Accuracy of blood culture for early diagnosis of mediastinitis in febrile patients after cardiac surgery

Routine Mediastinal Drainage Fluid Culture for Early Diagnosis of Poststernotomy Mediastinitis

BACKGROUND

Early diagnosis of poststernotomy mediastinitis (PSM) is challenging. Since 2016, we have routinely performed mediastinal drainage fluid culture (MDFC) in patients undergoing sternotomy. This study aimed to determine the utility of MDFC for early diagnosis of PSM.

METHODS

Between November 2016 and April 2020, we conducted MDFC in 1,012 patients on the third postoperative day and prospectively observed for PSM occurrence for 3 months. If bacteria were identified, additional MDFC or blood culture was performed to reduce the possibility of false positives. Based on MDFC results, the decision for early treatment for PSM was at the attending physician's discretion.

RESULTS

Bacteria were identified in MDFC of 29 patients, eight of whom subsequently developed PSM. Among 983 patients with negative MDFC, only 15 developed PSM. In multivariate analysis, previous sternotomy history and positive MDFC were predictors of PSM. Positive MDFC was regarded as true positive if (1) PSM occurred subsequently, and/or (2) the same bacteria were identified in additional MDFC/blood culture. Non-occurrence of PSM in the absence of antibiotic treatment was regarded as false-positive MDFC. The sensitivity, specificity, and positive and negative predictive values of routine MDFC for diagnosis of mediastinal infection were 46.4, 99.0, 56.5, and 98.5%, respectively. When categorizing cases with positive MDFC based on the identified bacteria, the positive predictive value was highest (76.9%) when Staphylococci were identified.

CONCLUSION

Routine MDFC after sternotomy can facilitate early diagnosis of PSM. Early treatment for PSM may be indicated in patients in whom Staphylococci are identified in the MDFC.

Staphylococcus aureus infections: epidemiology, pathophysiology, clinical manifestations, and management

Staphylococcus aureus is a major human pathogen that causes a wide range of clinical infections. It is a leading cause of bacteremia and infective endocarditis as well as osteoarticular, skin and soft tissue, pleuropulmonary, and device-related infections. This review comprehensively covers the epidemiology, pathophysiology, clinical manifestations, and management of each of these clinical entities. The past 2 decades have witnessed two clear shifts in the epidemiology of S. aureus infections: first, a growing number of health care-associated infections, particularly seen in infective endocarditis and prosthetic device infections, and second, an epidemic of community-associated skin and soft tissue infections driven by strains with certain virulence factors and resistance to β-lactam antibiotics. In reviewing the literature to support management strategies for these clinical manifestations, we also highlight the paucity of high-quality evidence for many key clinical questions.

Staphylococcus aureus and repeat bacteremia in febrile patients as early signs of sternal wound infection after cardiac surgery

BACKGROUND

Sternal wound infection is a devastating complication of cardiothoracic surgery that carries high postoperative morbidity and mortality rates. We explored whether our current program of extensive bacteriological examination including repeat blood cultures may contribute to the early diagnosis of sternal wound infection.

METHODS

We retrospectively analyzed 112 patients who were subjected to our bacteriological examination protocol including within 90 days after cardiothoracic surgery. Univariate and multivariate analyses were made in order to identify risk factors for sternal infection.

RESULTS

The median patient age was 75 years, and 65 patients were male. In 35 cases (31.2%) the blood cultures showed the presence of bacterial infection with the following frequencies: Staphylococcus aureus, 18 cases; Coagulase-negative Staphylococcus, 7 cases; other organisms, 10 cases. Eleven patients presented repeat bacteremia on at least 2 different occasions. Twenty patients (17.8%) presented sternal wound infections. There was no difference in operative mortality between the patients with and without sternal wound infection. Univariate and multivariate analyses demonstrated that bilateral mammary artery use (OR, 13.68, 95% CI, 1.09-167.36, p = 0.043), positive blood culture for Staphylococcus aureus (OR, 19.51, 95% CI, 4.46-104.33, p < 0.0001), repeat bacteremia (OR, 17.98, 95% CI, 2.51-161.77, p = 0.004) were risk factors that were associated for sternal wound infection.

CONCLUSION

Repeat blood cultures in febrile patients appear to be useful for the early detection of Staphylococcus aureus and repeat bacteremia, and these were associated with sternal wound infection. Bilateral internal mammary artery use was another risk factor of sternal wound infection in febrile patients. These factors may identify patients suitable for expeditious radiological examination and aggressive treatments.

Risk factors for mediastinitis and endocarditis after cardiac surgery

A prospective open-cohort study was performed in 838 adults undergoing coronary revascularization or valve surgery to define the risk factors for development of surgical site infections. Patients diagnosed with mediastinitis or endocarditis during follow-up were compared with patients with no such infection. After 1 year of follow-up, 22 (2.6%) patients had developed mediastinitis or endocarditis. No preoperative or intraoperative variables were identified as risk factors. By multivariate analysis of postoperative variables, respiratory insufficiency, microorganisms in blood cultures, and intensive care unit stay were independent risk factors for the development of these complications. The type of antibiotic prophylaxis had no influence on the incidence of organ or space infections after cardiac surgery.

Postoperative mediastinitis due to Finegoldia magna with negative blood cultures

We report a case of Finegoldia magna (formerly known as Peptostreptococcus magnus) mediastinitis following coronary artery bypass in a 50-year-old patient. Even if staphylococci remain the main causative organism of postoperative mediastinitis, the responsibility of anaerobic bacteria must be considered in cases of fever and sternal drainage with negative blood cultures.

Postoperative mediastinitis in children: improvement of simple primary closed drainage

BACKGROUND

Mediastinitis is a significant cause of postoperative morbidity. In 1989, we proposed simple primary closed drainage as a new treatment. Our goal is to describe improvements made to the original technique.

METHODS

After wound debridement, infected areas were drained with Redon catheters connected to strong negative-pressure drainage bottles. Mediastinal effluents were cultured every day, and the catheters were withdrawn when the effluent culture was negative for microorganisms. Patients were classified into three groups: isolated mediastinitis (group 1), mediastinitis associated with endocarditis (group 2), and mediastinitis associated with other organ failure (group 3).

RESULTS

Sixty-four patients were treated during a 10-year period: 15 neonates, 33 infants, and 16 children. Group 1 consisted of 40 patients. The time to mediastinal sterilization was 4 days (range, 1 to 14 days), and the antibiotic course was 11 days (range, 7 to 28 days), with a hospital stay of 13 days (range, 10 to 30 days). No deaths occurred in this group. Group 2 consisted of 7 patients. The time to mediastinal sterilization was 8 days (range, 3 to 10 days), and the antibiotic course was 30 days (range, 26 to 37 days), with a hospital stay of 37 days (range, 20 to 54 days). One patient in group 2 did not survive. Group 3 consisted of 17 patients. The time to mediastinal sterilization was 6 days (range, 1 to 10 days), and the antibiotic course was 15 days (range, 10 to 31 days), with a hospital stay of 20 days (range, 18 to 36 days). Two patients in group 3 did not survive. None of the deaths was directly related to mediastinitis, as the mediastinum was sterile in all 3 patients before death.

CONCLUSIONS

This simple treatment was efficient and reliable in achieving mediastinal sterilization. In addition, short antibiotic courses decreased restraint, which is poorly tolerated in pediatric patients.

Increase in the rate of sternal surgical site infection after coronary artery bypass graft: a marker of higher severity of illness

OBJECTIVE

To evaluate factors related to a gradual rise in sternal surgical site infection (SSI) rates.

DESIGN

Retrospective cohort study.

SETTING

A 608-bed, tertiary care teaching hospital.

PATIENTS

All patients who underwent coronary artery bypass graft (CABG) from January 2000 through September 2004.

RESULTS

Of 3,578 patients who underwent CABG, 144 (4%) had sternal SSI. There was an increase in infection rate, with a marked reduction in the number of operations per year. The percentage of patients with peripheral vascular disease increased from 12% to 24.3% (P<.001), and the percentage with congestive heart failure increased from 17% to 22% (P<.001). Between 2002 and 2004, the mean duration of surgery increased from 233 to 290 minutes (P<.001), the percentage of patients with a National Nosocomial Infections Surveillance System (NNIS) risk index of 2 increased from 14.3% to 38% (P<.001), and the percentage of patients with a postoperative stay in the intensive care unit of greater than 72 hours increased from 29% to 40.6% (P<.001). Multivariate analysis showed diabetes mellitus, peripheral vascular disease, obesity, duration of surgery, and postoperative stay in the intensive care unit of greater than 72 hours to be independently associated with infection.

CONCLUSIONS

An increase in infection in the CABG population not associated with an outbreak may be a reflection of a change in the severity of illness. Preoperative, intraoperative, and postoperative markers for increased infection risk may be used, in addition to the NNIS risk index, to assess the patient population risk.

Staphylococcus aureus, the major pathogen in orthopaedic and cardiac surgical site infections: a literature review

Due to the increasing number of orthopaedic and cardiac procedures, these units are considered as high-risk areas because of the potentially serious consequences of surgical site infections (SSI), primarily caused by Staphylococcus aureus. The goal of this review was to evaluate the impact of S. aureus on the incidence of SSI in these high risk wards. Studies were identified by a search on the MEDLINE literature using the following mesh terms: S. aureus, cardiac, orthopaedic, surgery, SSI. Beside, data from different surveillance systems were also included. Overall, biological investigation was performed only on a small proportion of identified SSIs. Of those identified, S. aureus represented the most common pathogen accounting for approximately 20% of all SSIs. Of the 59,274 hip prostheses reported from the HELICS surveillance network, S. aureus formed 48.6% of the pathogens (416 bacteria isolated). Similarly, it represented 43.7% of pathogens after coronary artery bypass grafting. Although S. aureus turned out to be the major pathogen, this work identifies the relative lack of knowledge on the overall incidence of S. aureus infections and on the impact of this pathogenic agent when taking into consideration the degree of wound contamination and category of SSI. There is a need for more detailed information on the role of S. aureus in the burden of surgical site infections and consequently how to establish multiple approach prevention programs.

Bloodstream infections after median sternotomy at a children's hospital

OBJECTIVES

Postoperative bloodstream infections are a major source of morbidity and increased health care costs. In adults, mediastinitis has been described as a risk factor for bloodstream infections. The objectives of this retrospective cohort study were to determine the incidence and to identify risk factors for postoperative bloodstream infections among children after median sternotomy in an urban tertiary care children's hospital.

METHODS

For this study, 192 patients were randomly selected from among all patients undergoing median sternotomy between January 1, 1995, and December 31, 2003.

RESULTS

Ninety-eight (51%) of the 192 eligible patients were male. The median patient age was 5.4 months (interquartile range: 1 day-41.5 years). Bloodstream infections occurred in 12 (6.3%; 95% confidence interval [CI]: 3.3%-10.7%) patients within the first 30 days after median sternotomy. Bloodstream infections developed a median of 11 days (range: 3-29 days) after median sternotomy. Gram-negative bacilli caused 6 (50%) of the 12 bloodstream infections. Specific causes of bloodstream infections included Pseudomonas aeruginosa (n = 3), coagulase-negative staphylococci (n = 3), Pseudomonas fluorescens-putida (n = 2), Staphylococcus aureus (n = 2), Serratia marcescens (n = 1), and Candida albicans (n = 1). Multivariable analysis revealed that the development of mediastinitis (odds ratio [OR], 28.16; 95% CI, 3.37-235.22) and the requirement for postoperative extracorporeal membrane oxygenation (OR, 12.52; 95% CI, 2.99-52.41) were associated with bloodstream infections after median sternotomy.

CONCLUSIONS

Postoperative bloodstream infections occurred in 6.3% of children undergoing median sternotomy. Postoperative mediastinitis and the requirement for extracorporeal membrane oxygenation were risk factors for bloodstream infections after median sternotomy. These findings warrant exploration in a larger, multicenter study.

Cultures of sternal wound and mediastinum taken at the end of heart surgery do not predict postsurgical mediastinitis

The aim of the study was to assess of the role of intraoperative cultures taken at the end of major heart surgery (MHS) in the prediction of postoperative mediastinitis (PM) in patients undergoing MHS over a 6-month period in a tertiary university hospital. Just before wound closure, a sample of the sternal border was taken, swabbing back and forth the sternal border and the subcutaneous tissues. A second sample was taken after irrigation of the deep mediastinal structures with 10 mL of Ringer lactate. Swabs were processed semiquantitatively and the mediastinal fluid with a quantitative technique. The observation of one or more colonies per plate was considered a positive culture. Cultures obtained at the end of 229 surgical interventions (227 patients) were positive with the semiquantitative or with the quantitative procedures in 31.0% (95% confidence interval [CI], 25.1-37.4%) and 34.5% (95% CI, 28.4-41.0%) of the times, respectively (P = NS). The number of microorganisms isolated in the wound swab or mediastinal fluid was 91 and 110, respectively. Of the 227 patients, 7 developed an episode of PM (3.1%; 95% CI, 1.2-6.2%) after a median time of 11 days (range, 5-19 days). The microorganisms causing the 7 cases of mediastinitis were not isolated in the intraoperative cultures in any of the cases. The value of intraoperative cultures as a test for prediction of PM depending on the breakpoint chosen were as follows: sensitivity (0%), specificity (66.2-97.3%), and positive (0%) and negative predictive values (96.8-98.0%). We recommend against surveillance cultures taken intraoperatively in patients undergoing MHS.