Analysis of blood / tracheal culture results to assess common pathogens and pattern of antibiotic resistance at medical intensive care unit , Lady Ridgeway Hospital for Children

Background: Intensive care units (ICUs) are burdened with a high frequency of nosocomial infections often caused by multi resistant nosocomial pathogens. Objectives: To determine the common pathogens in medical intensive care unit of Lady Ridgeway Hospital for Children (MICU-LRH) and to look for the pattern of antibiotic resistance of these pathogens. Design & Setting: This retrospective study was performed by tracing all the culture reports of MICU-LRH done at microbiology laboratory of LRH in the year 2006. Results: Total number of blood cultures done in 2006 was 659. Of them 123(18.7%) became positive. Out of positive blood cultures 38.2% were for spores and 24% for coliforms. Staphylococcus aureus (10.6%), streptococcus spp. (4.1%), pseudomonas spp. (4.1%) and candida spp. (4.9%) were the other pathogens in blood cultures. Out of 457 tracheal cultures done in 2006, 251(56%) were positive. Contamination with spores was 3.1%. Majority (43%) of tracheal cultures were positive for coliforms. Other common pathogens were pseudomonas spp. (19.5%) and candida spp. (9.8%) Resistance pattern of coliforms varied in blood cultures and tracheal cultures. There was significant resistance to aminoglycosides. Imipenem & meropenem resistant isolates were not found in blood cultures but in tracheal cultures 44% of isolates were resistant to imipenem & 42% were resistant to meropenem. _________________________________________ Senior Registrar in Paediatrics, Medical officer, Medical Intensive Care Unit, 3 Consultant Microbiologist, 4 Consultant Paediatrician, Medical Intensive Care Unit, Lady Ridgeway Hospital, Colombo (Received on 18 January 2011: Accepted on 25 February 2011) Resistance pattern of pseudomonas to amikacin was around 34% in both blood & tracheal cultures. 25% of isolates in blood cultures and 50% of isolates in tracheal cultures were resistant to ceftazidime. Although, there was no resistance to ticarcillin in blood cultures, 51% pseudomonas isolated in tracheal cultures showed resistance. Resistance rate to ciprofloxacin was 50% in blood cultures and 34% in tracheal cultures. Eighty three percent of staphylococcus spp. in both blood & tracheal cultures were resistant to cloxacillin. More than 70% were resistant to gentamicin. Around 33% isolates in blood cultures & 22% in tracheal cultures were resistant to fusidic acid. However, all staphylococcus spp. were sensitive to Vancomycin. Conclusions: There were more positive tracheal cultures than blood cultures. Majority of septicaemia were due to coliforms. Coliforms and pseudomonas were major pathogens in tracheal cultures. There was significant colonization of candida spp. in respiratory tract of patients at MICU-LRH in contrast to candida septicaemia. Emergence of antibiotic resistance to broad spectrum antibiotics is a significant problem. (


Introduction
Sepsis is a major problem in intensive care units (ICUs) and antibiotics are one of the most common therapies administered in the ICU setting.However, in addition to treating infections, extensive antibiotics usage may also contribute to the emergence of resistance among pathogenic microorganisms.
Antimicrobial resistance among ICU pathogens is generally increasing but many different patterns and variations do exist in different countries, probably due to different antimicrobial usage patterns.When new medical practices and alternative antimicrobials are introduced, changes in the dominant microbial aetiologies may emerge which would include novel resistant organisms.Appropriate therapy of ICU infections directed by local resistance data can have significant consequences for both patient and the healthcare system 1,2 .
The emergence of antimicrobial-resistant pathogens in ICUs has made treating these infections very difficult and, in some rare cases, almost impossible.ICU patients are particularly susceptible to nosocomial infections due to underlying illnesses, suppressed immune systems and frequent use of invasive devices 3 .
There is no data available up to the present time on the common pathogens of blood cultures or tracheal aspirates together with an assessment of the antibiotic resistance pattern in the medical intensive care unit at Lady Ridgeway Hospital (MICU -LRH).This is the largest children's hospital in Sri Lanka and this MICU has 10 beds with 10 ventilators and accepts transfers from the entire island.Both paediatric patients and neonates are being treated here.Therefore, an assessment of common pathogens and patterns of antibiotic resistance at MICU is very important to start empirical treatment for patients who are critically ill.The study presented in this manuscript was undertaken to mitigate this deficiency.

Probable Contaminants
From environment: Spores From skin: Diphtheroids, CONS or mixed growth Hospital associated: Acenetobacter, candida species

Species identification was not done in our laboratory
Percentages of true pathogens and probable contaminants in blood culture are shown in Figure 3.
The percentages of true pathogens and probable contaminants in tracheal culture are shown in Figure 4.
Organisms identified in blood cultures are shown in Figure 5. Coliforms were the most common pathogens identified in blood cultures.Out of the contaminants the majority were spores.
Organisms identified in tracheal cultures are shown in Figure 6.Coliforms were the commonest pathogens in tracheal cultures.Spores and acenetobacter were the common contaminants.
Tables 1-3 show the resistance patterns to some common pathogens.

Discussion
Majority of septicaemia in 2006 at MICU -LRH was due to coliforms.As species identification was not done at our laboratory we could not assess the common coliform species.There were more positive tracheal cultures compared to blood cultures.As we did not correlate culture reports with clinical findings of patients, it is difficult to say whether all positive cultures indicate ventilator associated pneumonias.Coliforms and pseudomonas were the major pathogens in tracheal cultures.They are the common pathogens found in ventilator associated pneumonias in other studies 1,2 .
One particular concern is the nosocomial infection caused by enterobacteria producing extendedspectrum beta lactamases (ESBLs).Organisms that possess these enzymes are usually resistant to multiple antimicrobials and hydrolyze third-generation cephalosporins and aztreonam, rendering these potent antibacterial agents useless 4 .In our study we found ESBL producing coliforms in one blood culture and four tracheal cultures.All ESBL producing coliforms at MICU -LRH were resistant to ceftriaxone and some were resistant to meropenem also.
Examination of Gram-positive microorganisms, such as S. aureus and coagulase-negative staphylococci shows that rates of methicillinresistant isolates in ICU have increased steadily over the past decade [5][6][7] .In our study methicillinresistant staphylococcus were found in 10 blood cultures & 12 tracheal cultures but all were sensitive to vancomycin.It was reassuring as we did not find staphylococcus resistant to vancomycin.In various studies, it was reported that increased resistance rates have been detected against carbapenems, quinolones and thirdgeneration cephalosporins for pseudomonas aeruginosa worldwide 2,8 .Data from a multicentre Intensive Care Unit Surveillance Study (ISS) in the United States demonstrated that resistance to anti pseudomonal agents among ICU isolates of P. aeruginosa, especially fluoroquinolones (ciprofloxacin) was 9 .Our study also shows that 50% of pseudomonas in blood cultures and 34% of pseudomonas in tracheal cultures were resistant to ciprofloxacin.51% of pseudomonas in tracheal aspirates were resistant to anti pseudomonal penicillin (ticarcillin) and majority of pseudomonas (>50%) isolated from both blood cultures and tracheal aspirates were also resistant to meropenem.
Many studies have demonstrated that the development of antimicrobial resistance at the hospital level is strongly correlated with the use of the relevant antimicrobial 10 .Data from project ICARE showed that their usage was significantly higher among ICU patients than non-ICU patients for third-generation cephalosporins, vancomycin, anti-pseudomonal penicillin, intravenous fluoroquinolones and imipenem 11 .Our study also shows that there are significant percentagesof common pathogens resistant to above mentioned antibiotics.

Limitations
As this is a retrospective study, it has several limitations including the fact that we cannot say that all positive culture reports represented active infection.In addition, as we did not have admission data for each patient/clinical specimen, we were not able to provide a more accurate description of community versus nosocomial onset.Ventilator associated pneumonia cannot be accurately identified in this study

Recommendation
A prospective study should be carried out to get more information.Then, each year we can audit to see emergence of new antibiotic resistance to prepare a protocol for empirical antibiotic therapy at MICU LRH.
number of blood cultures done in 2006 was 659.Out of these cultures 123 (18.7%) became positive.Total number of tracheal cultures done in 2006 was 457 and out of these 256 (56%) were positive.Figures 1 & 2 show these results in monthly aggregates: Organisms found in positive blood & tracheal cultures were as follows: True Pathogens Coliforms: E. coli, klebsiella or proteus Staphylococcus aureus: Methicillin resistant (MRSA) or methicillin sensitive Streptococcus: groups A, B or D Pseudomonas species