CRP/Neopterin Ratio and Neuropsychiatric Symptoms in Patients with Different Forms of Pneumonia: Results of a Pilot Study

Background: Pneumonia is one of the most common infectious diseases, mostly caused by viruses or bacteria. In response to bacteria or viruses which are different but which also are partly overlapping, innate and adaptive immune responses are induced, which can be quantified using the determination of specific biomarkers. Among these, C-reactive protein (CRP) has been established as a marker of innate immune function, whereas Neopterin, which is mainly produced upon stimulation with interferon-gamma, reflects cellular immune activation. Aim: We investigated inflammation markers in patients with microbiologically confirmed viral or bacterial pneumonia, and studied the potential of CRP, Neopterin, and the CRP/Neopterin ratio to distinguish between viral and bacterial pathogenesis. Furthermore, we examined, how often neuropsychiatric symptoms occur in patients suffering from different kinds of pneumonia. Patients and method: A total of 194 patients diagnosed with either coronavirus disease 2019 (COVID-19) (n = 63), bacterial pneumonia (n = 58), Influenza infection (n = 10), Influenza and a bacterial superinfection (n = 9), and COVID-19 patients with a bacterial superinfection (n = 54) were included in our pilot study. Clinical as well as laboratory parameters were determined shortly after admission. Results: We found significantly higher CRP/Neopterin ratios in patients with bacterial pneumonia (median: 0.34) and lower CRP/Neopterin ratios in patients hospitalized with COVID-19 infection (median: 0.03; p < 0.001). Both in men and in women, the CRP/Neopterin ratio was able to distinguish between viral and bacterial pathogens, but also was able to detect bacterial super-infection (BSI) in subjects with initial viral pneumonia (p < 0.001). Patients with BSI presented with significantly lower CRP/Neopterin ratios (median 0.08) than patients with bacterial infection only (median 0.34; p < 0.001). Interestingly, COVID-19 patients had a decreased physical functioning (as reflected in the ECOG score) and a higher frequency of fatigue (84.1%) and neurological symptoms (54.8%) than patients with pneumonia, due to other underlying pathogens. Patients that reported fatigue during viral and bacterial pneumonia presented with lower CRP concentrations than patients without it. Conclusions: The CRP/Neopterin ratio is useful to differentiate between viral and bacterial pathogenesis. The occurrence of neuropsychiatric symptoms in pneumonia appears to depend on the kind of pathogen causing the infection. Lower CRP concentrations at admission appear to be related to fatigue during acute viral and bacterial infection.