Prevalence and bacterial susceptibility of hospital acquired urinary tract infection 1

Purpose: Urinary tract infection is the most common nosocomially acquired infection. It is important to know the etiology and antibiotic susceptibility infectious agents to guide the initial empirical treatment. Objective: To determine the prevalence of bacterial strains and their antibiotic susceptibility in nosocomially acquired urinary tract infection in a university hospital between January and June 2003. Methods: We analyzed the data of 188 patients with positive urine culture (= 105 colonyforming units/mL) following a period of 48 hours after admission. Results: Half of patients were male. Mean age was 50.26 ± 22.7 (SD), range 3 months to 88 years. Gram-negative bacteria were the agent in approximately 80% of cases. The most common pathogens were E. coli (26%), Klebsiella sp. (15%), P. aeruginosa (15%) and Enterococcus sp. (11%). The overall bacteria susceptibility showed that the pathogens were more sensible to imipenem (83%), second or third generation cephalosporin and aminoglycosides; and were highly resistant to ampicillin (27%) and cefalothin (30%). It is important to note the low susceptibility to ciprofloxacin (42%) and norfloxacin (43%). Conclusion: This study suggests that if one can not wait the results of urine culture, the best choices to begin empiric treatment are imipenem, second or third generation cephalosporin and aminoglycosides. Cefalothin and ampicillin are quite ineffective to treat these infections.


INTRODUCTION
Hospitalized patients are predisposed to a variety of nosocomial infections, especially with multidrug-resistant organisms 1 .Urinary tract infection (UTI) is the most frequent nosocomial infection and has been suffering a shift in the etiology and antimicrobial susceptibility, as common as other infections detected in the last decade [2][3][4][5] .Since most of treatments began empirically, prior knowledge of the bacterial prevalence as well as the resistance patterns in a particular setting is essential.
Informations on the etiology and bacterial susceptibility of nosocomially acquired UTI in Brazil are scarce which makes the decisions on antibiotic choice almost entirely dependent of international data 6 .As both geographic and temporal factors can influence these data, they need to be constantly and locally re-evaluated.
The aim of this study was to determine the local prevalence of bacterial strains and the antibiotic susceptibility of the nosocomially acquired UTI in our institution to guide antibiotic choice and to achieve a maximal clinical response in empiric treatment while the antibiotic susceptibility of the pathogen is still unknown.

METHODS
All urinary specimens with significant bacteriuria, defined by Kass 8 as being urine culture with more than 10 5 colony forming units/mL, processed in the laboratory of the Hospital das Clínicas of the School of Medicine of Ribeirão Preto-University of São Paulo, between January and June of 2003, were included in this study.Nosocomial episode was defined as any UTI beginning 48 hours after admission.
We analyzed patient data and bacterial etiology as well as antimicrobial susceptibility to commonly used antibiotics.

RESULTS
We obtained clinical information of 188 patients that had nosocomially acquired UTI.Half of them were male (99 patients).Mean age was 50.26 ± 22.7 (SD) (range 3 months to 88 years).The prevalence increased after the 5 th decade in males and 4 th decade in the females (Table 1).There were a great variety of isolated pathogens and their frequency is listed on Table 2. E. coli was the most frequent bacteria (26%), followed by Klebsiella sp.(15%), Pseudomonas aeruginosa (15%), and Enterococcus sp (11%).Table 3 shows the antibiotic susceptibility of the four most frequent pathogens and the overall sensibility to antibiotics.Klebsiella sp were sensible to imipenem, second or third generation cephalosporin and fluoroquinolones, and highly resistant to ampicillin.P. aeruginosa had high levels of resistance, and was more sensible to ceftazidime, imipenem and specially to cefepime (100%), a forth generation cephalosporin that is not commonly tested, only in special situations of multidrug-resistant organism.
Enterococcus sp. was the only Gram-positive bacteria with a high incidence and was very sensible to ampicillin (89%) different from the Gram-negative organisms described above.It was more sensible to specific antibiotics not presented in Table 3, like penicillin G (83%) and vancomycin (100%).
The overall antibiotic susceptibility is highly influenced by the Gram-negative bacteria, which were involved in approximately 80% of nosocomially acquired urinary tract infections.The pathogens were more sensible to imipenem, second or third generation cephalosporin and aminoglycosides; and were highly resistant to ampicillin and cefalothin.It is important to note the low susceptibility to ciprofloxacin and norfloxacin.

DISCUSSION
The high mean age of our patients reflect the hospital population.The increase of prevalence of nosocomially acquired UTI in the male group after fifty years might be caused by the higher incidence of urinary tract pathologies like prostate diseases.The female group has a more uniform distribution, and the elevated incidence in the twenties and forties might be caused by the obstetric and gynecologic causes, respectively.
We found that E. coli is the predominant bacterium in urine samples, followed by P. aeruginosa and Klebsiella sp, reflecting the predominance of Gram-negative bacteria.This is in accordance to previous studies in other countries [9][10][11] .There is a high prevalence of Grampositive bacteria, corresponding to 22% of total, mainly due to Enterococci and Staphylococci, which correlates with previous data from other studies that report an increase in the number of Gram-positive bacteria and yeasts as nosocomial UTI pathogens 4,9 .

CONCLUSION
This study suggests that if one could not wait the results of urine culture, the best choices to begin empiric treatment of nosocomial UTI are imipenem, second or third generation cephalosporin and aminoglycosides.Cefalothin and ampicilin are quite ineffective to treat these infections.

TABLE 1 .
Prevalence of nosocomially acquired urinary tract infections according to gender and age.

TABLE 2 .
Micro-organisms isolated in urine