Asthma rates in children and adolescents tripled in some groups over a 20-year period, says a study that adds to evidence of a puzzling growth of the disease across the country.
The trend toward making homes more energy-efficient by reducing air leakage may have played a role by trapping inside more airborne particles like cat dander, researchers speculated.
But there is no evidence yet for any explanation about why the rates rose from 1964 to 1983 in Rochester, Minn., a co-author of the study, Dr. Marc Silverstein, said Thursday.
The annual rate of new asthma cases roughly tripled in boys and girls ages 10 to 14 and in girls ages 5 to 9. The rate doubled or nearly so in boys and girls ages 1 to 4 and boys ages 5 to 9. No increases appeared in other age groups.
The report follows studies elsewhere that indicated asthma became more common in children during the 1970s and 1980s, hospitalized more young children during the 1980s and caused more deaths.
The federal Centers for Disease Control reported last week that the national rate of asthma deaths rose 46 percent during the 1980s.
Scientists say they cannot yet explain the trends. Proposed explanations include more energy-efficient homes, greater survival of low birth-weight infants who may be prone to asthma, more cigarette smoking by mothers and greater use of day care, which could expose more infants to viral infections.
The work is presented in October's American Review of Respiratory Disease by Silverstein, Dr. John Yunginger and others at the Mayo Clinic and Foundation.
The study is important because it adds to evidence of a genuine increase in asthma, rather than just greater recognition of the disease, said Dr. Kevin Weiss of George Washington University.