Sewers could detect deadly fungal infections before hospitals do

The precedent comes from COVID-19, when levels of virus in sewage rose four to 14 days before confirmed case counts did. For fungi the evidence is thinner, and nearly all of it concerns C. auris, a yeast first identified in a patient's ear in Japan in 2009 and now spreading worldwide.

• In southern Nevada, researchers found C. auris in 79% of wastewater samples over 10 weeks, with detections more frequent in areas served by health care facilities.
• In Florida, 47% of hospital wastewater samples tested positive, compared with 16% at treatment plants farther downstream.
• In a U.K. hospital, the fungus appeared in the wastewater from one particular ward during an outbreak.

What can sewage not tell us?

These studies show only that the fungus can be detected. They do not show that sewage readings can predict an outbreak, and nobody yet knows how much of the fungus each person sheds, so a reading cannot be converted into a number of patients. The evidence also comes almost entirely from C. auris; recent work that recovered several disease-causing yeasts from wastewater suggests the approach could extend further.

Two technical limits constrain the method. Genetic tests detect fungal DNA but cannot show whether the organism is alive or drug-resistant, and because many Candida species live harmlessly in people, finding one alone says little. Culturing the samples in the laboratory will be needed as well. And some fungi, such as Aspergillus, are inhaled rather than passing through the gut, so sewage may not reflect those infections at all.

Why might the fungus persist outside hospitals?

Wastewater treatment does not remove every pathogen, and storm overflow pipes release untreated sewage directly into rivers and the sea. Researchers have found C. auris on remote beaches in India's Andaman Islands, which suggests it lived in the environment long before it reached hospitals. In Hong Kong's mangroves, every multidrug-resistant yeast the team recovered came from sites near wastewater treatment plants. Low levels of antifungal drugs reaching rivers and soil may favor resistant strains, a link that remains possible but unproven.

What would it take to put the system in place?

Wastewater monitoring would not replace hospital testing of individual patients. Its value lies in directing health services toward the places where they should look, particularly where testing people at scale is not feasible. For that, researchers need standardized methods, a measurement of how much fungus people shed, and agreed thresholds for what a sewage reading should trigger. The review's authors want wastewater data linked with hospital, animal and farm monitoring rather than standing alone.

The tools already exist, as the pandemic showed. What has been missing, the authors say, is "the will to prioritize fungi before the next resistant one outpaces us."