Syndromic testing for respiratory pathogens but not National Early Warning Score can be used to identify viral cause in hospitalised adults with lower respiratory tract infections.

Background: Community-acquired lower respiratory tract infection (LRTI) is a common reason for hospitalisation. Antibiotics are frequently used while diagnostic microbiological methods are underutilised in the acute setting.

Objectives: We aimed to investigate the relative proportion of viral and bacterial infections in this patient group and explore methods for proper targeting of antimicrobial therapy.

Methods: We collected nasopharyngeal samples prospectively from adults hospitalised with LRTIs during three consecutive winter seasons (2016-2019). Syndromic nasopharyngeal testing was performed using a multiplex PCR panel including 16 viruses and four bacteria. Medical records were reviewed for clinical data.

Results: Out of 220 included patients, a viral pathogen was detected in 74 (34%), a bacterial pathogen in 63 (39%), both viral and bacterial pathogens in 49 (22%), while the aetiology remained unknown in 34 (15%) cases. The proportion of infections with an identified pathogen increased from 38% to 85% when syndromic testing was added to standard-of-care testing. Viral infections were associated with a low CRP level and absence of pulmonary infiltrates. A high National Early Warning Score did not predict bacterial infections.

Conclusions: Syndromic testing by a multiplex PCR panel identified a viral infection or viral/bacterial coinfection in a majority of hospitalised adult patients with community-acquired LRTIs.