In the 2008 study conducted by Charles Gerba, professor of microbiology at the University of Arizona, it was found that in almost two weeks, shoes accumulated nearly 420,000 bacteria outside, of which 96% was coliforms.
But the worst is yet to come: among the thousands of microorganisms on shoes, there are large amounts of Klebsiella pneumoniae and Serratia marcescens.
K. pneumoniae is one of the causes of infections of the urinary system, pneumonia and other soft tissue diseases and due to open wounds.
On the other hand, S. marcescens tends to generate conjunctivitis, keratitis and in some cases meningitis and endocarditis.
These two varieties of bacteria are those that attack the body when it does not have enough antibodies to defend itself. These are the ones that cause complications in hospitals (nosocomial diseases).
However, it should be noted that the likelihood of infection from footwear is minimal, unless it has direct contact with the mouth or an open wound.