Nosocomial infections or healthcare-associated infections (HAIs) are infections that hospitalized patients acquire throughout their period of stay. Symptoms of the disease may appear during the hospitalization or after discharge from the hospital (1). Infections that appear after 48 to 72 hours are usually classified as nosocomial, and if the infection occurs less than 48 hours of hospitalization, it is likely that the patient might have obtained the infection during the administration process and may have been in the common phase of the disease (2). A recent meta-analysis conducted by Mohammadi et al., from 2001 to 2017, reported a 4.6% overall prevalence rate of HIAs in Iranian hospitals (3). A 2014 CDC report including 183 US hospitals and 11,282 hospitalized patients indicated that 4% of the patients suffered from one or more HAIs (4). This results in a rise in costs, length of recovery, disabilities and even death amongst patients and attaches great importance to development of regionally studied and validated diagnostic and therapeutic guidelines for these infections.
Bacteria are microorganisms that are found in various environments, especially in clinical settings. The ability of bacteria to cause hospital outbreaks and epidemics is indicative of the importance of these microorganisms. Bacteria are mainly labeled as opportunistic pathogens and can create various acquired infections in clinical settings including bacteremia, meningitis, surgical wound infections, urinary tract infections (UTIs), hospital-acquired pneumonia, etc. (5). UTIs are bacterial infections that affect various parts of the urinary tract. Physiologic and anatomic differences have made UTIs more prevalent among women than men; however, the prevalence rate is similar in elderly males and females (6). Infections of the lower urinary tract and the upper urinary tract are referred to as cystitis (bladder infection) and pyelonephritis (kidney infection), respectively (7). Symptoms of the lower urinary tract infections include frequent urination accompanied by pain (dysuria), while symptoms of pyelonephritis include fever, shivering and flank pain in addition to the symptoms of lower urinary tract infections (8). The main cause of both types of infections is uropathogenic Escherichia coli, a gram negative rod- shaped bacterium from the Enterobacteriaceae family (9). The increasing antibiotic resistance and the emergence of multidrug-resistant (MDR) and extensively-drug resistant (XDR) E. coli strains have led to a global health crisis. In most of the infections, the hospital environment is the source and reservoir and, in several studies, it has been observed that environmental pollution has been the source of sudden epidemics caused by bacterial infections (1). Bacteria play an important role in UTIs; therefore, it is necessary to be aware of their prevalence and the causative pathogens for better prognosis, rapid treatment and elimination of the infectious agents in clinical settings. This study aims to evaluate the prevalence of bacterial isolates involved in UTI samples and their antibiotics resistance pattern.

 

From December 2016 to December 2018, a total number of 6299 urinary, respiratory tract, blood, and stool culture tests were performed for the patients who referred to Valie-Asr Hospital Laboratory in Zanjan, Iran, including 3168 (50.3%) males and 3131 (49.7%) females. Urine culture was the most frequently requested culture (n=3582, 56.87%), followed by sputum (n=1058, 16.8%), blood (n=854, 13.4%) and stool (n=182, 2.9%) cultures. In this study, we analyzed microbial cultures of patients with bacterial infections of the urinary tract and the associated antimicrobial resistance patterns. The study population consisted of a total number of 3582 patients with positive urine cultures (85%), including 2006 (56%) females and 1576 (44%) males in the 0-99 age range. The study population mainly consisted of middle-aged and elderly patients (n=2228, 62.2%), followed by young adults (n=1021, 28.5%). Positive urine cultures were the least frequent among adolescents and children (n=333, 9.3%). The average age of the study population was 63.4 years. With 1275 positive bacterial growth results, the emergency ward had the highest positive culture ratio (35.6%), followed by the following wards: internal (17.8%, n=638), neurosurgery (16.9%, n=605), intensive care unit (11.8%, n=423), infectious diseases (10.4%, n=373), cardiology (3.7%, n=133), surgery (1.6%, n=57), coronary care unit (0.9%, n=32) oncology (0.7%, n=25), and ophthalmology (0.6%, n=21).
According to urine cultures results, E. coli and Staphylococcus epidermidis were the most frequently isolated gram negative and gram-positive bacteria from the urine samples with isolation rates of 53.43% and 15.99%, respectively. Table 1 reveals information on the prevalence of the isolated bacteria.

Table 1. Prevalence of isolated bacteria from the urine samples of a total number of 3582 patients with positive urine cultures.

Among gram negative bacteria, nitrofurantoin and vancomycin represented the lowest resistance rates at 25.27% and 26.74% respectively. Piperacillin showed the least efficacy with a resistance rate of 76.04%, followed by cefazolin which had a resistance rate of 74.94%. Antibiotic susceptibility results of the isolated gram-negative bacteria are demonstrated in Table 2.

Table 2. Antibiotic susceptibility pattern of the gram-negative bacteria isolated from 2442 urine samples of the clinical origin and the associated resistance rates.

Among gram positive bacteria, vancomycin and gentamicin showed more promise with respective resistance rates of 19.34% and 27.34%. The highest resistance was associated with ampicillin (68.61%) and Trimethoprim/Sulfamethoxazole (66.06%). Antibiotic susceptibility results of the isolated gram-positive bacteria are demonstrated in Table 3.

Discussion

A total number of 3582 ambulatory and hospitalized patients with bacterial UTI were included in our study. The overall prevalence of UTI was significantly high (85%, P<0.001) among the patients with a urine culture request compared to several similar studies, which reported overall UTI prevalence of 12.1% to 45.32% (12-15). Even though this prevalence variation can be due to geographical and environmental factors, diagnostic methods applied in the study and the characteristics of the included patients such as personal hygiene standards and diet (15), high prevalence ratio in our study raises the concern of sufficiency of the quantity of microbiologic tests requested by the physicians in this clinical setting in Zanjan, Iran from 2016 to 2018.
Similar to other studies in this timeframe and as expected from the general epidemiology of UTIs (14), the female patients consisted the majority of the population in our study. Furthermore, a significant increase was observed in the prevalence of UTI with age, given that most of the patients were from the middle-aged and the elderly group (P=0.016). This can be explained by higher number of hospital admission, longer duration of stay and previous antibiotic therapy in the elderly. UTI incidence in women over 60 was 1.7 times higher than the overall incidence in females, putting this group at the highest risk. This result is similar to that of a study by Alós, which reported 20% and 11% UTI prevalence rates in women over 65 years and in the overall population, respectively (16).
Gram-negative bacteria were significantly more prevalent (68%) than gram positive-bacteria (32%) in this study (P<0.001) and E. coli was the pathogen behind more than half of the infections. This is in accordance with results from several other studies, which reported the dominance of gram-negative bacteria and especially E. coli in their study populations (12). The second most common gram-negative bacteria -S. marcescens- nevertheless, was not reported to be frequently isolated in UTIs in other studies, as normally, E. coli, K. pneumoniae, P. aeruginosa, Enterobacter, Citrobacter, P. mirabilis are the most common bacterial uropathogens (17). S. marcescens usually accounts for 1-2% of HAIs; however, its isolation rate was significantly higher in this study (5.38%) (P<0.001) (18). This reveals that even though S. marcescens rarely causes community-acquired infections, its importance should be taken into account in healthcare settings and as a nosocomial infection, which plays a critical role in hospital outbreaks.
S. epidermidis and group D streptococci were the most prevalent gram-positive bacteria in the patient population with respective prevalence rates of 15.99% and 7.7%. This result was consistent with previous literature reporting Enterococcus spp., Staphylococcus spp., and Streptococcus agalactiae as dominant gram-positive uropathogens. Gram-positive bacteria nevertheless, are more likely to be contaminants in the urine cultures and should be analyzed along with other factors including symptoms and urine analysis results such as WBC count (19, 20). Lactobacilli-containing samples were excluded from antibiotic susceptibility tests since they are a part of vaginal bacterial flora and commonly indicative of contamination while collecting urine specimens (21).
Gram-negative bacteria were the most sensitive and resistant to nitrofurantoin and piperacillin with resistance rates of 25.27% and 76.04%, respectively. Gram-positive bacteria were widely resistant to ampicillin (68.61%) and Trimethoprim/Sulfamethoxazole (66.06%).
These results are in line with resistance patterns reported from Iran and worldwide (3, 12, 17, 22, 23). Vancomycin resistance was relatively low in both gram-negative (26.74%) and gram-positive (19.34%) bacteria. However, it is considered as a last-resort antibiotic and should only be included in the antibiotic therapy regimen according to regional guidelines and only when needed. The vancomycin resistance result in our study was higher compared to that of a UTI study conducted by Mihankhah et al., in northern Iran, in the same timeframe (11.7%) (22). Furthermore, in a study by Khoshbakht et al., conducted in Karaj, Iran in 2013, vancomycin resistance was reported 7.7% (24). This rate was reported lower and under 5% in a ten-year surveillance European study conducted on the prevalence and susceptibility patterns of UTI-associated bacteria, in 2013 (13).
The limitations of the study included exclusive application of conventional biochemical microbiological tests for bacterial identification and not determining resistance-associated genes.

 

Conclusion

The overall prevalence of UTIs was relatively high in this study, which emphasizes the importance of proper quantity and quality of urine cultures and susceptibility tests, as well as development of novel efficient surveillance guidelines for each area. E. coli and S. epidermidis were the most prevalently isolated uropathogens and there was a notable S. marcescens outbreak in the study timeframe. Alarming resistance rates were observed in ampicillin and piperacillin, which should be taken into account in therapy guidelines in this area. Prevalence of resistant strains can be avoided by developing appropriate healthcare policies and community awareness. Further studies should focus on regional and periodical prevalence and susceptibility patterns of the UTIs, globally.

 

Limitations

Responsible genes to antibiotic resistance, genetic relationship between the resistant strains, and investigating any correlations with patient characteristics are not determined and these are the limitations of this study. Moreover, identification of isolates were merely performed taking advantage of biochemical aspect.

 

Consent for publication

All named authors meet the International Committee of Medical Journal Editors (ICMJE) criteria for authorship for this article, take responsibility for the integrity of the work as a whole, and have given their approval for this version to be published.

 

Funding

All data generated or analyzed during this study are included in this published article/as
supplementary information files.

 

Funding

Not applicable.

 

Authors’ Contributions

Supervision, methodology, final editing and review were done by Bahman Mirzaei. Bahman Mirzaei and Erfan Fakheri contributed to Conceptualization. Narges Moradi and Niloufar Kazemi contributed to data collection, writing and data curation.

 

Acknowledgements

The authors are grateful for the support of colleagues in Bacteriology and virology Departments at Zanjan University of Medical Sciences.

 

Conflicts of Interest

The authors declare that they have no competing interests.