Analiza epidemiologică a tulpinilor circulante în spital: germeni cu rezistențe la carbapeneme

Introduction

Carbapenems are beta-lactam antibiotics with a broad spectrum activity, mainly used as empiric therapy in the treatment of infections with suspected or documented multi-resistant strains and particularly for infections caused by Gram-negative germs^(1,2). These antibiotics are administered in hospital, mainly for severe bacterial infections with complications, which are often nosocomial. On the other hand, in hospitals, the extensive use of antibiotics creates a selection pressure and allows, in favorable environmental conditions, a massive multiplication of resistant strains. In addition, in clinical wards, the probability of germs transmission can be high, and for opportunistic germs the first step in the development of an infection it’s the carriage status⁽³⁾. Further, the carriage duration, alongside the personal risk factors (as age, chronic pathology and immunodeficiency) and medical invasive interventions (particularly medical devices implantation) accelerate the occurrence of infections.    

 

For the class of carbapenems, the emergence of the resistance (more than 20 years ago) created multiple and important implications in different directions: regarding the efficacy of the possible etiologic treatment (especially for Gram-negative pathogens), existing only a few alternatives, that entail a severe clinical evolution of the patient, with a high risk of death and thus epidemiologically, increasing the probability of transmission in clinical wards to other patients^(4,5). The impact of the consequences of the carbapenems-resistant strains can be reduced by a careful epidemiological surveillance of circulating strains, the monitoring and description of their sensibility for gathering information to select appropriate control and prevention measures, in the condition of the absence, until now, of new effective antibiotics^(5,6). Regarding the epidemiological importance, there are already observations about nosocomial transmissions and outbreak manifestations in intensive care units, particularly caused by Klebsiella pneumoniae producing carbapenemase (KPC) strains^(1,2,7,8).

The resistance mechanisms to carbapenems may be due to the modification of the target molecule into mutation-derived penicillin-binding proteins (PBPs) developed by Gram-positive pathogens, while Gram-negative bacteria become resistant by reducing porin’s permeability, efflux pumps or by producing carbapenemases^(4,5,7). New mechanisms are possible to emerge and the exact identification of the pathogen, the description of the phenotypic sensibility and, if possible, the resistance mechanisms are necessary for an appropriate characterization and management of the assisted cases in healthcare settings^(4,7,8). 

The objectives of this study were to know the prevalence and to describe some epidemiological characteristics of carbapenems-resistant strains, isolated from hospitalized patients.

Methods

We conducted a cross-sectional survey for the period 2009-2015, in which there were similar reported data regarding the performed antibiograms and the use of the antibiotics in hospital. There were included strains which were characterized phenotypically through antibiogram who involved at least one carbapenem, regardless the pathology for which patients were hospitalized and the reason for the bacteriological testing. We did not include strains without test to carbapenems. 

The strains identification was done prospectively through the program of surveillance for the circulation of bacterial strains that is part of the routine nosocomial infections surveillance. The source for data was the patient’s computerized file from which there were extracted the bacteriological determinations accompanied by the antibiotic sensitivity tests. Epidemiological data were the age, gender and the biological product from which the germ was identified and the antibiogram was performed. The data were collected on paper and then registered into a computerized database using Excel.

Another database in Excel was created for the monthly monitoring of antibiotics consumption in hospital, based on the reports made by the hospital pharmacy. The antibiotic products were recorded and classified on the basis of the antibiotic content as active substance.

 

The statistical analysis was done in EpiInfo and Excel, calculating the prevalence of phenotypic sensitivity forms to carbapenems among identified strains, ratios, range, frequency distributions of epidemiological parameters, the confidence intervals and statistical significance through the z test for the proportions comparison in large samples, and ANOVA for the difference among the means in two samples. Inferences were made by Pearson correlation coefficient calculated from linear regression equation. The analysis of antibiotic utilization was made by linear regression for multiannual evolution and a descriptive comparison among the trend of the prevalence for carbapenems-resistant strains and the quantity of carbapenems antibiotics, in grams per capita used yearly for each inpatient.  

Results

In the period 2009-2015, we have identified 1,036 strains, for which an antibiogram including carbapenems testing was performed (Table 1). Among all isolates, 792 (76.45%) have been tested for Meropenem and 777 (75%) to Imipenem. The annual evolution of resistance in the analyzed period was growing for both tested carbapenems, ranging between 5.6% and 23.3% for Meropenem, meaning a 4.2 times increase, while for Imipenem the range was from 5.6% to 37.8%, with a 6.8 times growth. Globally, in the analyzed period, the level of resistance to Imipenem was 20.1% and significantly higher (z=3.032; p=0.002432) than to Meropenem, for which it was 15.8% of the tested strains.   

The number of isolates resistant to carbapenems, in the survey period, reached to 188 strains. Regarding the category of germs, the carbapenems-resistant bacterial species most commonly identified were Pseudomonas, Acinetobacter, Klebsiella pneumoniae and less Staphylococcus, Enterococcus and Enterobacter (Table 2). It is noticeable the constant identification as carbapenems-resistant strains for Pseudomonas and Acinetobacter species. The results for 2010 show a very low number of strains due to a lack (impossibility to identify) of data.

 

The level of prevalence among isolates tested to at least one carbapenem reached in the entire period a value of 18.1% of strains for all carbapenems, 12.1% for Meropenem, and 15.1% of strains for Imipenem (Figure 1). Among all isolates, the prevalence of resistance was significant (z=2.728; p=0.0063) higher for Imipenem than for Meropenem. In the evolution for the survey period, the prevalence of carbapenems-resistant strains had a moderate elevation, the correlation coefficient being 80.5% for Meropenem, 66.3% for Imipenem, and 79% for all carbapenems.

Isolates were cultivated mainly from the urine (45.6%), blood (18.4%) and wounds (14%), and less from tracheal secretions (8.1%), sputum (7.4%) and other biological fluids (Figure 2). 

Among patients, there were significantly (z=5.906; p<0.0001) more men (65.9%; CI 95%: 57.63-73.5) than women, taking into account the higher proportion that was 55.5% (51.88-59.1) of male patients, for whom a biological products sampling for microbiological determination was recommended and a sensitivity test was done (Figure 3).

The age of patients ranged between 1-year-old and 89-years-old, the mean age was 61.45 years (standard deviation: 16.2 years) and the age group with the highest weight was 60-79 years, 92.6% of the patients being over 40-years-old (Figure 4).


 

In the same patient population and time period, the use of carbapenems had increased, except for Ertapenem, which was less used and in quantities that have remained relatively constant (Figure 5). The most used carbapenem, in the survey period, was Imipenem-Cilastatin, and secondly came Meropenem. The utilization had been rising significantly each year, expressed by a correlation coefficient of 93.9% for all carbapenems, 94.3% for Imipenem/Cilastatin and 81.4 for Meropenem.

Considering the size of hospitalized patients population for which carbapenems were used and from whom resistant strains were isolated, the quantity in grams/capita for each inpatient and for the entire year elevated significantly (p<0.0001), from 0.28 g/patient in the entire year 2010 to 1.12 g/patient in the entire year 2015. For the inpatient population, the carbapenems administration in grams/capita, as independent variable in the linear regression, elevated the prevalence of carbapenems-resistance as dependent variable, with a strong association for 86.9% Pearson correlation coefficient (Figure 6).


 

Discussions 

The carbapenems-resistant strains are multidrug resistant (MDR) germs that are considered a global health threat, mainly because they are recognized as being widespread in healthcare settings from many counties; they allow few possibilities for the etiologic treatment of patients and their resistance is developed through several distinct mechanisms, of which is distinguished the possibility of transmission of the resistance by transferable carbapenemase-encoding genes between microbial species and thus increasing the nosocomial risk and diffusion^(1,4,9,10).

In our survey, the phenotypic evaluation of the resistance to carbapenems used for some isolates only Imipenem or Meropenem, and for others the both antibiotics. Only a few strains were tested to Ertapenem, which was not included in the evaluation because of the low number and because the tests were made only in 2015. The inconsistence in the manner of tests achievement deeply affected the validity of the epidemiological evaluation. Also, in our observation, the absence of data regarding a part of strains isolated in 2010 was due to a lack of access to both basic records categories, electronic or in paper. All these suggest the need for standardization of common evaluations for carbapenems sensitivity in the practical surveillance activity as more and more knowledge is cumulated regarding these antibiotics.  

As our results in multiannual evolution, the prevalence of the resistance to carbapenems has grown in others studies, regardless the method of determination and the geographical region of provenance of healthcare facilities^(9,10,11). The difference from other regions are the bacterial species, that were constantly in our observations Pseudomonas and Acinetobacter, and more frequently identified, against species of Enterobacteriaceae, particularly Klebsiella, that was involved also in outbreaks in intensive care units from developed countries^{(10,11,12,13)}.  

The fact that the resistant isolates were from adult persons, over 40-years-old, and predominantly men, can be explained by the characteristic of opportunistic germs that cause infections in patients with chronic pathology, immunodeficiency, those requiring ventilation and urinary or intravenous catheters^(10,14).

The use of antibiotics was considered for a long time a selection factor for antibiotic-resistant strains, but in the case of carbapenems they are used in the treatment of patients with infections caused by multidrug-resistant germs^(2,15). This particularity makes important the monitoring of carbapenems use and the resistance of bacterial strains⁽¹⁴⁾. 

The problem of bacterial resistance is complex, until the identification of the factors that cause the resistance and until some efficient control measures will be taken. Till then, the evaluation is stringently necessary, and also the control interventions involving the prudent utilization of antibiotics and reducing (interrupting) the transmission^(10,11,12). 

The important limit of the presented survey is the inclusion in the study of strains for which the necessary data were identified in the medical records. We preferred to keep this valid data than to introduce uncertain data. Another constraint was the fact that the data reporting the use of antibiotics were available only since 2010. More assessments are needed for the description of the dynamics of resistance to carbapenems and its determinism, for having timely information to implement effective measures.  

Conclusions

In our survey, for the analyzed period we observed a significant elevation of the prevalence of carbapenems-resistant strains and particularly to Imipenem. The resistant strains were mainly species of Pseudomonas and Acinetobacter, isolated mainly from the urine, but also from the blood, mostly from male adult persons, over 40-years-old. In the inpatient population, the elevation of the carbapenems quantity that had been administered was highly correlated with the increasing prevalence of the carbapenems-resistant isolates. 

Conflict of interests: The authors declare no conflict of interests.