Preoperative screening cultures in the identification of staphylococci causing wound and valvular infections in cardiac surgery

Source and route of methicillin-resistant Staphylococcus epidermidis transmitted to the surgical wound during cardio-thoracic surgery. Possibility of preventing wound contamination by use of special scrub suits

The objective of this study was to trace the source and route of transmission of methicillin-resistant Staphylococcus epidermidis (MRSE) in the surgical wound during cardio-thoracic surgery, and to investigate the possibility of reducing wound contamination by wearing special scrub suits. In total 65 elective operations for coronary artery bypass grafting (CABG) with or without concomitant valve replacement were investigated. All staff present in the operating room wore conventional scrub suits during 33 operations and special scrub suits during 32 operations. Samples were taken from the hands of the scrubbed team after surgical scrub but before putting on sterile gowns and gloves, and from patients' skin (incisional area of sternum and vein harvesting area of legs) after preoperative skin preparation with chlorhexidine gluconate. Air samples were taken during operations. Samples were also taken from the wound just before closure. Total counts of bacteria on sternal skin and from the wound (cfu/cm2) were calculated as well as total counts of bacteria in the air (cfu/m3). Strains of MRSE recovered from the different sampling sites were compared by pulsed field gel electrophoresis (PFGE). It was found that wearing special scrub suits did not reduce the number of air-samples where MRSE was found compared with conventional scrub suits. The risk factor most strongly associated with MRSE in the wound at the end of the operation was preoperative carriage of MRSE on sternal skin; RR 2.42 [95% CI 1.43-4.10], P= 0.021. By use of PFGE, it was possible to identify the probable source for four MRSE isolates recovered from the wound. In three cases the source was the patients own skin. Finding MRSE in air-samples, or on the hands of the scrubbed team, were not risk factors for the recovery of MRSE in the wound at the end of operation. In conclusion, with a total bacterial air count around 20 cfu/m3 and a low proportion of MRSE, the reduction of total air counts by use of tightly woven special scrub suits did not reduce air counts of MRSE or wound contamination with MRSE. The patients' sternal skin was the main source for wound contamination with MRSE

New approaches to reduce Staphylococcus aureus nosocomial infection rates: treating S. aureus nasal carriage

BACKGROUND

Nosocomial infections cause significant patient morbidity and mortality. The 2.5 million nosocomial infections that occur each year cost the US healthcare system $5 million to $10 million. Staphylococcus aureus has long been recognized as an important pathogen in human disease and is the most common cause of nosocomial infections.

OBJECTIVE

To describe the epidemiology of S. aureus nosocomial infections that are attributable to patients' endogenous colonization.

DATA SOURCES

Review of the English-language literature and a MEDLINE search (as of September 1997).

DATA SYNTHESIS

The ecologic niche of S. aureus is the anterior nares. The prevalence of S. aureus nasal carriage is approximately 20-25%, but varies among different populations, and is influenced by age, underlying illness, race, certain behaviors, and the environment in which the person lives or works. The link between S. aureus nasal carriage and development of subsequent S. aureus infections has been established in patients on hemodialysis, on continuous ambulatory peritoneal dialysis, and those undergoing surgery. S. aureus nasal carriers have a two-to tenfold increased risk of developing S. aureus surgical site or intravenous catheter infections. Thirty percent of 100% of S. aureus infections are due to endogenous flora and infecting strains were genetically identical to nasal strains. Three treatment strategies may eliminate nasal carriage: locally applied antibiotics or disinfectants, systemic antibiotics, and bacterial interference. Among these strategies, locally applied or systemic antibiotics are most commonly used. Nasal ointments or sprays and oral antibiotics have variable efficacy and their use frequently results in antimicrobial resistance among S. aureus strains. Of the commonly used agents, mupirocin (pseudomonic acid) ointment has been shown to be 97% effective in reducing S. aureus nasal carriage. However, resistance occurs when the ointment has been applied for a prolonged period over large surface areas.

CONCLUSIONS

Given the importance of S. aureus nosocomial infections and the increased risk of S. aureus nasal carriage in patients with nosocomial infections, investigators need to study cost-effective strategies to prevent certain types of nosocomial infections or nosocomial infections that occur in specific settings. One potential strategy is to decrease S. aureus nasal carriage among certain patient populations.

Nasal carriage of Staphylococcus aureus: epidemiology, underlying mechanisms, and associated risks

Staphylococcus aureus has long been recognized as an important pathogen in human disease. Due to an increasing number of infections caused by methicillin-resistant S. aureus (MRSA) strains, therapy has become problematic. Therefore, prevention of staphylococcal infections has become more important. Carriage of S. aureus appears to play a key role in the epidemiology and pathogenesis of infection. The ecological niches of S. aureus are the anterior nares. In healthy subjects, over time, three patterns of carriage can be distinguished: about 20% of people are persistent carriers, 60% are intermittent carriers, and approximately 20% almost never carry S. aureus. The molecular basis of the carrier state remains to be elucidated. In patients who repeatedly puncture the skin (e.g., hemodialysis or continuous ambulatory peritoneal dialysis [CAPD] patients and intravenous drug addicts) and patients with human immunodeficiency virus (HIV) infection, increased carriage rates are found. Carriage has been identified as an important risk factor for infection in patients undergoing surgery, those on hemodialysis or CAPD, those with HIV infection and AIDS, those with intravascular devices, and those colonized with MRSA. Elimination of carriage has been found to reduce the infection rates in surgical patients and those on hemodialysis and CAPD. Elimination of carriage appears to be an attractive preventive strategy in patients at risk. Further studies are needed to optimize this strategy and to define the groups at risk.

Dynamics of coagulase-negative staphylococcal colonization in patients and employees in a surgical intensive care unit

Because there is little information about the frequency of carriage of various species of coagulase-negative staphylococci (CNS) in hospital staff, we prospectively investigated nasal CNS in patients and personnel in a Surgical Intensive Care Unit (SICU). The majority of CNS from personnel were Staphylococcus epidermiditis. The CNS species from patients on admission were more diverse and included multiply antibiotic-resistant S. haemolyticus. Patients' CNS became more like CNS colonizing personnel after admission with respect to both antimicrobial susceptibility and speciation. Plasmid and antibiotic sensitivity profiles of S. epidermidis resistant to multiple antibiotics from five patients were identified as those from one employee, but there was no evidence that this was of clinical significance. A variety of factors influence nasal colonization by CNS in SICUs. The nasal CNS of patients change after admission and may become more resistant and less diverse. The factors influencing changes in the antibiotic susceptibility and the aetiology of CNS infection require further study.

New laboratory techniques for hospital infection control

The clinical microbiologist has important responsibilities in hospital infection control. Duties include participating in hospital-wide infection control activities (especially the infection control committee), recovering and identifying accurately the organisms responsible for nosocomial infection, characterizing antimicrobial susceptibility of many of these nosocomial pathogens, reporting in timely fashion laboratory data relevant to infection control, carrying out the few routine microbiologic studies of the hospital environment that are useful, supporting investigations of specific hospital infection problems as they arise, and providing special typing studies when necessary to establish similarity or difference of organisms. In the past decade, improvements in laboratory instrumentation and/or procedures have provided dramatic help to infection control efforts in several of these areas. Among these are new techniques for more rapid detection and differentiation of organisms and improved systems of reporting for both patient data and trend analysis. Perhaps the most dramatic advances have come in special procedures for examining (typing) hospital organisms for similarity or difference; here, molecular and other techniques have permitted more definitive examination of a wider range of organisms than previously was possible. With health care resources in the United States now at a premium, the current and future challenge for laboratories is to make their participation in infection control more efficient as well as effective. Establishing adequate quality control of methods and obtaining clinical data to allow correct interpretation will be crucial for efficient use of the new typing procedures. Deciding when these techniques are needed and whether they should be performed on site also will be an important part of this process.

Prosthetic valve endocarditis: a continuing challenge for infection control

Conventional medical thought accepts the risks of nosocomial prosthetic valve endocarditis (PVE) to be between 0.7 and 1.4%, the incidence within several months after surgery. More careful actuarial analysis of recent series suggests the risk of nosocomial PVE is 1.4-3.0%, with cases occurring throughout the year after surgery. Methicillin-resistant coagulase-negative staphylococci are the predominant cause of nosocomial PVE and account for 60% of cases. Intraoperative contamination by Staphylococcus epidermidis of nosocomial origin has led to small epidemics of PVE. Aside from the fundamental elements of aseptic surgical technique, studies have failed to identify elements of intraoperative or postoperative care that might be modified to reduce the incidence of sporadic cases of nosocomial PVE. Prophylactic antibiotics have become an essential element in the effort to prevent PVE. Some recent studies have advocated using cefamandole or cefuroxime for prophylaxis; however, other studies have failed to find these agents more effective than cefazolin. The use of vancomycin for prophylaxis requires additional study. Intensive studies are needed to define elements of perioperative and postoperative care that can be modified to reduce the frequency of nosocomial PVE.