Mupirocin for controlling methicillin-resistant Staphylococcus aureus: lessons from a decade of use at a university hospital.

BACKGROUND: From 1990 to 1995 at Hospital Universitário Clementino Fraga Filho, patients colonized or infected with methicillin-resistant Staphylococcus aureus (MRSA) were treated with mupirocin to eliminate MRSA carriage. In 1995, 65% of MRSA patients at this hospital had mupirocin-resistant isolates. Starting in 1996, mupirocin use was restricted to patients colonized, but not infected, with MRSA. OBJECTIVES: To describe the use of mupirocin for controlling MRSA over a decade and to analyze the molecular epidemiology of mupirocin-resistant MRSA infections at this hospital. SETTING: A 490-bed, tertiary-care university hospital. METHODS: The incidence densities of patients with MRSA and acquisition of mupirocin by the hospital were calculated for the period 1992-2001. S. aureus isolates from 1999-2000 were analyzed by pulsed-field gel electrophoresis. Mupirocin-resistant MRSA isolates from 1994-1995 and 1999-2000 were analyzed for ileS-2 gene background polymorphisms. RESULTS: The incidence density of MRSA patients increased slightly over time, whereas the purchase of mupirocin decreased dramatically. Mupirocin-resistant MRSA infections decreased from 65% in 1994-1995 to 15% in 1999-2000. The MRSA Brazilian clone, detected in 1992, was still highly prevalent. The same ileS-2 encoding plasmid found in 1994-1995 persisted in three identical MRSA isolates from 1999-2000 belonging to the Brazilian clone. CONCLUSIONS: After mupirocin use decreased, the ileS-2 encoding plasmid persisted in only a few Brazilian clone isolates. Our data on mupirocin-resistant MRSA incidence and mupirocin use strongly suggested that restricted use was related to decreased rates of mupirocin resistance at our hospital.     

National hospital infection surveillance on methicillin-resistant Staphylococcus aureus

Surveillance of methicillin-resistant Staphylococcus aureus (MRSA) infections in Japan was performed in 1995 and 1996. Hospital infection rates of MRSA appear to have remained stable in recent years, and this study was undertaken to test this hypothesis. In national surveillance, the incidence of MRSA hospital infections per 100 admissions remained stable at between 0.7 and 0.8 from 1999 to 2003, with a tendency towards a slight decline. This study shows that precautions against MRSA infection in Japan may prove to be an effective preventive measure.     

A maternity hospital outbreak of methicillin-resistant Staphylococcus aureus.

A maternity hospital outbreak of methicillin-resistant Staphylococcus aureus with a strain other than EMRSA-1 is described. In contrast to previously documented outbreaks, which have usually centered on special care baby units, this outbreak mainly involved the routine ante-natal and postnatal wards. Thirty-seven mothers, 18 babies and nine staff were affected over a 6-week period. The high turnover of very mobile maternity patients and the open-plan design of the hospital influenced the course of the outbreak and adversely affected implementation of infection control measures. Significant environmental contamination and a very high rate of maternal perineal MRSA colonization were notable epidemiological features.     

Epidemiology of methicillin-resistant Staphylococcus aureus at a children's hospital.

OBJECTIVE: To describe the relative contribution of and risk factors for both community-acquired and nosocomial methicillin-resistant Staphylococcus aureus (MRSA) infections. DESIGN: Retrospective cohort study. SETTING: 270-bed, tertiary-care children's hospital. PARTICIPANTS: All MRSA-infected children from whom MRSA was recovered between October 1, 1999, and September 30, 2001. METHODS: Demographic, clinical, and risk factor data were abstracted from medical records. Categorical variables were analyzed using the chi-square or Fisher's exact test and continuous variables were analyzed using the Mann-Whitney test. RESULTS: Of the 62 patients with new MRSA infection, 37 had community-acquired MRSA and 25 had nosocomial MRSA. Most community-acquired MRSA infections were of the skin and soft tissue, the middle ear, and the lower respiratory tract. Nosocomial MRSA infections occurred in the lower respiratory tract, the skin and soft tissue, and the blood. Risk factors for infection, including underlying medical illness, prior hospitalization, and prior surgery, were similar for patients with community-acquired MRSA and nosocomial MRSA. History of central venous catheterization and previous endotracheal intubation was more common in patients with nosocomial MRSA. Only 3 patients with community-acquired MRSA had no identifiable risk factor other than recent antibiotic use. Resistance for clindamycin, erythromycin, and levofloxacin was similar between strains of community-acquired MRSA and nosocomial MRSA. CONCLUSIONS: Similarities in patient risk factors and resistance patterns of isolates of both community-acquired and nosocomial MRSA suggest healthcare acquisition of most MRSA. Thus, classifying MRSA as either community acquired or nosocomial underestimates the amount of healthcare-associated MRSA.     

Outbreak of methicillin-resistant Staphylococcus aureus in a German tertiary-care hospital.

A biphasic outbreak of methicillin-resistant Staphylococcus aureus in intensive-care units of a German tertiary-care hospital afflicted 89 patients within 4 years. The spread of the outbreak most likely was facilitated by the contamination of mobile radiograph equipment. The outbreak was controlled by measures of hospital hygiene.     

Phages for methicillin-resistant Staphylococcus aureus: an international trial.

An internationally agreed and validated set of phages is used worldwide for the typing of strains of Staphylococcus aureus of human origin. However, because of the sometimes reduced susceptibility of methicillin-resistant strains (MRSA) to these phages, some of the national typing centres use locally isolated and characterized sets of experimental phages. In this trial, 42 such phages were distributed to 6 centres and tested against 744 isolates of MRSA with the intention of defining a phage set to augment the international set. The use of these experimental phages increased the percentage typability from 75% with the international set to 93% and the number of identifiable lytic patterns from 192 to 424. A subset of 10 experimental phages was selected. When this subset was compared with the experimental panel, the typability rate was 91% and 370 distinct patterns were obtained. This subset of phages has been distributed for international trial.     

Nasal carriage of methicillin-resistant Staphylococcus aureus among hospital staff and outpatients.

This study sought to determine the rate of nasal methicillin-resistant Staphylococcus aureus (MRSA) carriage among hospital staff and outpatients. Nasal swabs were obtained from 500 outpatients and 500 hospital staff. Hospital staff were 2.3-fold more likely to carry MRSA than were outpatients (6% vs 2.6%, P = .013).     

Prevalence of and risk factors for methicillin-resistant Staphylococcus aureus carriage at hospital admission.

To determine the prevalence of and risk factors for methicillin-resistant Staphylococcus aureus (MRSA) carriage at the time of admission to our hospital, we screened the medical records of 1,128 patients for demographic and clinical data. The antimicrobial resistance pattern and genotype of MRSA isolates were studied. The prevalence of MRSA carriage at hospital admission was 1.4%. Older patients and patients previously admitted to healthcare centers were the most likely to have MRSA carriage at admission.     

Community-associated methicillin-resistant Staphylococcus aureus in hospital nursery and maternity units

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has rarely been reported in the hospital setting. We report an outbreak of 7 cases of skin and soft tissue infections due to a strain of CA-MRSA. All patients were admitted to the labor and delivery, nursery, or maternity units during a 3-week period. Genetic fingerprinting showed that the outbreak strain was closely related to the USA 400 strain that includes the midwestern strain MW2. All isolates contained the staphylococcal chromosome cassette mec type IV. Genes for Panton-Valentine leukocidin and staphylococcal enterotoxin K were detected in all isolates, and most contained other enterotoxin genes. Testing of nearly 2,000 MRSA isolates collected during citywide surveillance studies from 1999 to 2003 showed that approximate, equals 1% were genetically related to MW2. CA-MRSA strain MW2 has been present in this region at least since 1999. This study documents the spread of this strain among healthy newborns at 1 hospital.     

Epidemiology of methicillin-resistant Staphylococcus aureus at a university hospital in the Canary Islands.

OBJECTIVES: To describe the epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) at a university hospital in Tenerife, Canary Islands, during a 40-month period and to evaluate the effectiveness of the application of control measures. DESIGN: Laboratory-based surveillance, medical charts and microbiological records review, and characterization of strains by pulsed-field gel electrophoresis (PFGE) were used to describe the epidemiology. Infection control practices were introduced as an intervention. SETTING: A 650-bed, tertiary-care university hospital. SUBJECTS: Patients with clinical and nasal isolates of MRSA and colonized staff members. RESULTS: The rate of nosocomial MRSA infections was 32.5% for 1997, 17.9% for 1998, 14.5% for 1999, and 25.6% during the first 4 months of 2000. The major sites of isolation for nosocomial MRSA infection included surgical wounds (25%) and the lower respiratory tract (24%). Intensive care units and surgical specialties had more frequent MRSA cases. Characteristics associated with nosocomial MRSA isolates included prior use of intensive antibiotic therapy, prolonged hospital stays, major underlying illness, invasive procedures, and older age. PFGE type A (subtype A1) was the strain most frequently found and the only PFGE type involved in clusters. CONCLUSIONS: Surveillance cultures and contact droplet precautions were followed by decreased rates for 2 years. Nevertheless, the spread of PFGE subtype A1 to many different areas of the hospital and the increase in incidence during the first third of 2000 indicates either that surveillance cultures were not used widely enough or that compliance with isolation measures was suboptimal.     

The epidemiology of mupirocin resistance among methicillin-resistant Staphylococcus aureus at a Veterans' Affairs hospital.

OBJECTIVE: To describe the clinical and molecular epidemiology of mupirocin-resistant (MR) and mupirocin-susceptible (MS) methicillin-resistant Staphylococcus aureus (MRSA) at a Veterans' Affairs hospital and to assess risk factors associated with the acquisition of MR MRSA. DESIGN: All clinical MRSA isolates for the period October 1990 through March 1995 underwent susceptibility testing to mupirocin. Mupirocin resistance trends were measured, and MS MRSA and MR MRSA isolates underwent typing by pulsed-field gel electrophoresis (PFGE). A retrospective case-control study was conducted to evaluate risk factors for having MR versus MS MRSA. SETTING: The James H. Quillen Veterans' Affairs Medical Center in Mountain Home, Tennessee, included a 324-bed acute-care hospital, a 120-bed nursing home, and a 525-bed domiciliary. Colonizations and infections with MRSA were endemic, and mupirocin ointment was commonly used. PATIENTS: Inpatients and outpatients at the facility. RESULTS: MS MRSA was recovered from 506 patients and MR MRSA from 126. Among MR MRSA isolates, 58% showed low-level mupirocin resistance (minimum inhibitory concentration [MIC] > or = 4 to 256 microg/mL), and 42% showed high-level mupirocin resistance (MIC > or = 512 microg/mL). A significant increase (P=.002) in the number of high-level MR isolates occurred during the 1993 to 1995 period. A case-control study showed that presence of a decubitus ulcer correlated with high-level resistant isolates (P<.05). The distribution of PFGE patterns did not differ for MR and MS MRSA CONCLUSIONS: Use of mupirocin ointment in a program aimed at managing endemic MRSA infection or colonization resulted in a significant increase in the recovery of high-level MR MRSA isolates. These isolates appeared to emerge from our existing MRSA pool. A case-control study provided few clues concerning patients likely to harbor MR MRSA. We confirmed the position that the extended use of mupirocin ointment should be avoided in settings where MRSA is endemic.     

Nasal carriage of methicillin-resistant Staphylococcus aureus by hospital staff in north Jordan.

The nasal carriage of methicillin-resistant Staphylococcus aureus was detected in 550 hospital staff members of four hospitals in north Jordan. Of the 109 (19.8%) individuals tested who were nasal carriers of S. aureus, only 32 (5.8%) were found to be carriers of methicillin-resistant Staphylococcus aureus. The carriers were four doctors, 23 nurses, three laboratory technicians, one maid and an administrator. It was noted that 25 (78.1%) of these carriers were in constant contact with patients in operating theatres, surgical wards or intensive care units. It was not clear whether the carriers were short- or long-term carriers, or whether they were persistent sources of methicillin-resistant Staphylococcus aureus. Decontamination of these carriers was considered among other control measures to avoid the dangerous outcome of hospital outbreaks caused by this potential pathogen.     

Community-acquired methicillin-resistant Staphylococcus aureus: an emerging pathogen.

The prevalence of MRSA in the nosocomial setting has been well studied, and its control remains a challenge for infection control professionals. Complicating this problem is the increasing number of reports on the spread of community-acquired MRSA (CA-MRSA). CA-MRSA strains differ from hospital-acquired MRSA (HA-MRSA) strains in that they are generally susceptible to most antibiotics. These strains share the presence of staphylococcal cassette chromosome mec (SCCmec) type IV in their genomes, are frequently virulent, and predominantly cause skin and soft tissue infections. The genome sequence of the prototypic CA-MRSA strain, MW2, revealed the presence of additional virulence factors not commonly present in other S. aureus strains. We determined the genetic relatedness of 30 geographically diverse CA-MRSA isolates clustered based on SCCmec type IV by sequence analysis of the polymorphic repeat region of the protein A gene (spa typing). These results indicated that most strains shared a common spa type (131), identical to MW2. Because this group tends to infect healthy individuals with no known risk factors for nosocomial acquisition of MRSA, we refer to it as CA-MRSA without risk factors. A second group, CA-MRSA with risk factors, consists of two related genotypes, spa types 1 and 7, which differ by one nucleotide change. These strains have caused severe infections in HIV-positive patients in Los Angeles and New York. Although CA-MRSA strains share genetic determinants, they are not clonal but rather are derived from different genetic backgrounds. The genetic characteristics and the epidemiology of CA-MRSA with and without risk factors are discussed.     

Ten years' experience with methicillin-resistant Staphylococcus aureus in a large Australian hospital.

The Royal Brisbane Hospital (RBH) is a 1200-bed teaching hospital with acute, general and specialist units for adult patients. Methicillin-resistant Staphylococcus aureus (MRSA) was first detected at the RBH in 1975 and the number of new patients colonized and infected increased from one in 1975 to 720 in 1989, with a peak of 811 in 1987. Virulence may be inferred from blood culture isolates. Between 1979 and 1989 the number of patients with S. aureus bacteraemia increased from 40 to 138 per year. The percentage of these isolates which were MRSA varied from a low of 4% in 1980 to a peak of 37% in 1984 with 28% in 1989. The control attempts, sensitivity patterns, sources of the isolates and their probable impact and importance will be discussed.     

Modeling transmission of methicillin-resistant Staphylococcus aureus among patients admitted to a hospital.

OBJECTIVE: To determine the impact of the screening test, nursing workload, handwashing rates, and dependence of handwashing on risk level of patient visit on methicillin-resistant Staphylococcus aureus (MRSA) transmission among hospitalized patients. SETTING: General medical ward. METHODS: Monte Carlo simulation was used to model MRSA transmission (median rate per 1,000 patient-days). Visits by healthcare workers (HCWs) to patients were simulated, and MRSA was assumed to be transmitted among patients via HCWs. RESULTS: The transmission rate was reduced from 0.89 to 0.56 by the combination of increasing the sensitivity of the screening test from 80% to 99% and being able to report results in 1 day instead of 4 days. Reducing the patient-to-nurse ratio from 4.3 in the day and 6.8 at night to 3.8 and 5.7, respectively, reduced the number of nosocomial infections from 0.89 to 0.85; reducing the ratio to 1 and 1, respectively, further reduced the number of nosocomial infections to 0.32. Increases in handwashing rates by 0%, 10%, and 20% for high-risk visits yielded reductions in nosocomial infections similar to those yielded by increases in handwashing rates for all visits (0.89, 0.36, and 0.24, respectively). Screening all patients for MRSA at admission reduced the transmission rate to 0.81 per 1,000 patient-days from 1.37 if no patients were screened. CONCLUSION: Within the ranges of parameters studied, the most effective strategies for reducing the rate of MRSA transmission were increasing the handwashing rates for visits involving contact with skin or bodily fluid and screening patients for MRSA at admission.     

The clinical significance of methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is responsible for the largest outbreak of hospital-acquired infection (HAI) that the world has ever seen. It is not replacing methicillin-susceptible S. aureus (MSSA), but seems largely to be an additional burden of HAI with double the mortality of MSSA infections, at least in the bacteraemic form. It is often highly transmissible and carriage seems to lead to clinical infection much more frequently than with MSSA carriage. Additional screening for MRSA needs to be performed, not only to establish the size of the problem and to allow initiation of decolonization measures to prevent the onset of clinical disease, but also to allow implementation of infection control precautions that will be necessary to control the epidemic. MRSA is a huge clinical burden that is causing great public and political concern. Current treatments are suboptimal. Control measures are likely to be effective and cost saving if they have a broad enough base, and should be implemented without further delay.     

The international spread of methicillin-resistant Staphylococcus aureus

A genetic analysis of representative methicillin-resistant Staphylococcus aureus (MRSA) being isolated in London and Dublin hospitals has demonstrated that the epidemic strains from two London hospitals are different from the Dublin strains, but indistinguishable from the epidemic strains of eastern Australia. The possibility that some strains of MRSA are more likely than others to spread within hospitals is discussed.