Indoor Endotoxin Levels Are Associated with Pet Ownership, Regardless of Surrounding Greenspace

The study was performed in homes in Munich, Germany

Photo: Douglas Sprott

 Indoor levels of bacterial endotoxins are strongly associated with cat and dog ownership, and these associations are not modified by the amount of greenspace around the home. These are the results of a study performed by ISGlobal, an institution supported by the “la Caixa” Foundation, in collaboration with the Helmholtz Zentrum München – German Research Center for Environmental Health, and published in Science of the Total Environment.

Endotoxins are molecules associated with the cell membranes of certain bacteria. They are ubiquitous in indoor environments and early exposure to them may play a role in the development of respiratory and allergic disorders. Pet ownership has been shown to be one factor that is consistently associated with higher indoor endotoxin concentrations. However, this association could simply reflect the amount of greenspace around the home: pets may act as vectors of the outdoor microbial environment, or simply be a proxy of living in greener suburban or rural areas.

This study examined whether the association between pet ownership and higher indoor endotoxin concentrations is modified by residential greenspace, using data from participants of the German LISA birth cohort living in Munich. Endotoxin levels were measured in house dust sampled from mothers’ mattresses and living room floors. Greenspace was defined by two indicators: vegetation level (determined by high resolution satellite images and expressed as a vegetation index) and proximity of green spaces around a home (shortest distance to the nearest green space). The association between endotoxin levels and pet ownership was assessed using mathematical models.  Results show that dog and cat ownership were associated with higher endotoxin levels in the home (both were associated with higher endotoxin levels in mothers’ mattresses, while only dog ownership was associated with higher endotoxin levels on the floor).  These associations were highly robust, and were not modified after considering greenspace levels in the mathematical models.

“These results confirm previous reports that have identified dogs and cats as important predictors of indoor endotoxin levels. We also show that this association occurs only for outdoor pets and is independent of the amount of residential greenspace” explains first author and ISGlobal researcher Elaine Fuertes.  

The authors conclude that further studies are now needed to better understand how outdoor pets influence indoor endotoxin levels, as greenspaces around the home doesn’t seem to be the key.  


Fuertes E, Standl M, Markevych I, Bischof W, Heinrich J. Is the association between pet ownership and indoor endotoxin levels confounded or modified by outdoor residential greenspace? Sci Total Environ. 2018 Jan 3;625:716-721. doi: 10.1016/j.scitotenv.2017.12.333.