Respiratory failure or multiple organ failure is the direct cause of death in patients with COVID-19, and SBIs play an important role in this process [16]. Among the 1495 patients with COVID-19, the incidence of SBIs was 6.8%. Perhaps because of the larger sample size in our study, the incidence of SBIs was lower than the data in previous studies (10%~15%, Wuhan, China) [2, 3]. The incidence in critical patients was much higher than in severe patients, which was consistent with the higher rate of central catheter placement and invasive mechanical ventilation in critical patients [2]. Almost half (49.0%) of the patients with SBIs died during hospitalization, in agreement with the previous study (50%) [3]. Compared with the severe group, the critical group had a significantly increased mortality. Recent studies related to COVID-19 reported that male was a risk factor for disease severity status, and age 65 or older was a risk factor related to death [3, 17, 18]. In our research, no differences in gender and age were found between the severe and critical groups. It revealed that gender and age were not risk factors for death in patients with SBIs. The risk factors for death in patients with SBIs needed to be explored in the next study.
According to the sites of SBIs, lung infections were the main type, which may be related to the decrease of airway defense function after infected with SARS-CoV-2 [19]. Invasive operations such as trachea intubation and ventilator-assisted breathing during hospitalization may also be the causes of SBIs in the lungs. There were 35 patients with bloodstream infections, 27 of which were bloodstream infections mixed with lung infections. We compared the bacteria of mixed infections and found that 21 patients had the same bacteria in lungs and bloodstream, including K. pneumoniae (66.7%, 14/21) and A. baumannii (33.3%, 7/21). We inferred that the migration of K. pneumoniae or A. baumannii from the lungs resulted in bloodstream infections in these patients.
A total of 159 strains of bacteria were isolated in this study and mainly were Gram-negative bacteria. The top three bacteria of secondary lung infections were A. baumannii, K. pneumoniae and Stenotrophomonas maltophilia (S. maltophilia). The etiological distribution was different from the previously reported bacteria of hospital-acquired pneumonia (HAP) [20, 21]. The proportion of A. baumannii and K. pneumoniae was significantly increased and the proportion of Pseudomonas aeruginosa (P. aeruginosa) and Staphylococcus aureus (S. aureus) was decreased. It suggests that the initial empirical antimicrobial program of HAP should not be completely copied if SBIs in the lungs occur. The lower proportion of P. aeruginosa and S. aureus indicates that it is not necessary to first choose antimicrobial with antibacterial activity of P. aeruginosa and S. aureus for SBIs in the lungs. The choice of antimicrobial program should be more inclined to treat the infections of A. baumannii and K. pneumoniae. The antimicrobial susceptibility tests showed that most of A. baumannii and K. pneumoniae were multi-drug resistant bacteria. The isolation rate of carbapenem-resistant A. baumannii and K. pneumoniae were 91.7% and 76.6%, respectively. When the patients suffer SBIs, the possibility of infections by drug-resistant strains should be adequately considered. The resistance rate of tigecycline and cefoperazone sulbactam was relatively lower and the combination can be considered for the initial empirical treatment of SBIs in the lungs. According to reports [22, 23], avibactam compound has a better effect on carbapenem-resistant K. pneumoniae, but systematic research in patients with COVID-19 has not been launched.
Although the bacteria of secondary bloodstream infections were mainly Gram-negative bacteria, the proportion of Gram-positive bacteria was relatively higher than lung infections. If the bacteria derived from lung infections were excluded in the statistics, Gram-positive bacteria would be the main bacteria for bloodstream infections. 80.0% (16/20) of patients infected with Gram-positive bacteria were given central venous catheter implantation during hospitalization. We analyzed that the bloodstream infections of Gram-positive bacteria were associated with central venous catheter implantation. Therefore, we suggest that the management of venous catheter in severe patients should be strengthened to avoid bloodstream infections. According to antimicrobial susceptibility tests, methicillin resistance was in 100% of Staphylococcus, and vancomycin resistance was not yet found. It suggests that vancomycin can be used as the empirical choice for Gram-positive bacteria if secondary bloodstream infections occur.
The number of secondary urinary tract infections was relatively small and E. coli was still the main bacterium. According to antimicrobial susceptibility tests, the isolation rate of ESBL-producing E. coli was 75%. As the initial empirical choice, β-lactams combinations with β-lactamase inhibitors can be recommended, rather than levofloxacin and ceftriaxone.
This was a single center study in the Wuhan Union hospital. The etiology and antimicrobial resistance in different medical institutions or different regions may be different.