|Year : 2015 | Volume
| Issue : 2 | Page : 248-254
Incidence, risk factors, microbiology of venous catheter associated bloodstream infections - A prospective study from a tertiary care hospital
M Kaur, V Gupta, S Gombar, J Chander, T Sahoo
Department of Microbiology, Government Medical College Hospital, Chandigarh, India
|Date of Submission||12-Mar-2014|
|Date of Acceptance||29-Sep-2014|
|Date of Web Publication||10-Apr-2015|
Department of Microbiology, Government Medical College Hospital, Chandigarh
Source of Support: Department of Microbiology, Government Medical
College Hospital, Chandigarh, Conflict of Interest: None
Purpose : Central venous catheters (CVCs) though indispensable in current medical and intensive care treatment, also puts patients at risk of catheter related infection (CRI) resulting in increased morbidity and mortality. We analysed the incidence, risk factors, bacteriological profile and antimicrobial susceptibility pattern of the isolates in central venous catheter associated bloodstream infection (CVC-BSI) in the intensive care unit (ICU) patients and studied the formation of biofilm in CVCs. Materials and Methods: The following case control study included 115 patients with CVC in situ. Quantitative blood cultures (QBC) and catheter tip cultures were performed for the diagnoses. Direct catheter staining was done for an early diagnosis by acridine orange (AO) and Gram staining methods. Biofilm production in catheters was detected by 'tissue culture plate' (TCP) method. The results were analysed using the computer-based program statistical package for the social sciences (SPSS). Results : In 25/115 patients, definite diagnosis of CVC-BSI was made. The mean age was 48.44 ± 17.34 years (cases) vs 40.10 ± 18.24 years (controls) and the mean duration of catheterisation was 25.72 ± 8.73 days (cases) vs 11.89 ± 6.38 days (controls). Local signs of infection (erythema, tenderness and oozing) were found more significantly in CVC-BSI cases. The AO staining was more sensitive and Gram staining of catheters showed higher specificity. Staphylococcus aureus followed by Pseudomonas aeruginosa and non-albicans Candida were common CVC-BSI pathogens. Multidrug-resistant (MDR) strains were isolated in bacterial agents of CVC-BSI. Non-albicans Candida and Enterococcus faecalis showed strong biofilm production. Conclusion : The incidence of CVC-BSI was 21.73% and the rate was 14.59 per 1000 catheter days. Prolonged ICU stay and longer catheterisation were major risk factors. S. aureus was isolated most commonly in CVC-BSI cases. The menace of multidrug resistance and biofilm formation in CVCs is associated with CVC-BSI.
Keywords: Antimicrobial susceptibility, biofilm formation, CVC-BSI, multidrug resistance, S. aureus
|How to cite this article:|
Kaur M, Gupta V, Gombar S, Chander J, Sahoo T. Incidence, risk factors, microbiology of venous catheter associated bloodstream infections - A prospective study from a tertiary care hospital. Indian J Med Microbiol 2015;33:248-54
|How to cite this URL:|
Kaur M, Gupta V, Gombar S, Chander J, Sahoo T. Incidence, risk factors, microbiology of venous catheter associated bloodstream infections - A prospective study from a tertiary care hospital. Indian J Med Microbiol [serial online] 2015 [cited 2020 Jun 4];33:248-54. Available from: http://www.ijmm.org/text.asp?2015/33/2/248/153572
| ~ Introduction|| |
Central venous access plays an important role in the management of critically ill patients and also puts patients at risk of various iatrogenic complications including central venous catheter associated bloodstream infection (CVC-BSI). The rate of CVC-BSI across Indian hospitals range from 4.01/1000 catheter days to 9.26/1000 catheter days citing the need for effective infection control programmes including surveillance and antibiotic policies. ,,
Gram-positive cocci are responsible for at least two-thirds of the infections followed by Gram-negative bacilli, which are responsible for a higher proportion of catheter related infections (CRIs) in intensive care unit (ICU) than in non-ICU patients.  Biofilm formation in catheters has not only been implicated as an important factor involved in device related infection but also confers resistance to antimicrobial treatment.  The preventive strategies like the use of antimicrobial impregnated catheters and foremost the aseptic catheter insertion technique using maximal sterile barrier (MSB) precautions have been shown to reduce the rate of CVC-BSI. 
Due to the scarcity of CVC-BSI data from our region of the country, we planned to conduct this study in our ICU of the tertiary care government hospital determining the incidence, risk factors for CVC-BSI, microbiological profile, antimicrobial susceptibility and biofilm formation by the CVC-BSI isolates.
| ~ Materials and Methods|| |
The prospective observational case-control study was conducted on 115 adult ICU patients from October 2010 to September 2011 after due ethical approval of the hospital ethics committee. The patients with in situ central venous catheters (CVCs) (>3 days of insertion) and sterile blood culture immediate after catheterisation were enrolled in the study after taking informed consent. Patients who got CVCs inserted outside our hospital and less than 12 years of age were excluded from the study. Cases were defined as the patients who were diagnosed to have CVC-BSI while the control population did not suffer from CVC-BSI.
The patient's clinical data and the CVC related information were collected and analysed [Table 1]. The surveillance for CVC-BSI and catheter colonisation was conducted among all eligible ICU patients based on following definitions:
Catheter colonisation - Growth of organisms from a catheter segment by either semi-quantitative [≥15 colony forming unit (CFU)] or quantitative culture [≥10 3 CFU] from a proximal or distal catheter segment in the absence of accompanying clinical symptoms. 
The central venous catheter associated blood stream infection - Positive simultaneous blood cultures from CVC and peripheral vein yielding the same organism in the presence of either significant catheter-tip colonisation with ≥10 3 CFU of the same organism isolated from the blood cultures, or simultaneous quantitative blood cultures (QBCs) in which the number of CFUs isolated from the blood drawn through the CVC was at least 5-fold greater than the number isolated from blood drawn percutaneously. 
Patients presenting with signs of sepsis were investigated by performing QBC from the central and peripheral vein. The QBCs were performed using pour plate method due to lack of automated blood culture techniques at our institute. The significant colony count in unpaired central line blood culture was ≥ 100 CFU while a central-to-peripheral blood culture colony count ratio of 5:1 was considered indicative of CVC-BSI. ,
In significant QBCs, the CVCs were aseptically removed from the patients and the catheter tips were processed in the microbiology laboratory by performing direct catheter staining on a part of the catheter tip while its distal end was used for quantitative culture by vortex method.  Direct catheter staining by both acridine orange (AO) and Gram staining were done to assess the catheter colonisation early before the culture report [Figure 1].  The in situ colonisation of catheters was determined by performing QBC from central line at zero, third, seventh and tenth day of catheter insertion and was confirmed by catheter tip culture after catheter removal.
|Figure 1: Microphotograph showing coccobacillary forms on fluorescent staining of catheter (a) and yeast cells (encircled) in gram stained catheter (b) and the lower picture shows mounting of catheter tip on the glass slide (c) for microscopic observation|
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The antimicrobial susceptibility of the bacterial isolates obtained by QBC and catheter tip culture was done by using Kirby-Bauer disc diffusion method and in case of vancomycin resistant enterococci (VRE), minimal inhibitory concentration (MIC) was calculated by agar dilution method.  Multidrug-resistant  (MDR) isolates were phenotypically characterised into methicillin-resistant S. aureus (MRSA), VRE, metallo-β-lactamase (MBL) and extended-spectrum β-lactamase (ESBL) producers. ,,, The biofilm formation by the CVC-BSI isolates and the colonisers of catheter tip was studied by 'tissue culture plate' (TCP) method. 
The infection was labelled as CVC-BSI, when the organism isolated from the two different blood cultures and the catheter tip culture was similar in genus, species and their antibiogram (the difference in antibiogram should be ≤ 1 antibiotic) and the rate of CVC-BSI was expressed in number of CVC days and was calculated by the following formula: ,
The patient and catheter-related information was collected and analysed amongst cases and controls using computer-based program statistical package for social sciences (SPSS Inc, Chicago, IL, version 17.0 for Windows). The significance of the differences between the two study groups were determined using the Chi-square test or the Fisher's exact test for categorical variables, student's t-test for continuous variables and logistic regression analysis for independent predictors. All P values were based on 2-tailed tests (level of significance, P < 0.05). The sensitivities, specificities, positive predictive value (PPV) and negative predictive value (NPV) of the two staining procedures performed in the study were also calculated.
| ~ Results|| |
Among 115 patients with 1713 total catheter days, the incidence of CVC-BSI was 21.73% (25/115) and the rate of CVC-BSI was found to be 14.59 per 1000 catheter days.
The demographics, clinical characteristics [Table 1] and the risk factors for CVC-BSI [Table 2] have been studied and shown in the tabulated forms. In our study, mean age of the cases was significantly higher than controls while the gender showed no significant difference. The patients admitted with surgical complaints especially perforation peritonitis and those showing local signs of infection around catheter site (P < 0.05) were affected more. The comorbid conditions studied in majority of CVC-BSI cases were hypertension followed by diabetes, malignancy and chronic obstructive pulmonary disease while 28% cases showed no comorbid condition. The mortality among CVC-BSI patients (32%) was not significantly higher when compared to controls (40%).
A total of 106 catheter tips were received from 115 patients in the microbiology laboratory where they were subjected to staining and quantitative culture via vortex technique. The staining of catheter tip by the two staining procedures found AO fluorescent staining [Figure 1](a) to be more sensitive but less specific (83.87% sensitivity, 70.45% specificity, 80% PPV, 75.61% NPV) when compared to Gram's staining [Figure 1](b) which showed higher specificity (77.27% specificity; 72.58% sensitivity, 81.82% PPV, 66.67% NPV) than the fluorescent staining.
The colonisation was observed in 58.49% (62/106) catheters with both bacterial and fungal agents. A total of 81 catheter tip isolates were recovered from monomicrobial (n = 45; 72.6%) and polymicrobial colonisation (n = 17; 27.4%) of catheters. It was seen that the catheter colonisation usually started after the third day with maximum colonisation being detected after 10 days of catheter insertion. The microorganism most commonly colonising the catheters was S. aureus (n = 21; 25.9%), followed by Acinetobacter calcoaceticus aumannii complex (cbc) (n = 17; 20.9%), Enterococcus faecalis (n = 11; 13.6%), Pseudomonas aeruginosa (n = n = 10; 12.3%), non-albicans Candida (n = 9; 11.1%), Escherichia More Details coli (n = 6; 7.4%), Klebsiella pneumoniae (n = 3; 3.7%), Proteus mirabilis (n = 2; 2.4%), Citrobacter koseri (n = 1; 1.2%) and Coagulase negative staphylococci (n = 1; 1.2%).
Out of 115 patients, bacteraemia was seen in 80 patients (69.56%) among which 25 showed significant counts on QBC and confirmed by catheter tip culture. A total of 29 isolates were recovered from the blood cultures with monomicrobial infection in 21 cases (84%) and four cases (16%) showed polymicrobial infection. S. aureus was the most commonly isolated agent (n = 8; 27.6%) responsible for CVC-BSI followed by P. aeruginosa (n = 6; 20.6%), non-albicans Candida (n = 5; 17.2%), E. faecalis (n = 4; 14.8%), Acinetobacter cbc (n = 3; 10.3%) and K. pneumoniae (n = 3; 10.3%). S. aureus with non-albicans Candida was the most frequently isolated polymicrobial infection while K. pneumoniae with E. faecalis and Acinetobater cbc with non-albicans Candida were the other two combinations.
The drug-susceptibility pattern based on CLSI guidelines for both Gram-negative and Gram-positive bacteria implicated in CVC-BSI is shown in the [Table 3] and [Table 4]. Seven strains of MRSA (87.5% of S. aureus strains) and one strain of VRE (MIC ≥ 512 μg/ml) were implicated in CVC-BSI when tested by disc diffusion and agar dilution test, respectively. Among Acinetobacter cbc isolates implicated in CVC-BSI, the MBL production was seen in one out of three imipenem resistant strains (33.3%) whereas two out of five catheter tip isolates of P. aeruginosa (40%) showed MBL production. All the CVC-BSI isolates of K. pneumoniae showed ESBL production when tested by disc potentiation test.
|Table 3: Antimicrobial susceptibility of Gram - positive cocci in CVC - BSI cases |
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|Table 4: Antimicrobial susceptibility of Gram - negative bacteria in CVC - BSI cases |
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Biofilm production by the culture isolates from blood and catheter tip was determined and the microorganisms were labelled as strong, moderate or weak biofilm producers. Our study showed non-albicans Candida spp. and E. faecalis as strong biofilm producers among both groups whereas Acinetobacter cbc, P. aeruginosa and S. aureus were moderate biofilm producers. Rest of the isolates showed weak biofilm production [Figure 2].
|Figure 2: Photograph showing 96 well tissue culture plate used for detection of biofilm production. Red arrow shows well with strong biofilm production, green arrow shows moderate and yellow arrow denotes well with weak biofilm production|
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| ~ Discussion|| |
Our hospital has a 14-bedded medical-surgical ICU with an approximate 500 admissions/year and a high CVC insertion rate. Considering the high rate of CVC insertion and mortality associated with blood stream infections (BSIs), a study determining central lines as the source of the BSIs, and studying the incidence and risk factors for CVC-BSI was planned.
The incidence of CVC-BSI in our study was 14.59/1000 catheter days which is higher, when compared to the study conducted by national nosocomial infection surveillance system in seven Indian hospitals with reported incidence of 0.0 to 11.86 per 1000 catheter days.  But a much higher incidence rates (47.31/1000 catheter days) have been reported by a recent study from a tertiary care hospital in India confirming the scenario of high infection rates in various Indian hospitals and poor infection control practices.  In the present study, higher rates could be attributed to poor nurse-patient ratio, compromised infection control practices and the critically-ill patients with pre-existing sepsis in the CVC-BSI group.
Among demographic analysis, significant mean age difference (P value < 0.05) was observed amongst cases and controls with higher mean age (48.44 ± 17.34) in the CVC-BSI group. But when less than 45 years and more than 45 years groups of cases and controls were analysed, no significant difference was seen. Also the gender difference was insignificant. Öncü et al. and Parameswaran et al. in their studies found no significant age and gender difference amongst the two groups. , Other significant risk factors (P value < 0.05) were presence of local signs of inflammation at the site of catheterisation and prolonged duration of CVCs. Hence, local signs of inflammation (erythema, tenderness and frank oozing) around the catheter insertion site can be used as a marker of catheter being a possible source of BSI and should warrant its removal. The ICU stay was significantly prolonged (P < 0.001) in CVC-BSI cases concluding that longer duration of catheterisation and ICU treatment might have contributed to the occurrence of CVC-BSIs. Parameswaran et al. in their study also showed significant difference in mean hospital stay and local signs of inflammation between cases and controls.  Surgical patients commonly of perforation peritonitis were affected more probably because of pre-existing sepsis in these patients.
Femoral venous site is most commonly associated with infectious complications followed by jugular and subclavian veins. Multilumen catheters have been found to be increasingly implicated in CVC-BSI than single lumen catheters. , We found no significant difference in the rates of infection based on the catheter insertion site and number of lumens, as in our study most often site of catheterisation was subclavian vein and multilumen catheters were most commonly inserted, hence the difference in number amongst the types of catheters and their site of insertion was insignificant.
Paired QBC was used for the diagnosis of CVC-BSI as it has been shown to be the best diagnostic method for implantable device-associated BSI.  Quantitative catheter tip culture was done to look for colonisation of catheters with one or more organisms by culturing both external surface and the luminal surface of the catheters.
Catheter tip colonisation has been studied to be a surrogate marker for CRIs; hence its rapid detection by directly staining the catheter tip is a useful procedure. We performed two different types of staining on the catheter tip and found that the positive staining results were significantly associated with CVC-BSI cases (P < 0.002 in Gram's staining and <0.001 in AO) and correlated well with the culture results of the catheter tip. In a study by Coutlee et al., Gram's staining of catheter showed sensitivity of 44% and specificity of 91% with 57% PPV and 86% NPV whereas the sensitivity, specificity, PPV and NPV of AO staining were 71%, 77%, 41% and 92%, respectively.  Hence, based on our results also, AO staining was found to be a useful and rapid method for detection of catheter colonisation.
Staphylococcus aureus was the most common pathogen of CVC-BSI in our study. The isolation of S. aureus in large numbers from CVC-BSI cases probably suggests the hub colonisation by the skin flora of the patient or medical personnel as the origin of infection and in our study also, the isolation of S. aureus in large number points towards the lapse in the catheter care.  the next most common CVC-BSI pathogen in our study was P. aeruginosa and the same scenario was cited by Latif et al., who found that non-fermenters like P. aeruginosa and Acinetobacter spp. are the second most common bacterial agents in ICU settings after Gram-positive cocci to be responsible for causing septicaemia.  Apart from bacterial pathogens, certain yeasts like Candida especially non-albicans Candida are increasingly being reported from nosocomial septicaemic cases  and in our study they have contributed to 20% (n = 5) of the CVC-BSI cases.
Biofilm formation was studied as this is inherently associated with device associated infections and contributes to antimicrobial resistance.  Common biofilm microbial species associated with nosocomial infection in CVCs are: S. epidermidis, S. aureus, E. faecalis, K. pneumoniae, P. aeruginosa, non-albicans Candida.  The TCP method showed non-albicans Candida and E. faecalis as strong biofilm producers while S. aureus produced biofilm in moderation.
Multidrug resistance was observed in almost all the isolates responsible for CVC-BSI and catheter colonisation. Amongst CVC-BSI isolates, MRSA (87.50%; n = 7/8 strains), VRE (25% n = 1/4 strains), MBL (33.33%; n = 1/3 strains of Acinetobacter spp.) and ESBL (100%; n = 3/3 strains of K. pneumoniae) producers were seen. In certain strains like CVC-BSI isolates of P. aeruginosa, total resistance to amikacin and gentamicin was observed. Such high degree of drug resistance among P. aeruginosa isolates has been observed in ICUs from other centres also. , Parameswaran et al., in his study found MRSA to be responsible for 26.7% CVC-BSIs and single isolate of A. baumannii resistant to all the routine drugs. 
The limitation in our study was that we could not culture the catheter tips from all 115 patients hence the true colonisation rate among the study group was not possible. But in the cases that were left out, follow-up of peripheral and central venous line blood cultures showed no signs of CVC-BSI. Another limitation is the short duration of the study and less number of CVC-BSI cases to draw any significant conclusion at the end, hence a study on a large scale for a sufficient time period can be planned.
In conclusion, CVC-BSI remains an important complication of central venous access in ICUs. Active intervention of the intensivist is required to ascertain the signs of sepsis in the patient at the earliest and to send properly collected samples at appropriate time for an early diagnosis, in turn decreasing the morbidity and mortality associated with CVC-BSIs.
| ~ Acknowledgment|| |
This is the publication from the thesis work done by Dr. Mandeep Kaur after due research and ethical clearance.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4]