Exposure to a farm-like house dust microbiome may be associated with reduced asthma development in children living in urban environments, reports a study published online this week in Nature Medicine.

The development of asthma has been linked with urbanization, which may involve the loss of critical house dust microbial species that are still present on farms. However, it has been unclear whether farm bacteria are also associated with reduced asthma prevalence when they are present in urban environments.

Pirkka Kirjavainen and colleagues studied indoor dust microbiota from the rural and suburban homes of 395 Finnish children and identified a distinct microbial abundance pattern associated with farm homes. They then replicated these findings in a cohort of 1,031 German children, showing a reduced risk of asthma in children living in non-farm homes with an indoor microbiota similar to that of Finnish farm homes.

Although this observational study could not conclusively establish that individual microbial species were directly responsible for protection against asthma, it provides further support for the role of environment-derived bacteria in asthma development. The authors suggest that measuring the composition of household microbiota may be useful for assessing and monitoring the relative risk of children developing asthma in suburban and urban homes.