Sick Building Syndrome Research Paper

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Definition And Background

Sick building syndrome (SBS) encompasses a spectrum of varied symptoms, including mucus membrane (eyes, nose, throat) or skin irritation, and general symptoms such as headache, nausea, fatigue, and generalized malaise. There is no single accepted definition of SBS symptoms, and these symptoms may be common in the general population. SBS is diagnosed when the symptoms occur in close temporal association with spending time in a particular nonindustrial building. The term SBS can be confusing, because it is the individual occupants who are ill, not the building. First coined in the 1970s, the term SBS is generally reserved for situations in which a substantial proportion (usually about 20% or more) of occupants in a building are symptomatic. The most prominent cases have occurred in office buildings, where large numbers of individuals may be affected, but SBS has been reported in smaller workplaces, schools, public buildings, hospitals, recreational facilities, and homes. Affected individuals typically report that symptoms progressively increase while in the building, subside shortly after leaving the building, and do not occur when away from the building.

Most case reports and studies of SBS have come from industrialized nations in Europe and North America, but SBS is believed to be a worldwide problem. In 1984, the World Health Organization (WHO) estimated that excessive building-related complaints may occur in as many as 30% of new and remodeled buildings worldwide (WHO, 1984). Among a random sample of U.S. office workers, Kriess (1989) reported that 20% had air quality-related complaints about their workplaces. Given that, on average, people in industrialized nations spend greater than 90% of their time indoors, the quality of indoor environments may significantly impact health and well-being. In a recent review, Mendell et al. (2002) estimated that absence and lost productivity due to nonspecific building-related symptoms costs U.S. industry $20–$70 billion per year.

SBS is distinct from forms of building-related disease or illness that can be linked to specific agents, such as infectious disease agents or toxic chemical exposures. By definition, SBS is a diagnosis of exclusion, in which known, specific causal factors have been ruled out. In other words, SBS is diagnosed when reported symptoms appear to be clearly related to a building, but no specific disease or etiological agent can be identified. Thus, SBS can be a particularly challenging problem for the affected individuals, building managers, medical clinicians, public health professionals, and indoor environment specialists. Investigations of the indoor environment may identify one or more factors that have been associated with SBS, but causal relationships between specific factors and SBS in a particular building are, by definition, difficult to establish. Many cases of SBS have been linked to poor building maintenance practices, including lack of maintenance of a building’s mechanical ventilation systems or a building’s structural integrity. However, even after extensive evaluation of occupant complaints and the indoor environment, investigations seldom yield satisfying conclusions about likely etiology. Fortunately, case reports and some studies provide evidence that symptoms of SBS can be improved by interventions such as mitigation of air contaminant sources and improved ventilation.

SBS is a complex, multifactorial condition that has generated much speculation and theory about potential causes. Numerous case studies of complaint buildings and a few epidemiological studies have supported roles for a number of specific causative agents, including chemical and biological air contaminants, physical factors, ventilation, and psychosocial factors. Mendell reviewed and summarized the results of 32 studies conducted between 1984 and 1992 that examined 37 factors potentially related to office worker symptoms (Mendell, 1993). He described several factors associated with ‘consistent’ higher symptom reports such as air conditioning, job stress/dissatisfaction, and allergies/asthma. Low ventilation rate, carpets, occupant density, video display terminals, and female gender had ‘mostly consistent’ associations with increased symptoms. The following discussion will provide an overview of the present understanding of SBS, while contrasting it with specific building-related illnesses and diseases. As with any diagnosis of exclusion, it is prudent to rule out known, preventable causes of serious building-related illness or disease before ascribing the problem to SBS.

Role Of Air Contaminants

Air contaminants are the category of potential environmental causes of SBS that have received the most attention and study. The focus on air contaminants arose from the prominence of respiratory and mucus membrane irritation symptoms in many outbreaks of SBS. Common complaints about air quality, including perceived ‘stuffiness’ and odors, often accompany reported symptoms. Air contaminants linked to SBS have included a range of synthetic chemical compounds and biological products.

Chemical Substances

A wide range of chemical substances can be identified and measured in indoor air in nonindustrial settings. Indoor sources of volatile organic compounds (VOCs) include building materials, furniture, paints, carpeting, environmental tobacco smoke, cleaning products, office supplies, personal care products, and many others. Many case reports of SBS have described new or newly remodeled buildings in which building materials and interior items were implicated as sources of VOCs. For example, in some cases SBS irritation symptoms have been attributed to formaldehyde that is slowly released into the air from urea-formaldehyde adhesives used in engineered wood products such as laminated wood and fiberboard found in construction materials and furniture.

In industrialized countries, the levels of many chemical air contaminants are greater indoors than outdoors (Wallace, 1989). These include a number that are regulated by the U.S. Environmental Protection Agency (EPA) and other environmental regulatory agencies as toxic air pollutants outdoors. Nonetheless, the concentrations of these and other indoor air contaminants are generally well below standards that have been set to protect workers in industry, such as the U.S. Occupational Safety and Health Administration Permissible Exposure Limits or the American Conference of Governmental Industrial Hygienist’s Threshold Limit Values.

Causal associations between these relatively low levels of VOCs and the acute symptomatic complaints of SBS have been difficult to firmly establish. Controlled exposure studies have demonstrated that VOCs can cause mucous membrane irritation at relatively high concentrations, providing some biological plausibility to reports of associations with symptoms such as eye, nose, and throat irritation. Studies that have attempted to assess pure irritation, mediated by the trigeminal nerve, can be subject to potential confounding by odor perception, mediated by the olfactory nerve. Many VOCs have estimated odor thresholds that can be orders of magnitude lower than their irritation thresholds. These threshold concentrations can vary greatly with different VOCs and among individuals, further complicating SBS studies. Even when levels of individual contaminants in indoor air are relatively low, mixtures of contaminants may interact, perhaps synergistically, to produce effects that are difficult to predict. Air contaminants may also interact with other factors such as preexisting allergy or asthma, physical factors like humidity, and psychological factors that may influence perception and interpretation of odors and irritation.

Inorganic chemical air contaminants that can affect health of building occupants are primarily related to combustion sources. If not properly vented and maintained, furnaces, heaters, and stoves can produce potentially dangerous levels of carbon monoxide and nitrogen oxides, which at lower levels of exposure may also produce some of the nonspecific (headache, fatigue, nausea) and irritation symptoms sometimes associated with SBS. These pollutants may also enter buildings from outside sources such as attached garages or exhaust stacks that are located in close proximity to ventilation air intakes.

Biological Agents

In many case reports and some epidemiological studies, SBS has been associated with poor maintenance of building structures and systems, creating conditions that permit the growth and accumulation of fungi and bacteria. Specific problems linked to SBS have included interior moisture and dampness resulting from water intrusion into buildings through exterior leaks and plumbing malfunctions. Ventilation systems that cool and/or humidify air may create moisture conditions that support microbial growth and then distribute its products throughout buildings. A recent Institute of Medicine (2004) review concluded that upper respiratory symptoms are associated with mold and other exposures in damp environments. Many case reports and limited epidemiology have linked exposure to mold with the nonspecific symptoms of SBS (fatigue, malaise, memory problems), but the Institute of Medicine (IOM) concluded that these associations are not established. Mold spores are recognized as allergens that can cause specific building-related illness such as allergic rhinitis and asthma exacerbation in sensitive individuals. Fungal spores and other bioaerosols have also been identified as causative agents in hypersensitivity pneumonitis and humidifier fever, two serious building-related diseases. These relatively rare and usually sporadic conditions have sometimes been reported in buildings where other occupants have reported SBS, leading to the suspicion that common etiologic agents are involved. Opportunistic fungal infections such as aspergillosis are rare and known to occur only in susceptible immunocompromised individuals. Distinct from SBS, outbreaks of Legionella pneumonia in buildings have been associated with growth of the bacteria in ventilation cooling towers and other aerosolized water sources.

Much speculation surrounds the pathophysiological mechanisms by which noninfectious microbes may cause SBS. Fungal spores may theoretically cause nonallergic, mucus membrane irritation. It has been suggested that the VOCs produced by microbial metabolic activity may cause symptoms, but levels of microbial VOCs in indoor air are typically lower than background indoor VOC levels, except in the most heavily contaminated buildings. Several species of fungi that may grow indoors under damp conditions can produce nonvolatile compounds that have potent toxic effects in animals and humans. Whether these mycotoxins at levels that may be present in indoor air can cause health effects, including specific building-related illness or SBS, has not been established. Endotoxin, a component of the cell walls of Gram-negative bacteria, is a potent inflammatory stimulus, and endotoxin levels in building dust have been associated with SBS.

Ventilation

Air contaminant levels in buildings are determined by rates of dilution and removal, as well as rates of contaminant generation. In most modern office buildings, the conditioned air that is delivered to building spaces serves to dilute air contaminants generated from sources indoors. When equipped with air filters, such as dust filters, these systems can also remove some contaminants from the air. Poor design, maintenance, or operation of these systems can lead to higher levels of contaminants that may be associated with SBS. As noted above, the mechanical ventilation system can itself be a source of microbial growth and other contaminants. In some studies of buildings not recognized as having indoor air quality problems, such as the Danish Town Hall Study (Skov et al., 1997) of 14 buildings, building-related symptoms were more common in mechanically ventilated buildings compared to buildings with natural ventilation systems.

The appropriate level of fresh air intake required for adequate dilution ventilation depends on the rate of generation of contaminants, which can vary greatly depending on the sources present in individual buildings. The American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE) has set a voluntary standard for outdoor air of 20 cubic feet per minute (cfm) per occupant. Some studies have shown increased symptoms associated with ventilation rates below this level, and improvement in occupant symptoms when ventilation rates were increased. The first recognized cases of SBS occurred in the 1970s, in an era of ‘tight buildings’ when the ASHRAE standard had been lowered to 5 cfm per occupant to reduce consumption of energy required to condition outdoor air. Seppanen and Fisk (2004) have recently summarized knowledge of the effects of ventilation on health and symptoms.

Physical Environmental Factors

Several physical factors have been associated with SBS, most prominently temperature, relative humidity, and lighting.

Temperature

In modern office buildings and other structures, ventilation systems play a role in controlling air quality factors such as temperature and humidity, in addition to air contaminant levels. Elevated temperatures have been associated with SBS in workplaces. Dissatisfaction with temperature and relative humidity were among the most prevalent symptoms reported in the investigations of SBS at two large EPA buildings in Washington, D.C. (U.S. EPA, 1989). Increased temperature was associated with mucus membrane irritation and general symptoms in the Danish Town Hall Study (Skov et al., 1997).

Humidity

Humidity may affect perceived air quality in several ways. Along with temperature, relative humidity is an important factor in thermal comfort. ASHRAE standard 55-2004 for thermal comfort sets a range of combinations of temperatures and humidity, with temperatures ranging from 20 to 28 C and relative humidity ranging from 30–60%. Low humidity has been reported in association with complaints about dryness and irritation of the skin, eyes, nose, and throat. High relative humidity has been reported in association with perceived ‘stuffiness’ and poor air quality. Other studies have shown no association between SBS symptoms and humidity levels. Excessive relative humidity can also contribute indirectly to SBS by increasing the moisture available for microbial growth on interior surfaces and ventilation system components.

Lighting

Lighting conditions can affect occupant comfort and may contribute to some SBS symptoms. Poor lighting can cause eye strain and fatigue. Common lighting problems can include inadequate illumination, excessive illumination, and glare. Whether poor lighting can explain SBS symptoms that are not directly related to the eyes is not clear.

Personal Risk Factors

The observation that SBS typically affects a minority of individuals in a building has led to speculation that individual susceptibility factors may play an important role in the etiology of SBS.

Gender

Investigators have consistently identified female gender as a powerful risk factor in studies of SBS. Gender differences that might explain the high ratio of females to males affected by SBS might include differences in exposure to one or more causal factors, susceptibility, job satisfaction, or tendency to observe or report symptoms. In a study of 14 German office buildings, Brasche et al. (2001) found that women were more likely to report SBS regardless of working conditions, job characteristics, or building-related factors.

Atopy

A number of case reports of SBS have described cases of specific building-related illnesses, such as allergy and asthma, among a larger number of cases of nonspecific SBS symptoms. Results from some controlled exposure experiments of chemical irritants have suggested that atopic individuals are more susceptible to irritant exposure. Reported triggers of asthma include irritants and odors, suggesting that asthmatics may be more sensitive to indoor air contaminants. However, it is not known to what extent allergy and asthma may be an effect modifier, an outcome, or a confounder in associations between building conditions and SBS symptoms.

Psychosocial Factors

Some studies of work environments have identified psychosocial stressors, job dissatisfaction, and work organization factors associated with SBS. At the time of investigation, SBS often occurs in a contentious working environment in which worker reports of building-related symptoms may be a cause or an outcome of job stress and dissatisfaction, and no prospective studies are available to establish the temporal relationship between measures of stress and symptoms. Studies of buildings not known to have indoor air problems have also demonstrated correlations between measures of stress and work organization factors and symptoms (Mendell, 1993).

Conclusion

In summary, SBS is a complex, multifactorial environmental health condition that is diagnosed when building occupants report subjective symptoms that are attributed to being inside a particular building. As defined here, SBS is diagnosed when other known causes of potentially serious building-related illness have been ruled out. A number of indoor environmental factors (air contaminants, bioaerosols, ventilation, temperature, humidity, lighting, etc.) and individual risk factors (gender, work stress, job dissatisfaction, etc.) have been linked to cases of SBS in specific buildings, but lack of consistency in findings precludes generalization. SBS is likely to result from a complex interaction of a number of environmental and psychosocial factors.

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