A 5- Year Surveillance of Nosocomial Infections in a University Hospital: A Retrospective Analysis


 OBJECTIVE: ‘Nosocomial infections’ or ‘healthcare associated infections’ are a significant public health problem around the world. This study aimed to assess the rate of culture confirmed nosocomial infections (NIs), frequency of nosocomial pathogens and the antimicrobial resistance patterns of bacterial isolates in a University Hospital. METHODS: A retrospective evaluation of NIs in a tertiary hospital, between the years 2015 and 2019 in Tekirdag, Turkey. RESULTS : During the five years, the overall incidence rates (NI/100) and incidence densities (NI/1000 days of stay) of NIs were 2.04% (range 1.76-2.41/100) and 3.50/1000 patients-days (range 2.85-4.64/1000), respectively. 57.4 % of the infections were originated from the Intensive Care Units. The most common NIs according to the primary sites were bloodstream infections (55.3 %) and, pneumonia (20.4%). 67.5% of the isolated microorganisms as nosocomial agents were Gram negative bacteria, 24.9% of Gram positive bacteria and 7.6 % of candida. The most frequently isolated causative agents were Esherichia coli (16.7%) and Pseudomonas aeruginosa (15.7%). The rate of extended spectrum beta-lactamase production among E. coli isolates was 51.1%. Carbapenem resistance was 29.8% among isolates of Pseudomonas aeruginosa; 95.1% among isolates of Acinetobacter baumannii, 18.2% among isolates of Klebsiella pneumoniae. Colistin resistance was 2.4% among isolates of Acinetobacter baumannii. Vancomycin resistance was 5.3% among isolates of Enterococci.CONCLUSION: Our study results demonstrates the microorganisms of isolated from Intensive Care Units demonstrates high level resistance to many antimicrobial agents. The rising in incidence of multidrug-resistant microorganisms indicate that more interventions are urgently needed to reduce NIs in our ICUs.


Introduction
Health care-related infections (HCAIs), previously referred to as nosocomial infections ( NIs), are infections acquired by patients in health care settings. It usually occurs 48-72 hours after the patient's hospitalization, or within 10 days after discharge. Many studies have shown that the most common events that affect hospitalized patients are drug side effects, nosocomial infection, and surgical complications. The US Center for Disease Control and Prevention reported that approximately 1.7 million hospitalized patients anually acquire HCAI sor NIs while being treated due to other health problems, and that more than 98 000 of these patients (approximately one in 17) die due to NIs. NIs are reported to be one of the 10 most important causes of death in the United States. However, the World Health Organization reports that NIs usually attract public attention when an outbreak occurs [1], [2], [3], [4], [5].
NIs have a dynamic process that varies in each center and over time. In many European multi-center studies, 4.6-9.3% of hospitalized patients have been reported to develop nosocomial infections. In another study, the frequency of NIs was 5.9% (country range: 2.9-10.0%). This rate was 7% in tertiary hospitals [2], [6], [7], [8]. NIs are most commonly associated with invasive medical devices or surgical procedures. Intensive care unit (ICU) patients have a higher risk of developing nosocomial infections compared to other hospitalized patients.
Despite the early diagnosis of infections and improvements in hospital conditions, NIs continue to pose a signi cant risk of morbidity and mortality. In addition to increased morbidity and mortality, length of hospital stay, antibiotic use, the risk of developing multiple antibiotic resistance of pathogens and maintenance costs increase. Lower respiratory tract and bloodstream infections are the most fatal.
Prevention of NIs is the responsibility of healthcare institutions and their employees. Everyone should work collaboratively to reduce the risk of infection for patients and staff. Surveillance of NIs is an important part of infection control and has been widely accepted worldwide as a primary step towards prevention. Local surveillance data are also important to guide empirical treatment and to ensure optimal therapy.Therefore, each center should determine its own disribution of NIs, causative agents and their antibiotic resistance status to guide in the development of infection control policies. In this study, we aimed to describe the incidence of NIs, distribution of infections, infectious agents and antibiotic resistance status of these agents in our hospital during the years 2015 and 2019.

Data collection
This study was a retrospective analysis of NIs of hospitalized patients at the Namik Kemal University Hospital, a tertiary care hospital with 430 beds, between the years 2015 and 2019. The intensive care units had 80 beds. Patient data were obtained by laboratory and patient-based active surveillance method. Follow-up, registration and examination of NIs were carried out by infection control team. The study included all patients hospitalized for more than 48 hours. The overall patient NI rate and the incidence density were determined. All NIs were culture-con rmed.
The bacterial identi cation was performed by the automatized VITEK 2 (bioMérieux, France) in addition to conventional microbiological methods. The antibiotic resistance patterns of isolated microorganisms were determined by the Kirby-Bauer disc diffusion method and automatized VITEK 2 system. Presence of ESBL positivity was detected using the double disk synergy test (DDST). Variations in the resistance rate during the 5-year period were analysed by the chi-square test for trends. P-value < 0.05 was considered signi cant.

De nition
NI was de ned as an new infection that occurred more than 48 hours after hospital admission. The patients were assessed for NIs by using the clinical criteria of the Centers for Disease Control and Prevention [3], [4]. The incidence rates of NIs was calculated by dividing the total number of patients with NIs to total number of patients (×100) during the observed period. The incidence density of NIs was calculated by dividing the total number of NIs recorded in the observed period to total number of patient days (×1000).
Multidrug resistant ( MDR) gram-negative bacteria were de ned as gram-negative bacteria resistant to at least one agent in each of three or more categories of antimicrobial agents including β-lactam/βlactamase inhibitor combinations (piperacillin/ tazobactam), extended spectrum cephalosporins (ceftriaxone, ceftazidime, cefepime), carbapenems (imipenem / meropenem), monobactams, aminoglycosides (gentamicin, amikacin) and/or uoroquinolones.In Gram-positive bacteria, vancomycin resistance for Enterococcus faecium and methicillin resistance for Staphylococcus aureus have been de ned as MDR.

Results
During the study period, 1050 NI episodes were detected in 705 patients aged < 1-100 years old. 382 (54.2 % ) of patients were male. The overall incidence rates (NI/100) and incidence densities (NI/1000 days of stay) of NIs were 2.04% (range 1.76-2.41) and 3.50/1,000 patient-day (range 2.85-4.64/1000), respectively. 603 (57.4 %) of the infections were originated from the Intensive Care Units. The distribution of infection rate and density by year was given in Table 1. NIs according to the primary sites were bloodstream infections (BSIs) (55.3%), pneumonia (20.4%), surgical site infections ( SSIs) ( 13.7% ) and urinary tract infections (UTIs) (9.5%). BSIs were the most common hospital infections, followed by ventilator-associated pneumonia (VAP) in 2015, 2017, 2018 and 2019, and SSIs in 2016. 19.5% of BSIs are secondary BSIs. 732 (67.5%) of the isolated microorganisms as nosocomial agents were Gram negative bacteria, 271 (24.9%) of Gram positive bacteria and 82 (7.6%) of candida. 35.3% of the candida were Candida albicans. The most frequently isolated microorganisms were Escherichia coli (E.coli) (16.7%) followed by Pseudomonas aeruginosa (P.aeruginosa) (15.7%), Acinetobacter baumannii (A.baumannii) (11.3%), Klebsiella pneumoniae (K.pneumoniae) (11.1%) and coagulase negative Staphylococci ( CoNS ) (10.0%). The most frequently isolated microorganisms were CoNS and E. coli in bloodstream infections; E.coli and P.aeruginosa in urinary tract infections; E.coli in surgical site infections; P.aeruginosa and A. baumannii in VAP respectively. The distribution of most commonly isolated microorganisms according to the type of infection was given in Table 2. The prevalence of extended spectrum beta-lactamase (ESBL)-producing K.pneumoniae was 60.3% and E.coli was found as 51.1%. In this study, all ESBL-producing E.coli isolates were sensitive (100%) to meropenem and K. pneumoniae showed 81.8% sensitive to meropenem. Carbapenem resistance was 29.8% among isolates of P.aeruginosa; 95.1% among isolates of A.baumannii. Colistin resistance was 2.4% among isolates of A.baumannii; 1.2% among isolates of P.aeruginosa, 1.7% among isolates of K.pneumoniae. Meticillin resistance was 31.7% and 83.4% among isolates of Staphylococcus aureus and CoNS respectively. No isolate was found to be resistant to vancomycin and linezolid among Staphylococci. Vancomycin resistance was 5.3% among isolates of Enterococci. The prevalence of nosocomial infections caused by MDR bacteria was 45.66 %. The distribution of the resistance pro les of nosocomial pathogens by year was given in Table 3. It is remarkable that NIs caused by colistin resistant P. aeruginosa, A. baumannii, K. pneumoniae have been detected in the last two years. In addition, the increasing rate of carbapenem resistant K. pneumoniae and vancomycin resistance Enterococcus (VRE) has also emerged. Carbapenem resistant A.baumannii isolates showed high resistance levels and the same change trends with time. P aeruginosa resistance to carbapenem decreased slightly from 53-27% in the last two years, however this trend was not signi cant statistically (p > 0.05). There was no statistically signi cant difference between ESBL-producing K.pneumoniae numbers in comparisons of ve years (P > 0.05). There was a statistically signi cant decrease in 2017 in EBSL-producing E coli (P < 0.05).

Discussion
NI prevelance in the European Union / European Economic Area was 5.9% (country range: 2.9-10.0%) [7]. The rate of NIs in our country is reported to be between 1.3-16.6% in the various studies [9]. According to the data of our hospital, culture con rmed NI rate was found to be 2.04%. NI density in our hospital was 3.50 / 1000 patient days. There are also studies with same values to our study results. In a study, NI rate was 1.6, NI density was 3.6 [10]. This rate is lower than the reported many studies in the world. The possible cause of this situation can be explained by the fact that the NIs in our hospital are predominantly originated by ICUs.
Wenzel et al. [11] reported that although 5-10% of hospitalized patients were followed in the ICU, 25% of NIs were seen in this unit. In our study, 57.4% of NIs were originated by Intensive Care Units. 18.6% of the beds in our hospital are intensive care beds. The rate of NIs was higher than other services in our hospital too. Because patients in ICUs are with a worse general condition who remain in the hospital for a long time period; and with a more frequent invasive procedures, more resistant bacterial infections and more frequent use of antibiotics.
The most common NIs are urinary tract infections (UTIs), pneumonia, bloodstream infections (BSIs) and surgical site infections (SSIs) [12]. In some studies was reported that respiratory tract infections were the most common type [13,[14], [15]. There are also some studies indicate that SSIs are more common [10]. In our hospital, 53.5 % of NIs were BSIs. While 34% were catheter-related BSIs, 19.5% were secondary BSIs. 20.4% of ventilator-associated pneumonia (VAP) were accompanied by BSIs, 13.7% were SSIs, 9.5% were UTIs. These results indicate that catheter care should be revised in our hospital.
Gram-negative bacteria have been reported as causative agents in approximately half of all NIs. These bacteria predominate in most cases of ventilator-associated pneumonia and urinary tract infections. Acinetobacter is the only gram-negative bacillus that increased signi cantly in incidence as a cause of ventilator-associated pneumonia compared to previous years. In the SENTRY study, Acinetobacter species were accounted for 7% of ICU infections in the USA and European countries [16], [17], [18], [19]. Infections caused by non-fermentative Gram negative bacteria have increased compared to previous years in our study.
Microorganisms that cause NIs are often resistant to antimicrobial agents. Unfortunately, the dramatic increase in multidrug-resistant (MDR) microorganisms including P.aeruginosa, A.baumannii, and ESBLproducing or carbapenemase-producing Enterobactericeae, are being reported as agents of nosocomial infections in recent decades. For example, 50-60% of more than 2 million NIs in the USA are caused by antibiotic-resistant pathogens. The incidence of MDR gram negative bacteria in the ICU is higher compared with other hospital units. Antibiotic use has been identi ed as an important risk factor in the emergence of antibiotic resistance [20]. In this study, The prevalence of nosocomial infections caused by MDR bacteria was 45.66 %.
MDR microorganism is a serious public health problem in the world. The treatment is di cult, morbidity and mortality are high. Antibiotics used in treatment are limited, patients have longer hospital stay and increased treatment costs. In a European study, one out of every 20 inpatients reported that health-related infections developed and the causative microorganisms (Klebsiella pneumoniae and Acinetobacter spp.) were generally multiple resistant [6], [8], [21]. In a systematic review of Southeast Asian countries (Brunei, Myanmar, Cambodia, East Timor, Indonesia, Laos, Malaysia, Philippines, Singapore, Thailand and Vietnam), the prevalence of NI was 9.1% and the common microorganisms P.aeruginosa, Klebsiella spp. and A.baumannii [22]. The most common causative agent of NIs were Gram negative bacteria in our hospital. The most resistant microorganism in our study was Acinetobacter spp. The rate of ESBLproducing E. coli and K. pneumoniae was high. About 51.1% of E.coli and 60.3 % of K.pneumoniae isolates were identi ed as ESBL producers. It is interesting that the susceptibility of P. aeruginosa to carbapenems remains high. Carbapenem resistance was 29.8%, 95.1%, 18.2% in P.aeruginosa, A.baumannii and Klebsiella pneumoniae isolates, respectively. Especially in A. baumannii isolates antibiotic resistance was higher than other isolates. Microorganisms isolated from ICUs showed high resistance to many antimicrobial agents. There was an increase in infections caused by colistin resistant P. aeruginosa, A. baumannii, K. pneumoniae and carbapenem resistant K. pneumoniae in the last two years. In addition, the increasing rate of vancomycin resistance Enterococcus (VRE) has emerged. Unnecessary antibiotic administration and prolonged intensive care hospitalization may increase the spread of multidrug resistant pathogens. Monitoring of antimicrobial susceptibility, and appropriate antimicrobial use might be effective to prevent in the emergence of antimicrobial resistance in ICUs.

Conclusion
In conclusion, this study demonstrates a high rate of antimicrobial resistance to commonly prescribed antibiotics among the microorganisms isolated from the patients with NIs hospitalized in ICUs. Infection control and antibiotic management strategies should be reconsidered in our ICUs. It is clear that if effective measures are not taken in the time, antibiotic resistance will be become alarming and will be a major challenge for years to come.

Declarations
Con icts of interest: The author(s) declared no potential con icts of interest with respect to the research, authorship, and/or publication of this article.
Financial Disclosure: The authors declared that this study has received no nancial support.
Ethical approval: