Aspergillus for patients

Health Complaints in Air Conditioned Buildings

Based on an analysis of existing scientific data about Sick Building Syndrome

Y Dombrowsky and J Hill L.R.I.C

According to the World Health Organization sick building syndrome (SBS) is an excess of work-related irritations of the skin and mucous membranes and other symptoms, including headache, fatigue, and difficulty concentrating, reported by workers in modern buildings (WHO 83). A prevalence of non-specific health disorders are recorded. Only limited cases of building-related diseases are reported by the medical literature and are usually limited to specific contamination problems (e.g., Legionella released by cooling tower,…).
SBS may have specific environmental causes in which air-conditioners play a crucial role, and which involve biological contamination. Organic dusts seem to play a major triggering role in indoor health disorders which themselves may fluctuate in accordance with individual susceptibility. It is clearly demonstrated that physical factors like temperature, lighting intensity, etc..., can increase the susceptibility of patients to immunologically active particles through increased stress activity (AIHA 96).
This paper discusses SBS and biological contamination of air-conditioning equipment. The paper particularly discusses strategies for tackling the problem at source, with appropriate maintenance measures and a strategy suggested.

1.0 SBS: ACTUAL STATE OF THE PROBLEM

SBS has been recognized for nearly two decades. A distinction has to be made between Building Related Illness (BRI) and Sick Building Syndrome (SBS). Morey proposed the use of the term SBS to refer to a constellation of non-specific symptoms experienced by a substantial number of occupants of large buildings (e.g., eye and upper respiratory irritation, headache, fatigue...). The term building-related illness generally is used to describe clinically recognizable disease resulting from exposure to indoor environment. Lung cancer from passive smoking, hypersensitivity pneumonitis caused by a contaminated water spray systems and Legionnaire's disease due to cooling tower drift are all building-related illness (Morey 88).

Scientific literature reports numerous extensive investigations. Hodgson et al. Reported that SBS has been studied in several broad fashions. From large epidemiologic investigations to population-based telephone interviews (Hodgson 91). In a recent review of available studies, Menzies et al. reported that in only 25% of the investigations of apparent outbreaks of SBS symptoms, a specific cause can be identified, e.g. microbial contamination of humidification systems, etc…. According to these authors, the remaining 75% of outbreaks are unexplained and are considered to be associated with SBS (Menzies 93).

Particular factors have been identified related to chemicals, biological compounds, physical parameters, and psychological conditions. However, specific causes have generally not been identified. From typically mentioned causes of SBS, thermal climate, chemical compounds, light, noise and dust, none has been consistently related to the symptoms (Teews 94).

Relationships between symptoms and possible causes have been statistically demonstrated (Hodgson 91). Gyntelberg et al. observed that although it is agreed which symptoms are characteristic of SBS, a standardized definition does not exist (Gyntelberg 94).

Mendell and Smith observed that there is still little understanding of how frequently the excess symptoms reported in SBS episodes actually occur among office workers, or what if any chronic health problems in this population are related to office buildings (Mendell 90).

According to Mendell and Smith the uncertainty observed is mostly due to typical investigation practices creating difficulties in studying a phenomenon characterized only by self-reported non-specific symptoms with no accepted syndrome definition or objective tests available. Occupant concerns are likely to upwardly bias symptom reporting in buildings. The registration of symptoms is usually based on subjective statements from questionnaires, and thus is reported with a degree of uncertainty (Mendell 90).

At present no scientific study has succeeded in qualifying objectively symptoms such as headache, general malaise, fatigue... So far the only correlation has been demonstrated between subjectively reported eye symptoms and objectively demonstrated eye changes (Franck).

However, a large number of people still report SBS symptoms. Since more than half of all workers in industrialized nations work in offices and 50% to 80% surveyed reported symptoms typical of SBS, the resultant economic impact is considerable. Symptomatic workers exhibit reduced productivity and increased absence from work (Menzies 93).

The only certainty so far, accepted by most authors is that air-conditioned buildings are consistently associated with increased prevalence of work related headache, lethargy and upper respiratory/mucus membrane symptoms (Mendell 90).

1.1 Air-conditioning - specific prevalence in SBS

In fully air-conditioned buildings, 10% to 50% of office workers may complain (Teews 94).

Mendell in his 1993 review of literature indicates that most studies of the SBS problem have been poorly designed. Nevertheless, the strongest studies indicate that poor ventilation and building cleanliness are important factors (Mendell 93).

Total particulate burdens carried away by air-conditioners have been shown by Hedge et al. to be a strong predictor of SBS symptoms. In mechanically ventilated office buildings, particulate burdens comprise of ash, mineral fibers, bacterial substances (i.e. endotoxin), and fungal load (Hedge 93). A number of recent studies have shown that the concentrations of endotoxin and fungi in office and residential dusts are very high. In these studies, the concentration of endotoxin and/or fungi are shown to be the best predictors of SBS (Gyntelberg 94 3; Teews 94).

Mendell and Smith observed that consistent associations found between type of building ventilation and reported prevalent symptoms have potentially important public health and economic implications (Mendell 90). However, the same authors observed that published studies of the relationship between type of building ventilation system and work-related symptoms prevalent in office workers have still been contradictory (Mendell 90).

Health disorders connected to air-conditioners are far more subtle and complex than initially thought. Indeed, SBS may have specific environmental causes, in which air-conditioners play a crucial role and involve specific biological contaminants.

2.0 BIOAEROSOLS IN THE INDOOR ENVIRONMENT AND THE IMPLICATION OF AIR-CONDITIONING

In an extensive field guide for the determination of biological contaminants in environmental samples, published in 1996, the American Industrial Hygiene Association, states that a substantial proportion of building-related illness and SBS in the non-industrial workplace is the result of exposure to biological contaminants (AIHA 96).

It seems of interest to look closely at the reasons and implications for such a statement. We have decided to comment in the first instance the health implication of bioaerosols in commercial buildings.

2.1 Health implication of bioaerosols in typical buildings: Distinction between infection and immunological disorders

The great majority of inhaled biological contaminants cause human illness or discomfort by three mechanisms (Seltzer 94): (1) Infection, (2) Intoxication, (3) Immunological responses.

However, when dealing with the health implication of bioaerosols, it is important to keep in mind as do the American Industrial Hygiene Association that environmentally related diseases are not recognized as a major occupational problem. Similarly, an increased risk of infection has not even been demonstrated in sewage treatment plants with its demonstrably increased numbers of pathogens (AIHA 96).

Air-conditioner related infections are rare, require special conditions, and are limited to a few germs (usually Legionella and Aspergillus). A distinction should be made between the rare cases of infections and the relatively well-spread cases of immunological disorders notified in the air-conditioned environment (Molina 85).

Bioaerosol exposure can create infectious diseases and diseases related to inflammation/cell sensitization but without invasive growth of microorganisms (AIHA 96).

Rylander suggested that the symptoms and clinical findings reported in indoor environments with microbial contamination comprise the following four different disease entities (Rylander 97):

1) Toxic pneumonitis,

2) Airways inflammation,

3) Hypersensitivity pneumonitis,

4) Asthma

Furthermore, still according to Rylander (Rylander 97), the symptoms caused by microbes indoors can also comprise a variety of non-specific symptoms, such as irritation in the eyes and nose, congested nose and cough, skin problems, tiredness and headache.

More important, Rylander reports that it has been recently proposed, referring to experience from occupational exposure to organic dusts, that the symptoms observed in indoor environments are an expression of the same diseases that are found in organic dust environments. These symptoms primarily reflect a non-specific airways inflammation (Rylander 97). Moreover, in another recent work Rylander (Rylander 95b) mentioned that repeated exposures over longer periods may also cause inflammation in the airways.

Rylander reports (personal communication 97): 'Organic dusts are a mixture of a variety of different substances and those of animal, vegetable as well as of microbial origin contain a number of substances capable of producing an inflammatory response without the involvement of an antigen. If one abandons the concept that an allergen mediated disease is the cause of SBS, the alternative is that we are dealing with a non-specific inflammation in the airways. There is quite a lot of data supporting this concept in terms of increased cell sensitivity, increased release of mediators, etc, after exposure to non-allergic agents such as endotoxin'.

According to Rylander (Rylander 97), it is only in a minority of cases that a classical IgE-mediated sensitization can develop against antigens. The reason why the symptoms are non-allergic is that no specific antibodies can be detected to a specific agent in the environment. It is a traditional belief, particularly among allergologists and chest physicians that reactivity in the airways is always related to an allergy. Enormous efforts have been spent on tests trying to determine relevant antibodies without much success except for asthma related allergens (Rylander personal communication 97).

As a consequence, as stipulated by Rylander, non-specific airways inflammation may play a crucial role in sick building syndrome conditions. The author observes that airways inflammation is a non-specific reaction that may be caused by several different environmental agents. The condition is often accompanied by systemic symptoms, such as headache, fatigue and joints pains. It is likely that several of these symptoms are caused by inflammatory mediators, produced in the lung after inhalation and distributed to different parts of the body via the blood (Rylander 97).

Rylander's (personal communication 97) current hypothesis is indeed that SBS could be a non-specific airways inflammation related to organic dust exposure. Rylander's team have described very similar symptoms among workers exposed to other kinds of organic dusts such as in sewage treatment plants, poultry houses and swine confinement buildings. In Rylander's current hypothesis this, of course, does not exclude that in certain cases, the SBS could be induced by other irritants which also cause inflammation in the airways. Data on such agents at levels which could cause inflammation are, however, very scarce and although chemicals can be found in indoor air environments, they are usually in quantities where they will not cause any symptoms probably other than mild irritation.

On the contrary, organic dusts are broadly recognized as major compounds able to create adverse effects to building occupants. Seltzer observed that immunogenic substances that are integral parts of the structures of various plants, animals, and microorganisms or that are released by them into the environment may induce human illness. These immunogenic epitopes can produce immunologically induced inflammation (Seltzer 94). John and Salvaggio mentioned that many organic dusts often contain endotoxin or similar toxic substances, many of which have enzymatic activity particles (John 94). The same authors stated that of increasing importance is the recognition that material of either toxic or allergenic origin can be absorbed onto the surface of particles. Once inhaled the particle can then display immunological properties (John 94).

Individual susceptibility to indoor pollutants seems to play a crucial role in the recurrent development of SBS onsets. Because of the non-specific nature of the health complaints notified in the SBS, presumably linked to the low level of potentially toxic and immunogenic particles found in commercial indoors, it may be that receptibility of occupant could play a crucial role in the onset of disorders.

2.2 Building occupant susceptibility to allergenic particles - implication of stress in the condition of individuals

In their summary of obvious causes of SBS the American Industrial Hygiene Association, observes a significant representation of microbial problems, the AIHA experts also state that SBS may be caused by acombination of recognized factors particularly when affected by thermal comfort and workplace stress (AIHA 96).

Cohen et al. observed that environmental stressors that are unpredictable or uncontrollable produce negative effects and less socially positive behavior. The authors argue that uncontrollable stressors place a greater load on information-processing capacities. With greater cognitive effort comes more fatigue that leads to stronger negative after effects. Particular reduced personal control over heat or air pollution may heighten adverse reactions to these discomforts (Cohen 86).

Cohen et al. also evoked the following common assumption: 'Prolonged or pronounced stimulation from environmental stressors leads to long-term physiological changes that promote chronic dysfunction in one or more bodily systems'. (Cohen 86).

A primordial body system which is altered by stress exerted by environmental stressors and which may play a crucial role in the development of indoor health disorders, is the immune system.

Cohen et al. report that research in the last two decades suggests that rather than being an autonomous defense agency, this system is integrated with other physiological processes and is sensitive to changes in central nervous system and endocrine functioning, such as those that accompany psychological stress. Accordingly, a new interdisciplinary area called 'Psychoneuroimmunology' or 'Neuroimmuno-endocrinology', studies interactions between behavioral and immunological processes (Cohen 86).

Blalock stipulated that the immune system may function as a sensory organ, confirming that in an anatomical sense, there is an appropriate environment for direct neural regulation of the immune system (Blalock 84). Furthermore various studies supported the concept that stress may significantly alter the immune response in man. A study from Canada described significant changes in immune function in vitro have been demonstrated prospectively in a group of healthy individuals subjected to major psychological stress (Barbara Dorian 82).

In the mean time, while stress has been scientifically demonstrated to decrease immune function, indoor air pollution has been clearly demonstrated to affect the psychology of building occupants (Collingan 81). In their extensive study about 'Behavior, health and environmental stress', Cohen et al. reported clinical studies documenting cases of psychological symptoms from indoor air pollution exposures. The studies are said to have linked depression, irritability, anxiety, and somnolence with indoor air pollution (Cohen 86).

The perception about indoor air quality without any objective basis having an active involvement in air quality deterioration is common. Recent publications describe the negative perception of air conditioning. Harrison et al. reported that in problem buildings the air inside is often perceived to be less clean than external air and to be the cause of symptoms (Harrison 92). A study by Fanger is significant in that it shows that HVAC systems are the most important contributors to the human perception of poor air quality (Fanger 88).

However, extensive analysis of well-known psychological determinants of response (i.e. more stress, more complaints) demonstrated that the stress factor alone could not explain the SBS phenomenon (Bauer 92).

In the mean time and as detailed previously, the immune system can be triggered by direct effect of biological particles, without 'neuroendocrine' involvement. A few recognized biological indoor pollutants may biologically depress or stimulate the immune system. Bioaerosols may cause non-specific irritation in the airways and reduce the capacity of the defense system against infectious, toxic, and particulate exposures (AIHA 86), or at contrary may produce deleterious airway inflammation following low contact with particulates (Gulyas et al. 92).

Indeed, small levels of airborne pollutants can stimulate the immune system and generate non-specific airway inflammation and thus act as pathogens (Gulyas et al. 92). This latest effect is particularly described on alveolar macrophages, the main cell implicated in non-specific lung clearance of any inhaled particle which located on the respiratory membrane are in close and permanet contact with airborne pollutants and are directly exposed to particles and toxic substances (Voisin 90). Alveolar macrophage stimulation following exposure to low level of pollutant and impairment consecutive to higher contact with foreign particles, is likely to increase the risk of respiratory disorders (Gulyas et al. 92). Organic dusts are particularly recognized to affect immune cells, even at low levels of exposure.

2.3 Organic dusts in indoor environments

In occupational spaces where excessive airborne organic dust is reported, occupational respiratory disorder is common, e.g. Farmer lung, Bird breeder lung etc…In the recent Biosafety Guide of the American Industrial Hygiene Association, it is mentioned that airway inflammation appears in a variety of organic dust environments, particularly in confinement buildings, and the numbers of persons affected may be high. The symptoms gradually disappear when leaving work (AIHA 96). For example, fatigue, headache, and diarrhea have been reported by about 40% of workers in sewage treatment plants exposed to an aerosol of sewage dust containing elevated levels of bacterial endotoxin (Mattsby 78).

Mygip in his classical book 'Essential Allergy' mentioned the role of microbial antigens and toxins in Organic Dust Toxic Syndrome (ODTS). He explains that extrinsic allergic alveolitis or hypersensitivity- pneumonitis is caused by a variety of inhaled organic materials, especially microbial products and proteins. The antigens are small airborne particles (<5µm) which can reach the alveoli. (Mygip 86).

The Committee on Organic Dust of the International Commission of Occupational Health (ICOH), defines organic dusts as vegetable or animal matter, often contaminated by microbes, which in themselves also constitute an organic dust. The organic dust is said to consist primarily of small particles which may deposit in the deep parts of the lungs (ICOH 91).

Moreover, the Committee observed that the dust particles may cause effects as a consequence of their nature as particles, and allergens including hyperreactivity, and as agents capable of initiating acute and chronic inflammation. At present, considerable research efforts are spent on defining the cellular reactions, symptoms and clinical entities appearing after exposures to organic dusts (ICOH 91).

The only certainty is that an exposure threshold must be reached for these reactions to occur and the same agent may provoke reactions at different levels of exposure; endotoxin for example, causes fever at a level between 1 and 2 µg/m 3 , acute bronchoconstriction at levels approximately 0.1 to 0.2 µg/m 3 (or lower for sensitive subjects) and mucous membrane irritation and dry cough at 0.02 to 0.05 µg/m 3 (ICOH 91)..

2.4 Organic dusts and air conditoners

The ALK researchers in Denmark have suggested that many vague complaints concerning indoor climate may in fact be due to reactions caused by prolonged exposure to organic dust. They further predicted that the 'dust disease' will be common in years to come, because present building styles involve the use of many factors that promote microbiological growth and thereby accumulation of organic dust.

Examples are the use of efficient insulation without sufficient ventilation and the use of air-conditioning devices not regularly cleaned (Gravesen 87).

From clinical allergy and occupational medicine it is well known that organic dust of biological nature may influence the immune system and may have a toxic or irritative effect.

The prevalence of Macromolecular Organic Dusts (MOD) has been extensively described in recent years. The hypothesis behind demonstration of Macromolecular Organic Dusts (MOD) from absorbed dust was based on Gravesen et al. knowledge of macromolecules of biological origin, i.e. proteins, rigid carbohydrates and DNA-molecules which are biologically active substances as they act as immunogenes (Gravesen 90).

The recent extensive study of Gyntelberg et al. supports the hypothesis that qualitative properties of dust are important to the building syndrome (Gyntelberg 94).

Gravesen et al. also mentioned that dust-particles were liberated to the air resulting in inhalation and deposition on the human mucosa. Macromolecules from the dust influenced the immune system and may have accounted for the general symptoms and some of the mucosal symptoms described in the author study (Gravesen 88).

Morey mentioned that disrupting or disturbing contaminated structural components, such as occurs during operation of air-conditioners, can increase the concentration of indoor air contaminants 1000-fold (Morey 88).

In his review of biological contaminants, Seltzer mentioned that biological contaminants can contaminate the indoor air in various situations: 'when living, dead, or debris from dead organisms are distributed by ventilation systems; when the contaminant is physically disturbed; when a solid component of the organism dissolves in water and then becomes aerosolized; and when noxious gases from contaminants are released into the indoor environment' (Seltzer 94).

In the same study Seltzer also observed that if an air-conditioning system does not provide adequate fresh air, air filtration, and exhausting of contaminants, it may actually concentrate outdoor and indoor contaminants within the building. As a result, it is interesting to study in detail the specific organic dust load emitted by air-conditioners (Seltzer 94).

2.4.1 ENDOTOXIN EXPOSURE: MAJOR ALLERGEN IN INDOOR AIR QUALITY

According to the American Industrial Hygiene Association, it has been recognized for many years that a number of bacterial products can have profound effects on humans. One class of bacterial components is endotoxin - heat stable, lipopolysaccharide (LPS) protein complexes that are integral components of the outer membrane of Gram-negative bacteria. Endotoxin is part of the well known, bacterial biofilm which invades wet surfaces and is commonly called 'slime'.

The first scientific study of biofilms was published by Zobel in 1943 (Zobel 43). It was not until the 1970s, however, that researchers realized that the phenomenon is almost universal in natural environments (Costerton 78). It would appear that microorganisms cannot properly colonize an inert surface unless organic polymers are produced (Allison 87). Bacteria gain a number of advantages from living in biofilms.

In a biofilm in a stream, for example, the microbial cells are protected from possible attack from the outside environment, e.g. from u.v. radiation. They are also resistant to anti-bacterial agents such as heat and disinfectants. (Carpentier 93).

Gram-negative bacteria and their endotoxins are ubiquitous in soil, water, and living organisms around the world. Water, airborne and settled dust have shown their presence (AIHA 96). Bacterial 'slime' have been commonly described to invade wet surfaces inside air conditioning (Hugenholtz 92).

Endotoxins are released into the environment after lysis of the bacterial cells, during active cell growth.

Biofilm is a living structure subject to constant evolution. Part of the film continuously becomes fragile and sloughs off. In mechanically active mechanisms (i.e., air-conditioners) surfaces contaminated with biofilm, release significant amounts of 'slime' matrix (Marshall 92) (Refer to 2.4.2).

Endotoxin found in the cell walls of Gram-negative bacteria has a number of effects on respiratory function, even at low concentration (Rylander 94) and produces many of the inflammatory effects observed after exposure to bioaerosols (AIHA 96).

Numerous data demonstrate the occurrence of toxic reactions following exposure to endotoxin emitted from wet surfaces (contaminated humidifiers and air-conditioners particularly). The results of several studies describe inflammatory response following exposure to endotoxin (Snella 87). Fogelmark et al. clearly demonstrate in a recent study that inhaled endotoxin influences the cell kinetics of the airway with a rapid increase in the number of inflammatory cells, particularly neutrophils with a return to normal values within a few days (Fogelmark 92).

Moreover, the demonstration of symptoms at low levels of exposure, presumes the possibility of individual sensitization after prolonged exposure (Pickering 86).

The mildest form noted in humidifier fever consists of malaise, myalgia and headache with no respiratory symptoms (Pickering 86). Similar mild symptoms noted in SBS are enough to create significant levels of absenteeism in common office buildings.

Potentially allergenic particles have indeed been observed in buildings and related to health conditions of occupants. It is the case with elevated levels of endotoxins which have been recorded in different environments including office buildings (Rylander 89; Michel 91). Therefore, recommendations have been made to limit exposure to this agent and consistent, standardized methods to measure and quantify exposure to environmental endotoxin have been implemented (Walters 94).

2.4.2 ORGANIC DUST EMITTED BY AIR-CONDITIONING SYSTEMS - KINETICS OF ORGANIC DUST CONTAMINATION

In all indoor environments human activity is responsible for a consequent particulate pollution. Small particles (< 10µm in size) 'fly away' from the surfaces to which they are attached as a result of air disturbances. There are many sources of such dust in buildings, humans being the dominant one (SDHA 90).

The technical specification and characteristics of most air-conditioners help in trapping airborne particles inside the unit. Their intricate design, with an air pattern passing along multiple constrictions and turns, all in a quite small distance, causes impingement and entrapment of airborne particles throughout the system.

Most air filters used are unable to trap small airborne particles, therefore vast quantities of airborne particles enter the air-conditioner and deposit on components. The common lack of ventilation in air-conditioned rooms also contributes to the deleterious conditions observed.

With the high rate of air re circulation and turbulence created by most room air-conditioners, they may increase the kinetics of contamination of the equipment: More turbulence will logically re-suspend more particles inside the room and will keep them in suspension longer consequently, increasing the chances of agglomerated particles entering and depositing inside the unit.

An important feature of dust accumulation inside air conditioners, is that it helps in creating Bio contamination.

The airborne dust particles sediment while going through the air-conditioner. If sedimented on wet surfaces, they are very likely to support the growth of microorganisms (Hugenholtz 92). Seltzer et al. observed that it is obvious that dust and dirt accumulation within ventilation components may provide an organic substrate for microorganism growth. According to the authors, stagnant water from humidifiers, condensate pans, cooling units, etc, can harbor bacteria, fungi, algae and protozoa (Seltzer 94, Hugenholtz 92).

Fox et al. (Fox 93), in a recent extensive study involving chemical analysis of dust from air-conditioners (gas chromatography - mass spectrometry) could demonstrate the presence, in appreciable number, of bacteria cell envelope components. The authors mentioned that such components in dust, may act as irritants causing respiratory and ocular symptoms and may be involved in building-related disorders.

As seen previously, the most important feature of air-conditioner biocontamination is the systematic development of bacterial biofilm in accumulated wet mud, wet surfaces, and collection of stagnant water:

When the dust deposited on the wet internal surfaces (mostly on cooling coil and draining installation), becomes contaminated by Gram-negative bacteria, these microorganisms will tend to produce exogenous substances. The main constituent is best described as one of the major potentially aerosolisable allergenic substances from air-conditioners, the bacterial endotoxin.

Hugenholtz and Fuerst demonstrated consequent biofilm development inside air-conditioners. Despite the lack of visible signs of microbial contamination, the air-handling system harbored significant reservoirs of bacteria, primarily as a biofilm on the cooling coils. The biofilm was invisible to the naked eye, and grew on regularly wetted surfaces of the cooling coils. The biofilm was present on several sampling occasions over the course of a year with little change in composition despite the annual cleaning of the coils (Hugenholtz 92). According to the same authors, previous descriptions of cooling coil biofilms include a microbial slime several millimeters thick of unknown composition reported in a building demonstrating building-related illness (Hugenholtz 92, Morey 86), with an offensive odour (Hugenholtz 92, Harris 91).

As seen above, biofilm-derived bacteria growing in air-handling system may be important in the etiology of building health disorders. Viable bacteria may not need to act as infectious units for their presence to be significant for the health of building occupants (Hugenholtz 92). This is especially so if these bacteria or their endotoxins are shed into the airstream and delivered to the occupied space, as appeared to be the case in the study by Hugenholtz et al. (Hugenholtz 92).

The release of biofilm materials and their aerosolization into occupied spaces via the air-conditioning system can play a major role in the etiology of building-related illness (Rylander 89). Teews et al. even recognized that airborne microbial contamination, in particular with Gram-negative rods and perhaps with endotoxin, shed from ventilation system, may have a role in the causation of SBS (Teews 94). The authors, in an extensive recent study (involving 19 buildings and over 1000 employees), showed that endotoxin levels are six times higher in 'sick' buildings than in 'healthy' buildings. Moreover, according to Rylander, elevated levels of endotoxins have been recorded in different environments including office buildings (Rylander 89).

Turbulence created by running air-conditioning fans have been described as a major source of aerobiocontamination. HVAC equipment can aerosolise water particles adsorbed with live organisms or pathogenic portions of the organism, disseminating them in the air stream, a great distance from their nutrient source. It is indeed recognized that biological contaminants most often disseminate in the indoor environment through air currents or water aerosols (Seltzer 94).

Numerous authors report this aerobiocontamination problem due to running air-conditioning (Seltzer 94, Bonnaud 86, John 94, Fink 86). According to John and co-authors, the more concentrated the exposure to allergenic particles, the more likely they are to induce allergic and immunogenic response (non-allergy inflammation) (John 94).

Another crucial feature in air-conditioner biocontamination is the presence of fungi growing on the dust deposited inside the unit. Air-conditioning systems indeed, often play an important role in the building-related syndromes associated to fungi (Jarvis 87), which themselves are an important constituent of the indoor organic dust load. The American Industrial Hygiene Association, observes that the biggest change in scientific appreciation of particulate contaminants in buildings is with respect to fungi. The Guide evokes more than 30 studies worldwide since 1982, conducted in association with dampness, mold, and respiratory health in buildings. The results demonstrated high correlation between mold and dampness and several respiratory and non-respiratory symptoms. The severity of respiratory symptoms was more extensive than those caused by second hand tobacco smoke (AIHA 96).

There are case reports of fungi from drain pans of air-conditioner units and central HVAC units resulting in allergy and hypersensitivity pneumonitis (Flannigan 94). Samples of the mycoflora from air-conditioned as well as evaporatively cooled buildings have been shown to have increased populations of Aspergillus and Penicillium species (Steller 87; Solomon 80).

Another frequent surface inside air-conditioning systems is commonly reported to support fungal growth: fungal colonization has been reported on dirty and damp fiberglass insulation materials from heating, ventilating, and air-conditioning systems (Morey 92, Morey 91, Bjurman 93).

Ezeonu et al. Reported that inside air-conditioning units, the porous nature of the fiberglass matrix results in absorption of moisture and organic dusts that permit growth of fungi (Ezeonu 94). Supply air being in constant contact with insulation material inside air-conditioning systems where fungal contamination has occurred within such a support, may contribute to the aeroallergenic load found in the associated indoor environment (Ezeonu 94).

Recently, relatively clean and unused fiberglass insulation materials were shown to be subject to fungal colonization, particularly by Aspergillus species (Ezeonu 94, Ahearn 92). It is interesting to remember that Aspergillus is well recognized as a source of the lethal aflatoxin, with 30% to 70% isolates from natural environment tending to produce the toxin (Abbas 84). According to the Canadian Public Health Association. It is prudent however, to assume that the strain is toxigenic until testing proves otherwise (HEC 87).

The above mentioned mycotoxins are known to be carried by various metabolites produced by fungi. The spores of many species of toxigenic molds have been demonstrated to contain mixtures of mycotoxins.

Another important factor to consider is that the level of mycotoxins in fungal spores and propagules may be very high (HEC 87). According to Wicklow (Wicklow 81), it is a basic tenet of fungal ecology that mycotoxins are concentrated within the spore. Aflatoxin concentrations in spores can reach 200 000 ppb.

The permitted concentration of aflatoxin in some Canadian foods is fixed at 15 ppb (HEC 81).

The spore size of many of the fungal species of concern is approximately 5 µm. Particles of this size are within the respirable range and, hence, they could be deposited in alveoli (Salvaggio 87). Thus, high concentration of mycotoxins adsorbed to spores or particulates could reach the alveoli via inhalation (Sorenson 87).

Furthermore, mycotoxins present in lung may interfere with cell mediated immunity and contribute to diffuse alveolitis (Northup 78). Mycotoxins that affect the immune system (e.g. aflatoxins, trichothecenes...) are of special interest. Acompromised immune system would affect the ability of the host to respond to the allergen and infection, and could enhance the oncogenicity of the inhaled spores and particulates (Eichner 84).

The kinetics of fungal contamination clearly demonstrates suspension of particles into the air from surfaces harboring mould growth. This motion creates a potential respiratory hazard for the building occupants. The propagules described are responsible for most health disorders related to fungi (Samson 87).

The worst cases of fungal implication with air-conditioning systems describe infection in the form of invasive Aspergillosis (Lentino 82). Fortunately, the cases are rare and always connected to immuno-depressed patients in hospitals (Feuillade 86).

Apart from infections, various fungal species have been implicated with immuno-allergic reactions linked to air-conditioners (Bonnaud 86). According to the National Academy of Science in the U.S.A. all fungi are allergenic (NAS 93).

Furthermore, the Health and Welfare Canada Working Group on fungi and indoor air stated: 'Buildings can become sufficiently contaminated to induce respiratory diseases including asthma and hypersensitivity pneumonitis. The vague symptoms of 'environmental hypersensitivity syndrome' reported by occupants of homes and buildings highly contaminated with molds may be due to mycotoxins or molds acting as antigens…' (HEC 87).

Among fungi biologically active agents such as mycotoxins, evidence suggested that a specific compound in molds, the cell wall constituent ß-1.3-glucan, could have a toxic effect (Rylander 93).

Rylander et al. (Rylander 92) observed that results from studies in a number of buildings found an association between the amount of airborne glucan and the extent of subjective symptoms, indicating irritation in the upper airways. In another study Rylander et al. (Rylander 92) has shown that in a school before and after restoration work, there was an excess of symptoms of irritation, fatigue and headache. The extent of symptoms decreased after renovation in the school.

Garrison et al. Mentioned that an air-conditioning system poorly installed or improperly maintained, can serve as a primary source for fungal aeroallergen proliferation and amplification and contribute to the indoor mycoflora. In their study the authors observed fungal contamination in several HVAC systems, mainly in the evaporative cooler. Drip pans, the supply air plenum and the vent outlets in the room had also shown contamination whilst the building evaluated had major fungal contamination (Garrison 93). For the same authors, a properly installed and maintained HVAC System, especially when coupled with high efficiency filtration, should contribute very little to the total airborne fungal content. Moreover, the sanitation of a Heating-Ventilation-Air Conditioning System, has been shown to produce a significant reduction in fungal metabolites into the air over several weeks (Garrison 93).

Because of all the above, appropriate actions should be taken to minimize the release of allergenic materials from air-conditioners and particularly from parts of biofilm matrix (Teews 94) and fungal growth. Such intervention should also logically take into account all the described specificities of fungi and biofilm build up and evolution.

The ASHRAE Standard 62-1989 in its current draft revision devotes considerable space to the need to eliminate stagnant water that can accumulate endotoxin which in turn can be released in building air (AHIA 96).

3.0 NEED FOR APPROPRIATE AND RESIDUAL TREATMENT AGAINST ALLERGENS INSIDE AIR-CONDITIONERS - AVOIDING SIDE EFFECTS

In his recent review of bioaerosols in the indoor environment, Morey classifies inadequate maintenance of HVAC systems as an important cause of microbial contamination in offices: "Neglect of routine maintenance probably is the single most important factor that leads to microbiological contamination in buildings. The internal components of air-handling units, fan coil units, etc, are seldom cleaned even when access doors to mechanical equipment facilitates cleaning.(Morey 89)

Air-conditioning sanitation seems to be an obvious requirement. However because of the 'sensitive role' played by air-conditioners, i.e. supplying treated air to building occupants, any sanitation procedures should focus on major discomfort sources (avoiding false security of inefficient treatment) and any possibility of adverse effects, particularly due to the nature of the chemical used to achieve sanitation.

The treatment priority advocates the removal of potentially immunogenic particles. Because of similarity in the kinetics of contamination (i.e., airborne contact between aerosolized allergens and patient), it is of interest to check what environmental treatment of asthma is proposed against the identified allergenic particles: In asthma, it is broadly accepted that the first action is allergen avoidance and removal.

If the allergens are reduced sufficiently the immunological reaction decreases accordingly (Platts-Mills 82, 88, 90, Murray 83, Editorial 92).

3.1 What to do, what to avoid with air-conditioning contamination

3.1.1 A PRE-LOGIC TO RESPECT

With the lack of medically recognized and reproducible dose-response thresholds for microbial substances emitted by contaminated air-conditioners, any unit should be considered with suspicion and included in a carefully selected treatment plan. Variations of the plan may be made according to the conditions of the air-conditioner to be treated (absence or presence of visible contamination on wet surfaces, etc...).

Classical annual cleaning program of cooling coils and drain pans (usually using high pressure mechanical cleaning, including spray of detergent and disinfectant, etc...) is not sufficient to avoid permanent build up of biofilm observed on cooling coils and drain pans (Hugenholtz 92). Even visibly 'healthy' cooling coils of air-handling units show biofilm contamination (Hugenholtz 92).

The above findings underlined the necessity for the implementation of a thorough appropriate sanitation procedure against biofilm formation, particularly on all moist components (Teeuws 94). New techniques, preferably holding residual activity, are necessary to maintain the level of Lipopolysaccharides (LPS) at a low risk level. A proper sanitation technique, avoiding side effects, should be considered. Such biofouling control, indeed requires carefully engineered interventions.

Action against fungi is also preferable, particularly in winter on commonly wet surfaces where the lack of condensation from the evaporator coils prevent bacterial growth. Fungi are favoured in invading the dirty surfaces and particularly cooling coils. Other similarly dirty but not so damp air conditioning surfaces, may promote fungal growth all year round (e.g. insulation,...). Extra care to handle fungal growth should be taken.

3.1.2 WHAT TO AVOID

Any inappropriate action will create, either no results and risk of creation of false security among the building occupants or adverse effects possibly on the health of building occupants.

In a recent study, Walters et al. could demonstrate: 'Gram negative bacteria and their associated endotoxins can become airborne during spray cleaning operations. The type of bacteria cultured from the incriminated washwater were similar to the ones present in the air. Airborne countable bacteria correlated well with endotoxin levels (Walters 94)…'.

In another recent study, Sesline et al. (Sesline 94) described a case where a ventilation technician sprayed a hospital grade disinfectant into an operating heating/ventilation/air-conditioning unit at a preschool. The action resulted in immediate onset of symptoms which were generally consistent with exposure to an irritating chemical. Several children and staff sought medical attention.

Extreme care should be taken when dealing with fungal growth spots. The extreme propensity of releasing propagules to the air due to turbulence (Miller 90), made fungal development a premium risk for aero-bio-contamination when cleaning an air-conditioner.

3.1.3 WHAT TO DO

It is of premium importance always to keep in mind that hygiene is a technology which needs to have its priorities and goals well defined. When dealing with air-conditioner sanitation, an adapted technique has to be designed, in accordance with the defined needs.

The main targets in air-conditioner sanitation are firstly defined. These are complex mixtures of inert potential allergens (organic dusts), comprising immunogenic and allergenic components of microorganisms, including pieces of their excreted substances (LPS, Peptidoglycan, etc...), all fungal metabolites (spores, mycotoxins, glucans, etc...).

Then, the main engineering requirements are determined. These are: (1) removal of accumulated immunogenic dirts, mainly on difficult to access wet surfaces, (2) focusing on allergen control treatment instead of classical priority given to surface disinfection, (3) particular avoidance of aerosol emission during sanitation procedures, (4) innocuity of chemicals used due to their application inside air distribution equipment, (5) the necessity of residual activity against biofilm, effective for several weeks, (6) dusty surfaces inaccessible for gentle cleaning should be treated with recognized allergen denaturant solutions (e.g. fan blades).

Moreover, a three phases hygienic treatment should be implemented on all wet surfaces susceptible to accumulate dirt, e.g. cooling coils, drip pans. The first phase should focus on cleaning (only) accumulated organic materials with a particular activity against biofilm matrix which are recognized to attract surrounding dirts (Carpentier 93).

The following second phase should be a proper rinsing of all parts cleaned in the first stage. Our experience shows us that the use of ozonated water may benefit in dissolving biofilm formation (Videla 94) and help the removal of cleaning material residues usually mixed with significant quantity of suspended dirts. The rinsing phase is crucial in hygienic view.

The common sense that only a clean surface can be disinfected should be respected when considering a third phase aiming at disinfection, in particular because the abundance of no viable material accumulated on surfaces to be treated may reduce, if not prevent the implemented disinfecting activity, while in the mean time those inert materials are in fact the main hygienic targets. The final disinfection phase should not be only directed to disinfection but should consider a kind of maintained and combined cleaning activity. Disinfectants have great difficulty to penetrate biofilm formation to reach their bacterial targets (Carpentier 93). Most bactericides have also very limited activity in time. A common air conditioning cooling coil (i.e. commercial building) is constantly impacted with airborne dusts carrying potentially viable microorganisms responsible to biofilm development.

When deposited on surfaces offering sufficient growing potential (i.e. food, water, temperature, etc...) bacteria can start colonizing a media and build up biofilm in hours (Carpentier 93). Even visually clean cooling coils support the development of significant biofilm matrix (Hugenholtz 92). Cleaning should indeed be the priority, while cleaning and disinfection should particularly aim at biofilm removal and fungal control.

Specific chemicals and processes have been recently developed to control fungal growth and biofilm building up on constantly wet surfaces. Some of these treatment techniques and materials, use slow-acting principles allowing extended activity while holding low toxicity to humans. Such properties make them perfect items for implementing preventive maintenance for air conditioners. Prevention using gentle (toxicity and corrosion) and repeated processes should be a must in air conditioner sanitation. Hygiene is prevention.

4.0 CONCLUSION

SBS is insidious and has been reported for many years. Causes are complex and related to both psycological and physiological factors. A major physiological cause of SBS is airborne potentially allergenic dust produced by air conditioning equipment. Recorded sicknesses are probably caused by inhalation of various types of organic material under conditions of occupational stress. The actual organic material inhaled, need not be living bacteria or fungi but simply the products or detritus from them. Air conditioning systems offer growing sites, dispersion mechanisms and distribution. This aspect of indoor air quality has not been generally reported due to a tendency to focus on airborne viable organisms rather than immunogenic inert particles when devising indoor air quality surveys and air conditioner treatment programs. Air quality surveys should include air sampling for recognized immunogens particularly in buildings with a history of health problems. When a properly engineered preventative maintenance program is deployed on air conditioning equipment, the risk for immunogenic organic dusts to be released by the unit to the indoor air should be dramatically reduced. Consecutively, the constellation of non-specific health complaints commonly recorded in 'sick' buildings and supposedly related to respiratory inflammation following exposure to low quantities of organic dusts, could be similarly reduced. An intervention program for air conditioners focusing on 'bio-active' dusts, while avoiding adverse side effects, may then be essential in helping to control sick building syndrome.

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1998 AIRAH International Conference Paper 29.19