Acute respiratory tract infections (ARTI) are among the most frequent reasons for seeking medical attention in primary care. Although from predominantly viral origin, ARTIs are the most important condition for the prescription of antibiotics (AB), mainly due to the difficulty in primary care to differentiate between viral and bacterial etiology. Unnecessary AB use increases drug expenditures, side effects and AB resistance. A novel approach is to guide AB use by procalcitonin (ProCT), since serum levels are elevated in bacterial infections but remain lower in viral infections and inflammatory diseases.

We aim to compare a strategy based on evidence-based guidelines with ProCT guided AB therapy in ARTIs with respect to outcome (days with restriction) and AB use. Patients presenting with ARTIs to primary care physicians and are intended to be treated with AB based on guidelines will be included and randomized 1:1 either to standard management or to the ProCT guided prescription of AB. All participating physicians will receive evidence-based guidelines for the management of patients with ARTIs. Patients with ARTI and in need of ABs by physicians’ clinical judgment and with informed consent will be randomized to ProCT plus guidelines ("ProCT group") versus only guidelines guided AB treatment ("control group"). In patients randomized to the ProCT group, the use of antibiotics will be more or less discouraged (<0.1 or <0.25 ug/L) or encouraged (>0.5 or >0.25 ug/L), respectively. A re-evaluation in patients with ProCT (<0.1 or <0.25 ug/L) after 6 to 24 hours is mandatory. All patients will be reassessed at day 3 and it is recommended to stop AB in the ProCT group as described above. Structured phone interviews at days 14 and 28 will be done in all patients from both groups.