Cleanliness in context: reconciling hygiene with a modern microbial perspective

Abstract

The concept of hygiene is rooted in the relationship between cleanliness and the maintenance of good health. Since the widespread acceptance of the germ theory of disease, hygiene has become increasingly conflated with sterilization. In reviewing studies across the hygiene literature (most often hand hygiene), we found that nearly all studies of hand hygiene utilize bulk reduction in bacterial load as a proxy for reduced transmission of pathogenic organisms. This treatment of hygiene may be insufficient in light of recent microbial ecology research, which has demonstrated that humans have intimate and evolutionarily significant relationships with a diverse assemblage of microorganisms (our microbiota). The human skin is home to a diverse and specific community of microorganisms, which include members that exist across the ecological spectrum from pathogen through commensal to mutualist. Most evidence suggests that the skin microbiota is likely of direct benefit to the host and only rarely exhibits pathogenicity. This complex ecological context suggests that the conception of hygiene as a unilateral reduction or removal of microbes has outlived its usefulness. As such, we suggest the explicit definition of hygiene as "those actions and practices that reduce the spread or transmission of pathogenic microorganisms, and thus reduce the incidence of disease."

Building upon current knowledge and techniques of indoor microbiology to construct the next era of theory into microorganisms, health, and the built environment

“…Overall, our understanding and our views of the relationships we have with microorganisms are evolving [20,31,202,245]. What remains is the ability to know why, when, and how microorganisms transfer from the built environment to occupants, when these interactions matter, under what circumstances these transfers lead to disease, and when these interactions are beneficial to built environment occupants [33].…”

“…Concurrent to this, urbanized populations saw a rise in allergies, asthma, and inflammation-related chronic diseases, many of which were or seemed to be linked to a lack of microbial exposure; a correlation which was described by the Hygiene Hypothesis [18,19]. In response, calls propose to redefine "hygiene" from practices that remove all microbiota to simply acting to prevent the spread of pathogenic microorganisms [20]. Yet, not all microorganisms interact with a host in the same way, and not all interactions lead to positive outcomes, and the Hygiene Hypothesis as originally defined did not encompass this nuance [21].…”

“…The change in ideology has permeated enough to be implemented into practice. The health sector has redefined its view of the roles that microorganisms play in human health, particularly in establishing an active, yet restrained, immune system and that of a stable and functional microbial community in preventing the overgrowth of certain taxa or activation of pathogenesis [17][18][19][20][21]. Health procedures have even begun to incorporate microorganisms into treatment or prevention regimens, in particular with fecal microbial transplant or probiotics to help stabilize the gut microbiota against disturbance or to recover a diverse community [23][24][25][26][27].…”

Transmission of the gut microbiota: spreading of health

“…The effects of antibacterial hygiene products and hand sanitizers on the intestinal microbiota are unclear and require further study150; however, efforts to use them more selectively may reduce the depletion of commensal bacteria. Hygiene practices currently act to decrease the total number of bacteria on a surface or individual, whereas a more targeted approach that specifically removes pathogenic microorganisms should be given greater consideration151. We anticipate that with more research we should be able to outline new approaches to safely preserve and nurture the transmission of commensal bacteria while maintaining protection from pathogens.…”

From one species to another: A review on the interaction between chemistry and microbiology in relation to cleaning in the built environment

“…1,158 How often do surfaces need to be cleaned to maintain them free of organic matter and organisms? This is true for studies that pertain to infection control on nonhuman surfaces.…”