K.pneumoniae is one of important pathogens in burn wards. In recent years, the infectious rate has shown an increasing trend, and its drug resistance has grown up to be an important issue, which has attracted great attention of clinical and microbiologists [14,15]. The main reason is that K.pneumoniae can cause respiratory tract, urinary tract, and even sepsis, etc [16], moreover, K.pneumoniae are widely distributed in hospital environment and can survive for a long time, which is a great threat to critically ill patients [17,18]. Due to the large number of CRKP, especially hypervirulent strains with high mucinous phenotype, they can avoid host immunity and antagonizing immune killing function, resulting in severe invasive infections and high lethal rate [19,20].
From 2009 to 2018, 593 strains of non-repetitive K.pneumoniae were isolated from burn center in the first affiliated hospital of Nanchang university. The proportion of isolates to the total number of strains showed an increasing trend, accounting for 0.89% (11/1235), 1.69% (21/1243), 2.03% (25/1230), 2.72% (35/1289), and 3.98% (54/1355), 4.69% (69/1472), 3.82% (55/1441), 5.09% (83/1630), 4.56% (74/1624), 9.09% (166/1827), respectively. Burn patients have skin barrier damage, long hospitalization period, ventilator and other interventional operations, which can easily lead to burn wound, bloodstream, respiratory tract and urinary tract infection [2,3,6,7,21,22]. From the sites of infection, K.pneumoniae mainly were isolated from wound secretion, bloodstream and sputum during the past 10 years, and the proportion of isolation almost being no change. This may be related to the fact that K.pneumoniae was a common nosocomial bacterium, which could easily lead to opportunistic infection. At the same time, doctors of burn department regularly timely applied antibiotics according to clinical practice and laboratory epidemiological data. During this 10-year period, the resistance rate of common antibiotics in burn center had shown an increasing trend. For example, the resistance rate of the third generation cephalosporins was 50–60% in 2009, and it increased to 80–90% in 2018. That was also higher than the average level of resistance from other departments in our hospital, and also higher than the average level in China [23]. Except for the first generation of cephalosporins and aminopenicillin, other β-lactam antibiotics had shown an obvious upward trend, and resistance to aminoglycosides and fluoroquinolones have also increased significantly (P < 0.05) (Table 1). In order to observe whether the increase of antibiotic resistance was related to the usage of antibiotics, we had statistics in drug resistance from ICU to non-ICU. The results showed that drug-resistant rate of strains in ICU was significantly higher than that in non-ICU isolates (Table 2) [24]. Because ICU patients had serious and deeper tissue damage, and interventional procedures and the exposure of antibiotics was significantly higher than that in non-ICU patients, this was related to the increase of antibiotic usage leading to increased drug resistance [25,26]. Previous data of drug-resistance in Staphylococccus aureus also confirmed this opinion [27].
To further understand whether K.pneumoniae infection was related to the length of hospitalization, we investigated the original data and found that the isolated rate increased following with the length of hospitalization, even reached a peak in 1–3 weeks (Figure 2). This was related to the early infection of burn patients with Gram-positive bacteria, Gram-negative bacteria in the middle and late stages [3]. Because CRKP had the characteristics of low cure rate and high mortality rate, we wanted to know whether infectious site was different between CRKP and non-CRKP patients [28]. We found that CRKP infection in ICU was obviously higher than that in non-ICU, and there was also a significant difference in drug resistance. According to the time point of isolation, we found that there was no significant difference in the proportion of CRKP in the early stage of admission, while CRKP were the main isolates in the middle and late stage. Tigacycline was a drug usually adopted in the treatment of severe burn patients in recent years [29]. Since 2014, we had included it in drug sensitivity monitoring. The results showed that CRKP strains didn’t show any drug resistance in that year. However, the drug-resistant rate showed an obvious upward trend in the following years (P = 0.02) (Table 1). Because we justly detected these carbapenem-resistant strains, the overall drug resistance rate may be below that level, however, the future development of drug resistance is not optimistic accordance with current trends. Furthermore, there was no difference in drug resistance among ICU and non-ICU isolates. The possible reason was that doctors apply tigacycline to treat patients much specifically in our hospital.
In summary, the isolated and drug-resistant rate of K.pneumoniae in our burn center showed an increasing trend during 2009 to 2018, and the infecting sites mainly focused on burn wound and bloodstream. How to reduce the incidence and drug resistance of K.pneumoniae is of great significance to reduce the morbidity and mortality. Therefore, hospital infection control department should continue to strengthen drug resistance surveillance, grasping its epidemic and drug resistance changes in burn department, conducting an epidemiological investigation, understanding its transmission rule as well as emphasizing rational usage of antibiotics. The aim is to avoid further increase and spread of drug-resistant bacterium.
This study has several limitations. At first, this study was conducted in a single burn center, as a result, these findings may not completely comply with other burn wards, however, it was certain was that there were obviously increasing antimicrobial resistance trends in the burn center. Secondly, we conducted a statistical analysis for all isolated K.pneumoniae, without distinguishing infection from colonial status, which might increase the number of infectious bacteria and even drug resistance. Finally, our study was a retrospective consequence, and collected data was no clear causal relationship, even no uniform tests and evaluation standard in this period, and it was possible that there were some deviations in our results. However, our findings provided valuable information on the dynamics of K.pneumoniae infection and drug resistance. In particular, it was clear that high antibiotic exposure increased bacterial resistance.