A leukocyte score to improve clinical outcome predictions in bacteremic pneumococcal pneumonia in adults

Abstract

Background: Bacteremic pneumococcal pneumonia (BPP) is associated with high and early mortality. A simple procedure to predict mortality is crucial.

Methods: All adult patients with BPP admitted from 2005 through 2013 to the University Hospital of Dijon, France, were enrolled to study 30-day mortality and associated factors, particularly leukocyte counts. A simple leukocyte score was created by adding 1 point each for neutropenia (<1500 cells/mm(3)), lymphopenia (<400), and monocytopenia (<200).

Results: One hundred and ninety-two adult patients (mean age, 69 years; standard deviation [SD], 19 years) who had developed and were hospitalized for BPP (58% community-acquired) were included. The 30-day crude mortality rate was 21%. The mean Pneumonia Severity Index score was high at 127.3 (SD = 41.3). Among the 182 patients who had a white blood cell count, 34 (19%) had a high leukocyte score (≥2). Multivariate analysis revealed that mortality was significantly associated with a high leukocyte score (odds ratio, 6.28; 95% confidence interval, 2.35-16.78), a high respiratory rate, a low serum bicarbonate level, and an altered mental status (all P < .05). The leukocyte score was not significantly dependent on the previous state of immunosuppression, alcoholism, or viral coinfection, but it did correlate with an acute respiratory distress syndrome and a low serum bicarbonate level.

Conclusions: This new leukocyte score, in combination with the well known predictive factors, seems of interest in predicting the risk of death in BPP. A high score correlated with organ dysfunction and probably reflects the level of immunoparalysis. Its predictive value has to be confirmed in other cohorts.

Keywords: Streptococcus pneumonia; bacteremia; leukocyte; mortality; pneumonia.

Figure 1.

The histogram shows the distribution of leukocytes in different strata for the 182 patients with bacteremic pneumococcal pneumonia and an available leukocyte count: (A) neutrophil count distribution; (B) lymphocyte count distribution; (C) monocyte count distribution. The clear bar represents survivors and the black bars represent nonsurvivors at 30 days.

Figure 2.

Kaplan-Meier survival analysis comparing 182 patients with bacteremic pneumococcal pneumonia according to their leukocyte score. (A) Patients with different classes of the leukocyte score (0–3) were compared (log rank: P < .0001). (B) Patients with a low (<2) leukocyte score (gray curve) were compared with patients with a high (≥2) leukocyte score (black curve) (log rank: P < .0001).

Figure 3.

Receiver operating characteristic (ROC) curves for the leukocyte score, the CURB-65 score, and the Pneumonia Severity Index (PSI), for (A) 48-hour mortality and (B) 30-day mortality; (C) area under the ROC curves; (D) measures of performance in predicting 48-hour and 30-day mortality by the 3 scores.