Indoor air particles and bioaerosols before and after renovation of moisture-damaged buildings: the effect on biological activity and microbial flora

Many building-related health problems coincide with moisture damage and mold growth within a building. Their elimination is assumed to improve indoor air quality. The aim of this study was to follow the success of remediation in two individual buildings by analyzing the microbial flora and immunotoxicological activity of filter samples. We compare results from samples collected from indoor air in the moisture-damaged buildings before and after renovation and results from matched reference buildings and outdoor air. The microbial characteristics of the samples were studied by analyzing ergosterol content and determining the composition of fungal flora with quantitative polymerase chain reaction (QPCR). In addition, the concentrations of particles were monitored with optical particle counter (OPC). The immunotoxicological activity of collected particle samples was tested by exposing mouse macrophages (RAW264.7) for 24 h to particle suspension extracted from the filters, and measuring the viability of the exposed cells (MTT-test) and production of inflammatory mediators (nitric oxide, IL-6 and TNF*) in cell culture medium by enzyme-linked immunoassay (ELISA). The results show that for Location 1 the renovation decreased the immunotoxicological activity of the particles collected from damaged building, whereas no difference was detected in the corresponding samples collected from the reference building. Interestingly, only slight differences were seen in the concentration of fungi. In the Location 2, a decrease was seen in the concentration of fungi after the renovation, whereas no effect on the immunotoxicological responses was detected. In this case, the immunotoxicological responses to the indoor air samples were almost identical to those caused by the samples from outdoor air. This indicates that the effects of remediation on the indoor air quality may not necessarily be readily measurable either with microbial or toxicological parameters. This may be associated with different spectrum of harmful agents in different mold and moisture-damaged buildings.

Diversity and seasonal dynamics of bacterial community in indoor environment

Background

We spend most of our lives in indoor environments and are exposed to microbes present in these environments. Hence, knowledge about this exposure is important for understanding how it impacts on human health. However, the bacterial flora in indoor environments has been only fragmentarily explored and mostly using culture methods. The application of molecular methods previously utilised in other environments has resulted in a substantial increase in our awareness of microbial diversity.

Results

The composition and dynamics of indoor dust bacterial flora were investigated in two buildings over a period of one year. Four samples were taken in each building, corresponding to the four seasons, and 16S rDNA libraries were constructed. A total of 893 clones were analysed and 283 distinct operational taxonomic units (OTUs) detected among them using 97% sequence similarity as the criterion. All libraries were dominated by Gram-positive sequences, with the most abundant phylum being Firmicutes. Four OTUs having high similarity to Corynebacterium-, Propionibacterium-, Streptococcus- and Staphylococcus- sequences were present in all samples. The most abundant of the Gram-negative OTUs were members of the family Sphingomonadaceae, followed by Oxalobacteraceae, Comamonadaceae, Neisseriaceae and Rhizobiaceae.

The relative abundance of alpha- and betaproteobacteria increased slightly towards summer at the expense of firmicutes. The proportion of firmicutes and gammaproteobacteria of the total diversity was highest in winter and that of actinobacteria, alpha- and betaproteobacteria in spring or summer, whereas the diversity of bacteroidetes peaked in fall. A statistical comparison of the libraries revealed that the bacterial flora of the two buildings differed during all seasons except spring, but differences between seasons within one building were not that clear, indicating that differences between the buildings were greater than the differences between seasons.

Conclusion

This work demonstrated that the bacterial flora of indoor dust is complex and dominated by Gram-positive species. The dominant phylotypes most probably originated from users of the building. Seasonal variation was observed as proportional changes of the phyla and at the species level. The microflora of the two buildings investigated differed statistically and differences between the buildings were more pronounced than differences between seasons.

Personal and microenvironmental concentrations of particles and microbial aerosol in relation to health symptoms among teachers

A total of 81 randomly selected elementary school teachers participated in two sampling campaigns conducted 2 weeks apart during the winter. A 24-h sample collection was performed using personal and microenvironmental sampling from homes, and an 8-h sample collection was performed from workplaces of the studied subjects. Filters were analyzed for particle mass, absorption coefficient of the filter, and for both total and viable microorganisms. Comprehensive questionnaire responses were collected from the teachers concerning weekly occurred symptoms during the previous 12-month period, and they filled in symptom diaries immediately after each sampling campaign concerning symptoms during the previous 24-h and 7-day periods. The effect of different recall periods on agreement between questionnaire responses was assessed. Factor analysis was used in order to identify factors explaining the pattern of correlations within the personal, home, and work measurements. Moreover, associations between personal, home, and work measurements of pollutants and symptoms were analyzed using general estimation equations. The recall period of 7 days seemed to provide the most reliable data for the health effect assessment. Information from the factor analysis may allow reduction of variables related to the exposure assessment, and better interpretation of results. Both personal exposure and concentrations of pollutants at home were more frequently associated with health symptoms than concentrations at work. In multipollutant analyses, absorbance coefficient was positively associated with eye symptoms, and total bacteria with both cough and blocked nose.

Control of aerosol contaminants in indoor air: combining the particle concentration reduction with microbial inactivation

An indoor air purification technique, which combines unipolar ion emission and photocatalytic oxidation (promoted by a specially designed RCI cell), was investigated in two test chambers, 2.75 m3 and 24.3 m3, using nonbiological and biological challenge aerosols. The reduction in particle concentration was measured size selectively in real-time, and the Air Cleaning Factor and the Clean Air Delivery Rate (CADR) were determined. While testing with virions and bacteria, bioaerosol samples were collected and analyzed, and the microorganism survival rate was determined as a function of exposure time. We observed that the aerosol concentration decreased approximately 10 to approximately 100 times more rapidly when the purifier operated as compared to the natural decay. The data suggest that the tested portable unit operating in approximately 25 m3 non-ventilated room is capable to provide CADR-values more than twice as great than the conventional closed-loop HVAC system with a rating 8 filter. The particle removal occurred due to unipolar ion emission, while the inactivation of viable airborne microorganisms was associated with photocatalytic oxidation. Approximately 90% of initially viable MS2 viruses were inactivated resulting from 10 to 60 min exposure to the photocatalytic oxidation. Approximately 75% of viable B. subtilis spores were inactivated in 10 min, and about 90% or greater after 30 min. The biological and chemical mechanisms that led to the inactivation of stress-resistant airborne viruses and bacterial spores were reviewed.

Do N95 respirators provide 95% protection level against airborne viruses, and how adequate are surgical masks?

BACKGROUND

Respiratory protection devices are used to protect the wearers from inhaling particles suspended in the air. Filtering face piece respirators are usually tested utilizing nonbiologic particles, whereas their use often aims at reducing exposure to biologic aerosols, including infectious agents such as viruses and bacteria.

METHODS

The performance of 2 types of N95 half-mask, filtering face piece respirators and 2 types of surgical masks were determined. The collection efficiency of these respiratory protection devices was investigated using MS2 virus (a nonharmful simulant of several pathogens). The virions were detected in the particle size range of 10 to 80 nm.

RESULTS

The results indicate that the penetration of virions through the National Institute for Occupational Safety and Health (NIOSH)-certified N95 respirators can exceed an expected level of 5%. As anticipated, the tested surgical masks showed a much higher particle penetration because they are known to be less efficient than the N95 respirators. The 2 surgical masks, which originated from the same manufacturer, showed tremendously different penetration levels of the MS2 virions: 20.5% and 84.5%, respectively, at an inhalation flow rate of 85 L/min.

CONCLUSION

The N95 filtering face piece respirators may not provide the expected protection level against small virions. Some surgical masks may let a significant fraction of airborne viruses penetrate through their filters, providing very low protection against aerosolized infectious agents in the size range of 10 to 80 nm. It should be noted that the surgical masks are primarily designed to protect the environment from the wearer, whereas the respirators are supposed to protect the wearer from the environment.

Manikin-based performance evaluation of N95 filtering-facepiece respirators challenged with nanoparticles

Protection of the human respiratory system from exposure to nanoparticles is becoming an emerging issue in occupational hygiene. The potential adverse health effects associated with particles of approximately 1-100 nm are probably greater than submicron or micron-sized particles. The performance of two models of N95 half-facepiece-filtering respirators against nano-sized particles was evaluated at two inhalation flow rates, 30 and 85 l min(-1), following a manikin-based protocol. The aerosol concentration was measured outside and inside the facepiece using the Wide-Range Particle Spectrometer. Sodium chloride particles, conventionally used to certify N-series respirators under NIOSH 42 CFR 84 regulations, were utilized as the challenge aerosol. The targeted particle sizes ranged from 10 to 600 nm, although the standard certification tests are performed with particles of approximately 300 nm, which is assumed to be the most penetrating size. The results indicate that the nanoparticle penetration through a face-sealed N95 respirator may be in excess of the 5% threshold, particularly at high respiratory flow rates. Thus, N95 respirators may not always provide the expected respiratory protection for workers. The highest penetration values representing the poorest respirator protection conditions were observed in the particle diameter range of approximately 30-70 nm. Based on the theoretical simulation, we have concluded that for respirators utilizing mechanical filters, the peak penetration indeed occurs at the particle diameter of approximately 300 nm; however, for pre-charged fiber filters, which are commonly used for N95 respirators, the peak shifts toward nano-sizes. This study has confirmed that the neutralization of particles is a crucial element in evaluating the efficiency of a respirator. The variability of the respirator's performance was determined for both models and both flow rates. The analysis revealed that the coefficient of variation of the penetration ranged from 0.10 to 0.54 for particles of 20-100 nm in diameter. The fraction of N95 respirators for which the performance test at 85 l min(-1) demonstrated excessive (>5%) penetration of nanoparticles was as high as 9/10. The test results obtained in a relatively small (0.096 m(3)) test chamber and in a large (24.3 m(3)) walk-in chamber were found essentially the same, thus, suggesting that laboratory-based evaluations have a good potential to adequately represent the respirator field performance.

Interactions between and can induce apoptosis and cell cycle arrest in mouse RAW264.7 macrophages

Exposure to complex mixtures of bacteria and fungi in moisture-damaged buildings is a potential cause of inflammatory related symptoms among occupants. The present study assessed interactions between two characteristic moldy house microbes Streptomyces californicus and Stachybotrys chartarum. Differences in cytotoxic and inflammatory responses in mouse (RAW264.7) macrophages were studied after exposure to the spores of co-cultivated microbes, the mixture of separately cultivated spores, and the spores of either of these microbes cultivated alone. The RAW264.7 cells were exposed to six doses (1 x 10(4) to 3 x 10(6) spores/ml) for 24 h, and the time course of the induced responses was evaluated after 4, 8, 16, and 24 h of exposure (1 x 10(6) spores/ml). The cytotoxic potential of the spores was characterized by the MTT test, DNA content analysis, and enzyme assay for caspase-3 activity. The production of cytokines (IL-1beta, IL-6, IL-10, TNFalpha, and MIP2) was measured immunochemically and nitric oxide by the Griess method. Co-cultivation increased the ability of the spores to cause apoptosis by more than 4-fold and the proportion of RAW264.7 cells at the G2/M stage increased nearly 2-fold when compared to the response induced by the mixture of spores. In contrast, co-cultivation decreased significantly the ability of the spores to trigger the production of NO and IL-6 in RAW264.7 cells. In conclusion, these data suggest that co-culture of S. californicus and S. chartarum can result in microbial interactions that significantly potentiate the ability of the spores to cause apoptosis and cell cycle arrest in mammalian cells.

Personal exposures to particles and microbes in relation to microenvironmental concentrations

The aim of this study was to compare the personal exposures of particles and microbes with the exposure being assessed by stationary samplers in the main microenvironments, i.e. home and the workplace. A random sample of 81 elementary school teachers in eastern Finland were selected to perform the two wintertime 24-h measurement periods. Particle mass concentration, black smoke (BS) concentration and concentrations of viable and total microorganisms on the sampled filters were determined using personal exposure sampling and microenvironmental measurements in homes and workplaces. In this paper, the correlations between different pollutants in each environment and correlations between personal exposures and home and work concentrations are presented. The results show that personal BS exposures correlated with both home and work BS concentrations. Furthermore, the concentrations of viable fungi and bacteria were related between personal and home concentrations. The time weighted microenvironmental model underestimated the personal exposures of particle mass, viable fungi, total fungi and total bacteria concentrations but the model might satisfactorily assess personal exposure to concentrations of BS and viable bacteria. The mass concentration of total fungi and bacteria was <1% of the total particle mass concentration.

PRACTICAL IMPLICATIONS

Stationary samples are only surrogate measures of personal exposures. Personal exposure measurements conducted on individuals' breathing zone are needed to assess the exposure to particles and microbes. The time weighted microenvironmental model is a useful method to assess personal exposure to combustion related particles and viable bacteria concentrations but the model underestimates personal exposures of particle mass, viable fungi, total fungi and total bacteria concentrations.

Viable fungi and bacteria in personal exposure samples in relation to microenvironments

Personal exposures to viable fungi and bacteria were compared with the concentrations being assessed by stationary samplers in home and workplace microenvironments. A random sample of 81 elementary school teachers in eastern Finland performed two 24-hour measurement periods in wintertime. Concentrations and prevalences of viable fungi and bacteria on the collection filters were determined by cultivation method. The geometric mean concentration was 3-12 cfu m(-3) for total viable fungi, 0.6-3.7 cfu m(-3) for Penicillium and mainly under 1 cfu m(-3) for other fungi. The samples with higher fungal concentrations also had higher diversity of fungi than samples with lower concentrations. The total number of fungal genera recovered was 39 for personal, 34 for home and 23 for work samples. The variation in concentration of Penicillium explained even 25-95% of the variations of total fungal concentration in personal exposure, home and workplace environments. There was an association between personal exposure and home concentration of viable fungi and between personal exposure and home and work concentrations of viable bacteria. Personal exposure and home concentrations of fungi were higher in rural areas than in urban areas. Our results also indicate that presence of a certain fungus in a microenvironment does not necessarily mean similar findings in personal exposure samples.

Inflammatory and cytotoxic potential of the airborne particle material assessed by nasal lavage and cell exposure methods

Exposure to bioaerosols in moisture-damaged indoor environments has been shown to be a potential health risk. The aim of the present study was to evaluate the inflammatory and cytotoxic potential of airborne particle material using both the nasal lavage (NAL) method and a cell exposure study. A 24-h sample collection for airborne particles was performed using personal sampling and microenvironmental measurements in homes and an 8-h sample collection in the working places of the studied subjects. At the end of the sampling period, the production of nitric oxide, tumor necrosis factor alpha, interleukin (IL)-1 beta, IL-4, and IL-6 was analyzed in the NAL samples of the subjects. The same mediators, excluding IL-4, were measured in the cell culture medium of mouse RAW264.7 macrophages, which were exposed to the pooled filter extracts representing personal, home, and workplace exposure of each individual during the 24 h before the NAL. Samplings were repeated after 2 wk. The subjects were divided into groups of "low exposure" and "high exposure" according to the concentrations of viable fungi, viable bacteria, or total microbial amount in the pooled extract. Cytokine levels in the NAL samples of subjects with high microbial exposure were slightly increased compared to the corresponding values of the subjects with low exposure. Filter samples collected from the subjects with high microbial exposure induced a significant increase in the production of cytokines in the RAW264.7 macrophages, as compared to those from the subjects with low exposure. The within-subject variation was low in all of the cytokine measurements, but the correlation between the studied methods was poor. In conclusion, both of the methods discriminate at the group level between subjects with high and low microbial exposure. Sampling of airborne particle material and exposure of the mammalian cells to the obtained samples seems to be highly applicable in the environmental monitoring, whereas examination of the exposed subjects directly, for example by using the NAL method, is essential when association between exposure and health effects is evaluated.

Mould specific IgG antibodies connected with sinusitis in teachers of mould damaged school: a two-year follow-up study

OBJECTIVES

The aim of this study was to describe the relationship between mould exposure induced by moisture damage and mould specific immunoglobulin G antibodies to 20 common mould species and their association with respiratory diseases.

MATERIALS AND METHODS

Mould specific immunoglobulin G (IgG) antibodies were monitored in teachers in a follow-up after an extensive mould remediation process in school buildings. IgG antibodies to 20 different microbes were determined from the sera of 26 teachers (19 exposed and 7 references) by enzyme-linked immunosorbent assay (ELISA). The serum samples were drawn twice, firstly at the completion of the remediation in the spring of 1997 and secondly, two years later in the spring of 1999. Health data was collected with self-administered questionnaires.

RESULTS

No statistical differences were found in the overall concentrations of 20 mould-specific IgG-antibodies between the study and control groups at the beginning of the study. An association between sinusitis and elevated mould-specific IgG-levels forAspergillus fumigatus, Aspergillus versicolor, Aureobasidium pullulans, Chaetomium globosum, Cladosporium cladosporioides, Phialophora bubakii, Rhodotorula glutinis, Sporobolomyces salmonicolor, Stachybotrys atra, and Tritirachium roseum was found in the study group.

CONCLUSIONS

In a two-year follow-up the total concentration of the IgG antibodies for Tr. toseum was lower at the end than at the beginning of the follow-up and this remained significant for the group of teachers with sinusitis. The decrease in mould specific IgG to Cl. cladosporioides, Geotrichum candidum, Ph. bubakii and Rhizopus nigricans was associated with bronchitis. According to our knowledge, this is the first study in which the association between elevated mould specific IgG antibodies and sinusitis was found in the school environment.

Effect of building frame and moisture damage on microbiological indoor air quality in school buildings

The effect of building frame and moisture damage on microbial indoor air quality was characterized in 17 wooden and 15 concrete or brick school buildings. Technical investigations to detect visible moisture and mold damage were performed according to a standardized protocol. Viable airborne microbes were determined by using a six-stage impactor (Andersen 10-800). Mean concentrations of viable airborne fungi were significantly higher in wooden schools than in concrete schools, showing that the frame material was a determinant of concentrations of airborne fungi. Moisture damage of the building did not alter the fungal concentrations in wooden school buildings. In contrast, in concrete schools the effect of moisture damage was clearly seen as higher concentrations compared with the reference schools. Aspergillus versicolor, Stachybotrys, and Acremonium were detected only in samples from moisture damaged buildings, and can be considered marker fungi of such damage in school buildings. In addition, the presence of Oidiodendron as well as elevated concentrations of Cladosporium and actinobacteria were associated with moisture damage in concrete schools.

Isolation and identification of Aspergillus fumigatus mycotoxins on growth medium and some building materials

Genotoxic and cytotoxic compounds were isolated and purified from the culture medium of an indoor air mold, Aspergillus fumigatus. One of these compounds was identified as gliotoxin, a known fungal secondary metabolite. Growth of A. fumigatus and gliotoxin production on some building materials were also studied. Strong growth of the mold and the presence of gliotoxin were detected on spruce wood, gypsum board, and chipboard under saturation conditions.

Personal exposures and microenvironmental concentrations of particles and bioaerosols

The aim of this study was to compare the personal exposure to particles and bioaerosols with that measured by stationary samplers in the main microenvironments, i.e., the home and the workplace. A random sample of 81 elementary school teachers was selected from the 823 teachers working for two councils in eastern Finland for the winter time measurement period. Bioaerosol and other particles were collected on filters by button samplers using personal sampling and microenvironmental measurements in homes and workplaces. The 24-hour sampling period was repeated twice for each teacher. Particle mass, absorption coefficient of the filter and the concentration of viable and total microorganisms were analyzed from each filter. In this paper, the study design, quality assurance principles and results of particle and bioaerosol exposure are described. The results show that particle mass concentrations, absorption coefficient and fungi were higher in personal exposure samples than in home and workplace samples. Furthermore, these concentrations were usually lower in the home than in the workplace. Bacterial concentrations were highest in heavily populated workplaces, while the viable fungi concentrations were lowest in workplaces. The fungi and bacteria results showed high variation, which emphasises the importance of quality assurance (duplicates and field blanks) in the microbial field measurements. Our results indicate that personal exposure measurements of bioaerosols in indoor environments are feasible and supplement the information obtained by stationary samplers.

Differences in inflammatory responses and cytotoxicity in RAW264.7 macrophages induced by Streptomyces Anulatus grown on different building materials

Streptomyces anulatus, an indicator microbe of mold in buildings, was grown on different building materials in order to study the impact of growth conditions on the ability of the spores of this microbe to induce toxicity and inflammatory responses. The microbes were grown for 2 months on sterilized and unsterilized wood, chipboard, concrete, plaster board and mineral wool in tight glass vessels under humid conditions. The highest microbial spore concentration was detected on the sterilized mineral wool followed by the sterilized plaster board and the unsterilized mineral wool. Mouse RAW264.7 macrophages were exposed in vitro for 24 h to the spores of S. anulatus and the production of the inflammatory mediators, nitric oxide (NO), tumor necrosis factor alpha (TNF alpha), interleukin-6 (IL-6), interleukin-10 (IL-10) and cytotoxicity, were measured. The dose equivalent to 5 x 10(5) spores/ml of medium was used to compare the different materials. The most intense production of NO (11.6 microM), TNF alpha (560 pg/ml) and IL-6 (2800 pg/ml) in macrophages was induced by the spores grown on sterilized plaster board. They also caused the greatest loss of cell viability (39%). The spores grown on sterilized concrete induced significant production of NO (1.5 microM) and decreased cell viability (22%), and the spores grown on unsterilized and sterilized mineral wool increased production of NO (4.1 microM and 0.8 microM, respectively). The spores did not stimulate production of the anti-inflammatory cytokine IL-10. These results indicate that the ability of S. anulatus to induce inflammatory responses and cytotoxicity in macrophages is dependent on the growth conditions provided by different building materials.

Induction of cytotoxicity and production of inflammatory mediators in raw264.7 macrophages by spores grown on six different plasterboards

Dampness and microbial growth in buildings are associated with respiratory symptoms in the occupants, but details of the phenomenon are not sufficiently understood. The current study examined the effects of growth conditions provided by six plasterboards on cytotoxicity and inflammatory potential of the spores of Streptomyces californicus, Penicillium spinulosum, Aspergillus versicolor, and Stachybotrys chartarum. The microbes were isolated from mold problem buildings and thereafter grown on six different plasterboards. The spores were harvested, applied to RAW264.7 macrophages (10(4), 10(5), 10(6) spores/10(6) cells), and evaluated 24 h after exposure for the ability to cause cytotoxicity and to stimulate production of nitric oxide (NO), interleukin-1 beta (IL-1beta), tumor necrosis factor alpha (TNFalpha) and interleukin-6 (IL-6). The data indicate clear differences between spores of different microbes in their ability to induce the production of these inflammatory mediators and to cause cell death in macrophages. Also, for each microbe, the induction ability specifically depended on the brand of plasterboard. The spores of Streptomyces californicus collected from all plasterboards were the most potent at inducing NO and cytokine production. Cytotoxicity caused by P. spinulosum and Streptomyces californicus spores was consistent with NO, IL-1beta and IL-6 production induced by those microbes. However, the production of these inflammatory mediators by the spores of Stachybotrys chartarum was not parallel to their ability to cause cell death. The low productions of NO and cytokines were associated with high cytotoxicity caused by the spores of the A. versicolor. These data suggest that growth condition of microbes on different plasterboards affect the ability of microbial spores to induce inflammatory responses and cytotoxicity in macrophages.

An approach to management of critical indoor air problems in school buildings

This study was conducted in a school center that had been the focus of intense public concern over 2 years because of suspected mold and health problems. Because several attempts to find solutions to the problem within the community were not satisfactory, outside specialists were needed for support in solving the problem. The study group consisted of experts in civil engineering, indoor mycology, and epidemiology. The studies were conducted in close cooperation with the city administration. Structures at risk were opened, moisture and temperature were measured, and the causes of damage were analyzed. Microbial samples were taken from the air, surfaces, and materials. Health questionnaires were sent to the schoolchildren and personnel. Information on the measurements and their results was released regularly to school employees, students and their parents, and to the media. Repairs were designed on the basis of this information. Moisture damage was caused mainly by difficult moisture conditions at the building site, poor ventilation, and water leaks. Fungal genera (concentrations <200 colony-forming units (cfu)/m(3), <3000 cfu/cm(2)) typical to buildings with mold problems (e.g., Aspergillus versicolor, Eurotium) were collected from the indoor air and surfaces of the school buildings. Where moisture-prone structures were identified and visible signs of damage or elevated moisture content were recorded, the numbers of microbes also were high; thus microbial results from material samples supported the conclusions made in the structural studies. Several irritative and recurrent symptoms were common among the upper secondary and high school students. The prevalence of asthma was high (13%) among the upper secondary school students. During the last 4 years, the incidence of asthma was 3-fold that of the previous 4-year period.

Carpal tunnel syndrome. Anatomical and clinical investigation

The anatomy of the carpal tunnel was studied by postmortem dissection of both wrists in ten adults with normal wrists. Preoperative clinical and EMG examinations were performed on 28 wrists in 23 patients suffering from carpal tunnel syndrome. Anatomical and histological studies were made in connection with operation, and postoperatively the condition was followed clinically and by EMG. Numbness, tingling, and pain of the hands were markedly relieved during 2 months of follow-up, whereas clumsiness and weakness showed no significant change. preoperatively, EMG showed sensory abnormalities in 96% of cases and motoric abnormalities in 82%. The diagnostic accuracy of EMG was good, in particular as regards the sensory aspect. The return to normal of EMg was slow. Pathoanatomical examination showed a normal tendon sheath and transverse carpal ligament in 52%, while rheuma was found in the specimens of 12%, fibrosis of the tendon sheath in 36%, and fibrosis of the transverse carpal ligament in 32%. No correlation was observed between the shape of the osseous carpal tunnel and the degree of clinical symptoms.