Researchers from the University of Washington, USA, developed the test which, were it to enter the clinic, would have its most likely application in paediatric medicine.
'It's a common problem that children develop a fever without any apparent cause', said Dr Gregory Storch, a senior author of the paper. 'Some of these kids have serious bacterial infections that can be life-threatening, but the largest number have viral infections. The trouble is, from a practical standpoint, it's hard to know which is which'.
Viral and bacterial infections require different treatment and antibiotics are only effective against bacterial infections. Overprescription of antibiotics can lead to the development of resistant strains of bacteria. But doctors sometimes prescribe antibiotics to children with fevers as a precaution before the cause of the infection has been established.
In the research, published in the journal PNAS, researchers took blood samples from 35 children who were suffering from a fever and had tested positive for one of three common viruses, or for acute bacterial infection. They looked at the pattern of expression of all the genes in white blood cells, which are important for fighting infection. They compared these findings with data from 22 healthy children and found that different sets of genes were active depending on whether a child had a bacterial or viral infection.
Dr Storch said that the test 'basically tells us how a patient is reading the infection. The very active genes tell us that an infection is making a patient sick, while quiet genes tell us either there's no infection or maybe a bacterium or virus is there, but it's not causing fever or illness'.
Currently the test is too expensive and time-consuming to be used in a clinical setting but the researchers are hopeful that it might be adapted and be in use before too long.
Dr Storch said: 'The possibility of designing a test so straightforward that it could be done in a doctor's office is very real. I would be optimistic that it could happen within five years'.