If doctors used an existing simple lab test on patients with coughs or flu-like symptoms they would be better able to decide which of them might benefit from antibiotics.
They said prescriptions of expensive antibiotics for respiratory tract infections could be reduced by more than 40% if tests became more commonplace.
The German researchers found that testing for a marker of bacterial infection known as procalcitonin (PCT) helped identify patients whose respiratory tract infections would respond to antibiotics, and stopped others being offered unnecessary drugs.
Respiratory infections are very common and doctors are taught to prescribe antibiotics on the basis of features like sputum or fever, which suggest there may be bacterial infection.
Bacterial or viral infection
But this judgment is not always easy, the researchers said, and lab tests can help sort bacterial from viral infections.
Excessive prescribing of antibiotics adds to healthcare costs and to the worldwide problem of multi-drug resistant bacteria, or "superbugs", like MRSA. Superbugs kill about 25,000 people a year in Europe and 19,000 in the United States.
Experts say varying patterns of antibiotic resistance around Europe are strongly linked to varied prescription habits among doctors, and more concrete guides are desperately needed.
The European Centre for Disease Prevention and Control said last year that overuse of antibiotics in the region was building widespread resistance to a level with could threaten modern medicine.
In a study in the European Respiratory Journal, Tobias Welte of Hannover Medical School said "a simple PCT-guided strategy of decisions on antibiotic treatment" could cut the antibiotic treatment rate by more than 40% with no risk to patients.
"There is huge potential for further reduction of antibiotic treatment," Welte wrote in the study, which used a test made by the German diagnostics maker Brahms AG.
In healthy people, PCT concentrations are low, but in those with bacterial infection it occurs at high concentrations in the blood as early as 3 hours after infection. In people with viral infections, PCT levels rise only marginally, if at all.
Welte's team ran a two part study involving more than 1,200 patients with respiratory tract infections and found that testing for PCT helped doctors decide which patients really needed antibiotics and which would safely recover without them.
"A PCT-guided strategy applied in primary care in unselected patients presenting with symptoms of acute respiratory infection reduces antibiotic use by 41.6% without compromising patient outcome," they wrote. - (Kate Kelland/Reuters Health, February 2010)