Study Title:

Infant Antibiotic Use Increases Asthma Risk

Study Abstract

Many studies have reported that antibiotic use may be associated with increased risk of childhood asthma. Respiratory tract infections in small children may be difficult to distinguish from early symptoms of asthma, and studies may have been confounded by “protopathic” bias, where antibiotics are used to treat early symptoms of asthma. These analyses of a cohort including 1,401 US children assess the association between antibiotic use within the first 6 months of life and asthma and allergy at 6 years of age between 2003 and 2007. Antibiotic exposure was associated with increased risk of asthma (adjusted odds ratio = 1.52, 95% confidence interval (CI): 1.07, 2.16). The odds ratio if asthma was first diagnosed after 3 years of age was 1.66 (95% CI: 0.99, 2.79) and, in children with no history of lower respiratory infection in the first year of life, the odds ratio was 1.66 (95% CI: 1.12, 3.46). The adverse effect of antibiotics was particularly strong in children with no family history of asthma (odds ratio = 1.89, 95% CI: 1.00, 3.58) (Pinteraction = 0.03). The odds ratio for a positive allergy blood or skin test was 1.59 (95% CI: 1.10, 2.28). The results show that early antibiotic use was associated with asthma and allergy at 6 years of age, and that protopathic bias was unlikely to account for the main findings.

From press release:

When babies are given antibiotics, their risk of developing asthma by age 6 may increase by 50 percent. This relationship between antibiotic use in babies less than six months old and risk of developing asthma was documented in a study conducted by Norwegian University of Science and Technology (NTNU) researcher Kari Risnes.

The research was conducted while Risnes was a visiting researcher at Yale University, and resulted in the recent online publication of the article in the American Journal of Epidemiology.

"Asthma is a very common disease. At the same time, about one-third of infants in our study were treated with antibiotics by the time they were six months old. This proportion is about 30 per cent in other Western countries," says Risnes.

The Yale study followed 1400 children and mothers from the beginning of pregnancy until the children were six years old.

"We found that the risk that children would have asthma as six year olds was 50 per cent higher when they had been given antibiotics as a baby. That is a significant increase," Risnes says.

While previous research has suggested an association between asthma and antibiotics, those studies may have been biased because antibiotics are used to treat respiratory tract infections that could themselves be early symptoms of asthma.

The study sought to eliminate this bias by excluding children who were treated for respiratory infections from the study. The study also considered a long list of other risk factors -- such as whether or not the mother, father or a sibling had asthma. That aspect also brought a surprise, Risnes said.

"We actually found that the relationship between antibiotic use in the first six months of life and asthma was particularly strong in children from families without a history of asthma," said Risnes.

"What we think is that antibiotics interfere with the beneficial bacteria found in the gut. These bacteria aid in helping the baby's immune system to mature. When the bacteria are affected, it can cause the child to have an "immature" immune system, which in turn leads to allergic reactions," says Risnes.

She believes that the results should remind doctors and policymakers of the consequences of overuse of antibiotics. While in Norway, for example, the policy is to limit the prescription of antibiotics "this is an additional reminder to doctors and parents that we should avoid unnecessary use whenever possible," she said.

Study Information

K. R. Risnes, K. Belanger, W. Murk, M. B. Bracken.
Antibiotic Exposure by 6 Months and Asthma and Allergy at 6 Years: Findings in a Cohort of 1,401 US Children.
American Journal of Epidemiology,
2010 December
Center for Perinatal, Pediatric, and Environmental Epidemiology, Yale University School of Public Health, 1 Church Street, Sixth Floor, New Haven, CT.

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