated ventilation systems, building construction, road construction and contaminated soil of potted plants may also serve as vehicles for the spread of bacteria and fungi to patients. Legionella spp and Aspergillus spp have been implicated in nosocomial outbreaks in hospitals, and with the source of these microbes has been associated with environmental sites within the hospital. This overview concerns the health risks associated with these microorganisms as potential opportunistic pathogens of indoor air and the significance of determining their presence in or absence from a site within the hospital setting. In addition, intervention strategies are outlined to reduce or prevent exposure of these organisms to severely ill patients. Legionella Legionella pneumophila was first associated with the outbreak of pneumonia among persons who attended in 1976 an American Legion convention in Philadelphia. Legionellosis or Legionnaires' disease, as it came to be called, may also take the form of a mild, self-limited illness of short duration known as Pontiac fever. This form of Legionella-associated disease is seen with few or no respiratory findings and no pneumonia. It is generally associated with elevated temperatures, myalgia, malaise, and headache. Legionnaires' disease can occur in persons of any age but is usually associated with middle-aged or older patients. Some predisposing factors include immunodeficiency, cardiovascular disease, renal transplantation, and hemodialysis. The vast majority of human infections are caused by Legionella pneumophilia serogroups 1 and 6, and L. micdadei. Legionella pneumophila as well as many other species of the microorganisms are ubiquitous in both natural and man-made environments. Legionnaires' disease and Pontiac fever may be acquired by exposure to a wide variety of environmental sources. There is no evidence of person-to-person transmission. Inhalation of aerosolized organisms from environmental sources or possibly the aspirations of organisms present in water or in oropharyngeal contents are the most likely routes of transmission. The usual source of Legionella is water in hot water systems, especially in showers or baths. It has also been isolated from cooling towers associated with air-conditioning systems. Other sources have included humidifiers, whirlpools, and respiratory therapy equipment. These bacteria have been demonstrated that Legionella spp can be isolated from soil samples (including potted soil), marine waters and from epiphytes (e.g., mosses, lichens) on trees. The presence of certain kinds of resins in gaskets, stagnation in water flow and the present of slime layers on the surface of pipes containing other microorganisms may favor the presence of legionellae. This bacterium is controlled by means of epidemiologic surveillance. Hyperchlorination of water and raising the temperature of hot water to more than 70° C (160° F) or a combination of hyperchlorination and heat flushing will reduce the numbers of Legionella to levels that minimize the risk of nosocomial Legionellosis. Eradication of Legionella spp from water sources has also included ultraviolet light sterilization, ozonation, and the incorporation of trace metals ions such as silver or copper.
Aspergilli are widespread in nature and may be recovered from virtually any site or organic debris. More than 200 species of Aspergillus are known, but only a few are truly opportunistic pathogens. Aspergillus fumigatus, A. flavus and A. niger are the most frequently isolated species in hospitalized patients. Aspergilli are one of the most ubiquitous of fungi whose airborne spores are released in large numbers, and a size (avg. 2-4 mm) small enough to reach the alveoli of the lung. Dissemination relies on disturbances of the environment followed by air currents. Once the spores (conidia) are in the air, their small size makes them buoyant and tends to keep them airborne both indoors and outdoors. Environmental surveys indicate that all humans inhale several hundred conidia per day, which settle mostly in the lung. During the last two decades, a sharp increase in the occurrence of invasive nosocomial aspergillosis associated with high mortality has been observed. This rise is due mainly to increasing numbers of immunocompromised patients. Nosocomial aspergillosis is acquired exogenously (vs. endogenous as noted in patients with candidiasis), as evidenced by outbreaks associated with building construction, earth moving, demolition or renovation works adjacent to or inside a hospital, and contaminated ventilation systems. In some hospital areas, Aspergillus spores are always present in low levels (e.g., Aspergillus versicolor) throughout the year, with a concentration range of 0-50 spores/m3 of air. The presumed route of acquisition of Aspergillus pneumonia is inhalation of the spores into the lung. However, Aspergillus niger recovered from rectal swabs has been reported, which suggests that the acquisition of the organism may occur via the gastrointestinal tract rather than the respiratory route. Invasive aspergillosis in hospitals is becoming one of the most severe diseases among immunocompromised patients, particularly patients in bone marrow transplant units. Most infections of invasive aspergillosis are due to Aspergillus fumigatus with a mortality rate of about 85 percent. Aspergillus flavus associated with sinusitis in immunocompromised patients has also been reported. As multiple environmental factors appear to play a role in acquiring invasive aspergillosis, manipulation of the environment may lower the risk of disease, and institution of alternative strategies to reduce pulmonary exposure becomes critical. Investigative Strategies A successful investigation of microbial contamination in the hospital setting is initiated by a team composed of microbiologists, health care (infection control nurse) and administrative personnel. This approach helps to define not only the sampling protocols to be used but also the optimum strategy for prevention of the biocontamination of the indoor air. Trained microbiologists (mycologists) should be consulted to determine the potential sources, decide on sampling methods (sampling instruments, sampling times, agar mediums, etc.) and identify the most significant bacterial or fungal contaminants. For example, it is unproductive to perform bioaerosols for detection of Legionella bacteria, since this organism is recovered near or in water-contaminated sites. However, it is extremely important to perform air sampling (culture-based impaction method) for the detection of opportunistic fungi such as Aspergillus and Fusarium spp. An environmental microbiology laboratory should provide a service that will generate data concerning the bioaerosol exposures to patients, especially those in critical care areas of the hospital. A complete analysis and interpretation of results should include: Determination/source of the biocontaminants Total fungal/bacterial
count in CFU/m3 of air, to statistically establish correlations relevant
to the occurrence of hospital-acquired aspergillosis In most reports, because prognosis of diagnosed aspergillosis is dismal, prevention is of the utmost importance. To limit fungal exposure to high-risk patients, several preventive measures have been recommended: *
The use of high-efficiency particulate filters (HEPA) with greater than
95 percent efficacy for removal of 0.3 um-diameter particles Summary Indoor air pollutants within the hospital or other medical facilities are associated with clinically relevant diseases. Public concern over the health risks associated with these biocontaminants is not likely to diminish in the foreseeable future. Environmental control strategies incorporating available technology may play an important role in controlling nosocomial outbreaks of Legionnaires' diseases and invasive fungal disease such as aspergillosis. Routine surveillance of the indoor air may not only reduce the risk of invasive nosocomial infections but also minimize the risk of legal consequences should this concern arise. In addition, it should be recommended that biological, clinical and environmental data be centralized and analyzed monthly by a staff composed of an environmental microbiologists, physicians, infection control surveillance persons and administrative personnel in order to determine the optimum strategy for prevention of invasive nosocomial disease in hospitalized patients. Indoor
Environment Review, Vol. 9, No. 3, June 1999. |
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United
Safety Services, Inc. 2003
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