Researchers from the latest study have dismissed the link previous studies have made between antibiotic use and childhood asthma, after accounting for shared risk factors within families, including genetics, environment and lifestyle.
The researchers, from the Karolinska Institutet in Sweden, publish their findings in the BMJ.
For one, they say, it may be difficult to diagnose asthma in small children; new asthma symptoms can often be misinterpreted as a respiratory infection. As such, many children may have received antibiotics for the "infection," which is actually asthma, and the antibiotics are then suspected to have caused the asthma when later discovered.
Furthermore, they note that respiratory infections could themselves increase asthma risks, whether or not they are treated with antibiotics.
But even more importantly, the researchers say that previous studies have not sufficiently examined shared risk factors within families that could increase asthma risks, including genetics, home environment and lifestyle.
As such, the team studied almost half a million children born in Sweden between January 2006 and December 2010. They add that theirs is the first study to use sibling control analyses to examine the link between antibiotics and asthma.
Link vanished after comparing children from same family
The researchers first studied the children who had been exposed to antibiotics in utero, when their mothers took antibiotics during pregnancy. From this initial analysis, the researchers found that the risk of asthma in the child increased by 28%.
However, when the team included risk factors such as genetics, home environment or lifestyle - carried out by conducting comparative analyses within families with multiple children - they found that the link between antibiotics during pregnancy and asthma vanished.
The researchers say there were a large number of families where one sibling had asthma and another did not develop asthma, despite exposure to antibiotics in early life. The number of these families was large enough that the researchers were able to rule out a link between antibiotic use during pregnancy and asthma in offspring.
Commenting on their findings, Anne Oertqvist, physician and doctoral student at Karolinska Institutet, says:
"Thanks to the Swedish population-based registers, we have been able to conduct a study designed to include factors that were previously not included. Our results show that there does not appear to be a causal link between early exposure to antibiotics and asthma, which is also valuable from an international perspective."
'Still important to use antibiotics very carefully'
Another part of their study examined children who received antibiotics in early life, comparing whether risk of developing asthma post-antibiotic treatment was as high if the child had been treated for infections of the skin, urinary tract or respiratory system.
Again, the team found the risk was significantly higher after a child was treated for a respiratory infection, indicating the link was down to asthma being mistaken for a respiratory infection and treated with antibiotics.
When they analyzed siblings by skin, urinary tract and respiratory infections, the researchers observed that the link between antibiotic use and asthma again vanished.
Though she notes their results show "there is no causal link between antibiotics treatment and childhood asthma," Prof. Catarine Almqvist Malmros, of Karolinska Institutet, says "it is still important to use antibiotics very carefully, considering the threat of antibiotic resistance." She adds:
"We also want to emphasize the importance of correctly diagnosing children with airway symptoms, where suspected symptoms of asthma should be separated from respiratory infection."
Despite the strengths of the large dataset and population-based design, there are some limitations to the study. For starters, the researchers were not able to take into account adherence to treatment or delayed prescribing.
Additionally, they were not able to control for antibiotics prescribed abroad, and they note that despite their large study population, "the number of families discordant for both urinary tract/skin antibiotics in childhood and asthma were fewer than in the analyses of fetal exposure, yielding broader confidence intervals."
They conclude their study by writing, "it is of great importance to acknowledge that though antibiotics might not cause asthma, careful consideration is required as to whether respiratory symptoms should be treated with them."
Medical News Today recently reported on findings that suggested antibiotic use in children is linked to juvenile idiopathic arthritis.