Bloodstream infection (BSI) are characterized by high mortality and multidrug resistance worldwide [12, 13]. The dynamic changes in species distribution and antimicrobial susceptibility are important clinical evidence for early empirical antimicrobial therapy of BSI, and these factors were the emphasis of the present study.
With the assistance of the highly sensitive and specific real-time nosocomial infection surveillance system (RT-NISS) in our hospital, we identified 9381 episodes of BSI out of 1,437,927 adult-hospitalized patients over 10 years in CPLAGH, and we found that the total number of adult-hospitalized patients over two consecutive years increased from 2010–2011 to 2018–2019 (211,546 to 359,547 patients every two years) and that the corresponding number of the episodes of BSI increased from 1743 to 2184 episodes every two years. However, it was encouraging that the corresponding average proportion of BSI decreased significantly from 8.24 to 6.07 episodes per 1000 adult-hospitalized patients per year. The proportion was less than that in a Swedish county, which was from 9.45 to 15.46 per 1000 hospitalized patients per year from 2000 to 2013. This result might be due to the increased awareness of nosocomial infections and national action on infection control in China . This decrease might be similar to that in the United States, in which the central line-associated BSI decreased by 46% between 2008 and 2013 as a result of national medical control .
However, we also found that the composition ratio of hospital acquired BSI increased significantly annually (from 73.4–76.2%). This result was consistent with the increase in various hospital-acquired infections in recent years [16, 17]. And the risk factors may be related to the risk factors for BSI and (or) hospital-acquired infections reported in many previous studies, such as ICU admission, the older age of hospitalized patients (aging population), prolonged hospital stay, leukocytopenia, acute myeloid leukemia and (or) increased use of invasive procedures including central venous catheters (CVC) [18–20]. However, more details of the risk factors require further statistical analysis of the decrease in hospital-acquired BSI in our hospital.
We found that the majority species in the 9381 episodes of BSI were bacteremia (93.1%) and that the average composition ratio over the two consecutive years gradually increased from 89.2% (2010–2011) to 95.0% (2018–2019) (time trend P < 0.001). Conversely, fungemia accounted for the minority of BSI (6.9%), and the average proportion decreased significantly from 10.8–5.0%. This result may be partially related to the increasing proportion of multidrug-resistant bacteria. Our data showed that the proportion of multidrug resistance of 6,224 bacteria increased significantly from 52.9–68.4% during the 10-year study period (time trend P < 0.001). This increase may have made bacteria more difficult to control and may have led to a relative increase in the proportion of bacterial BSI (bacteremia). The increase of multidrug-resistant bacteria deserves our more attention, because multidrug-resistant bacteremia was a risk factor for mortality, just as reported by Ju MH et al .
Although the composition ratio of bacteremia in the 9381 BSI increased over the 10-years study period, it did not mean that the composition ratio of all the species in bacteremia did not increase. Our data revealed that gram-positive cocci (45.9%) and gram-negative bacilli (42.8%) had a similar prevalence, and this result was different from the species distribution reported by the China Antimicrobial Surveillance Network (CHINET) in 2018 for all bacterial infections, including BSI and other bacterial infections (2018 CHINET report) . The results of the CHINET report suggested that more gram-negative bacilli (70%) were isolated than gram-positive cocci (30%) and that the composition did not change obviously from 2005 to 2017 in China.
Notably, although the composition ratios of the gram-positive cocci and gram-negative bacilli were different with the 2018 CHINET report, the most common species of bacteria were consistent with the 2018 CHINET report. The top four most common gram-negative species were Escherichia coli (14.3%), Klebsiella pneumonia (8.9%), Acinetobacter baumannii (4.9%) and Pseudomonas aeruginosa (3.4%), which are identical to the CHINET report. Coincidentally, our data also revealed that the proportions of Escherichia coli (9.8–13.6%, time trend P = 0.021) and Klebsiella pneumonia (5.3–10.4%, time trend P < 0.001) increased significantly, while the proportions of Acinetobacter baumannii (4.4–4.2%, time trend P = 0.905) and Pseudomonas aeruginosa (4.1–2.4%, time trend P = 0.032) both had decreased, similar to the CHINET report. In addition, because the composition ratio of gram-negative bacteria (42.8%) in our study was lower than that in the CHINET report (70%) and fungi were not included in the CHINET report, the composition ratios of various species of gram-negative bacteria were also different.
Among gram-positive cocci, the most common species were coagulase-negative staphylococci (26.2%), and their proportion increased (25.6–32.5%, time trend P = 0.005) over the 10-year study period. Staphylococcus aureus accounted for only 3.5% in our study, but were the most common gram-positive cocci in the CHINET report (9.0%). However, our result is not in conflict with the CHINET report because the CHINET report included various infections, not only BSI. Conversely, CoNS accounted for the minority of bacteria in the CHINET report (4.4%) because CoNS only originated from BSI. Therefore, the proportion of CoNS might be much higher only among BSI in CHINET report, and it was up to 26.2% in the present study.
In conclusion, we performed statistical analysis of the proportion, species distribution, and drug resistance of BSI as well as their dynamic changes over the past 10 years in one of the largest hospitals in China. We found that the proportion of BSI decreased dynamically over time and that the species distribution in BSI changed. The proportion of bacteria and multidrug resistance increased, and some species, such as Klebsiella pneumonia, were obviously increased in bloodstream infection. Many of the increasing data presented above exhibited significant time trends and deserve clinical attention regarding infection control.
This study also had several limitations. First, the proportion of BSI might be underestimated in this study. A few pathogens, such as mycoplasma and chlamydia, are difficult to detect in conventional blood cultures, and some BSI were missed in false-negative blood cultures. In addition, some BSI were mistakenly excluded by the RT-NISS system used in our study because of the lack of typical clinical symptoms related to BSI (such as fever and increased inflammation makers). However, missing data might have had little effect on the results of this study, since the RT-NISS system had been used to screen BSI in a previous study and showed high sensitivity and specificity. Second, the CSLS standards and the detection technology for blood cultures had been continuously updated and improved each year, which increased the positive detection rate of blood cultures and might have increased the proportion of BSI in recent years. Thus, this improvement in technology might have led to bias in the statistics of the dynamic time trend of the proportion over the 10 years. However, our data showed that the dynamic time trend of the proportion of BSI in adult-hospitalized patients decreased significantly. Therefore, the results of the statistical analysis of the time trend of the proportion could not be affected in this study. Last, the proportion and the species distribution of BSI were changing up and down in the past 10 years, since various related factors were also dynamic changing, such as the number, age, disease composition and severity of hospitalized patients. For this reason, all the R values in our study were relatively small and they were acceptable since the hospital had not undergone a particularly large adjustment. However, from an overall perspective, the proportion and species distribution of BSI were dynamically changing along certain trends. These trends deserved more attention from clinicians and researchers.