Nasal mucosal reactivity after long-time exposure to building dampness

Abstract

An association between working and/or residing in damp buildings and respiratory health has been reported in a number of studies. A major limitation has been difficulty in objectively verifying any effects on the mucous membranes of the respiratory tract in order to explain symptoms of irritated eyes, nasal congestion and cough that are often reported by occupants in buildings with indoor air problems. The main aim was to objectively study changes in the nasal mucosal reactivity after longtime exposure to a deteriorated indoor climate.

Twenty-eight teachers who had worked for at least five years in a recently renovated school, which for years had had severe moisture problems, were randomly selected to participate in this study. Eighteen teachers randomly selected from another school, with no known moisture problems, formed the control group (in 1995). Although remedial measures had been taken, an increased prevalence of mucous membrane irritations was still reported by the teachers from the target school. A nasal challenge test with three concentrations of histamine (1, 2 and 4 mg/ml) was used. Recordings of the swelling of the nasal mucosa were made using rhinostereometry. The analysis of the mucosal swelling induced by the three concentrations of histamine showed a significant difference in the growth curves of the two groups, indicating that long-time exposure to indoor environments with moisture problems may contribute to mucosal hyperreactivity of the upper airways.

A study comparing students who began their high-school studies at both schools in 1995 and the teachers was performed regarding mucosal reactivity, frequency of atopy and symptoms. A nasal histamine provocation test and a skin-prick test were administered to 45 students from each school. They also answered a standardized questionnaire. The teachers had significantly greater mucosal histamine reactivity than the students, compatible with an age-related pattern of mucosal reactivity. The students had significantly higher frequency of allergic sensitization.

In 1997 the nasal histamine provocation test was repeated among the teachers. This showed that the teachers from the repaired water-damaged school still demonstrated an increased reactivity to histamine compared to those in the control school, but the differences between the growth curves of the provocation tests were less than in 1995. No major differences were observed in the technical investigation between the two schools and the measurements were all within the range of values usually seen in schools in northern countries.

In a longitudinal study the students were followed during their high school studies. They underwent a nasal histamine provocation test and answered a questionnaire on three occasions, in 1995, 1996 and 1997. No significant differences in the nasal histamine provocation curves between the students at the target school and those at the control school could be shown from the start to the end of the study period. Nor were there any differences concerning perceived indoor air or mucosal symptoms between the target group and the control group. Based on both technical and objective medical measures, this study indicated that the indoor air in the remediated moisture-damaged school did not exert an irritant effect on the upper airway mucosa of the students.

In 2000, six years after remedial measures had been taken, the teachers underwent a nasal histamine provocation test. In addition to using mucosal swelling as a measure of mucosal reactivity, we also examined the mucosal microcircular reaction to histamine provocation with Laser-Doppler flowmetry (LDF). We found that the difference in nasal histamine reactivity between the two study groups, measured as mucosal swelling, was no longer significant. However, Laser-Doppler flowmetry showed a significant difference between the two teacher groups regarding microcircular perfusion and CMBC (concentration of moving bloodcells), indicating a more pronounced plasma leakage and oedema from the nasal mucosa upon histamine provocation among the target school teachers.

In conclusion, we found a restored nasal histamine reactivity, measured as the mucosal swelling reaction, among the teachers six years after long-time exposure to building dampness. LDF showed remaining changes in the microcircular pattern of the target school teachers. Consequently, longtime exposure to building dampness may increase the risk for hyperreactivity of the upper air-ways. This aquired hyperreactivity may last for years and decrease only slowly, even after the indoor climate has been properly improved. A possible explanation for this slowly decreasing reactivity might be a slow but ongoing restoring process in the mucosa of the upper airways.

It is of importance to determine if residing in bad indoor environment implies a risk of future health problems. Following a group of people exposed to building dampness with objective mucosal tests over several years provides knowledge about how long and in what way the increased mucosal reactivity persists. It is equally important to identify both particular risk environments and predisposed people.