Population-based studies showed the incidence rate of BSI has been rising in recent years, especially in elderly patients. A recent study showed that the average incidence rate of age group over 65 was 6000 times per 100 thousand population.[8, 9]. More than half of BSI occurs in patients aged 65 and over, and 70% of deaths occur in this age group, highlighting the severity of BSI in elderly patients. Klebsiella spp.is the common pathogen causing BSI in the elderly, accounting for about 3% − 10% . It is worth noting that CRKP infection is becoming a serious problem and has attracted much attention due to limited treatment options and adverse effects on prognosis. However, currently, there is a lack of epidemiological data on BSI caused by CRKP in the elderly population, especially the studies on specific measures to prevent BSI infection of older patients are still insufficient.
In the present study, we described the clinical characteristics, risk factors and outcome of BSI due to KP in the elderly population, in order to reveal the severity of CRKP related bloodstream infection and provide a theoretical basis for further prevention of multidrug-resistant bacterial infection in the elderly patients. In this retrospective observational study with 252 elderly patients with KP BSI, we identified over 10% of the patients suffered BSI caused by CRKP. It is worth noting that the incidence of CRKP was the highest in the age group over 90 years old, suggesting that these patients should be vigilant about the isolation of CRKP in other parts to avoid further BSI. Almost all of the study subjects have an underlying disease/comorbidity. The common underlying diseases/comorbidities of the study subjects included hypertension, previous bacterial infections, malignant tumors, diabetes mellitus, organ dysfunction and septic shock. This finding is similar to previous studies[12, 13]. It is reported that the most common source of BSI in older patients is the urinary tract, increasing with age, and accounting for 20–40% and up to 60% of bloodstream infections[14–16]. Compared with young patients, the elderly have a higher risk of BSI in pyelonephritis. Our results showed that more than one fifth of patients had a history of admission to the ICU. Most of these patients were severe patients with consciousness disorder, limb movement disorder, language disorder and so on. They sufferd from a variety of underlying diseases, immunosuppression, exposure to a variety of antibiotics, and invasive operation, such as indwelling urinary catheter, gastric tube, endotracheal intubation, mechanical ventilation, etc., which increased the risk of bloodstream infection. Meanwhile, receipt of broad-spectrum antibiotics has also been identified as risk factors of CRKP BSI[17, 18]. The inadequacy of empirical antimicrobial regimens also emerged as a predictor of mortality of BSI caused by antibiotic resistant Enterobacteriaceae in the general populations.The present study proved that exposure to carbapenems was one of the independent risk factors for developing CRKP BSI in elderly.
In the present study, the 28 days-mortality of those who suffered from bloodstream infection caused by KP was 10.7% (27/252). This mortality was lower compared with another study with 46.2% (48/104).The mortality associated with CRKP-BSI was significantly (48.3%) higher in elderly patients. Significantly, the mortality associated with CRKP-BSI in ICU patients was much higher. As identified in previous studies, ICU stay is a critical risk factor to develop CRKP BSI [[20, 21]]. According to a systematic review and meta-analys, pooled mortality among 2462 patients infected with CRKP was 42.14%, while 21.16% in those infected with CSKP. The mortality of patients with bloodstream infection (BSI) was 54.30%, and 48.9% in patients admitted to the intensive care unit (ICU) . In our study, totally 48 (48/252, 19.0%) patients developed KP-BSI in ICU and mortality of these patients was 43.6%, which was much higher than overall mortality (10.7%). It is worth noting that the separation rate of CRKP in ICU is significantly higher than that in ordinary ward. It can be detected in ICU environment and various equipment, including bed, table, floor and ventilators. In addition, patients admitted to the ICU are more likely to undergo invasive surgery, which will lead to a higher probability of CRKP-BSI. Studies have proved that KP colonization is another important risk factor for ICU infection[22, 23], and more than 50% of the infections are caused by the strains carried by themselves. More importantly, it is believed that the reason for obtaining CRKP BSI during ICU hospitalization may be that after the extensive use of broad-spectrum antibiotics, the pre-existing CRKP in the gastrointestinal tract is screened out to become dominant, which develops into sequent infections. Therefore, screening for colonization on admission and intervention strategies are urgently needed in.
There were some limitations in this study. First of all, it was a retrospective study conducted in a single center, including 252 elderly patients. This may affect the ability to analyze and identify risk factors. Further prospective multicenter investigations are needed. Moreover, molecular characterization on the clinical isolates to examined the carbapenem resistance mechanisms was not performed in this study. To our knowledge, this is the first study in China to demonstrate the epidemiological characteristics of the risk factors and mortality of BSI caused by CRKP in the elderly for the last decade, which provides a useful basis for the diagnosis and treatment of KP BSI in the elderly.
In summary, hypertension, exposure to carbapenems and ICU stay were associated with the development of CRKP BSI in elderly patients. We also found a high mortality caused by K. pneumoniae BSI in elderly patients in ICUs. Active screening of CRE for high-risk groups, especially for elderly patients, is conducive to the early identification, treatment and control of CRE infections, so as to achieve the successful management.