Inflammatory response in mixed viral-bacterial community-acquired pneumonia

Abstract

Background: The role of mixed pneumonia (virus+bacteria) in community-acquired pneumonia (CAP) has been described in recent years. However, it is not known whether the systemic inflammatory profile is different compared to monomicrobial CAP. We wanted to investigate this profile of mixed viral-bacterial infection and to compare it to monomicrobial bacterial or viral CAP.

Methods: We measured baseline serum procalcitonin (PCT), C reactive protein (CRP), and white blood cell (WBC) count in 171 patients with CAP with definite etiology admitted to a tertiary hospital: 59 (34.5%) bacterial, 66 (39.%) viral and 46 (27%) mixed (viral-bacterial).

Results: Serum PCT levels were higher in mixed and bacterial CAP compared to viral CAP. CRP levels were higher in mixed CAP compared to the other groups. CRP was independently associated with mixed CAP. CRP levels below 26 mg/dL were indicative of an etiology other than mixed in 83% of cases, but the positive predictive value was 45%. PCT levels over 2.10 ng/mL had a positive predictive value for bacterial-involved CAP versus viral CAP of 78%, but the negative predictive value was 48%.

Conclusions: Mixed CAP has a different inflammatory pattern compared to bacterial or viral CAP. High CRP levels may be useful for clinicians to suspect mixed CAP.

Figure 1

Flow diagram for patient enrollment or exclusion in the study. After excluding patients who did not meet the inclusion criteria, those with no comprehensive microbiological study, those with a final diagnosis other than CAP, and those with negative microbiological diagnosis, we obtained 185 patients with CAP and isolation of at least 1 microorganism. We subsequently excluded 4 patients with atypical bacteria-involved CAP, all of which were Mycoplasma pneumoniae (1 M pneumoniae + E coli, 1 M pneumoniae + influenza A, 1 M pneumoniae + influenza A + influenza B + syncytial respiratory virus [RSV], and 1 M pneumoniae isolated), and a further 7 due to a bacterial yield of improbable CAP cause because of their low pathogenicity (2 from bacterial group [1 Enterococcus faecalis and 1 Staphylococcus hominis) and 5 from mixed (2 S. hominis + Adenovirus, 1 S. hominis + Virus influenza A + RSV, 1 Staphylococcus coagulase-negative + metapneumovirus, and 1 Morganella morgagnii + coronavirus]). We then had 174 patients with viral, bacterial and mixed pneumonia. A biomarker search could not be performed in three patients, and we finally included 171 patients in our study with both etiology and biomarkers.

Figure 2

Median procalcitonin (PCT) and C reactive protein (CRP) values for bacterial, viral and mixed CAP.

Figure 3

Receiving operating characteristic curve of PCT for differentiating bacterial-involved (bacterial and mixed) from viral CAP. AUC: 0.640, 95% CI: 0.557-0.723. p = 0.002.

Figure 4

Receiving operating characteristic curve of CRP for differentiating mixed from bacterial and viral CAP. AUC: 0.642, 95% CI: 0.537-0.747. p = 0.004.