A new blood test can help doctors tease out whether an infection is caused by a virus or bacteria within two hours, research in Plos One suggests.
It could stop patients being given antibiotics when they are not needed, scientists say.
It is still at a laboratory stage but the team is working on a portable device too.
Independent experts say the work addresses a serious problem. Further studies are being carried out.
Appropriate drugs
Doctors face a number of challenges when deciphering which bug is responsible for an infection and the treatment that would best tackle it.
Routine tests to check the definitive identity of bugs can take days – they often involve taking a sample and then trying to grow the organism in a lab.