Bloodstream infections (BSIs) 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 BSIs, 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 incidence rates of BSI decreased significantly from 8.24 to 6.00 episodes per 1000 adult hospitalized patients per year. The incidence rate 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[4]. This result might be due to the increased awareness of nosocomial infections and national action on infection control in China[14]. This decrease might be similar to that in the United States, in which the central line-associated BSI rate decreased by 46% between 2008 and 2013 as a result of national medical control[15].
However, we also found that the composition ratio of hospital acquired BSIs 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 BSIs 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 (CVCs)[18–20]. However, more details of the risk factors require further statistical analysis of the decrease in hospital-acquired BSIs in our hospital.
We found that the majority species in the 9381 episodes of BSIs 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 BSIs (6.9%), and the average composition ratio 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 BSIs (bacteremia).
Although the composition ratio of bacteremia in the 9381 BSIs 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 BSIs and other bacterial infections (2018 CHINET report)[21]. 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 similar in BSIs in our study, the most common species of bacteria was 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 = 0.004) and Klebsiella pneumonia (5.3–10.4%, time trend P < 0.001) increased significantly and the proportions of Acinetobacter baumannii (4.4–4.2%, time trend P = 0.879) and Pseudomonas aeruginosa (4.1–2.4%, time trend P = 0.007) 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. However, the most common species were similar.
However, 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 < 0.001) 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 bloodstream infections. Conversely, CoNS accounted for the minority of bacteria in the CHINET report (4.4%) because CoNS only originated from bloodstream infections. Therefore, the proportion of CoNS might be much higher only among BSIs in CHINET report, and it was up to 26.2% in the present study.
In conclusion, we performed statistical analyses of the incidence rate, species distribution, and drug resistance of BSIs as well as their dynamic changes over the past 10 years in one of the largest hospitals in China. We found that the incidence rate of BSIs decreased dynamically over time and that the species distribution in BSIs changed. The proportion of bacteria and multidrug resistance increased, and some species, such as Klebsiella pneumonia, were obviously increased in bloodstream infections. Many of the increasing data presented above exhibited significant time trends and deserve clinical attention regarding infection control. We compared the species distribution of bacteria-causing BSIs with those reported in CHINET for all infections (2018 CHINET report above) and found that the species distributions of BSIs were partially consistent with the 2018 CHINET report, but there were also many differences. Therefore, our study on BSIs could be supplements to the 2018 CHINET report on BSIs.
Limitations
This study also had several limitations. First, the incidence of BSIs might be underestimated in this study. A few pathogens, such as mycoplasma and chlamydia, are difficult to detect in conventional blood cultures, and some BSIs were missed in false-negative blood cultures. In addition, some BSIs were mistakenly excluded by the RT-NISS system used in our study because of the lack of typical clinical symptoms related to BSIs (such as fever and increased inflammation makers). However, a previous study used the RT-NISS system to screen BSIs and showed high sensitivity and specificity[11], and missing data might have had little effect on the results of this study. 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 incidence rate of BSIs in recent years. Thus, this improvement in technology might have led to bias in the statistics of the dynamic time trend of the incidence rate over the 10 years. However, our data showed that the dynamic time trend of the incidence rate of BSIs in adult hospitalized patients decreased significantly. Therefore, the results of the statistical analysis of the time trend of the incidence rate could not be affected in this study.