Incidence and risk factors for secondary pulmonary infections in patients hospitalized with coronavirus disease 2019 pneumonia

Background: Secondary pulmonary infections (SPI) have not been well described in COVID-19 patients. Our study aims to examine the incidence and risk factors of SPI in hospitalized COVID-19 patients with pneumonia.

Methods: This was a retrospective, single-center study of adult COVID-19 patients with radiographic evidence of pneumonia admitted to a regional tertiary care hospital. SPI was defined as microorganisms identified on the respiratory tract with or without concurrent positive blood culture results for the same microorganism obtained at least 48 h after admission.

Results: Thirteen out of 244 (5%) had developed SPI during hospitalization. The median of the nadir lymphocyte count during hospitalization was significantly lower in patients with SPI as compared to those without SPI [0.4 K/uL (IQR 0.3-0.5) versus 0.6 K/uL (IQR 0.3-0.9)]. Patients with lower nadir lymphocyte had an increased risk of developing SPI with odds ratio (OR) of 1.21 (95% CI: 1.00 to 1.47, p = 0.04) per 0.1 K/uL decrement in nadir lymphocyte. The baseline median inflammatory markers of CRP [166.4 mg/L vs. 100.0 mg/L, p = 0.01] and d-dimer (18.5 mg/L vs. 1.4 mg/L, p<0.01), and peak procalcitonin (1.4 ng/mL vs. 0.3 ng/mL, p<0.01) and CRP (273.5 mg/L vs. 153.7 mg/L, p<0.01) during hospitalization were significantly higher in SPI group.

Conclusions: The incidence of SPI in hospitalized COVID-19 patients was 5%. Lower nadir median lymphocyte count during hospitalization was associated with an increased OR of developing SPI. The CRP and d-dimer levels on admission, and peak procalcitonin and CRP levels during hospitalization were higher in patients with SPI.