A comparison of pneumonia caused by gentamicin, methicillin-resistant and gentamicin, methicillin-sensitive Staphylococcus aureus: epidemiologic and clinical studies

Staphylococcus aureus Ventilator-Associated Pneumonia: A Study of Bacterio-Epidemiological Profile and Virulence Factors

Ventilator-associated pneumonia (VAP) represents a major cause of nosocomial infections in the intensive care units in which Staphylococcus aureus is frequently involved. Better knowledge of this pathogen is required in order to enhance the patient’s treatment and care. In this article, we studied the bacteriological profile and virulence factors of S. aureus-related VAP on a 3-year period. We included a collection of S. aureus strains (n = 35) isolated from respiratory samples from patients diagnosed with VAP in the intensive care units. We studied the bacteriological aspects and we searched for the presence of virulence factors (SpA, FnbpA, Hla, and PVL genes) in the strains, and we also studied the clinical and biological aspects of the infections. The average age of our patients was of 36 years and they were predominantly males (sex ratio = 3.37). A severe head trauma or a history of coma was noted in 73.43% of the patients. The average duration of ventilation was 29 days. Among the studied strains, five were Methicillin-resistant S. aureus of which three expressed the mecA gene. Overall, the Hla gene was detected in 85.7% of the strains and it was more prevalent in Methicillin-susceptible than Methicillin-resistant strains (93.3% versus 40%; P = 0.014). FnbpA, Spa, and PVL genes were detected, respectively, in 80%, 45.7%, and 20% of the strains. Therefore, our studied strains were essentially associated with the production of Hla and FnbpA genes. It is, however, important to elucidate their expression in order to establish their role in the VAP pathogenesis.

Effectiveness of Simple Measures to Control an Outbreak of Nosocomial Methicillin-Resistant Staphylococcus aureus Infections in an Intensive Care Unit

Between June 1985 and March 1986, 14 cases of severe nosocomial methicillin-resistant Staphylococcus aureus (MRSA) infection, including septicemia, were observed in the intensive care unit (ICU) of a 400-bed cancer reference center. Simple control measures including contact isolation of colonized patients and reinforcement of handwashing practices among personnel were followed by a sharp decrease in the rate of infection and colonization. An epidemiological investigation showed that a single serophage variant MRSA strain was involved; peak incidence of infection was 17 per 100 ICU patient discharges; the index case was identified as a patient admitted from another hospital and the epidemic strain was then transmitted from patient-to-patient in the ICU; risk factors for acquiring infection were length of prior hospitalization, invasive procedures and number of antibiotic treatments; dissemination of the strain to other wards was only anecdotal. These results stress the effectiveness of simple measures to control outbreaks of MRSA nosocomial infections even in immunocompromised cancer patients.

No Outbreak of Vancomycin and Linezolid Resistance in Staphylococcal Pneumonia over a 10-Year Period

BACKGROUND

Staphylococci can cause wound infections and community- and nosocomial-acquired pneumonia, among a range of illnesses. Staphylococcus aureus and methicillin-resistant S. aureus (MRSA) have been rapidly increasing as a cause of infections worldwide in recent decades. Numerous reports indicate that S. aureus and MRSA are becoming resistant to many antibiotics, which makes them very dangerous. Therefore, this study retrospectively investigated the resistance to antimicrobial agents in all hospitalized patients suffering from community- or nosocomial-acquired pneumonia due to S. aureus and MRSA.

METHODS

Information from the study groups suffering from either community- or nosocomial-acquired pneumonia caused by S. aureus or MRSA was gathered by searching records from 2004 to 2014 at the HELIOS Clinic Wuppertal, Witten/Herdecke University, Germany. The findings of antibiotic resistance were analyzed after the evaluation of susceptibility testing for S. aureus and MRSA.

RESULTS

Total of 147 patients (63.9%, 95% CI 57.5%-69.8%), mean age 67.9 ± 18.5 years, with pneumonia triggered by S. aureus, and 83 patients (36.1%, 95% CI 30.2%-42.5%), mean age 72.3 ± 13.8 years, with pneumonia due to MRSA. S. aureus and MRSA developed no resistance to vancomycin (P = 0.019 vs. < 0.0001, respectively) or linezolid (P = 0.342 vs. < 0.0001, respectively). MRSA (95.3%) and S. aureus (56.3%) showed a high resistance to penicillin. MRSA (87.7%) was also found to have a high antibiotic resistance against ß-lactam antibiotics, compared to S. aureus (9.6%). Furthermore, MRSA compared to S. aureus, respectively, had increased antibiotic resistance to ciprofloxacin (90.1% vs. 17.0%), cefazolin (89.7% vs. 10.2%), cefuroxime (89.0% vs. 9.1%), levofloxacin (88.2% vs. 18.4%), clindamycin (78.0% vs. 14.7%), and erythromycin (76.5% vs. 20.8%).

CONCLUSION

No development of resistance was found to vancomycin and linezolid in patients with pneumonia caused by S. aureus and MRSA.

Relationship of teicoplanin MICs to treatment failure in teicoplanin-treated patients with methicillin-resistant Staphylococcus aureus pneumonia

BACKGROUND/PURPOSE

The objective of this study was to determine the predictive value of teicoplanin minimal inhibitory concentrations (MICs) for treatment failure among patients with methicillin-resistant Staphylococcus aureus (MRSA) pneumonia.

METHODS

In this study, all patients with ≥1 tracheal aspirates or sputum cultures positive for MRSA admitted to the hospital between April 2011 and September 2011 were reviewed. We enrolled patients who are ≥18 years of age, with a diagnosis of pneumonia, and with a receipt of teicoplanin therapy throughout the course. The relationship between teicoplanin Etest MICs and treatment outcomes of MRSA pneumonia was analyzed to identify the breakpoint of teicoplanin MICs influencing treatment outcomes.

RESULTS

Of the 80 patients enrolled, 31 had a lower teicoplanin MIC level (<2.0 mg/L) and 49 had a higher MIC level (≥2.0 mg/L) for MRSA. The lower MIC group had a higher clinical resolution rate in 14 days [24 (77.4%) vs. 23 (46.9%), p = 0.007] and a lower treatment failure rate at the end of teicoplanin treatment [4 (12.9%) vs. 18 (36.7%), p = 0.020]. A comparison between the treatment success and failure groups showed that the former had a longer duration of teicoplanin use (18.76 ± 10.34vs.12.41 ± 5.65 days; p = 0.014). Results of a multivariate analysis showed that teicoplanin MICs ≥ 2.0 mg/Land shorter duration of teicoplanin therapy were independent risk factors for treatment failure.

CONCLUSION

A higher teicoplanin MIC value (≥2.0 mg/L) may predict the treatment failure among patients with teicoplanin-treated MRSA pneumonia.

Health care-associated Staphylococcus aureus pneumonia

INTRODUCTION

While Staphylococcus aureus is an uncommon but serious cause of traditional community-acquired pneumonia (CAP), it is a predominant cause of nosocomial pneumonia in addition to the unique clinical entity of health care-associated pneumonia (HCAP). A cohort of bacteremic S aureus pneumonia cases was reviewed to determine the role of HCAP among the cohort, and to assess for differences between CAP and HCAP.

PATIENTS AND METHODS

Bacteremic S aureus pneumonia cases were identified from a prospective study of all patients diagnosed with CAP who presented to hospitals in Edmonton, Alberta, between November 2000 and November 2002. These cases were subsequently reviewed retrospectively. Demographic, clinical and microbiological data were obtained, and patients were classified as having CAP or HCAP. Relatedness of isolates was determined by pulsed-field gel electrophoresis analysis in conjunction with epidemiological information.

RESULTS

There were 28 cases of bacteremic S aureus pneumonia identified. Fifty-seven per cent were reclassified as having HCAP, and 43% remained classified as having CAP. The CAP cohort was significantly younger than the HCAP cohort (mean age 49.0+/-23.7 years versus 67.8+/-18.6 years; P=0.035) with higher rates of intravenous drug use (50% versus 0%; P=0.002). Long-term care facility residence (44%) was common in the HCAP cohort. The HCAP cohort presented with more severe illness, having a higher mean pneumonia severity index score (143.1+/-41.1 versus 98.2+/-54.6; P=0.028), and despite fewer embolic complications, there was a trend toward a significantly higher mortality rate (31% versus 0%; P=0.052). Two community-acquired isolates cultured in the setting of intravenous drug use were methicillin-resistant, and no isolates were positive for Panton-Valentine leukocidin. There was evidence of relatedness involving 44% of the HCAP isolates by pulsed-field gel electrophoresis analysis.

CONCLUSION

HCAP accounts for a significant number of cases that, when using traditional definitions, would be classified as CAP. Severity of illness and mortality was excessive within the HCAP group. There was evidence of relatedness and spread of common strains in the HCAP cohort. The present study supports recommendations for treatment guidelines directed toward the entity of HCAP and the empirical coverage of S aureus among certain high-risk groups.

[Staphylococcus aureus: role and impact in the treatment of nosocomial pneumonia]

INTRODUCTION

Staphylococcus aureus (SA) has acquired a leading role in nosocomial pneumonia in terms of both frequency and severity, and poses therapeutic problems, namely antibiotic resistance and difficulties in the management of anti-staphylococcal drugs.

STATE OF THE ART

Epidemiological data confirm that SA is implicated in almost a quarter nosocomial pneumonias, of which about a half are due to methicillin resistant SA (MRSA) in France. The pathophysiology of these infections most often involves inhalation following oropharyngeal carriage. In addition to the risk factors common to all nosocomial pneumonias there are the particular roles of head injury and coma, leading to an increased frequency of SA infection in neuro-surgical patients.

PERSPECTIVES

The non-specific clinical picture, the grave prognosis of these pneumonias and the ineffectiveness against MRSA of the antibiotics used in the treatment of Gram negative infections make empirical treatment difficult.

CONCLUSION

In addition to the antibiotics classically active against SA (notably methicillin for sensitive strains and glycopeptides for MRSA) new agents may allow improvement in the treatment of these patients, even if their place is not yet definitively established.

Is Methicillin Resistance Associated with a Worse Prognosis in Staphylococcus aureus Ventilator-Associated Pneumonia?

BACKGROUND

Excess mortality associated with methicillin resistance in patients with Staphylococcus aureus ventilator-associated pneumonia (SA-VAP), taking into account such confounders as treatment adequacy and time in the intensive care unit (ICU), have not been adequately estimated.

METHODS

One hundred thirty-four episodes of SA-VAP entered in the Outcomerea database were studied. Patients from whom methicillin-resistant S. aureus (MRSA) was recovered were compared with those from whom methicillin-susceptible S. aureus (MSSA) was recovered, stratified for duration of stay in the ICU at the time of VAP diagnosis and adjusted for confounders (severity at admission, characteristics at VAP diagnosis, and treatment adequacy).

RESULTS

Treatment was adequate within 24 h after VAP diagnosis for 86% of the 65 MSSA-infected patients and 77% of the 69 MRSA-infected patients (P = .2). Polymicrobial VAP was more commonly associated with MSSA than with MRSA (49.2% vs. 25.7%; P = .01). MRSA infection was associated with a lower prevalence of coma at hospital admission and a higher rate of use of central venous lines and fluoroquinolones during the first 48 h of the ICU stay. The rates of shock, recurrence, and superinfection were similar in both groups. The crude hospital mortality rate was higher for MRSA-infected patients than for MSSA-infected patients (59.4% vs. 40%; P = .024). This difference disappeared after controlling for time in the ICU before VAP and parameters imbalanced at ICU admission (odds ratio [OR], 1.23; 95% confidence interval [CI], 0.49-3.12; P = .7) and remained unchanged after further adjustments for initial treatment adequacy and polymicrobial VAP (OR, 0.98; 95% CI, 0.36-2.66).

CONCLUSIONS

Differences in patient characteristics, initial ICU treatment, and time in the ICU confounded estimates of excess death due to MRSA VAP. After careful adjustment, methicillin resistance did not affect ICU or hospital mortality rates.

Methicillin-resistant Staphylococcus aureus and beyond: what's new in the world of the golden staph?

Methicillin-resistant Staphylococcus aureus (MRSA) continues to plague our hospitals. With the appearance of isolates that are resistant to vancomycin, now, more than ever, we must direct our efforts to controlling its development and spread. New antimicrobials have become available for treatment, but may only be a short-term answer. Our efforts towards control must be directed towards infection control measures such as improved hand hygiene with user-friendly products, such as alcohol-based hand disinfectants. Intranasal mupirocin may have a place in prevention of surgical site infection, although this role has not yet been clearly defined. Other areas where MRSA control may be effected include prudent controlled use of antibiotics, including surgical prophylaxis.

Impact of Methicillin Resistance on Outcome ofStaphylococcus aureusVentilator-associated Pneumonia

The impact of methicillin resistance on morbidity and mortality of patients suffering from severe Staphylococcus aureus infections remains highly controversial. We analyzed a retrospective cohort of 97 patients with methicillin-susceptible and 74 patients with methicillin-resistant Staphylococcus aureus ventilator-associated pneumonia (VAP). Initial empiric antibiotic therapy was appropriate for every patient. Patients with methicillin-resistant Staphylococcus aureus VAP were older, had higher disease-severity scores, and had been on mechanical ventilation longer at onset of VAP. Factors associated with 28-day mortality retained by multivariate logistic regression analysis were: age (odds ratio [OR] = 1.05, 95% confidence interval [CI], 1.02-1.08, p = 0.001) and Day 1 organ dysfunctions or infection (ODIN) score (OR = 1.90, 95% CI, 1.31-2.78, p = 0.001), but not methicillin resistance (OR = 1.72, 95% CI, 0.73-4.05, p = 0.22). The percentages of infection relapse or superinfection did not differ significantly between the two patient groups. In conclusion, after controlling for clinical and physiologic heterogeneity between groups, methicillin resistance did not significantly affect 28-day mortality of patients with Staphylococcus aureus VAP receiving appropriate antibiotics.

Bacteremic pneumonia due to Staphylococcus aureus: A comparison of disease caused by methicillin-resistant and methicillin-susceptible organisms

We performed a prospective study of all patients with bacteremic pneumonia due to Staphylococcus aureus over a period of 6 years during an outbreak of methicillin-resistant S. aureus (MRSA). Patients with bacteremic pneumonia due to MRSA (32 cases) or methicillin-susceptible S. aureus (MSSA; 54 cases) were compared. The patients with MRSA pneumonia were older and were more likely than those with MSSA pneumonia to have predisposing factors for acquisition of the infection. There were no differences in clinical findings, radiological pattern, or complications in clinical evolution among patients with MRSA and MSSA pneumonia. Mortality was significantly higher among MSSA-infected patients treated with vancomycin than among those treated with cloxacillin (47% vs. none; P<.01). Multivariate analysis (stepwise logistic regression method) showed a relationship between mortality and the following variables: septic shock (odds ratio [OR], 61), vancomycin treatment (OR, 14), and respiratory distress (OR, 8).

Risk factors for colonization or infection due to methicillin-resistant Staphylococcus aureus in HIV-positive patients: a retrospective case-control study

OBJECTIVE

To determine the risk factors for colonization or infection with methicillin-resistant Staphylococcus aureus in human immunodeficiency virus (HIV)-infected patients.

DESIGN

Retrospective matched-pair case-control study.

SETTING

Continuity clinic and inpatient HIV service of a university medical center.

POPULATION

Patients with HIV infection from the general population of eastern and coastal Texas and from the Texas Department of Criminal Justice.

DATA COLLECTION

Patient charts and the AIDS Care and Clinical Research Program Database were reviewed for the following: age, race, number of admissions, total hospital days, presence of a central venous catheter, serum albumin, total white blood cell count and absolute neutrophil count, invasive or surgical procedures, any cultures positive for S. aureus, and a history of opportunistic illnesses, diabetes, or dermatologic diagnoses. Data also were collected on the administration of antibiotics, antiretroviral therapy, steroids, cancer chemotherapy, and subcutaneous medications.

RESULTS

In the univariate analysis, the presence of a central venous catheter, an underlying dermatologic disease, lower serum albumin, prior steroid therapy, and prior antibiotic therapy, particularly antistaphylococcal therapy or multiple courses of antibiotics, were associated with increased risk for colonization or infection with methicillin-resistant S. aureus. Multivariate analysis yielded a model that included presence of a central venous catheter, underlying dermatologic disease, broad-spectrum antibiotic exposure, and number of hospital days as independent risk factors for colonization or infection with methicillin-resistant S. aureus.

CONCLUSIONS

In our HIV-infected patient population, prior hospitalization, exposure to broad-spectrum antibiotics, presence of a central venous catheter, and dermatologic disease were risk factors for acquisition of methicillin-resistant S. aureus.

Clinical and epidemiological findings in mechanically-ventilated patients with methicillin-resistant Staphylococcus aureus pneumonia

Over the 5-year period from 1990 to 1994, a prospective cohort study was conducted to define the clinical and epidemiological characteristics of ventilator-associated methicillin-resistant Staphylococcus aureus (MRSA) pneumonia acquired during a large-scale outbreak of MRSA infection. Of 2411 mechanically ventilated patients, 347 (14.4%) acquired MRSA, 220 (63.4%) had MRSA positive respiratory tract samples and 41 (18.6%) developed ventilator-associated MRSA pneumonia. The overall attack rate for ventilator-associated MRSA pneumonia was 1.56 episodes/1000 ventilator days, but annual attack rates varied according to the trend of the outbreak (range 4.9-0.2). In comparison with methicillin-sensitive Staphylococcus aureus (MSSA), which was implicated in 98 episodes of ventilator-associated pneumonia, MRSA caused exclusively late-onset ventilator-associated pneumonia, while MSSA caused both early-onset [55 of 98 (56.1%) episodes] and late-onset [43 of 98 (43.8%) episodes] ventilator-associated pneumonia. Logistic regression analysis of all patients with Staphylococcus aureus pneumonia revealed intubation for more than 3 days (odds ratio (OR),1.11; confidence interval (CI):1.03-1.18) and prior bronchoscopy (OR,5.8; CI,1.85-18.19) to be independent variables associated with MRSA pneumonia. The results indicate that MRSA ventilator-associated pneumonia is a frequent complication in intensive care patients, manifesting itself as late-onset pneumonia in patients who have been intubated for prolonged periods and/or have often undergoing previous bronchoscopy.

Methicillin-resistant Staphylococcus aureus (MRSA) isolated in clinics and hospitals in the Fukuoka city area

Bacteriological and clinical studies were carried out on 280 strains of Staphylococcus aureus isolated in clinics and hospitals in the Fukuoka city area from September 1990 to March 1991. The percentage of methicillin-resistant S. aureus (MRSA) strains studied was 41.4% (116 of 280). Of 116 MRSA strains, 48 (41.3%) produced coagulase VII and 21 (18.1%) produced coagulase II. The mean age of the patients who harboured MRSA, 70.5 +/- 16.9 years, was significantly higher than that of patients with methicillin-sensitive S. aureus (MSSA), 44.2 +/- 29.3 years (P < 0.001). MRSA was detected more frequently than MSSA in sputum (P < 0.01), while MSSA was detected more frequently than MRSA in pus (P < 0.01). Ninety (89.1%) of 101 strains of MRSA were isolated from inpatients and 98 (71.0%) of 130 strains of MSSA were isolated from outpatients. Similar number of MRSA strains were recovered in a variety of hospitals, indicating that there was no relationship between hospital size (number of beds) and the incidence of MRSA. As for drug susceptibility, coagulase VII-producing MRSA strains were more sensitive to clidamycin (P < 0.01) and more resistant to minocycline (P < 0.01) than were other MRSA strains.

Cell surface hydrophobicity and adherence to extra-cellular matrix proteins in two collections of methicillin-resistant Staphylococcus aureus

Non-specific and specific mechanisms of adherence have been examined in two collections of methicillin-resistant Staphylococcus aureus (MRSA). Determination of hydrophobicity by salt aggregation, hydrophobicity indices and of adherence to the extra-cellular matrix proteins fibronectin, vitronectin, laminin and collagen type 1 have failed to reveal any correlation with phage-type, plasmid profile or antibiogram. Further, the strain collections, made over a period of years in two countries, differ markedly in their adherence characteristics; MRSA are heterogeneous in this respect. Such heterogeneity may explain the polarization of views on the epidemicity or 'virulence' of MRSA. With the exception of adherence to collagen a small group of methicillin sensitive S. aureus had characteristics intermediate between the two groups of MRSA.

Effectiveness of simple measures to control an outbreak of nosocomial methicillin-resistant Staphylococcus aureus infections in an intensive care unit

Between June 1985 and March 1986, 14 cases of severe nosocomial methicillin-resistant Staphylococcus aureus (MRSA) infection, including septicemia, were observed in the intensive care unit (ICU) of a 400-bed cancer reference center. Simple control measures including contact isolation of colonized patients and reinforcement of handwashing practices among personnel were followed by a sharp decrease in the rate of infection and colonization. An epidemiological investigation showed that a single serophage variant MRSA strain was involved; peak incidence of infection was 17 per 100 ICU patient discharges; the index case was identified as a patient admitted from another hospital and the epidemic strain was then transmitted from patient-to-patient in the ICU; risk factors for acquiring infection were length of prior hospitalization, invasive procedures and number of antibiotic treatments; dissemination of the strain to other wards was only anecdotal. These results stress the effectiveness of simple measures to control outbreaks of MRSA nosocomial infections even in immunocompromised cancer patients.

Use of plasmid analysis and determination of aminoglycoside-modifying enzymes to characterize isolates from an outbreak of methicillin-resistant Staphylococcus aureus

We compared disk susceptibility, plasmid analysis, aminoglycoside resistance patterns, and DNA hybridization for their usefulness in characterizing isolates from a hospital outbreak of methicillin-resistant Staphylococcus aureus. Fifteen isolates were susceptible (group 1) and 28 were resistant (group 2) to gentamicin. A total of 15 of 15 (100%) group 1 and 22 of 28 (79%) group 2 isolates carried a 21.5-megadalton plasmid. All group 2 isolates and none of the group 1 isolates possessed a 33-megadalton plasmid. Aminoglycoside resistance pattern determinations revealed the presence of the ANT(4')-I enzyme (aminoglycoside 4' adenyltransferase) in all group 1 isolates but was unable to demonstrate presence of this enzyme in group 2 organisms. The APH(2") + AAC(6')-II enzyme (aminoglycoside 2" phosphotransferase plus 6' acetyltransferase) was found in all of the group 2 isolates but in none of the group 1 isolates. Use of DNA hybridization revealed the presence of the ANT(4')-I enzyme in both groups (group 1, 14 of 15; group 2, 26 of 28). In this hospital outbreak, we found good correlation between disk susceptibility, plasmid profile, aminoglycoside resistance patterns, and DNA hybridization results. It was difficult to predict the presence of the ANT(4')-I enzyme in the presence of the bifunctional [APH(2") + AAC(6')-II] enzyme by the aminoglycoside resistance pattern method because of overlap of the substrate profile.

Pulmonary infection due to methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) are now causing severe clinical infection on a worldwide basis. Pulmonary infection due to MRSA although widely reported is poorly documented. We report the predisposing factors, underlying diseases, treatment and outcome in 4 patients with pneumonia, 3 patients with empyema thoracis, 1 patient with pneumonia and empyema thoracis, 1 patient with pneumonia plus lobectomy wound infection and 2 patients with lung abscess. Vancomycin was highly effective in treatment, a finding compatible with experience treating other severe MRSA infections.

Methicillin-resistant Staphylococcus aureus in Veterans Administration Medical Centers

To determine the frequency of isolation of methicillin-resistant Staphylococcus aureus (MRSA) at Veterans Administration Medical Centers, 163 hospitals were surveyed; 137 responded. Between 1975 and 1984, the number of Veterans Administration Medical Centers with known MRSA increased from 3 to 111. This increase was geographically widespread and occurred in hospitals of all sizes. In Veterans Administration Medical Centers, isolation policies for MRSA-infected patients were (% of hospitals using): strict (19%), contact (52%), site-related (28%), no isolation (1%). For patients colonized with MRSA policies were: strict (15%), contact (44%), site-related (35%), and no isolation (6%). Only 41% of Veterans Administration Medical Centers reported discharging known MRSA-colonized patients to nursing homes. Most attempts to eradicate MRSA carriage used trimethoprim-sulfamethoxazole plus rifampin with or without bacitracin ointment; success rates were low. MRSA incidence is increasing at Veterans Administration Medical Centers across the United States. Improved regimens to eliminate MRSA carriage are needed.

Prospective microbiologic surveillance in control of nosocomial methicillin-resistant Staphylococcus aureus

A prospective microbiological surveillance (PMS) program was developed in a comprehensive hospital-wide effort for control of nosocomial methicillin-resistant Staphylococcus aureus (MRSA). This PMS program entailed: active identification of colonized and infected patients; application of a screening microbiologic system for MRSA; isolation of colonized and infected patients; antibiotic decolonization of MRSA; and educational efforts. The PMS program was studied over three and one half years for its contribution to infection control of MRSA, early identification of nosocomial MRSA outbreaks, use of the highest yield surveillance culture sites, and cost effectiveness. Following initiation of the PMS program in December 1982, during an MRSA outbreak, the frequency of new MRSA cases declined from 14 to none by the end of a 3-month pilot study. The frequency of new MRSA cases stabilized at approximately 2 per month until October 1983, when the PMS system allowed prompt detection of a new outbreak of 11 cases. Following isolation and antibiotic decolonization, the frequency of cases again declined to 3 per month. A third outbreak in December 1985 again was promptly detected and controlled. Infection to colonization ratio decreased from a maximum of 1.5 during outbreaks to a minimum of 0.17 after outbreaks. Wounds and tracheostomy sites provided the greatest yield of detection of new cases of MRSA. During one 15-month period, 35 of the 43 new cases were detected initially at wounds and tracheostomy sites. No new MRSA cases were detected by a positive axillary or nares site alone. The estimated quarterly cost of outbreaks and infection paralleled the quarterly frequency of new MRSA cases.(ABSTRACT TRUNCATED AT 250 WORDS)

Outbreak due to methicillin- and rifampin-resistant Staphylococcus aureus: epidemiology and eradication of the resistant strain from the hospital

A methicillin- and rifampin-resistant strain of Staphylococcus aureus was introduced into a university hospital by interstate transfer of an infected surgical patient. An outbreak occurred, and 17 patients became infected or colonized with the epidemic strain. Reservoirs appeared to be patients who were infected or colonized with the resistant S aureus and possibly two nurses who were nasal carriers. The outbreak isolate was likely spread by contact with contaminated hands of personnel. A retrospective case-control study identified tracheostomy, débridement, and irrigation of wounds by power spray and prolonged nasogastric intubation as risk factors for acquisition of the epidemic strain. Analysis of factors by groups indicated that surgical procedures, wound care procedures and instrumentation of the respiratory tract were significantly associated with cases. The nasal carrier state was eradicated in two nurses by topical application of 5% vancomycin. The epidemic strain was eradicated from the hospital 8 months after it was introduced.

Comparison of in vitro activity of quinolone antibiotics and vancomycin against gentamicin- and methicillin-resistant Staphylococcus aureus by time-kill kinetic studies

Quinolone antibiotics have been proposed as possible alternatives to vancomycin for methicillin-resistant Staphylococcus aureus infections. We investigated the activities of amifloxacin, ciprofloxacin, norfloxacin, and vancomycin by time-kill kinetic studies. Antibiotic concentrations of 0, 1.0, and 4.0 times the MIC were used against four strains of gentamicin- and methicillin-resistant S. aureus. Staphylococci were plated onto ciprofloxacin-containing agar at all time points, in repeat time-kill kinetic studies. Macrobroth dilution MICs and MBCs were determined. Ciprofloxacin levels were measured by bioassay. Replica plating was performed from the original susceptible inoculum (MIC, 0.125 micrograms/ml) onto ciprofloxacin-supplemented agar. At 4.0 times the MIC, only with ciprofloxacin was there regrowth at 24 and 48 h. All four strains of staphylococci grew on agar supplemented with 1 microgram of ciprofloxacin per ml; three of four grew on agar supplemented with 2 micrograms of ciprofloxacin per ml. MICs and MBCs for these resistant clones ranged from 8 to 32 micrograms/ml. No degradation in activity or amount of ciprofloxacin could be detected in the bioassay. Replica-plated staphylococci grew on agar containing 1 microgram/ml but not higher concentrations of ciprofloxacin at 48 h. Amifloxacin and norfloxacin sustained bactericidal activity comparable to that of vancomycin. We conclude that heteroresistant subpopulations of gentamicin- and methicillin-resistant S. aureus can emerge under antibiotic selection pressure. Such resistant clones may then mutate in the presence of subinhibitory concentrations of antibiotic to higher levels of ciprofloxacin resistance.