A teenage girl’s science project has led researchers to pinpoint the source of a fungus that’s long been sickening HIV-positive people in Southern California: It grows on trees, as HealthDay reports. Publishing their findings in PLOS Pathogens, researchers studied soil and tree samples gathered in the Los Angeles area by 13-year-old Elan Filler, comparing them to samples of Cryptococcus gattii infections taken from people with HIV.

C. gattii leads to lung and brain infections and is the cause of a third of all AIDS-related deaths in the United States.

The researchers found that fungal samples from three species of trees—Canary Island pine, Pohutukawa, and American sweetgum—were nearly genetically identical to the samples of C. gattii from the people with HIV.

“Just as people who travel to South America are told to be careful about drinking the water, people who visit other areas like California, the Pacific Northwest and Oregon need to be aware that they are at risk for developing a fungal infection, especially if their immune system is compromised,” Deborah J. Springer, PhD, lead study author and postdoctoral fellow in the Center for Microbial Pathogenesis at Duke University School of Medicine, said in a release.

The researchers determined that the fungal samples from the trees were fertile and could reproduce both sexually and asexually. This suggests that C. gattii has staying power in the environment and is an ongoing threat.

To read the HealthDay story, click here.

To read the press release, click here.

To read the study, click here.