Reducing the rate of nosocomially transmitted respiratory syncytial virus

BACKGROUND

A large number (17) of nosocomial respiratory syncytial virus cases led to the development of control measures to prevent transmission of respiratory syncytial virus (RSV) within the Johns Hopkins Hospital's Children's Center.

METHODS

The control plan is based on a 2-stage process. In stage 1, the staff are notified that RSV is in the community, and information is distributed through a communication tree. Stage 2 requires that nasopharyngeal aspirates be obtained from all children <3 years of age who have respiratory symptoms. The aspirates are tested directly for RSV antigen and cultured for RSV. The children are placed on pediatric droplet precautions pending those results.

RESULTS

The proportion of nosocomial RSV cases dropped from 16.5% before the use of RSV control measures to 7.2% after the initiation of the control program. A case of RSV identified in the hospital was 2.6 times more likely to be nosocomially acquired before the intervention compared with after the intervention. Approximately 14 cases of RSV are prevented each year, which results in a savings of 56 hospital-days and more than $84,000 in direct hospital-related charges alone.

CONCLUSIONS

The nosocomial spread of RSV can be reduced by a specific and feasible control plan that includes early identification and rapid isolation of potential RSV cases.

Investigation of suspected nosocomial clusters of Staphylococcus haemolyticus infections

OBJECTIVE

To determine whether typing methods can discriminate among Staphylococcus haemolyticus isolates.

DESIGN

Molecular epidemiological evaluation of S. haemolyticus isolates obtained from patients hospitalized on a hematology service and in a surgical intensive-care unit (SICU).

SETTING

A large Midwestern teaching hospital.

INTERVENTIONS

None.

RESULTS

Over 22 days, S. haemolyticus was isolated from five patients on the hematology service. Isolates from four patients had the same unusual antibiogram and biotype. Ribotyping, restriction endonuclease digestion of plasmid DNA (REAP), and whole chromosomal DNA analysis by pulsed-field gel electrophoresis (PFGE) confirmed that these isolates were identical and different from the fifth patient's isolate and from 6 control isolates. In a second cluster, 11 S. haemolyticus isolates obtained from eight patients in the SICU had similar antibiograms and biotypes. By REAP and ribotype analysis, isolates from four patients were identical. However, PFGE indicated that only two of these patients shared a common strain.

CONCLUSIONS

Antibiograms or biotyping may discriminate among isolates of S. haemolyticus if the results of these tests are unusual. Many clinical isolates can be differentiated by REAP analysis, ribotyping, or PFGE. However, some isolates are identical by all of these methods, suggesting that they may have been transmitted nosocomially.

An outbreak of Serratia marcescens infections related to contaminated chlorhexidine

An outbreak of Serratia marcescens infections occurred in a university tertiary-care hospital. Alcohol-free chlorhexidine solutions were contaminated with S marcescens. The majority of patient and chlorhexidine strains had similar pulsed field-gel electrophoresis banding patterns. Chlorhexidine was recalled, and the rate of S marcescens isolation returned to baseline. Chlorhexidine without alcohol should not be used as an antiseptic.

Learning and memory difficulties after environmental exposure to waterways containing toxin-producing Pfiesteria or Pfiesteria-like dinoflagellates

BACKGROUND

At the beginning of autumn, 1996, fish with "punched-out" skin lesions and erratic behaviour associated with exposure to toxins produced by Pfiesteria piscicida or Pfiesteria-like dinoflagellate species were seen in the Pocomoke River and adjacent waterways on the eastern shore of the Chesapeake Bay in Maryland, USA. In August, 1997, fish kills associated with Pfiesteria occurred in these same areas. People who had had contact with affected waterways reported symptoms, including memory difficulties, which raises questions about the human-health impact of environmental exposure to Pfiesteria toxins.

METHODS

We assessed 24 people who had been exposed. We collected data on exposure history and symptoms, did a complete medical and laboratory assessment (13 people), and carried out a neuropsychological screening battery. Performance on neuropsychological measures was compared with a matched control group.

RESULTS

People with high exposure were significantly more likely than occupationally matched controls to complain of neuropsychological symptoms (including new or increased forgetfulness); headache; and skin lesions or a burning sensation of skin on contact with water. No consistent physical or laboratory abnormalities were found. However, exposed people had significantly reduced scores on the Rey Auditory Verbal Learning and Stroop Color-Word tests (indicative of difficulties with learning and higher cognitive function), and the Grooved Pegboard task. There was a dose-response effect with the lowest scores among people with the highest exposure. By 3-6 months after cessation of exposure, all those assessed had test scores that had returned to within normal ranges.

INTERPRETATION

People with environmental exposure to waterways in which Pfiesteria toxins are present are at risk of developing a reversible clinical syndrome characterised by difficulties with learning and higher cognitive functions. Risk of illness is directly related to degree of exposure, with the most prominent symptoms and signs occurring among people with chronic daily exposure to affected waterways.

Occupationally acquired infections and the healthcare worker

Much of the recent research related to occupational infections in healthcare workers has focused on the evaluation of the effectiveness of preventive measures, the cost-effectiveness of such measures, and alternative approaches to preventing common occupational infections. This article reviews recent information on healthcare workers about occupationally acquired diseases and considers the risks from unusual or re-emerging pathogens. Among recent advances of note are effective post-exposure prophylaxis for HIV, approaches to achieving immunity to hepatitis B in vaccine non-responders, better diagnostic tests for hepatitis C and improved equipment for preventing blood exposure and tuberculosis.

Septic shock: an analysis of outcomes for patients with onset on hospital wards versus intensive care units

OBJECTIVE

To determine if early interventions for septic shock were associated with reduced mortality.

DESIGN

Retrospective cohort study.

SETTING

University hospital intensive care unit (ICU) and general wards.

PATIENTS

Forty-one consecutive patients prospectively identified with positive blood cultures and septic shock. Although all patients were eventually treated in an ICU, ten (24%) patients were on a general ward at the onset of septic shock, and 31 (76%) were in an ICU setting.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Over a period of 9 mos, a cohort of 41 patients who had positive blood cultures and septic shock was prospectively identified. The 28-day crude mortality was 46% (19 deaths). We compared the management of septic shock and outcome for patients on a general ward vs. those patients in an ICU setting. Of the ten patients on the ward at time of shock onset (median age 55.5 yrs; median Acute Physiology and Chronic Health Evaluation [APACHE] II score of 18.5), seven (70%) died. In contrast, the 31 patients receiving intensive care when shock developed were older and more ill (median age 66 yrs; median APACHE II 24), yet had a mortality of 39% (12 deaths). The odds ratio (OR) for death for ward patients compared with ICU patients was 3.57 (p=.17). In a multivariate logistic regression analysis, two risk factors for mortality were important: APACHE II score (p=.015) and ward status (p=.08). Candida species in the bloodstream is known to have a high attributable mortality. When type of bloodstream pathogen (Candida species vs. bacteria) was added to the model, APACHE II (OR 2.64 for 10-unit increase) remained significant (p=.014), but ward status (OR 3.97) became statistically nonsignificant (p=.222). The patients who were on a general ward when their shock developed had a median delay of 67 mins before transfer to an ICU setting. Ward patients received an intravenous fluid bolus after a median delay of 27 mins, whereas those in the ICU who received a fluid bolus did so after a median of 15 mins (p=.48). Ward patients also had a median delay of 310 mins to receive inotropic support compared with a median 22.5 mins (p=.037) for the patients in an ICU setting when shock started.

CONCLUSIONS

The data suggest that for patients with septic shock on wards, there were clinically important delays in transfer of patients to the ICU, receipt of intravenous fluid boluses, and receipt of inotropic agents. However, the most powerful predictors of mortality were APACHE II scores and bloodstream infection with Candida species.

Pfiesteria in Maryland: preliminary epidemiologic findings

In the fall of 1996, fish kills in Maryland rivers were attributed to the dinoflagellate, Pfiesteria piscicida. After a group of researchers established a potential link between exposure to Pfiesteria and an illness causing memory problems, state health authorities closed a portion of the Pocomoke River. To determine the extent of illness, the range of symptoms, potential risk factors for disease, and to provide information to concerned citizens, a toll-free hotline was created. All symptomatic persons who called the toll-free number were administered a standardized questionnaire. Persons who had been exposed to Pfiesteria or Pfiesteria-laden waters were more likely to have respiratory, neurologic, dermatologic, and gastrointestinal problems than those persons without exposure. Among the persons calling the hotline, many had extensive neuropsychologic testing. Of the neuropsychologic test battery, low scores on the Rey Auditory Verbal Learning Test (RAVLT), a standardized measure of learning and memory, best characterized illness related to Pfiesteria exposure. Patients with low RAVLT scores were more likely to have neurologic symptoms and skin lesions than control subjects. Low RAVLT scores were associated with fishing (OR, 9.00, 95% CI, 106, 409.87), catching fish with lesions (OR, 6.17, 95% CI 1.27, 32.10), and handling fish with lesions (OR, 5.34, 95% CI, 1.05, 29.92), but not with consumption of seafood. While preliminary, these results do suggest that some risk factors for Pfiesteria-related illness may be easy to modify and used to prevent unnecessary human exposure.

The epidemiology of hemorrhage related to cardiothoracic operations

OBJECTIVE

To define the epidemiology, risk factors, and unadjusted cost of hemorrhages related to cardiothoracic operations.

STUDY DESIGN

We conducted two case-control studies to evaluate the risk of hemorrhage following cardiothoracic operations. The definition of hemorrhage required one of the following: reoperation for bleeding, postoperative loss of greater than 800 mL of blood over 4 hours, or surgeon-diagnosed excessive intraoperative bleeding.

SETTING

The cardiothoracic surgery service of a university hospital.

RESULTS

Of 511 patients undergoing cardiothoracic operations, 93 (18%) met the definition of hemorrhage. In the first case-control study, 3 (14%) of 21 cases and 0 of 42 controls died (odds ratio [OR], 15.0; 95% confidence interval [CI95], 1.18-191.55). Compared with controls, cases received significantly more packed red blood cells intraoperatively (OR, 1.18/100 mL; CI95, 1.01-1.38), and significantly more platelets (OR, 3.26/100 mL; CI95, 1.47-7.26) and fresh frozen plasma (OR, 1.73/100 mL; CI95, 1.05-.84) in the intensive-care unit. Cases were more likely than controls to receive protamine postoperatively (OR, 3.74; CI95, 1.27-11.02). Previous sternotomy, preoperative aspirin or heparin, and preoperative laboratory values did not predict bleeding. The median unadjusted hospital cost was $3,458 higher for patients who suffered hemorrhage than for controls. To decrease costs, hetastarch (acquisition cost $45/500 mL) was substituted for albumin (acquisition cost $76/100 mL) in the pump priming solution (estimated possible cost savings, $7,000-$53,000/year). Because hemorrhage rates increased subsequently, we conducted a second case-control study that identified patient age (P=.02) and use of greater than 5 mL/kg of hetastarch (OR, 1.82) as risk factors for hemorrhage. The cost of treating hemorrhages exceeded all estimates of possible cost savings ($7,000-$53,000 per year).

CONCLUSIONS

Our definition of hemorrhage identified patients who required increased volumes of blood products and who had an increased crude mortality rate and a higher unadjusted cost of hospitalization. Patient age and hetastarch use were risk factors for hemorrhage. Efforts to save money by substituting less expensive products inadvertently may increase costs by increasing the probability of perioperative adverse events.

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.

Basics of surgical-site infection surveillance

Surgical-site infections, the third most common class of nosocomial infections, cause substantial morbidity and mortality and increase hospital costs. Surveillance programs can lead to reductions in surgical-site infection rates of 35% to 50%. Herein, we will discuss the practical aspects of implementing a hospital-based surveillance program for surgical-site infections. We will review surveillance methods, patient populations that should be screened, and interventions that could reduce infection rates.

Basics of surveillance--an overview

Surveillance of nosocomial infections is the foundation of an infection control program. This article describes components of a surveillance system, methods for surveillance, methods for case-finding, and data sources. We encourage the epidemiology team to use this background information as they design surveillance systems that meet the goals of their individual institution's infection control program.

Staphylococcus cohnii: a case report on an unusual pathogen

Coagulase-negative staphylococci have become increasingly important causes of infection in predisposed hosts. such as patients receiving immunosuppressive therapy and broad-spectrum antimicrobial drugs, patients who have prosthetic devices, or those who have prolonged hospital or intensive care unit stays. However, human infections caused by Staphylococcus cohnii rarely have been reported in the literature. In this report, we review the current literature and describe a 38 year-old immunosuppressed woman who developed catheter-related S. cohnii bacteremia. The case illustrates why microbiology laboratories under certain circumstances should identify coagulase-negative staphylococci to the species level. This information may be critical because it may allow clinicians to identify the source of the infecting organism and to choose appropriate antibiotics. Yet in this era of cost containment many laboratories may decrease costs by decreasing services, including species identification.

The significance of nasal carriage of Staphylococcus aureus and the incidence of postoperative wound infection

Staphylococcus aureus infections are associated with considerable morbidity and, in certain situations, mortality. The association between the nasal carriage of S. aureus and subsequent infection has been comprehensively established in a variety of clinical settings, in particular, patients undergoing haemodialysis and continuous ambulatory peritoneal dialysis (CAPD), and in patients undergoing surgery. Postoperative wound infections are associated with a high degree of morbidity and represent an important medical issue. Until recently, eradication of S. aureus nasal carriage by various topical and systemic agents had proved unsuccessful. Mupirocin is a novel topical antibiotic with excellent antibacterial activity against staphylococci. Recent studies have demonstrated that intranasal administration of mupirocin is effective in eradicating the nasal carriage of S. aureus and in reducing the incidence of S. aureus infections in haemodialysis and CAPD patients. It has been suggested that sufficient evidence now exists to test the hypothesis that eradication of the carrier state in surgical patients preoperatively may reduce the incidence of S. aureus postoperative wound infections.

Long-term survival and function after suspected gram-negative sepsis

OBJECTIVE

To determine the long-term (> 3 months) survival of septic patients, to develop mathematical models that predict patients likely to survive long-term, and to measure the health and functional status of surviving patients.

SETTING

A large tertiary care university hospital and an associated Veterans Affairs Medical Center.

DESIGN

From December 1986 to December 1990, a total of 103 patients with suspected gram-negative sepsis entered a double-blind, placebo-controlled efficacy trial of monoclonal antiendotoxin antibody. Of these, we followed up 100 patients for 7667 patient-months. Beginning in May 1992, we reviewed hospital records and contacted all known survivors. We measured the health status of all surviving patients.

MAIN OUTCOME MEASURES

The determinants of long-term survival (up to 6 years) were identified through two Cox proportional hazard regression models: one that included patient characteristics identified at the time of sepsis (bedside model) and another that included bedside, infection-related, and treatment characteristics (overall model).

RESULTS

Of the 60 patients in the cohort who died at a median interval of 30.5 days after sepsis, 32 died within the first month of the septic episode, seven died within 3 months, and four more died within 6 months. In the bedside multivariate model constructed to predict long-term survival, large hazard ratios (HRs) were associated with severity of underlying illness as classified by McCabe and Jackson criteria (for rapidly fatal disease, HR = 30.4, P < .001; for ultimately fatal disease, HR = 7.6, P < .001) and the use of vasopressors (HR = 2.5; P = .001). In the overall model for long-term survival, severity of underlying illness (rapidly fatal disease, HR = 23.7, P < .001; ultimately fatal disease, HR = 6.5, P < .001), number of active comorbid illnesses (HR = 1.3; P = .04), use of vasopressors at the time of sepsis (HR = 2.0; P = .02), and development of adult respiratory distress syndrome (HR = 2.3; P = .02) predicted patients most likely to die. The Acute Physiology and Chronic Health Evaluation II score was not a significant predictor of outcome when either model included the simpler McCabe and Jackson classification of underlying disease severity. We compared the health status scores with norms for the general population and found that patients with resolved sepsis reported more physical dysfunction (P < .001), including problems with work and activities of daily living (P = .02), and more poorly perceived general health (P < .01). In contrast, patients' scores for perceived emotional health were higher than those in the general population (P = .004). The mean Barthel score of our patients was 85 (100 = total independence) and the mean Eastern Cooperative Oncology Group score was 0.7 (0 = normal, 4 = 100% bedridden), suggesting that the patients' physical function was not normal.

CONCLUSIONS

At the onset of suspected gram-negative sepsis, severity of underlying illness and in-hospital use of vasopressors are strong and consistent predictors of short- and long-term survival. Our data validate the McCabe and Jackson severity of illness scoring system for predicting long-term survival after sepsis. Physical dysfunction and more poorly perceived general health occur commonly after sepsis.

Postoperative wound infections: risk factors and role of Staphylococcus aureus nasal carriage

In the United States the rate of postoperative wound infection varies from one to nine per cent, depending on the surgical procedure. Each postoperative wound infection increases the length of stay in hospital, the cost of the procedure and is associated with significant morbidity. Staphylococcus aureus is the causative agent in 15 to 20% of these infections, although the pathogen isolated varies according to the surgical site. Risk factors for acquiring an infection can be divided into the following categories: host factors, surgical and environmental factors, and microbial characteristics. Host factors which may contribute to an increased risk of infection include: age, prolonged pre-operative length of stay, and concurrent infection at another body site. Increased infection risk may result from an extended surgical procedure, the wound classification, the use of a razor for hair removal before surgery and may also be dependent on the surgeon's technical skill. Microbial factors related to the risk of developing an infection postoperatively are less well defined, however, many outbreaks of surgical wound infections have been linked to personnel carrying an organism which is then transmitted to the patient. Furthermore, patients who carry intranasal S. aureus have a two-to ten-fold increased likelihood of developing a postoperative wound infection due to S. aureus. Identification of patients most at risk of developing an infection is the ultimate goal, however, risk indices must be highly sensitive, specific and accurate. To summarize, the epidemiology of postoperative wound infections remains poorly studied, however, since wound infections contribute significantly to morbidity, mortality and cost, future research is warranted.

A second large controlled clinical study of E5, a monoclonal antibody to endotoxin: results of a prospective, multicenter, randomized, controlled trial. The E5 Sepsis Study Group

OBJECTIVE

To evaluate the safety and efficacy of E5, a murine, monoclonal antibody directed against endotoxin, in the treatment of patients with Gram-negative sepsis.

DESIGN

A multicenter, randomized, double-blind, placebo-controlled trial.

SETTING

Fifty-three hospitals across the United States, including university medical centers, Veterans Affairs Medical Centers, and community hospitals.

PATIENTS

847 patients were randomized into this study. Enrolled patients met criteria for three conditions: a) known or suspected Gram-negative infection; b) clinical evidence of sepsis; and c) signs of end-organ dysfunction. Patients with refractory shock were excluded from the study.

INTERVENTIONS

Two doses of E5 (2 mg/kg/day by intravenous infusion 24 hrs apart), or placebo that was identical in appearance were administered. In addition, all patients received standard supportive therapy and broad-spectrum antibiotics.

MEASUREMENTS AND MAIN RESULTS

The primary end point was mortality over 30 days. Secondary outcome measures included the resolution and prevention of organ failure in the same two populations. Additionally, the safety of E5 was evaluated. There was no significant improvement in survival over 30 days among patients with Gram-negative sepsis who received E5 compared with those patients who received placebo (n = 530; p = .21). In addition, E5 did not improve survival for patients with Gram-negative sepsis and organ failure (n = 139; p = .3). However, a significantly greater percentage of patients with Gram-negative sepsis experienced resolution of major organ failure if they received E5, compared with those patients who received placebo (n = 139; 48% E5 vs. 25% placebo; p = .005). This result extended to all patients who entered the study with one or more major organ failures, regardless of the etiology of the infection (n = 225; 41% E5 vs. 27% placebo; p = .024). E5 also provided protection against the development of some organ failures, but significant prevention was only observed for adult respiratory distress syndrome (p = .007) and central nervous system dysfunction (p = .050). Hypersensitivity reactions attributable to E5 occurred in 2.6% of patients. An asymptomatic antibody response occurred in 44% of the E5-treated patients and in 12% of the patients who received placebo.

CONCLUSIONS

In this study, E5 did not reduce mortality in nonshock patients with Gram-negative sepsis whether or not those patients also had organ failure. However, E5 did result in greater resolution of organ failure in patients with Gram-negative sepsis. This benefit extended to those patients with suspected Gram-negative etiology. This finding is important because patients with suspected Gram-negative sepsis and organ failure can be identified without waiting for culture results. In addition, E5 resulted in the prevention of adult respiratory distress syndrome and central nervous system organ failure. However, more studies are needed to determine if this result can be extended to organ failure in general. E5 is safe as a treatment for patients with Gram-negative sepsis.

Nosocomial transmission of Serratia odorifera biogroup. 2: Case report demonstration by macrorestriction analysis of chromosomal DNA using pulsed-field gel electrophoresis

OBJECTIVES

To investigate a cluster of Serratia odorifera in a cardiothoracic surgery unit (CTSU) and to evaluate the applicability of three typing methods for this species.

DESIGN

During a surveillance surgical wound study, S odorifera was isolated from two patients in the CTSU. The patients' hospital charts were reviewed for the details of surgery and for common personnel, procedures, or medications. Cultures were obtained of water, soap, and unit dose medications from the CTSU, the operating room, and the surgical intensive care unit. The isolates' antibiograms, biotypes (Vitek identification card and API 20E), and patterns of chromosomal DNA (chrDNA) by pulsed-field gel electrophoresis (PFGE) were examined. S odorifera isolates from our organism collection were used as controls.

SETTING

A 900-bed university hospital with a 22-bed CTSU.

RESULTS

ChrDNA patterns of isolates from the two patients were identical, suggesting a possible nosocomial source. However, no source of organisms or mode of transmission was identified. Neither biotype nor antibiogram were useful for epidemiologically typing S odorifera, and PFGE was necessary to discriminate among isolates.

CONCLUSIONS

Although rarely isolated, S odorifera and other non-marcescens Serratia species may cause nosocomial outbreaks. PFGE of chrDNA seems to be a reliable method for epidemiologically typing this species.

Comparison of identification systems for Staphylococcus epidermidis and other coagulase-negative Staphylococcus species

Three commercially available systems (API Staph-Trac, API 20GP, and Vitek GPI), used to identify coagulase-negative staphylococci, were evaluated against 277 bloodstream isolates, including 94 isolates of Staphylococcus epidermidis and 183 isolates of other coagulase-negative Staphylococcus species. The conventional method of Kloos and Schleifer served as the reference method. Controls included 14 ATCC type culture strains of coagulase-negative staphylococci. The API Staph-Trac system showed the highest rate of agreement with reference method, correctly identifying 73% of the isolates. The Vitek GPI System had an overall rate of agreement of 67% and the API 20GP system correctly identified 61%. The API Staph-Trac system correctly identified 94% of the isolates of S. epidermidis compared with 64% by both Vitek GPI and API 20GP. The most common error for both Vitek GPI and API 20GP systems was the failure to identify organisms contained within the database of the systems. Because none of the tested commercial identification systems identified "non-epidermidis" coagulase-negative Staphylococcus species with a high degree of accuracy, the systems need to be markedly improved or new systems developed.

Effect of serum on the in vitro activities of 11 broad-spectrum antibiotics

We evaluated the effect of serum on the in vitro activities of 11 antimicrobial agents against gram-negative isolates obtained from 100 patients with nosocomial bacteremia. The test organisms included 25 stains of Pseudomonas aeruginosa and 75 strains of the family Enterobacteriaceae. MICs were determined by broth microdilution with Mueller-Hinton broth alone or supplemented with 25 or 50% pooled, heat-inactivated human serum (25S or 50S, respectively). Among the antibiotics evaluated, the protein binding ranged from 9 to 95%. The antibiotics tested and their MICs for 90% of the strains tested in 50S included ciprofloxacin (0.12 micrograms/ml), ceftazidime (1 micrograms/ml), imipenem (1 micrograms/ml), aztreonam (4 micrograms/ml), cefpirome (4 micrograms/ml), cefotaxime (16 micrograms/ml), cefoperazone (16 micrograms/ml), desacetylcefotaxime plus cefotaxime (32 micrograms/ml), ceftriaxone (greater than 32 micrograms/ml), ticarcillin (128 micrograms/ml), and desacetylcefotaxime (greater than 128 micrograms/ml). MICs for 90% of the strains tested were calculated with 95% confidence intervals to show the precision of the MICs for these strains. With the exceptions of ceftriaxone (greater than 95% protein bound) and cefoperazone (90% protein bound), serum had no significant effect on the in vitro activities of various agents. A fourfold-or-greater increase in the MIC of ceftriaxone was observed in 45 of 100 isolates with 50S and in 30 of 100 isolates with 25S. With cefoperazone, 17 of 100 isolates demonstrated more than 2 twofold dilution increases in 50S. Testing of antibiotics which were less protein bound illustrated minor effects primarily with members of the Enterobacteriaceae. The presence of serum did not adversely affect the in vitro activities of broad-spectrum agents against these nosocomial isolates.