In the past several years, there has been much discussion on the influence of indoor environments on the spread of diseases caused by viruses and bacteria. A third category of microorganisms, fungi, originated in the natural environment and has evolved over centuries to coexist with humans along a continuum from mutually beneficial cohabitation to invasive pathogenesis. Whether a particular type of fungus causes human disease is partly determined by environmental forces which guide genetic, reproductive, and biofilm adaptations that increase the fungi’s survival, transmission, and reproduction. Interestingly, adaptations which increase fungal survival in hostile ecological niches may also increase the ability to cause disease in human hosts.

A fungal organism now causing an exponential rise in life-threatening invasive diseases in healthcare facilities worldwide is Candida auris (C.auris), a member of the fairly harmlessly Candida family that is responsible for oral thrush. In 2009, C. auris, was identified in a patient’s infected ear (Latin – auris) canal but was not particularly newsworthy until this year when infections ramped up quickly in health care facilities. In a very short period, C. auris has emerged simultaneously on six different continents and caused outbreaks of infections with mortality rates as high as 60% in hospitals. In March of 2023, the CDC issued a warning that C. auris is an “urgent antimicrobial resistance threat.”

The outbreaks of C. auris and the devastating consequences in healthcare facilities demands understanding and management of indoor and outdoor conditions that contribute to worsening fungal disease.

How Is C. auris Different?

C. auris has gained the capabilities to live in environmental conditions that would kill closely related Candida organisms. Specifically, corpated to other fungi, C. auris can survive in higher temperatures and salt concentrations, possibly due to adaptation to higher global temperatures. Unfortunately, however, these thermotolerant characteristics give C. auris the ability to endure the high body temperatures of mammals and overcome the natural thermal barrier has protected humans from other pathogenic fungi.

The adaptions allowing C. auris to tolerate higher temperatures and osmotic pressure from salts not only enhance survival on the human body, they also allow C. auris to form protective biofilms. These biofilms act as tenacious substrates which bind anti-fungal medications and prevent the drug from reaching its target. In short, the proteins synthesized by C. auris leading to thermotolerance and multi-drug resistance may be key in the opportunistic leap from the natural environment to human hosts.

A few examples of other changes have contributed to the virulence and spread of C. auris are:

More people are vulnerable to fungal infections because they have some degree of compromised immunity due to auto-immune diseases, co-morbidities associated with aging, and diseases such as HIV

Viruses co-mingle with fungi, so a new virus could have increased the virility of C. auris

Dry indoor and outdoor climates induce spore formation and increased airborne transmission

In summary, the adaptations of C. auris to environmental stresses have resulted in a microbe that is more threatening to humans than most fungi. Increased resistance to anti-fungal medications, formation of tenacious and protective surface biofilms and increased airborne transmission of spores are some of the worrisome changes. Experts in mycology (fungi) have hypothesized that C. auris may be the first human pathogenic fungus to emerge as a result of climate change. It is critical that we learn how to manage our buildings to mitigate the spread of fungal diseases, because global warming is not going away soon.

What Can We Do?

Limit carbon emissions that contribute to atmospheric warming.

When treating people with infections, carefully identify the infectious agent so that treatment is effective. Do not foster increased virulence with inappropriate dosing or incorrect use of anti-fungal medications.

Clean biofilms effectively and thoroughly.

Don’t be naïve — airborne transmission of spores is well documented. C. auris reproduces through forming and disseminating tiny, light-weight spores which can be easily dispersed through the air. Be safe and take appropriate airborne precautions in hospitals.

Manage IAQ to support occupant health.

To minimize the risk of disease from airborne fungal spores, maintain humidity in a midrange zone of 40 to 60%. Promptly address any water leaks or areas with condensation and ensure proper ventilation.