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Multiple Fluid Collections: CT- or US-guided Aspiration-Evaluation of Microbiologic Results and Implications for Clinical Practice¹

¹ From the Department of Radiology (J.P.H., R.C.N.) and the Clinical Microbiology Laboratory (R.J.E.), Duke University Medical Center, Erwin Rd, Box 3808, Durham, NC 27710. From the 1998 RSNA scientific assembly. Received November 25, 1998; revision requested December 30; final revision received January 24, 1999; accepted March 1. Address reprint requests to J.P.H. (e-mail: heneg002@mc.duke.edu).

	Abstract

TOP Abstract Introduction MATERIALS AND METHODS RESULTS DISCUSSION References

 
PURPOSE: To determine if patients with multiple fluid collections need every collection aspirated and if cross-contamination is a risk if separate sterile procedures are not followed for each aspiration.

MATERIALS AND METHODS: Records from 1,076 imaging-guided percutaneous aspirations and drainages over 39 months were retrospectively reviewed; 124 patients had multiple fluid collections drained, which yielded 287 aspirates. The patients were divided into two groups: those (n = 82) with multiple collections aspirated on any 1 day, and those (n = 61) with multiple collections aspirated over 10 days. Nineteen patients were included in both groups. Gram stain microscopy and culture results were compared between sequential aspirates in each patient, and their potential effects on antimicrobial therapy and theoretic risk for cross-contamination were evaluated.

RESULTS: In 82 patients undergoing multiple aspirations on any 1 day, multiple microorganisms differed in 32 patients, which indicated a need for therapy change in 18 (22%) patients. In 61 patients undergoing aspiration on different days, microorganisms differed in 32 patients, which indicated a need for therapy change in 15 (25%) patients. Cross-contamination could have occurred in 28 of 93 (30%) aspirates from patients with a second or subsequent collection if separate sterile procedures had not been undertaken.

CONCLUSION: When multiple fluid collections are identified, aspirates from all collections should be obtained through separate sterile procedures to ensure optimal antimicrobial coverage and avoid cross-contamination.

Index terms: Abdomen, abscess, 70.201, 70.202, 70.204, 70.21, 70.1262 • Abscess, CT, 70.1211 • Abscess, US, 70.12986 • Pelvic organs, abscess, 80.201, 80.202, 80.204, 80.211, 80.1262

	Introduction

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Percutaneous drainage is the primary management option for intraabdominal or pelvic abscesses (1–3); aspiration and drainage of such collections under imaging guidance is routine in most radiology practices. For the most part, ultrasonographic (US) or computed tomographic (CT) guidance is employed. Often, patients have multiple fluid collections, which prompts a management question of whether to drain all collections immediately or initially drain the dominant collection and assume that other collections may be sympathetic or contain similar microorganisms. Furthermore, when multiple fluid collections are drained at one time, it is unknown how great the risk is of cross-contamination from an infected collection to another potentially sterile collection if separate sterile fields and separate sterile equipment are not used.

Management of abscesses has been repeatedly discussed in the surgery and radiology literature, particularly with regard to location, cause, and associated factors (carcinoma, enteric fistula, etc) (1–6). In addition, attention has been focused on management in terms of choice and number of catheters required for drainage, as well as the potential use of urokinase to facilitate drainage (7). However, to our knowledge, no study has specifically addressed the role of microbiologic data in determining the management of such collections.

In this study, we evaluated microbiologic data in patients whose multiple fluid collections were drained under US or CT guidance. Our specific purpose was to answer these questions: (a) Do multiple collections in an individual patient each require aspiration? (b) Is it necessary to create separate sterile fields and use separate equipment for each aspiration and drainage?

	MATERIALS AND METHODS

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We retrospectively reviewed the database of interventional procedures performed from November 1994 to January 1998 in the abdominal imaging section of our department. During this 39-month period, 1,076 aspirations and drainages of fluid collections were performed under CT or US guidance in 694 patients. Of these, 140 patients had two or more fluid collections aspirated within a 10-day period. We arbitrarily selected 10 days as a reasonable time in which to group sequential aspirates relating to the same episode of illness.

The results of Gram stain microscopy and culture were available for 287 aspirates obtained from the 124 patients who formed the study group. Data on the 16 remaining patients were incomplete; thus, they were excluded (although radiology reports indicated that two samples were obtained from each of these 16 patients, the microbiology laboratory received only one sample from each). Of the 124 patients who had multiple collections aspirated, 63 patients (51%) were postsurgical; 30 (24%) had pancreatitis; 10 (8%) had experienced trauma (motor vehicle accident or gunshot wound); and 21 (17%) had miscellaneous primary causes of infection, including diverticular disease and pelvic inflammatory disease. Ninety-two of 124 (74%) patients were in medical or surgical units, and the remaining 32 patients (26%) were in the intensive care unit.

Each procedure was performed by using a separate sterile biopsy tray, separate sterile equipment, and separate skin disinfection methods, even when multiple procedures were required in an individual patient at the same time. All but two patients had collections within the abdomen or pelvis (one patient had a collection in the thigh; the other had a collection in the chest wall).

Aspirated fluid was sent in an anaerobic transport container to the microbiology laboratory, examined by using Gram stain microscopy, and then cultured on the following media: tryptic soy agar with 5% sheep blood (Trypticase; Becton Dickinson Microbiology Systems, Sparks, Md), Columbia colistin-nalidixic acid agar with 5% sheep blood, MacConkey II agar, and, in nearly all cases, anaerobic Brucella blood agar and anaerobic laked blood agar with kanamycin and vancomycin (Becton Dickinson Microbiology Systems).

The 124 study patients were divided into two groups: those (n = 82) with two or more collections aspirated on 1 day and those (n = 61) with two or more collections aspirated on separate days over a 10-day period. There was an overlap of 19 patients between these two groups: These patients had multiple collections aspirated on any 1 day and underwent additional aspiration within 10 days. Our practice is to aspirate all fluid collections in a patient with sepsis (unless technically impossible; for example, a deep interloop abscess). Thus, patients who underwent procedures on separate days were those in whom a new collection was identified on a subsequent day and was duly drained. When multiple collections were present, we did not elect to aspirate some but not other collections on the basis of clinical or radiographic data. There was a mean of 4.9 days between aspiration of initial and subsequent collections.

The microbiologic results of different fluid collections in an individual patient were compared by a clinical microbiologist (R.J.E.); correlation of the interventional procedure report with the labeling of each specimen allowed for deduction of the order of aspirates (ie, first, second, etc). Then, the clinical microbiologist assessed whether a relevant change in antimicrobial therapy would have been indicated by the isolation of a different microorganism in a subsequent collection. A "relevant change" was defined as the need for introduction of a new antimicrobial agent. Cases in which different microorganisms were identified in subsequent fluid collections but in which therapy would not have been altered as a result were considered as "no change." Patient notes were not reviewed to determine whether such a change had actually taken place.

Finally, to assess the risk of cross-contamination, a second comparison was made by the microbiologist for the group of patients (n = 82) who underwent same-day aspirations. In each case, if microorganisms found in one collection were not present in subsequently aspirated collections, the latter collections were considered to be at risk for cross-contamination by microorganisms from the previous collection.

	RESULTS

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Of 124 patients who underwent multiple aspirations, 86 patients (69%) had microorganisms present in at least one aspirate, and 38 patients (31%) had fluid samples that were negative at Gram stain microscopy and culture. Of the 86 patients with infection, 34 patients had infections that involved a single microorganism, and 52 (60%) had infections that were polymicrobial. Overall, the following microorganisms were isolated: aerobic gram-positive bacteria, 55 patients (64%); aerobic gram-negative bacteria, 43 patients (50%); anaerobic bacteria, 30 patients (35%); and yeast, 30 patients (35%).

Of 82 patients who underwent multiple aspirations on any 1 day, 39 patients (48%) had first collections that were infected, and 43 patients (52%) had first collections that were sterile. The second aspirate was infected in 38 patients (46%) and sterile in 44 patients (54%). Microorganisms differed between sequential aspirates in 32 patients (39%). Detailed results of aspirations and implications for therapy are summarized in Table 1. In the group of patients who underwent multiple aspirations on any 1 day, a change in antimicrobial therapy was indicated by the results of the second aspiration in 18 of 82 patients (22%) (Figure). Nine patients had a third collection aspirated, and two had a fourth collection aspirated; none of these samples provided additional therapeutically relevant information.

View larger version (125K): [in this window] [in a new window]   Figure 1. Nonenhanced axial CT image of the upper abdomen of a 29-year-old man with a history of Crohn disease demonstrates two air-containing fluid collections, one in the lesser sac (open arrows) and one in the right flank (solid arrow). Morganella morganii was isolated from the lesser sac collection; a single Enterococcus species was isolated from the right flank collection. These microorganisms had different antimicrobial susceptibility profiles.

Microorganisms differed between sequential aspirates in 32 patients (52%). Detailed results of aspirations and potential effects on subsequent therapy are summarized in Table 2. Irrespective of the results of first and second aspirations, four samples from the 12 patients who provided a third sample, one sample from the seven patients who provided a fourth sample, and zero samples from the two patients who provided fifth samples provided new therapeutically relevant information. Overall, a change in antimicrobial therapy was indicated by the results of second or subsequent samples in 15 of 61 patients (25%) in this group.

Moreover, in the 82 patients in whom a second aspirate was obtained at the same session, microorganisms were present in previous aspirates that were not present in five of nine third aspirates and one of two fourth aspirates. Overall, 28 of 93 second or subsequent aspirates (30%) could have led to contamination of the sample or deep tissue if separate sterile procedures had not been followed for each aspiration.

	DISCUSSION

TOP Abstract Introduction MATERIALS AND METHODS RESULTS DISCUSSION References

 
Intraabdominal and pelvic abscesses develop as a result of localization of peritonitis, usually in the perihepatic spaces, pelvis, and paracolic gutters. An abscess may also develop near diseased organs, including the bowel, or as a complication of trauma or surgery. These infections tend to be polymicrobial, as was the case in our review for 60% of the 86 patients with infection. Previous investigators (8,9) have isolated anaerobic bacteria from 60% to 70% of patients; however, we found anaerobes in only 35% of patients with infected aspirates. This may reflect a relatively aggressive policy of aspirating and draining fluid collections that did not necessarily demonstrate classic features of anaerobic infection, such as the presence of air.

In addition, if fluid from an intraabdominal collection was mislabeled as having been collected from a drainage catheter rather than by direct aspiration, it was not cultured anaerobically in our clinical microbiology laboratory. We have found this to be a problem in our practice. Specimens sometimes are labeled with the patient's name by the radiologist or nurse at the time of the procedure, but clinical details on the microbiology laboratory request form are subsequently completed by staff members on the ward.

With regard to the need to aspirate multiple fluid collections in the same patient, we found that sampling a second collection resulted in information indicating a need for change in therapy in 22% of patients with multiple same-day aspirates and in 25% of patients with multiple subsequent-day aspirates. It is interesting that aspiration of a third collection yielded no new therapeutically relevant information in the same-day group but did indicate a need for alteration of therapy in one-third of patients in the subsequent-day group (albeit a very small number of patients; 12 underwent a third aspiration). Although these small numbers do not allow for meaningful comparison, it may be that patients who had a third collection aspirated over several days had chronic sepsis, which prompted repeat imaging and subsequent aspiration; the group undergoing a third aspiration on the same day had the third collection drained simply because it was present. Aspiration of fourth and fifth collections rarely provided new microbiologic information.

Patients with multiple or recurrent abscesses have been shown to have a greater mortality (6), and care must be taken to examine these patients for underlying anatomic defects (eg, fistula) that prevent resolution of the infected collection (1). Our study findings have demonstrated that these patients' complex conditions do need to be approached aggressively from the standpoint of aspirating multiple collections, as therapeutically important differences in microorganisms may be missed by aspirating fluid for culture only from a dominant collection. Indeed, untreated pathogens within unsampled fluid collections may contribute to the increased mortality seen in patients with multiple abscesses.

We also found that sterile collections frequently coexist with infected collections and that microorganisms requiring different therapy may be present in adjacent collections. For this reason, we advocate meticulous maintenance of separate sterile fields to prevent cross-contamination when aspirating or draining multiple collections at the same sitting. Most important, cross-contamination of deep tissues can, in theory, lead to the creation of a new abscess in a previously sterile collection. In addition, cross-contamination of samples sent for laboratory testing can lead to an inability to relate microbiologic results to a specific drainage site, which has implications for catheter management in terms of knowing whether an infected or sterile collection is being drained. Creation of a separate sterile field and use of separate sterile equipment does necessitate higher expense (for fresh sterile packs, guide wires, and dilators) and slightly longer procedure times.

We did not categorize collections by anatomic location or by complicating clinical features (fistula, compromised immune status, etc). These factors are of great importance in general management and prognosis and have been addressed in previous studies (1,9,10) but are not relevant to the purpose of this study.

Previous authors (3) have discussed the importance of adequately draining all foci of infection, as this follows the surgical axiom for achieving cure. Our findings complement this axiom. We are not aware of an analysis of microbiologic results in a similarly large study group. Our study was retrospective and was limited by the fact that data were incomplete for several patients (n = 16) with multiple collections aspirated and drained over the study time who were thus excluded from analysis. However, our results provide microbiologic support for the practice believed by the surgeons and radiologists in our institution to be correct; that is, aspiration of all collections in the patient who may have sepsis by using separate sterile procedures.

Initial surgery and radiology articles (2,11,12) suggested strict criteria for selecting patients for percutaneous drainage. These criteria specified that the collection should be unilocular and not associated with a fistula or communication, that there should be a clear access route, and that there should be surgical backup available. In the ensuing 15 or more years, these criteria have been abandoned, and percutaneous drainage is now considered to be the most appropriate initial treatment for almost all infected fluid collections, including those in critically ill patients in whom percutaneous drainage allows temporization prior to surgical treatment, if necessary (13). In light of the ever-increasing indication for percutaneous aspiration and drainage of fluid collections and the increasing complexity of diseases so managed, it is very important to consider microbiologic information in the decision-making process with regard to interventional procedures, not just in relation to antimicrobial therapy.

We conclude that all intraabdominal fluid collections should be aspirated to optimize selection of antimicrobial therapy. In addition, a rigorous separate sterile technique should be employed for each aspiration to prevent cross-contamination and the creation of a new abscess.

	Footnotes

 
Author contributions: Guarantor of integrity of entire study, J.P.H.; study concepts, J.P.H., R.J.E., R.C.N.; study design, J.P.H., R.J.E.; definition of intellectual content, J.P.H., R.J.E., R.C.N.; literature research, J.P.H.; clinical studies, J.P.H., R.J.E.; data acquisition, J.P.H., R.J.E.; data analysis, R.J.E.; manuscript preparation, J.P.H.; manuscript editing, J.P.H., R.J.E., R.C.N.; manuscript review, R.C.N.

	References

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