Middle East Journal of Family Medicine

Correspondence:
Dr. Rubina Lone
Assistant professor, Department of Microbiology
SKIMS Medical College, Srinagar
E-mail: kadrism@gmail.com

ABSTRACT

OBJECTIVE: Recently, Acinetobacter emerged as an important pathogen and the prevalence of isolation has increased since the last two decades worldwide. Our objective was to see the impact of acinetobacter infection in our hospital; its demographic features, speciation and antibiotic sensitivity and resistance pattern. METHODS: A study of the clinical samples submitted to the microbiology laboratory of a teaching hospital over a period of 2 years (June2001 to June 2003). Identification, speciation and anti-biotyping were performed for the isolates of Acinetobacter recovered from infective samples. Clinical demographic characteristics were studied retrospectively.

RESULTS: Out of a total 5352 infected samples, 258 (4.8%) were found to be due to Acinetobacter. The organism was responsible for 76 (39.64%) cases of urinary tract infection and 38 (29.45%) cases of wound infection and was most prevalent in the intensive care unit (29.84%). A. baumannii was the most predominant species. A high level of resistance was recorded for Ampicillin (86.3%), Cefazolin (93.2%) Gentamicin (61.5%), Cefotaxime (65.8%), Ceftriaxone (61.5%) and Ciprofloxacin (69.2%). Although no peculiar pattern during anti-biotyping was observed, but most of them were multi-drug resistant.

CONCLUSION: Multi-drug resistant Acinetobacter nosocomial infection has emerged as an increasing problem in intensive care units of the hospital. The analysis of risk factors and susceptibility pattern will be useful in understanding epidemiology of this organism in a hospital setup.

Key words: acinetobacter, nosocomial, infection, anti-biotyping, multi-drug resistant

Acinetobacter spp. is one of the important nosocomial pathogens and has been known to cause different kinds of opportunistic infections⁽¹⁾. These gram negative coccobacilli are ubiquitous in nature, and responsible for causing intermittent outbreaks especially in regions where temperature is hot and humid. Infections caused by them are difficult to control due to multidrug resistance, which limits therapeutic options in critically ill and debilitated patients especially from the intensive care unit, where its prevalence is most noted⁽²⁾. Acinetobacter baumannii is now recognized to be the genomic species of great clinical importance capable of causing life threatening infections including pneumonias, septicemias, wound sepsis, urinary tract infections, endocarditis and meningitis⁽³⁾.

Also, it is currently the commonest isolate from gram negative sepsis in immunocompromised patients posing a risk for high mortality⁽⁴⁾. The organism prefers moist environments, therefore, its colonization in persons and damaged tissues is common⁽⁵⁾. It is very difficult to explain the role of Acinetobacter acquisition in the ICU, since Acinetobacter does not always act as an infecting pathogen as it is widely distributed and has tremendous colonizing potential^(1,6). Also, there is a significant difference in the behavior of this organism among isolates recovered from various geographic locations⁽⁷⁾. In addition, risk factor for Acinetobacter acquisition, may vary in different set-ups with epidemic outbreaks of infection or endemic colonization⁽⁸⁾. Although various factors predisposing to Acinetobacter infection have been analyzed in different studies, there are only few authentic reports from India that have attempted to determine the risk factors and in-vitro susceptibility and resistance patterns of clinically significant Acinetobacter isolates^(9,10,11). The present study describes our experiences of clinical materials and cases from which strains of Acinetobacter were isolated and to determine the resistance patterns of Acinetobacter isolates to various antimicrobial agents by disc-diffusion methods and micro-broth dilution methods obtained from a tertiary care hospital.

After taking consent from the hospital ethical committee, the study was carried out in a 600-bed tertiary care hospital located in North India during a 2 year period (June 2001 through to June 2003). Nosocomially acquired Acinetobacter infection was defined as the isolation of the organism repeatedly from blood cultures and other specimens, 72 hours after a patient was admitted to the hospital. Standard definitions as given by Centre for Disease Control and Prevention were used to differentiate categories of infection versus colonization⁽¹³⁾.

In brief, patients from whom Acinetobacter was isolated in absence of clinical disease suggested colonization and were not included in the study. Clinical specimens included were blood, CSF, endo-tracheal aspirate, urine, sputum, pus and other body fluids. The following variables were analyzed: patient age, sex, and the presence of underlying diseases or conditions, admission to ICU, mechanical ventilation, urinary and IV catheterization, number of hospital days and surgery, if any.

All clinical specimens were initially processed by the routine microbiological laboratory tests to separate the non-fermenters from gram-negative bacilli and eventually identified as Acinetobacter. Typical colonies were enumerated, selected and examined further. Acinetobacter was identified by gram-stain, cell and colony, activity of oxidation/ fermentation tests, absence of motility and negative oxidase and positive catalase test. Speciation of Acinetobacter into various genomic species (GS) was done by using a battery of bio-chemical tests⁽¹⁴⁾.

Disc diffusion susceptibility testing was performed on Mueller-Hinton agar for following anti-microbial agents with their concentrations given in parenthesis: Ampicillin (10mg), Amikacin (30mg), Gentamicin (10mg), Ciprofloxacin (5mg), Ofloxacin (5mg), Cefazolin (30mg), Cefotaxime (30mg), cefoperazone+Sulbactam (75mg) and Imipinem (10mg). Strains found resistant to various antimicrobials by disc-diffusion method were tested by NCCLS broth micro-dilution method⁽¹⁵⁾. Pseudomonas aeroginosa ATCC 27853 was used as a control strain.

We compared the difference in the risk-factors among patients with Acinetobacter infection and patients with other gram-negative bacterial infections and investigated for significant risk factors in patients with these infections. Contingency tables were calculated with Pearson's test of Fischer's exact test by comparing the proportions, wherever necessary. The odds ratio (OR) was calculated and differences were considered to be significant if the P-value associated with the test was less than 0.05. For all the analysis SPSS-software analysis was used.

During the period of two years in the clinical microbiological laboratory at Sheri Kashmir Institute of Medical Sciences, a tertiary care hospital in J&K, 25,200 samples were cultured, of which 5352 (21.23%) were found to be infected. Out of these 258 (4.8%) samples were found to be due to Acinetobacter. The variables such as age, sex, possible source of infection, duration of hospital stay, previous antibiotic therapy and risk-factor distribution are shown in Table 1.
The patients ranged in age from 18 days to 84 years (Mean age ± SD, 33.2± 22.8 yrs, median age 42 years). Acinetobacter was isolated from various types of infections; among these urinary tract infections were extremely significant (p<0.05) followed by pus and wound exudates (p<0.05).

Likewise the risk factor distribution associated with infection is shown in Table 1. Acinetobacter infection was significantly observed (p<0.05) in the intensive care unit, postoperative ward, and patients on mechanical ventilation. Also, a longer stay in hospital, that is beyond the first week, was significantly associated with a remarkably higher rate of infection (p<0.05). The underlying chronic debilitating conditions in order of frequency included diabetes mellitus with complications, hypertensive stroke, chronic renal failure, leukaemias, and chronic obstructive lung disease.

No statistical significance was found in relation to age, sex, surgery and duration of hospital stay. The following variables were considered to be biologically plausible risk-factors: admission to ICU, mechanical ventilation, chronic debilitating conditions and prolonged use of IV, and urinary catheters.
A. baumanni was the main species responsible for 72% of the infections followed by A. calcocaeticus and A. junii (10.6% and 7.5 % respectively). A. lwoffii and A. haemolyticus were predominantly found in wound exudates.

The disc-diffusion susceptibility testing results are given in Table 2, which show the percentages of resistance and susceptibility among all isolates. High level of resistance was recorded for Ampicillin (86.3%), Cefazolin (93.2%) Gentamicin (61.5%), Cefotaxime (65.8%), Ceftriaxone (61.5%) and Ciprofloxacin (69.2%). Amikacin, Cefoperazone+Sulbactam and Imipinem showed maximum activity with an overall low resistance of 17%, 11.5%, and 1.5% respectively. Strains of A. baumainnii were found to be more resistant to all antibiotics as compared to other DNA groups. Table 3 shows the range of MIC results obtained which were found to be highly elevated in these isolates. The highest resistance was observed in ICU isolates where A. baumanni was most prevalent.

Acinetobacter has emerged as an important nosocomial pathogen, with a rising prevalence, is often multi-drug resistance and associated with life threatening infections^(15,16). The overall incidence of Acinetobacter from all infective samples was 4.8 % (258 out of 5352) indicating its importance as a nosocomial pathogen, since in most of the cases the patients were symptomatic for sepsis. There was a significantly higher incidence of infection among males, which is in tandem with other studies from India⁽¹²⁾. The literature search demonstrates that A. baumannii together with A.calcoaceticus; GS 3, GS13 are predominantly involved in infection and are collectively known as A.calcoaceticus- A. baumannii (Acb) complex group⁽¹⁷⁾. A. baumanni was the major species isolated from 72% of our clinical samples, and is reportedly a major species in other parts of the world as well⁽⁷⁾ In our study the maximum number of isolates was from the urinary tract (39.64%) and these were the strains that showed maximum multidrug resistance. These results are comparable to some of the studies done previously⁽²⁾ About 15% of these isolates were associated with the use of indwelling catheters and 30% of the patients had a serious underlying debilitating disease. The incidence of respiratory tract infection was 14.7%. Mechanical ventilation and admission to ICU were found to be independent risk factors for these infections. Bacteremia is known to be associated with risk factors like intravenous catheterization⁽¹⁹⁾ In the present study 17% of the bacteraemic cases were associated with catheterization, about 50% of them had undergone surgery and 24% had been intubated and ventilated. Overall, the significant risk factors for Acinetobacter infection were mechanical ventilation, admission to ICU, underlying chronic debilitating condition and a prolonged hospital stay. A longer stay in a high-risk unit and use of mechanical ventilation has been identified as a risk factor in previous studies as well^(17,19,20) Despite many intensive efforts, the nosocomial acquisition of Acinetobacter remains problematic especially in the ICUs. There are difficulties in control of infections due to their high resistance to antimicrobials in the hospital environment. Exposure to certain antibiotics provides a selective advantage to a small number of resistant organisms in patients already colonized, thereby enabling them to turn into pathogens.

Susceptibilities of Acinetobacter against various antimicrobials are considerably different among countries, centers and even among different wards of the same hospital, therefore, such type of local surveillance studies are found important in deciding the most adequate therapy for Acinetobacter infection⁽²⁾. The high level resistance of Acinetobacter to antimicrobials seems unstoppable⁽²²⁾. Only few authentic data are available regarding in- vitro susceptibility of clinical isolates of A. baumannii in India⁽²³⁾. Increasing resistance to cephalosporins was observed mainly in strains belonging to the Acb complex. Amikacin, cefoperazone+Sulbactam and Imipinem showed maximum levels of activity with susceptibilities of 83%, 87.5%and 98.5% respectively. This susceptibility pattern conforms to the recent introduction of these antibiotics in our hospital. MIC range of our strains was higher than many other recent reports^(19,22). This means MDR isolates are increasing day by day, probably due to indiscriminate use of these antibiotics in our setting. We re-emphasize that broad spectrum antibiotics should be used with caution. Cefotaxime, and or ceftriaxone should be discontinued in units where resistant strains for these two antibiotics are being reported. With revelation of Cefotaxime and/or ceftriaxone resistant strains from our study, the hospital ICU was advised to use other antibiotics combinations like effective beta lactams or carbepenem along with amikacin.

In conclusion MDR A. baumannii was the species responsible for the majority of Acinetobacter infection in our hospital. It was also the cause of severe clinical diseases, associated with a high mortality rate. Mechanical ventilation and admission to ICU were found to be potential independent risk factors in our setup. Strict infection control measures may prevent nosocomial infection. Further research related to mechanism of resistance and extended spectrum beta lactamases and carbepenem is under way.