Monday, April 16, 2007

Sick building syndrome: psychosocial and physical factors

Is health in office buildings related only to psychosocial factors?

M J Mendell and W J Fisk
Indoor Environment Department, Lawrence Berkeley National Laboratory, California, USA


It has been clear for years, on the basis of much published research, that symptoms in office workers are associated with several environmental factors in office buildings and also, independently, with psychosocial stressors at work. So, we were surprised to see a recent article by Marmot et al reporting that, in offices in the Whitehall II Study, "raised symptom levels appear to be largely due to a working environment characterized by poor psychosocial conditions". The article concluded that the physical environment in the offices had a small and unimportant influence on these symptoms. The analyses, however, had substantial limitations that were not mentioned. Further, the conclusions were inconsistent with much of the current scientific literature, but the discussion cited only other studies that agreed with the findings and none of the substantial literature that disagreed.

We expand on these points.
1. Key environmental measurements and interpretations used by Marmot et al in the 1991–3 data collection are no longer considered relevant by most indoor environmental scientists. Single metrics of total volatile organic compounds that lump all compounds together have long been considered inappropriate for predicting human response, because irritancy and odour vary by orders of magnitude among specific volatile organic compounds. Metrics based on counts of culturable airborne fungi and bacteria do not detect most indoor microbial matter and "provide little information about the microbial status of an indoor environment". Also, many of the thresholds for acceptability used by Marmot et al are not considered relevant for studying building-related symptoms—for example, dry bulb temperature between 19 and 24°C, carbon dioxide (CO2) 500 parts per million, or any particular number for total airborne fungi, bacteria or volatile organic compounds. In addition, the lumping together of extreme high and low levels for many of the parameters (eg, combining very hot and very cold temperatures in one category and comparing with a broad middle range of temperatures) is inappropriate—high and low temperature (or high and low humidity) may have quite different, even opposite, effects. Researchers using more current or precise metrics have reported consistent associations of building-related symptoms in office workers with both lower ventilation rates and higher temperatures. There is also a substantial amount of literature showing that visible dampness and mould, but not traditional airborne mould counts, are consistently associated with asthma exacerbation and respiratory symptoms in building occupants.

2. The authors do not report the association of passive tobacco smoke exposure at work with symptoms, although it is included in their models as a confounding factor. It was strongly correlated with increased symptoms (p = 0.004) in prior analyses of their data. The current article, without explanation, does not consider passive tobacco smoke exposure to be an indoor environmental risk factor, although it reports risk estimates for other indoor air pollutants.

3. The paper cites prior studies that agreed with its findings, but is inexplicably silent about the many prior studies that have disagreed. Ventilation rate and temperature, both objectively assessed indoor environmental risk factors, have been significantly and independently associated with symptoms in multiple prior office studies.

A 1999 review of studies reported between 1986 and 1999 found that (1) in six studies using measured ventilation rates, 20 of 27 comparisons of different ventilation rates found increased symptoms associated with lower measured office ventilation rates, and (2) 9 of 18 studies using CO2 measurements as simpler but less accurate indicators of ventilation rate also found such associations. Nine articles on associations between temperature and symptoms in offices, published between 1989 and 2004, show overall that symptom prevalence increased systematically as temperatures increased between about 21 and 24.5°C, almost entirely within the "acceptable" reference level used by Marmot et al.

We suggest further analyses of the Whitehall II data by Marmot et al to refine their findings and help resolve discordant results: (1) the use of environmental metrics based on current knowledge that symptoms in office workers generally increase as temperatures increase >21–22°C, as indoor CO2 increases above about 600–800 ppm, with the presence of passive tobacco smoke, and in buildings with air-conditioning or humidification; (2) statistical adjustment for season of study; (3) the inclusion of the additional psychosocial variables available in the Whitehall II study; and (4) separate analyses for outcomes of biologically related symptom subgroups—rather than continuing to use the non-specific "sick building syndrome" metric (for instance, lumps, rash/itch, together with cold/flu), which may be sensitive to stress-related over-reporting but insensitive to specific biological effects.

In conclusion, substantial evidence suggests that psychosocial and physical factors in indoor environments, as well as biological and chemical factors, influence the symptoms experienced by office workers, through multiple mechanisms that we still do not understand. Dismissing the importance of any of these indoor environmental risk factors is not useful or, based on all that we know, justified.

Ultimately, researchers in many disciplines will need to help us understand causation and prevention of this problem.

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