IT HAS BEEN a summer of floods. Northern Virginia at the end of last week, and Texas at the beginning, thanks to Tropical Storm Nicholas. Louisiana and New York City last month, following Hurricane Ida. New Jersey, Rhode Island, and Connecticut, after Tropical Storm Henri. North Carolina, from Tropical Storm Fred. Deadly flash floods caused by heavy rains in Tennessee.

The floods swamped roads, toppled trees, crushed houses, and killed close to 100 people—but as the water recedes, authorities are watching for signals of a second, slower-moving harm. Wherever water has invaded buildings, mold and fungi follow. They are deadly to people with damaged immune systems and dangerous even for the apparently healthy. Yet we have not built the surveillance systems that would reveal how serious their effect may be.

This is not a new problem. In 2004, the Institute of Medicine of the National Academies of Science, Medicine, and Engineering warned in a major report that the health threats posed by whatever grows in damp indoor spaces were under-researched. A year later, Hurricane Katrina broke the levees surrounding New Orleans and flooded 80 percent of the city. One month afterward, Hurricane Rita flooded coastal areas south and east. The waters stood in New Orleans for weeks, and when they were finally pumped out, four out of five buildings were caked with mold.

The extent of the devastation—and the inevitability of families having to go back into ruined houses to strip and restore them—created the conditions for a natural experiment. Researchers leapt into studying human health risks from mold, investigating rates of allergiesasthmatoxin exposure, and dangerous internal infections among people who endured the storm or returned to its aftermath. But those observations didn’t solve the problem the IOM had identified before the storm: a lack of comprehensive data, collected over years, that could help doctors and public health experts predict when people will be most in danger of mold and fungus-related problems.

“We don’t have systematic surveillance for mold infections in the United States,” says Luis Ostrosky-Zeichner, a physician and professor, and director of the mycology research laboratory at UTHealth’s McGovern Medical School in Houston—a city that was flooded by Hurricane Harvey in 2017.