Ventilation rate in 400 homes and its impact on asthma and allergy among children in Sweden, a case of control study

Background. A low ventilation rate has been shown to increase the risk for health and comfort problems in offices. However, very few studies have investigated the impact of ventilation rate at home on health effects, (Wargocki et al. 2002). The aim of this study was to investigate if low ventilation rates in homes do increase the risk for asthma and other allergic symptoms among pre-school children in Sweden.
Method. The first step of the study Dampness in Buildings and Health started in March 2000 with a questionnaire investigation including all children (1-6y) in Vrmland, Sweden (n=14 077). The questionnaire included 84 questions concerning family background, symptoms among children and parents, home characteristics including dampness indications and food habits. Parents to 10 851 children responded to the questionnaire, corresponding to a response rate of 79 %. In a second step 400 children were selected for a case-control study. The children were selected from the questionnaire data in the first step. Cases (n=198) were children with at least two symptoms of three possible (i.e. wheezing, rhinitis and eczema). Controls (n=202) were children without any symptoms. The 400 homes of the children were investigated by professional inspectors and measurements were made of ventilation rate, temperature and relative humidity (RH). Ventilation was measured with passive tracer gas technique during one week, during wintertime, from October 2001 to April 2002.
Results. The 400 children lived in 352 single family houses (SH), (88 %), 45 multi family houses (MH), (11 %), and 3 children lived in another type of buildings. Valid samples for ventilation rate were collected for 396 children (198 cases and 198 controls). Mean values for ventilation rate were 0.37 ach with significant differences (p<0.001) between SH and MH, (SH:0.36 and MH:0.48 ach respectively). Cases had lower ventilation rate than controls, (0.36 and 0.39 ACRH respectively), However, the difference was not significant (p=0.13). When only children living in SH were included in the analysis (n=349) there was a significant (p<0.05) lower ventilation rate among cases compared with controls (0.34 and 0.39 ach respectively). Furthermore, data on ventilation rate in single family houses were divided into quartiles: (0-25%) 0.17 ach (0.05-0.24 ach min-max) (n=87); (25-50%) 0.29 ach (0.24-0.33) (n=88); (50-75%) 0.38 ach (0.33-0.44) (n=87) and (75-100%) 0.62 ach (0.44-1.43) (n=87). Logistic regression was used for estimation of the risk for being a case. The analysis indicated a dose response relationship when the highest quartile was used as reference: (0-25% quartile) OR 1.92 (1.05-3.50); (25-50% quartile) OR 1.49 (0.82-2.70); (50-75% quartile) OR 1.39 (0.76-2.53). Concerning multi family houses no difference in ventilation rate was found between cases and controls.
Conclusion. The study have showed that the ventilation rate in Swedish homes are below recommended values of 0.5 ach. Low ventilation increased the risk for health effects.