Diagnosing sternal wound infections with 99mTc-labeled monoclonal granulocyte antibody scintigraphy

Prevention, Diagnosis and Management of Post-Surgical Mediastinitis in Adults Consensus Guidelines of the Spanish Society of Cardiovascular Infections (SEICAV), the Spanish Society of Thoracic and Cardiovascular Surgery (SECTCV) and the Biomedical Research Centre Network for Respiratory Diseases (CIBERES)

This is a consensus document of the Spanish Society of Cardiovascular Infections (SEICAV), the Spanish Society of Thoracic and Cardiovascular Surgery (SECTCV) and the Biomedical Research Centre Network for Respiratory Diseases (CIBERES). These three entities have brought together a multidisciplinary group of experts that includes anaesthesiologists, cardiac and cardiothoracic surgeons, clinical microbiologists, infectious diseases and intensive care specialists, internal medicine doctors and radiologists. Despite the clinical and economic consequences of sternal wound infections, to date, there are no specific guidelines for the prevention, diagnosis and management of mediastinitis based on a multidisciplinary consensus. The purpose of the present document is to provide evidence-based guidance on the most effective diagnosis and management of patients who have experienced or are at risk of developing a post-surgical mediastinitis infection in order to optimise patient outcomes and the process of care. The intended users of the document are health care providers who help patients make decisions regarding their treatment, aiming to optimise the benefits and minimise any harm as well as the workload.

Radiochemical Approaches to Imaging Bacterial Infections: Intracellular versus Extracellular Targets

The discovery of penicillin began the age of antibiotics, which was a turning point in human healthcare. However, to this day, microbial infections are still a concern throughout the world, and the rise of multidrug-resistant organisms is an increasing challenge. To combat this threat, diagnostic imaging tools could be used to verify the causative organism and curb inappropriate use of antimicrobial drugs. Nuclear imaging offers the sensitivity needed to detect small numbers of bacteria in situ. Among nuclear imaging tools, radiolabeled antibiotics traditionally have lacked the sensitivity or specificity necessary to diagnose bacterial infections accurately. One reason for the lack of success is that the antibiotics were often chelated to a radiometal. This was done without addressing the ramifications of how the radiolabeling would impact probe entry to the bacterial cell, or the mechanism of binding to an intracellular target. In this review, we approach bacterial infection imaging through the lens of bacterial specific molecular targets, their intracellular or extracellular location, and discuss radiochemistry strategies to guide future probe development.

Rapid serodiagnosis of Staphylococcus aureus surgical site infection following median sternotomy

OBJECTIVES

To determine the sensitivity and specificity of a novel ELISA for the serodiagnosis of surgical site infection (SSI) due to staphylococci following median sternotomy.

METHODS

Twelve patients with a superficial sternal SSI and 19 with a deep sternal SSI due to Staphylococcus aureus were compared with 37 control patients who also underwent median sternotomy for cardiac surgery but exhibited no microbiological or clinical symptoms of infection. A further five patients with sternal SSI due to coagulase-negative (CoNS) staphylococci were studied. An ELISA incorporating a recently recognised exocellular short chain form of lipoteichoic acid (lipid S) recovered from CoNS, was used to determine serum levels of anti-lipid S IgG in all patient groups.

RESULTS

Serum anti-lipid S IgG titres of patients with sternal SSI due to S. aureus were significantly higher than the control patients (P<0.0001). In addition, patients with deep sternal SSI had significantly higher serum anti-lipid S IgG titres than patients with superficial sternal SSI (P = 0.03). Serum anti-lipid S IgG titres of patients with sternal SSI due to CoNS were significantly higher than the control patients (P = 0.001).

CONCLUSION

The lipid S ELISA may facilitate the diagnosis of sternal SSI due to S. aureus and could also be of value with infection due to CoNS.

Staphylococcus aureus bacteremia after median sternotomy: clinical utility of blood culture results in the identification of postoperative mediastinitis

BACKGROUND

Mediastinitis is a complication of coronary artery bypass graft surgery (CABG) that can be difficult to diagnose. This study evaluated the utility of blood culture results in identifying patients with mediastinitis.

METHODS AND RESULTS

All unique patients undergoing CABG at our institution over a 60-month study period (n=5500) and all blood cultures performed on these patients <or=90 days after CABG were identified. Mediastinitis was identified by prospective active infection control surveillance. Eight hundred fifty-five (15.5%) patients had >or=1 blood culture drawn within 90 days of CABG. Mediastinitis occurred in 46 of 60 (76.7%) patients with blood cultures positive for Staphylococcus aureus, 15 of 126 (11.9%) patients with blood cultures positive for other pathogens, 37 of 669 (5.5%) patients with blood cultures with no growth, and 44 of 4645 (0.9%) patients with no blood cultures obtained. The isolation of S aureus from even 1 blood culture drawn after <or=90 days of CABG was strongly associated with mediastinitis (likelihood ratio [LR], 25; 95% CI, 14.7 to 44.4). Bacteremia attributable to other organisms did not alter pretest suspicion for mediastinitis (LR, 1.0; 95% CI, 0.6 to 1.7). Patients with negative blood cultures were less likely to have mediastinitis (LR, 0.45; 95% CI, 0.35 to 0.58). The association between S aureus bacteremia and mediastinitis remained highly significant when all unique patients undergoing CABG were analyzed in a logistic regression model and when a case-control analysis was used to evaluate patients with >or=1 blood culture obtained after CABG.

CONCLUSIONS

Among patients with blood cultures drawn after CABG, S aureus bacteremia strongly suggests the presence of mediastinitis.

Mediastinitis in heart and lung transplantation: 15 years experience

BACKGROUND

Mediastinitis after sternotomy carries a very high mortality, especially in patients receiving immunosuppressive treatment.

METHODS

A retrospective analysis of the data for patients who had undergone cardiopulmonary transplantation between May 1985 and December 2000 was undertaken. A total of 776 patients had either a median sternotomy or a transverse sternotomy through a clam-shell incision. Transplantations were as follows: 591 heart (3 simultaneous heart and renal, and 1 heart and liver), 126 bilateral sequential lung, 57 heart-lung, 1 en bloc double-lung, and 1 heart and single-lung.

RESULTS

In all, 21 (2.7%) recipients had mediastinitis. Of these, 14 had heart, 3 heart-lung, and 4 bilateral lung transplantation. There were 18 median and 3 transverse sternotomies. There were 6 deaths (28.6%). Treatment consisted of antibiotics alone in 2 patients and subxiphisternal drainage in another 2 patients. The sternum was reopened in 17 (80.95%) patients, with debridement and primary closure alone in 5 of these 17 patients and additional irrigation in the other 12. Those who had resternotomy, debridement, and substernal irrigation had a better outcome when compared with the outcomes of other modes of treatment (1 death among 12 patients) (p = 0.06). Age, cardiopulmonary bypass time, body mass index, time to diagnosis, and treatment did not differ between those who survived and those who did not.

CONCLUSIONS

Early aggressive debridement with substernal irrigation is the best mode of treatment for patients with posttransplantation mediastinitis.

Mediastinitis after cardiac surgery: improvement of bacteriological diagnosis by use of multiple tissue samples and strain typing

The diagnosis of postsurgical mediastinitis (PSM) among patients with sternal wound complication (SWC) after cardiac surgery is sometimes difficult, as fever, elevated C-reactive protein levels, and chest pain can be caused by a general inflammatory reaction to the operative trauma and/or sternal dehiscence without infection. The definitions of PSM usually used emphasize clinical signs and symptoms easily observed by the surgeon. The aim of the study was to investigate whether the use of standardized multiple tissue sampling, optimal culturing methods, and strain typing, together with a microbiological criterion for infection, could identify more infected patients than clinical assessment alone. Patients reexplored due to SWC after cardiac artery bypass grafting (CABG) or heart valve replacement (HVR) with or without CABG performed at the Department for Cardio-Thoracic Surgery at the Uppsala University Hospital between 10 March 1998 and 9 September 2000 were investigated prospectively. Tissue samples were taken from the sternum or adjacent mediastinal tissue, preferably before the administration of antibiotics. Culturing was performed both directly (on agar plates) and using enrichment broth. Species identification was performed by standard methods, and strain typing was performed by pulsed-field gel electrophoresis. A total of 41 cases with at least five tissue samples each were included in the study group. Of these patients, 32 were infected according to the microbiological criterion (i.e., the same strain was found in >/=50% of the samples). Staphylococcus epidermidis was the primary pathogen in 38% of the cases (12/32), S. aureus was the primary pathogen in 31% (10/32), P. acnes was the primary pathogen in 25% (8/32), and S. simulans and S. haemolyticus were the primary pathogens in 3% (1/32) each. All cases of S. aureus infection and 86% (12/14) of coagulase-negative staphylococcus (CoNS) infections were identified from primary cultures. All cases fulfilling the microbiological criterion for S. aureus infection were clinically diagnosed as cases of infection, but among the 14 cases fulfilling the criterion for microbiological diagnosis of CoNS infection, only 10 appeared to qualify clinically as cases of infection. Among the patients with sternal dehiscence in whom a microbiological diagnosis was established, 67% (12/18) had a CoNS infection, compared to 14% (2/14) of those without sternal dehiscence. The difference was statistically significant. PSM caused by S. aureus is readily identified by the surgeon, whereas 30% of cases with CoNS infections may be misinterpreted as noninfected. Multiple sampling before administration of antibiotics, primary culturing on agar plates, species identification, strain typing, and susceptibility testing should be used to ensure a fast and microbiologically correct diagnosis which identifies the primary pathogen and infected patients among those with minor infective symptoms. The role of P. acnes as a possible cause of PSM needs further investigation. PSM caused by CoNS is significantly related to sternal dehiscence.

Computed tomography of the sternum and mediastinum after median sternotomy

BACKGROUND

Computed tomography is used in our hospital to diagnose complications after median sternotomy, but its efficiency is unknown. Nor is the computed tomographic appearance of normal healing of a median sternotomy known. Computed tomography was evaluated for its ability to diagnose mediastinitis and sternal dehiscence, and a reference material of normally healing median sternotomies was created.

METHODS

In a prospective study, 20 patients with a normally healing median sternotomy were examined 1 week, 1 month, 3 months, and 6 months after operation. In a retrospective study, 87 scans from 65 patients that were made because a postoperative complication was suspected were reviewed.

RESULTS

In the prospective study, all patients had clinically uneventful healing. None of the computed tomographic scans showed radiologic signs of healing at 3 months. At 6 months, half of the patients had healed completely. In the retrospective study, 49 scans were performed on suspicion of infection; 7 of them indicated mediastinitis, 2 were false-positive, while mediastinitis was present in a total of 16 of the scans. Thirty-eight scans were made because of sternal pain or suspected dehiscence; after 21 of the scans, recovery was uneventful, and in 11, the definite diagnosis was dehiscence or pseudarthrosis.

CONCLUSIONS

Clinical healing of the sternotomy does not correlate with the computed tomographic image. Computed tomography is not a sensitive tool for diagnosing mediastinitis, and in patients with sternal pain, it adds little information.

Postcardiac surgery infections

Infections following cardiac surgery, although generally uncommon, are associated with difficult management decisions and significant morbidity and mortality. They often present while the patient is either in a critical care unit, or requires CCU management. This review analyzes infections related to median sternotomy wounds, prosthetic heart valves, transvenous permanent pacemakers, automatic implantable cardioverter-defibrillators, and left ventricular assist devices. The diagnosis, microbiology, treatment and outcome of each is also discussed.