Stop the presses! We have a new addition to the list of diseases that benefit from next-generation sequencing – infections.

In a case study published last week in The New England Journal of Medicine, routine medical and laboratory testing failed to identify the cause of encephalitis in a 14-year old patient [1], leaving him in a medically induced coma, with few treatment options and little hope. Encephalitis is brain inflammation, and can lead to severe neurologic abnormalities and death. Identifying the exact cause is critical for therapy but may be challenging. In this case, routine testing failed to provide a definitive diagnosis. Even a brain biopsy was inconclusive. As a last resort, doctors used a novel approach to figure out what was wrong with the patient. They analyzed his cerebrospinal fluid (CSF) using next-generation sequencing.

Basically, researchers studied the CSF for evidence of microorganisms, in the form of DNA sequences. They used an unbiased approach to next-generation sequencing. I asked Charles Chiu, MD, PhD, Assistant Professor and Director of UCSF-Abbott Viral Diagnostics and Discovery Center, who is senior author on the study, about this approach.

“The term alludes to the fact that we are not targeting any specific pathogen or type of pathogen,” explained Chiu. It means that the researchers used sequencing and analysis to search for all known pathogens, including rare organisms.

Within 48 hours of receiving the CSF sample, next-generation sequencing and bioinformatics analysis revealed an obscure cause of encephalitis in this teenager – leptospirosis, an infection caused by the bacterium leptospira. Inability to accurately diagnose and treat this condition can be fatal. The good news: once diagnosed, leptospirosis is easily treatable with regular, old-fashioned penicillin. This antibiotic was administered in high doses, and the patient recovered completely.

Next-generation sequencing identified the cause of infection in 2 days – something that months of traditional testing had not achieved. It saved the life of this teenager.

Clinical Translation of Next-Generation Sequencing

Next-generation sequencing is increasingly used in oncology for tumor profiling; in addition, it is a valuable tool for the diagnoses of various rare diseases and genetic disorders. The big question is: can successful diagnosis of an infection lead to the routine use of sequencing for other difficult-to-diagnose infections?

Charles Chiu believes so.

“I view this technology as being used as a broad-spectrum, second-line diagnostic assay after initial screening tests are negative and physicians have to resort to costly additional tests for rare and uncommon infections”, said Chiu.

However, this technology is far from clinic-ready. We need to come up with means to reliably identify disease-producing organisms, with high sensitivity and specificity, and differentiate them from the normal microbiome in relevant areas of the body. For example, the human gut contains 300-500 different species of bacteria [2]. So, one can appreciate the challenge of identifying an infection-causing microorganism from among the gut microbiome, by sequencing. Moreover, using next-generation sequencing routinely in the clinic for infectious diseases would require comprehensive testing and technology validation in order to obtain regulatory approval.

Clinically diagnosing infections (especially in cases of emergency) requires rapid sequencing and reliable analysis to deliver actionable results to the clinician. And all this needs to happen at affordable costs. Elaine Mardis, PhD, Professor of Medicine and Co-Director of The Genome Institute at Washington University, St. Louis, who was not part of The New England Journal of Medicine study agrees, “Probably the biggest hurdle is making it faster, cheaper and better than current assays.”

The Future

Once in routine clinical use, next-generation sequencing can prove critical for diagnosing cases of encephalitis and meningitis, like the one reported here. In addition, it will be beneficial for many zoonotic and infectious diseases that are difficult to diagnose using routine testing. Sequencing-driven diagnoses may be valuable, especially in critically ill patients with severe infections, including sepsis. In such cases, sequencing may not only identify the responsible microorganisms, but may also provide clues on drug resistance.

The successful use of next-generation sequencing by Chiu and colleagues provides us a rare window into a world where this technology can drive treatment decisions by diagnosing infections. As Elaine Mardis reflects, “(This study) beautifully illustrates how an unbiased look and smart bioinformatic analysis can provide answers that are life-saving.”

References Cited

Wilson, M.R., et al., Actionable Diagnosis of Neuroleptospirosis by Next-Generation Sequencing. N Engl J Med, 2014. DOI: 10.1056/NEJMoa1401268 Guarner, F. and J.R. Malagelada, Gut flora in health and disease. Lancet, 2003. 361(9356): p. 512-9. DOI: 10.1016/S0140-6736(03)12489-0

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