Specialized Test Detects Bacterial Infections in Youngest Infants with Fever

Physicians from Children’s Hospital of Michigan, UC Davis Medical Center and Nationwide Children’s Hospital, in collaboration with 19 other pediatric emergency departments around the country, have established a “proof of principle” for measuring patterns of ribonucleic acid (RNA) expression in the bloodstream that can enable clinicians to distinguish bacterial infections from other causes of fever in infants up to two months old.

The findings from this study, conducted in the Pediatric Emergency Care Applied Research Network (PECARN), were published in the Journal of the American Medical Association. The research was led by principal investigators Octavio Ramilo, MD, at Nationwide Children’s, Prashant Mahajan, MD, MBA, MPH, at Children’s Hospital of Michigan, and Nathan Kuppermann, MD, MPH, at UC Davis Medical Center.

The diagnostic test—a high through-put RNA analysis that yields specific markers known as RNA biosignatures—means that emergency department physicians could someday avoid ordering painful, invasive exams for many of the more than 500,000 febrile infants who arrive at hospitals each year and must be evaluated to determine whether a bacterial infection is the cause of their fevers. Results that indicate no bacterial cause would also help reduce unnecessary hospitalizations and antibiotic treatments.

Typically, fewer than 10 percent of infants evaluated for fever in emergency departments have serious and potentially life-threatening bacterial infections, including bacteremia (bacteria in the blood), bacterial meningitis or a urinary tract infection. But because of their age and current treatment guidelines, many febrile infants undergo invasive testing and are hospitalized and given antibiotic treatment until a bacterial infection can be ruled out.

“Finding an accurate but less invasive method to determine if babies with fevers have bacterial infections is a ‘holy grail’ for emergency department physicians,” says Dr. Kuppermann, professor and chair of the Department of Emergency Medicine at UC Davis School of Medicine. “This proof-of-concept study demonstrates that the evaluation of RNA biosignatures could one day be that tool.”

Current guidelines for evaluating young febrile infants call for culturing bacteria from blood, urine and cerebrospinal fluid samples. Cultures typically take 24 to 48 hours to determine if bacteria are present. The tests, while effective, are invasive and can be painful for young patients as well as stressful for parents. Testing also is costly, involves some degree of clinical risk and may require hospitalization, all of which pose important questions for pediatricians and emergency department physicians who do not want to miss a serious infection.

Although the RNA biosignatures approach has been shown to be valuable in detecting certain infections in older children and adults, the current study is the first to show that the test could also be used in very young febrile infants. Some physicians and researchers had concerns that RNA biosignatures may not work in this patient population because the immune cells in the blood of these youngest patients were too immature to mount a detectable response to bacterial infection.

“Despite the young age of the babies in this study, they did carry robust RNA biosignatures,” says Dr. Ramilo, chief of Infectious Diseases and principal investigator in the Center for Vaccines and Immunity in The Research Institute at Nationwide Children’s. “Regardless of whether they had a viral or bacterial infection, their immune systems were already programmed to respond with specific patterns.”

Cultures are the current standard for diagnosing bacterial infections, but they can deliver false results. If not enough blood is drawn—a common problem with the youngest babies—bacteria may not grow in a culture medium even if present, causing the diagnosis to be missed. In addition, bacteria can be picked up from the skin during a blood draw, contaminating the culture and leading to a false-positive result.

In contrast to blood cultures, an RNA biosignature assay requires only a small amount of blood to detect immune system responses to pathogens. DNA within white blood cells are prompted to produce different RNAs according to environmental cues, the first step in making proteins that are essential for keeping the cell functioning and able to cope with changes in the surroundings. By analyzing the patterns of RNAs produced—the RNA biosignatures—it can be determined with a high degree of certainty whether an individual has a bacterial infection or not.

“The implications of these findings are potentially paradigm-changing,” says Dr. Mahajan, professor of Pediatrics and Emergency Medicine at Wayne State University and chief of Pediatric Emergency Medicine at Children’s Hospital of Michigan. “For 100 years, doctors have looked directly for bacteria in body fluids to make a diagnosis. We have now shown that genomic analysis to detect the response of the human immune system is also very accurate and potentially can be more rapid in determining if a young baby has a bacterial infection.”

With a renewed five-year grant from the National Institutes of Health’s Eunice Kennedy Shriver National Institute of Child Health and Human Development, the research team will be validating the study findings on a larger patient population and evaluating whether the RNA biosignature is stable at two different time-points. They also will be testing a new RNA biosignatures polymerase chain reaction platform—currently available only for research purposes—which they anticipate will produce faster results and be more applicable in clinical laboratories. The new study will also determine if RNA biosignatures testing can detect the presence of a simultaneous bacterial and viral infection in a single patient.

This article was a joint collaboration between Children’s Hospital of Michigan, Nationwide Children’s Hospital and UC Davis Medical Center, with Charlie Casey, Senior Public Information Officer in the Office of Public Affairs at UC Davis, as a contributing author.