Using antibiotics in the first year of life may significantly increase a child's risk of contracting asthma by age 7, according to a study conducted by researchers at University of Manitoba and McGill University in Montreal and published in "CHEST," the journal of the American College of Chest Physicians.

The researchers examined a prescription database that included information on 13,116 children and compared incidence of asthma with a variety of risk factors, including antibiotic use, gender, maternal asthma history, living location, neighborhood income, the presence of pets in the home and the number of siblings at the age of seven.

The study concluded that those who had received antibiotics for the treatment of a non-respiratory tract infection in their first year were twice as likely to suffer from asthma at the age of seven than those who had not. The higher the number of treatments, the higher the child's risk of asthma.

Eighty-seven percent of children who had received antibiotics were treated for respiratory tract infections. Because respiratory tract infections early in life may be a sign of developing asthma, however, the researchers excluded these cases from the sample in order to be sure the effect they were observing was related only to the antibiotics.

The researchers also found that maternal history of asthma significantly increased a child's risk of the disease. The presence of the dog in the house during the first year of life, however, led to a reduced risk of contracting asthma. Among children who received multiple treatments with antibiotics, those with the dog in the house suffered half the asthma risk of those without.

"Dogs bring germs into the home, and it is thought that this exposure is required for the infant's immune system to develop normally. Other research has shown that the presence of a dog in early life protects against the development of asthma," said lead researcher Anita Kozyrskyj.