Sunday, February 19, 2006

More on Ventilation and Childhood Asthma

Indoor Air
Volume 15 Page 275 - August 2005
Volume 15 Issue 4

Association between ventilation rates in 390 Swedish homes and allergic symptoms in children
C. G. Bornehag1,2,3, J. Sundell2, L. Hägerhed-Engman1, T. Sigsgaard4

Abstract The aim of the study was to test the hypothesis that a low-ventilation rate in homes is associated with an increased prevalence of asthma and allergic symptoms among children. A total of 198 cases (with at least two of three symptoms: wheezing, rhinitis, eczema) and 202 healthy controls, living in 390 homes, were examined by physicians. Ventilation rates were measured by a passive tracer gas method, and inspections were carried out in the homes. About 60% of the multi-family houses and about 80% of the single-family houses did not fulfill the minimum requirement regarding ventilation rate in the Swedish building code (0.5 air changes per hour, ach). Cases had significantly lower ventilation rates than controls and a dose–response relationship was indicated.

Practical Implications

A low-ventilation rate of homes may be a risk factor for allergies among children. Families with allergic children should be given the advice to have good ventilation in the home. In investigations, of associations between environmental factors and allergies, the air change rate in homes has to be considered.


BrooklynDodger(s) comment: The Dodger(s) again take advantage of new technique for grabbing a table from a pdf.

The public health finding is straightforward, so the Dodger(s) will muse on other things. Actually measuring air movement and presenting the range and central tendency is a great public health value. Boy would it be nice to get this data for the US.

First, it's unfortunate the investigators tabulate the mean rather than the median. The Dodger(s) would be quite surprised if ventilation rates were distributed symmetrically about the mean, so the median would be a better statement of the central tendency.

Second, natural ventilation and the oldest construction - the Dodger(s) assumes windows and doors, provides more air changes than "mechanical exhaust." It's a little unclear what this middle period ventilation and construction was. Even with active exhaust, ventilation is poor.

The ASHRAE book says a room with no windows and no door [we assume] to the outside enjoys 0.5 ACH. ASHRAE air changes include "appropriately cleaned" recirculated air. So natural ventilation may be superior to an office with ASHRAE design criteria of 1 ACH. The Dodger(s) assumes 1 ACH implies a half life of a contaminant of 1 H, not that it's all gone in an hour.

Third, we come back to the conundrum that living an a farm early in life - exposed to all kinds of biologicals - protects against asthma, while living in a damp and moldy apartment, which likely has less of all kinds of biologicals than the farm, and maybe even less than the apartment specific biologicals, agonizes asthma.

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