Soles bring in what you step on outside.

Faeces and urine: residue may be difficult to see

A sole may contact traces of faeces and urine mixed with soil, water and material along the route. Attached residue can be picked up while walking and reach the entrance with the shoe. Looking at a sole can reveal visible dirt, but it does not measure contamination.

The origin of the material matters. The CDC documents, for example, that urine from infected animals can contaminate water and soil with the bacteria that cause leptospirosis. This describes possible environmental contamination; it does not establish that an ordinary return home in shoes causes that disease.

CDC — Leptospirosis in animals, 2026

Bacteria and spores: what has been found on soles

A 2016 systematic review brought together 13 studies on infectious agents found on shoe soles. Documented organisms included methicillin-resistant Staphylococcus aureus, C. difficile and multidrug-resistant Gram-negative bacteria. Studies covered different healthcare, community and occupational settings: they do not describe every shoe in the same way.

Detection is a concrete finding about contamination. Transfer, the amount of material and possible risk for people living in the home are further questions. A sound assessment therefore specifies the sample, setting and what was actually measured.

Rashid et al., 2016

Viruses: RNA detected on shoe soles in hospital

In 2020, Guo and colleagues sampled air and surfaces in COVID-19 wards in Wuhan. They detected SARS-CoV-2 genetic material on the shoe soles of intensive-care staff. The result shows that viral material can be present on footwear in that setting.

The study used PCR: the authors state that the test did not indicate the amount of viable virus. RNA detection documents genetic material, without establishing infectious virus or quantifying household risk through shoes.

Guo et al., 2020

Pesticides: from treated lawns to household surfaces

Nishioka and colleagues studied 11 occupied and two unoccupied homes before and after the herbicide 2,4-D was applied to lawns. The compound was detected in indoor air and on indoor surfaces. Transport by an active dog and the person who applied the product was among the most significant factors.

The US EPA also identifies contaminated soil and dust tracked in from outdoors as possible sources of indoor pesticides. Findings concern defined substances, exposures and conditions: the route travelled and any treatment of the area help explain what residue may reach the threshold.

Nishioka et al., 2001 · US EPA — Indoor pesticides

From residue to the floor: why the entrance matters

Soles and floors touch as people pass through. Acting at the threshold means addressing material carried from outside at the transition into domestic spaces. Shoe removal, entrance systems and floor cleaning remain strategies to assess around the home and the people who use it.

HOME KLINX is in development to integrate footwear treatment into the return-home routine. Tests will need to measure attached-material removal, microbiological performance and safety of use, alongside compatibility with different shoes and habits.