The unbiased approach to finding the infectious agent is called metagenomic next-generation sequencing, a powerful technology that analyzes all of the genetic material in a patient’s tissue sample and as a result can screen for a wide range of disease-causing microbes in a single test.

“This is very different than all other clinical diagnostics,” said Joseph DeRisi, a molecular biologist at UCSF and a pioneer of metagenomic sequencing.

Dr. DeRisi and other proponents of metagenomic sequencing say it is poised to transform how doctors tackle one of medicine’s toughest challenges—the diagnosis of major infections that are often lethal and extremely costly to treat unless they are quickly identified. Dr. DeRisi foresees metagenomic testing for infectious disease eventually rolling out across medicine.

“Hundreds of things“ can give you a brain infection, said Dr. DeRisi, who is also president of Chan Zuckerberg Biohub, San Francisco. Conventional testing typically looks for one type of bug at a time. A metagenomics test “doesn’t care if it’s bacteria, a fungus or a parasitic worm or a virus. They all have RNA or DNA.”

n 2014, Dr. DeRisi was among a team of researchers and clinicians at UCSF who reported on one of the first patients to be successfully treated based on metagenomics sequencing—a 14-year-old boy whose treatable, but potentially fatal Leptospirosis bacterial brain infection went undiagnosed for several months until the test was performed.

The case convinced Dr. DeRisi and his colleagues that a metagenomics test should be deployed as a clinical tool for diagnosing brain infections and eventually led UCSF to offer the tests to other hospitals. Innovation in semiconductor technology is helping make the service possible, Dr. DeRisi said. “If we dial back 10 or 12 years ago, we couldn’t do this,” he said. “If we didn’t have increases in computer storage, memory and speed, we’d be sunk.”