Methicillin-resistant Staphylococcus aureus in a London hospital

Methicillin-Resistant Staphylococcus aureus: Molecular Characterization, Evolution, and Epidemiology

Staphylococcus aureus, a major human pathogen, has a collection of virulence factors and the ability to acquire resistance to most antibiotics. This ability is further augmented by constant emergence of new clones, making S. aureus a "superbug." Clinical use of methicillin has led to the appearance of methicillin-resistant S. aureus (MRSA). The past few decades have witnessed the existence of new MRSA clones. Unlike traditional MRSA residing in hospitals, the new clones can invade community settings and infect people without predisposing risk factors. This evolution continues with the buildup of the MRSA reservoir in companion and food animals. This review focuses on imparting a better understanding of MRSA evolution and its molecular characterization and epidemiology. We first describe the origin of MRSA, with emphasis on the diverse nature of staphylococcal cassette chromosome mec (SCCmec). mecA and its new homologues (mecB, mecC, and mecD), SCCmec types (13 SCCmec types have been discovered to date), and their classification criteria are discussed. The review then describes various typing methods applied to study the molecular epidemiology and evolutionary nature of MRSA. Starting with the historical methods and continuing to the advanced whole-genome approaches, typing of collections of MRSA has shed light on the origin, spread, and evolutionary pathways of MRSA clones.

Methicillin-Resistant Staphylococcus aureus Outbreak at a Veterans' Affairs Medical Center: Importance of Carriage of the Organism by Hospital Personnel

The reported prevalence of nasal carriage of methicillin-resistant Staphylococcus aureus (MRSA) by hospital personnel averages 2.5%. From August 1985 to September 1987, 155 patients at our Veterans' Affairs Medical Center (VAMC) were colonized or infected with MRSA. In December 1986, only two (2.1%) of 94 healthcare workers were identified as nasal carriers. Prompted by a sharp increase in the number of patients with MRSA in early 1987, contact tracing identified 450 employees, of whom 36 (8%) were nasal carriers. Thirty-five percent of surgical residents (7 of 20) were nasal carriers. Prior to being identified as a nasal carrier, one surgical resident was associated with the inter-hospital spread of the VAMC MRSA strain to the burn unit of the affiliated university hospital. Three family members of two employee carriers were also found to harbor the epidemic strain. All 36 carriers were decolonized with various antimicrobial combinations. Vigorous infection control measures were effective in controlling the epidemic. The frequency of MRSA carriage by hospital personnel at our medical center during the epidemic proved higher than previously appreciated. Thus, healthcare workers may comprise a sizable MRSA reservoir. During an MRSA epidemic, infection control should attempt to identify and decolonize this hospital reservoir, as these individuals can disseminate MRSA both within the hospital as well as into the community.

A randomized controlled trial to compare the use of homeopathy and internal Teat Sealers for the prevention of mastitis in organically farmed dairy cows during the dry period and 100 days post-calving

INTRODUCTION

Routine use of antibiotics to prevent mastitis in dairy cows is prohibited by organic farming regulations. Internal Teat Sealers have been proposed as an alternative. We compared two drying-off (DO) supporting measures (Internal Teat Sealer and Homeopathy) to an untreated control group to assess their protective effects against clinical mastitis and intra-mammary infections during dry period of dairy cows.

METHODS

A field trial with 102 dairy cows from 13 Swiss organic dairy farms was conducted. Cows were randomly assigned to one of three groups within a herd. In the Internal Teat Sealer group (ITS; 36 cows) cows were treated with the commercial ORBESEAL (Pfizer) in all four quarters immediately after the last milking. In the Homeopathy group (HDT; 32 cows) the cows were treated per-orally by a herd-specific homeopathic formulation consisting of two remedies in 1:10(6) dilution over 5 days before and after DO. The untreated group received no therapy (U; 34 cows).

RESULTS

For ITS, HDT and U the clinical mastitis incidence rates for the first 100 days post-calving were 11%, 9% and 3%, respectively, and the proportion of normally secreting quarters was (quarter somatic cell count (SCC) [QSCC]<100,000/ml) 70%, 68%, and 65%, respectively. Power analysis indicates that a proportion of 75% would support the rejection of null hypothesis in the HDT, and 74% in the ITS group against untreated control. Quarters of cows with SCC<200,000/ml at DO showed significantly higher normal secretion in HDT group (odds ratio [OR] 9.69) compared to untreated control, whereas Teat Sealing lead to an OR of 3.09 (not significant, post hoc power 31.3%).

CONCLUSIONS

Under the studied conditions herd-specific homeopathic dry cow therapy was effective in increasing the number of animals with normal milk secretion after subsequent parturition, compared to untreated control. It may be an effective alternative to Teat Sealing, particularly in animals with relatively low SCCs. Further research is required to confirm these results, and under different environmental conditions.

The role of healthcare personnel in the maintenance and spread of methicillin-resistant Staphylococcus aureus

Healthcare workers may acquire methicillin-resistant Staphylococcus aureus (MRSA) from patients, both hospital and home environments, other healthcare workers, family and public acquaintances, and pets. There is a consensus of case reports and series which now strongly support the role for MRSA-carrying healthcare personnel to serve as a reservoir and as a vehicle of spread within healthcare settings. Carriage may occur at a number of body sites and for short, intermediate, and long terms. A number of approaches have been taken to interrupt the linkage of staff-patient spread, but most emphasis has been placed on handwashing and the treatment of staff MRSA carriers. The importance of healthcare workers in transmission has been viewed with varying degrees of interest, and several logistical problems have arisen when healthcare worker screening is brought to the forefront. There is now considerable support for the screening and treatment of healthcare workers, but it is suggested that the intensity of any such approach must consider available resources, the nature of the outbreak, and the strength of epidemiological associations. The task of assessing healthcare personnel carriage in any context should be shaped with due regard to national and international guidelines, should be honed and practiced according to local needs and experience, and must be patient-oriented.

Health-care workers: source, vector, or victim of MRSA?

There is ongoing controversy about the role of health-care workers in transmission of meticillin-resistant Staphylococcus aureus (MRSA). We did a search of the literature from January, 1980, to March, 2006, to determine the likelihood of MRSA colonisation and infection in health-care workers and to assess their role in MRSA transmission. In 127 investigations, the average MRSA carriage rate among 33 318 screened health-care workers was 4.6%; 5.1% had clinical infections. Risk factors included chronic skin diseases, poor hygiene practices, and having worked in countries with endemic MRSA. Both transiently and persistently colonised health-care workers were responsible for several MRSA clusters. Transmission from personnel to patients was likely in 63 (93%) of 68 studies that undertook genotyping. MRSA eradication was achieved in 449 (88%) of 510 health-care workers. Subclinical infections and colonisation of extranasal sites were associated with persistent carriage. We discuss advantages and disadvantages of screening and eradication policies for MRSA control and give recommendations for the management of colonised health-care workers in different settings.

Inducibility and potential role of MecA-gene-positive oxacillin-susceptible Staphylococcus aureus from colonized healthcare workers as a source for nosocomial infections

To determine the carrier rate of methicillin-susceptible mecA-positive Staphylococcus aureus (dormant MRSA) among healthcare workers (HCWs), 447 nurses and physicians from 13 general wards and intensive care units were investigated for nasal or oropharyngeal S. aureus carriage during one year whenever an MRSA patient was treated. Induction of phenotypic resistance in all mecA-positive oxacillin-susceptible aureus was attempted by 24 h exposure to oxacillin and cefotaxime. Organisms from the broth tube with the highest antibiotic concentration and visible growth after incubation were re-exposed for a total of seven repetitive exposures. Two mecA-negative oxacillin-susceptible S. aureus served as negative control. A population analysis before and after antibiotic exposure was performed. A third of the HCWs were found to be S. aureus carriers. Only three nurses were MRSA positive (0.7%). Seven isolates of dormant MRSA were isolated in six nurses and one doctor (1.6%). After four days of repetitive antibiotic exposure six of seven dormant MRSA were highly resistant to oxacillin. Resistance of the two control S. aureus without the mecA gene was not changed by repetitive antibiotic exposure. Two of the seven dormant MRSA were clonally related as shown by pulsed-field gel electrophoresis (PFGE). The PFGE pattern of one dormant MRSA (HCW) was identical to an MRSA (HCW). The pattern of another dormant MRSA was indistinguishable from an MRSA isolated from a patient who was treated at the same time on the same ward suggesting transmission from the HCW to the patient. Dormant MRSA may be isolated twice as often as MRSA from HCWs. Transmission to patients is possible, which may lead to clinical infections. It might be useful to screen methicillin-susceptible S. aureus isolates from HCWs for the mecA gene when recurrent infections with MRSA occur on a ward and a source cannot be found.

Phenotypic and genotypic properties of methicillin resistant Staphylococcus aureus strains isolated in Hungary, 1997-2000

An account is given on the activity of the National Center for Phage Typing of Staphylococci in Hungary in the period between 1997 and 2000 related to methicillin resistant Staphylococcus aureus (MRSA) strains originating mainly from hospital infections and sporadic cases. The rate of multiresistant MRSA strains has decreased gradually from 98.1% in 1997 to 74.6% in 2000, accordingly the typability by phages showed a considerable improvement by the international basic phages. Resistance pattern of MRSA strains became narrower in the period of the examinations. With the exception of erythromycin the rate of resistance decreased probably as a consequence of the increased use of erythromycin. The typing method was completed with the phenotypic and genotypic characterization of macrolide resistance. Among 73 MRSA strains type A was the most frequent macrolide resistance group, while type B, C1 and C2 occurred rarely. Type A was frequent also among the few MSSA and CNS strains. Out of the 168 examined S. aureus strains ermA genes occurred in 81.5%; in MSSA and CNS strains ermC1 genes were frequent, both genes are responsible for the target modification. The msrA gene, encoding the increased efflux, occurred only in CNS strains. Comparing the results obtained by phenotyping (phage typing) and genotyping (AP-PCR) methods it is of note that MRSA strains which proved non-typable by phage typing gave suitable results by the AP-PCR.

A purpose built MRSA cohort unit

The control of hospital-acquired infection, in particular methicillin-resistant Staphylococcus aureus (MRSA) remains a challenge. Our hospital has established a purpose built 11-bed cohort unit with on-site rehabilitation for care of patients colonized with MRSA, in an attempt to improve their quality of care. Prior to the opening of this unit a number of concerns were voiced and the aim of this study was to address these. First, to establish if patient cohorting reduces the likelihood of successful decolonization, second, to evaluate the risk of staff colonization, and finally to see if successful environmental control of MRSA is possible.A patient database was established detailing patient demographics, infection rates, eradication and reacquisition rates. Staff screening was performed weekly, at the start of a period of duty. Sixty environmental sites were screened before unit opening, at 48h, six weeks and at six months. There were 88 admissions in the first six months; 62 patients were colonized with MRSA, and 26 patients (10 surgical, 16 medical) had MRSA infections. Twenty-three of 88 patients (26%) were successfully decolonized, which compares favourably with an eradication rate of 20% for the rest of the hospital. Twenty staff members participated in weekly screening. Five staff members colonized with MRSA were detected and all were successfully decolonized. Environmental control was achieved with a combination of a daily detergent clean and a once weekly clean with phenolic disinfectant. Our preliminary data suggest that, despite cohorting patients colonized with MRSA, with proper education and supervised cleaning protocols, it is possible to control environmental MRSA load, successfully decolonize patients and limit the risk of staff colonization.

Effect of delayed infection control measures on a hospital outbreak of methicillin-resistant Staphylococcus aureus

All patients positive for methicillin-resistant Staphylococcus aureus (MRSA) at the University Hospitals of Geneva, Switzerland, between 1989 and 1997 (N = 1771) were included in a cohort study to evaluate the consequences of delayed containment of a hospital-wide outbreak occurring during a 4-year absence of MRSA control measures. The effects of efforts to control both the MRSA reservoir and the number of bacteraemic patients were assessed. Intensive infection control measures were initiated in 1993 and included patient screening, on-site surveillance, contact isolation, a computerized alert system, and hospital-wide promotion of hand hygiene. An increase in the rate of new MRSA-infected or -colonized patients was observed between 1989 and 1994 (from 0.05 to 0.60 cases per 100 admissions), which subsequently decreased to 0.24 cases in 1997 (P<0.001). However, the proportion of laboratory-documented methicillin-resistant isolates among all S. aureus showed little variation in the years from 1993 onwards (range, 19-24%), reflecting the result of an increase in the number of screening cultures. The annual number of patients with MRSA bacteraemia strongly correlated with the hospital-wide prevalence of MRSA patients (R(2)= 0.60; P = 0.01) and the rate of new MRSA patients (R(2)= 0.97; P<0.001). Consequently, the attack rate of nosocomial MRSA bacteraemia served as an excellent marker for the MRSA patient reservoir. In conclusion, despite delayed implementation, infection control measures had a substantial impact on both the reservoir of MRSA patients and the attack rate of MRSA bacteraemia.

Combined use of ribotyping, PFGE typing and IS431 typing in the discrimination of nosocomial strains of methicillin-resistant Staphylococcus aureus

We have previously reported the phenotypic characterization of methicillin-resistant Staphylococcus aureus (MRSA) clinical strains isolated in Malaya University Hospital in the period 1987 to 1989 using antibiogram, coagulase typing, plasmid profiles, and phage typing. Here, we report the analysis of the same strains with three genotyping methods; ribotyping, pulsed-field gel electrophoresis (PFGE) typing, and IS431 typing (a restriction enzyme fragment length polymorphism analysis using an IS431 probe). Ribotyping could discriminate 46 clinical MRSA strains into 5 ribotypes, PFGE typing into 22 types, and IS431 typing into 15 types. Since the differences of the three genotyping patterns from strain to strain were quite independent from one another, the combined use of the three genotyping methods could discriminate 46 strains into 39 genotypes. Thus, the powerful discriminatory ability of the combination was demonstrated.

Strategies for the management of healthcare staff colonized with epidemic methicillin-resistant Staphylococcus aureus

An outbreak of epidemic methicillin-resistant Staphylococcus aureus (MRSA) caused by EMRSA-16 has affected hospitals in north east Northamptonshire since April 1991. Between the start of the outbreak and December 1995, 74 healthcare staff (0.9% of the staff screened) were colonized by the outbreak strain. Thirty-two percent of colonized staff were excluded from work, and six were excluded for periods of longer than three weeks. Twenty-four percent of staff had more than one course of treatment to eradicate carriage. The contribution of staff carriage in hospitals where EMRSA-16 is endemic and strategies for the management of colonized staff are discussed. We conclude that screening of staff has a limited role in the control of outbreaks caused by EMRSA-16 and that when resources for screening are scarce priority should be given to patients.

Characteristics of Staphylococcus aureus strains isolated from clinical and non-clinical human sources in Trinidad: susceptibility to bacteriophages and antimicrobial agents, and toxigenicity

The susceptibility of Staphylococcus aureus strains isolated from human clinical and non-clinical sources in Trinidad to bacteriophages and antimicrobial agents was determined. The ability of the strains to produce enterotoxins and toxic shock syndrome toxin-1 (TSST-1) was also investigated. Of the 554 strains tested, 454 (81.8%) were susceptible to international phage set (IPS) phages with strains isolated from bacteruria (57.1%) and bacteremia (53.3%) having a low sensitivity compared to isolates from aspirates (87.3%) and anterior nares (97.4%). All sources combined, strains were most susceptible to phages belonging to several groups (mixed). Overall, 419 (75.6%) strains were resistant to one or more of nine antimicrobial agents tested. Resistance to penicillin was most prevalent, with 413 (74.5%) strains found to be resistant. Prevalence of resistance to tetracycline, gentamicin, oxacillin, cefuroxime and ciprofloxacin was 5.1%, 2.0%, 0.7%, 0.4% and 0.4%, respectively. Of the 554 strains tested, 307 (55.4%) produced staphylococcal enterotoxins A (SEA), B (SEB), C (SEC) and D (SED) singly or in combination. Strains recovered from high vaginal swabs were least enterotoxigenic (40.0%) as compared to umbilical infection isolates which were most enterotoxigenic (78.9%). TSST-1 was produced by 95 (19.0%) out of 499 strains tested, with isolates from bacteruria found to be most toxigenic (33.3%). It was concluded that the S. aureus strains tested were highly susceptible to bacteriophages and antimicrobial agents (except penicillin) and that enterotoxigenic and TSST-1 producers were widespread and have an aetiologic potential.

Use of 0.3% triclosan (Bacti-Stat) to eradicate an outbreak of methicillin-resistant Staphylococcus aureus in a neonatal nursery

BACKGROUND

Once established in an institution, methicillin-resistant Staphylococcus aureus (MRSA) outbreaks have proved difficult to eradicate, despite intensive infection control measures. This report describes the nosocomial infection with MRSA of 22 male infants in a neonatal nursery during a 7-month period and the infection control procedures that effectively brought this outbreak under control and eliminated recurrence for more than 3 1/2 years.

METHODS

After a single index case of bullous impetigo caused by MRSA in a neonate discharged from the nursery 2 weeks previously, an additional 18 cases of MRSA skin infections were clustered in a 7-week period. Aggressive infection control measures were instituted, including changes in umbilical cord care, circumcision procedures, diapers, handwashing, gloves, gowns, linens, disinfection, placement in cohorts of neonates and staff, surveillance, and monitoring.

RESULTS

These measures were not effective in slowing the outbreak. The single additional measure of changing handwashing and bathing soap to a preparation containing 0.3% triclosan (Bacti-Stat) was associated with the immediate termination of the acute phase of the MRSA outbreak.

CONCLUSION

The nursery has remained free of MRSA for more than 3 1/2 years, attesting to the success of our program.

Methicillin-resistant Staphylococcus aureus in Western Australia, 1983-1992

A statewide screening programme has prevented imported strains of methicillin-resistant Staphylococcus aureus (MRSA) from becoming established in any hospital in Western Australia (WA). Recently, notifications of MRSA in WA have increased, prompting a review of surveillance data for the period 1983-1992. Our aims were to determine: (i) the distribution by age and sex of persons with MRSA; (ii) changes in notification rates over time and by location in WA; and (iii) temporal changes in antimicrobial resistance patterns. There were 631 notifications of MRSA for the 10 year period 1983-1992, ranging from a low of 36 in 1988 to a high of 117 in 1992. When the distribution by age and sex was examined, three age group peaks were apparent: 0-9 years, 20-39 years and 60-79 years. There was a predominance of females in the 20-39 years age group, reflecting a greater proportion of hospital nursing staff carrying MRSA. In those aged 50 years or more, there was a marked predominance of males. The highest notification rates overall occurred in the remote Kimberley region of WA, however, rates increased significantly in all regions of the state in 1992. Based on antimicrobial resistance patterns, MRSA was classified into two groups: multiresistant imported strains which often caused outbreaks in hospitals; and a less resistant MRSA (WA MRSA). WA MRSA appears to have originated in the Kimberley region and then spread widely in the community to other regions of the state, and the proportion of WA MRSA has increased significantly since 1989.

A major outbreak of methicillin-resistant Staphylococcus aureus caused by a new phage-type (EMRSA-16)

An outbreak of methicillin-resistant Staphylococcus aureus (MRSA) infection caused by a novel phage-type (now designated EMRSA-16) occurred in three hospitals in East Northamptonshire over a 21-month period (April 1991--December 1992). Four hundred patients were colonized or infected. Seven patients died as a direct result of infection. Chest infections were significantly associated with the outbreak strain when compared with methicillin-sensitive S. aureus. Twenty-seven staff and two relatives who cared for patients were also colonized. A 'search and destroy' strategy, as advocated in the current UK guidelines for control of epidemic MRSA was implemented after detection of the first case. Despite extensive screening of staff and patients and isolation of colonized and infected patients, the outbreak strain spread to all wards of the three hospitals except paediatrics and maternity. A high incidence of throat colonization (51%) was observed. Failure to recognize the importance of this until late in the outbreak contributed to the delay in containing its spread. Key parts of the strategy which eventually contained the local outbreak were the establishment of isolation wards in two hospitals, treatment of all colonized patients and staff to eradicate carriage and screening of all patients upon discharge from wards where MRSA had ever been detected. EMRSA-16 spread to neighbouring hospitals by early 1992 and to London and the South of England by 1993. It is distinguished from other epidemic strains by its characteristic phage-type, antibiogram (susceptibility to tetracycline and resistance to ciprofloxacin), and in the pattern given on pulse field electrophoresis.

Staphylococcus aureus: a review of the literature

Staphylococcus aureus has a long association with nosocomial infection. Problems date from the 1950s, although methicillin-resistant Staphylococcus aureus (MRSA) did not emerge until the following decade. Initially the pathogenicity of antibiotic-resistant strains was underestimated, and is still sometimes questioned, but today most authorities consider MRSA a serious threat, especially given current preoccupation with cost-effectiveness within the health service: nosocomial infection is associated with increased expenditure and may be regarded as a hallmark of indifferent nursing and medical care. This review documents the emergence of MRSA and recognition of the ensuing problems throughout the 1980s and early 1990s, with suggestions for nursing activities which could contribute towards improved control. Lessons learnt during outbreaks are seen to be of value, but there is also a need for staff at ward level to review routine practice continually so that awareness of activities likely to result in cross-infection is maintained. The use of protective clothing emerges as less important than handwashing, which may be periodically audited to maintain standards.

Strategies for mastitis control: dry cow therapy and culling

The effects of three selection strategies for dry cow therapy on prevention of new infections and rate of antibiotic usage were compared. Quarter infection status of 1044 cows in 12 herds was determined by bacteriological methods at drying off, calving and three to five months into the following lactation. Cows that were uninfected at drying off were randomly allocated to treatment (whole udder, dry cow therapy) and non-treatment groups. Infected cows were randomly allocated to whole udder or infected quarter only treatments. The strategies compared were blanket treatment (treat all quarters of all cows), selective cow treatment (treat all quarters of any cow infected in one or more quarters) and selective quarter treatment (treat infected quarters only). Selective cow treatment was identified as the preferred strategy. Blanket treatment resulted in increased antibiotic usage (15.5 vs 6.4 tubes per infection eliminated) with no additional benefit, and selective quarter treatment resulted in a higher new infection rate (6.4% vs 3.9% quarters) in the dry period. The prevalence of infection within a herd at drying off had no influence on new infection rates in the dry period or early lactation. The cure rate after dry cow treatment (mean of 66%) decreased significantly with increasing age (P < 0.001). Cows infected in the previous lactation contributed over 76% of infections at calving and nearly 70% at mid-lactation. To lower the incidence of mastitis in a herd, a greater emphasis on culling of older infected cows and prevention of new infections during lactation is needed.

Molecular epidemiology for local outbreaks of methicillin resistant Staphylococcus aureus (MRSA). The need for several methods

Subtyping isolates may be useful for epidemiological studies of methicillin-resistant-Staphylococcus aureus (MRSA) outbreaks. Among subtyping methods, DNA-based techniques have been applied very effectively for this purpose. An outbreak of MRSA infections took place in one hospital in Barcelona early during 1991. From the beginning of the outbreak to December 92, 70 MRSA isolates from different patients and sources were collected. All strains were evaluated by restriction endonuclease analysis of plasmid DNA (REAP) and macrorestriction endonuclease analysis of genomic DNA using Sma I and pulsed-field-gel-electrophoresis (PFGE). Plasmid screening and REAP using Hind III demonstrated two plasmid subtypes: subtype A showing a large plasmid, and subtype B showing the same large plasmid plus a smaller one. Subtypes A and B corresponded to the more recent and older isolates, respectively, suggesting the loss of the small plasmid during the epidemic. PFGE using Sma I displayed two closely related profiles (PFGE subtype A and A'; CS = 0.90). These subtypes were different from those subtypes exhibited from 4 methicillin-susceptible-Staphylococcus aureus (MSSA) isolates from the same hospital and from 2 epidemiologically unrelated MRSA isolates. Almost all isolates showing PFGE subtype A preceded those isolates showing PFGE subtype A'. This fact and the similarity between both subtypes suggested minor chromosomal DNA rearrangement during the outbreak from a unique strain. While PFGE using Sma I is a useful tool in evaluation of clonal dissemination, our data suggest epidemic or local outbreaks may need several methods to best delineate the source and spread of MRSA strains. The reproducibility and discriminatory power of REAP makes it a useful adjunct in this context.

Clinical and epidemiologic investigations of nosocomial pulmonary infections caused by methicillin-resistant Staphylococcus aureus

We evaluated the clinical features of 32 patients with pulmonary infections caused by methicillin-resistant Staphylococcus aureus (MRSA). Most of the patients were elderly, postoperative, and had severe underlying diseases. Chest radiograph typically showed bilateral and multilobar involvement. Empyema was not common and no abscess was identified. Mortality rate was 38 percent. We also performed an epidemiologic study of MRSA infections by chromosomal DNA analysis using pulsed-field gel electrophoresis. Thirty-two strains were classified into 20 different types by chromosomal DNA pattern, and 5 epidemic strains were observed. These strains were considered to be transmitted among patients by hospital personnel.

Methicillin-resistant Staphylococcus aureus nasal carriage and infections in CAPD

In view of the increasing concern about methicillin-resistant Staphylococcus aureus (MRSA) infections, we studied the characteristics and outcome of MRSA nasal carriage and infections in our CAPD program. All patients entering into the CAPD program from January 1989 to December 1991 were enrolled into the study. The patients' anterior nares were cultured before the implantation of the catheters. Peritoneal dialysis-related infections were diagnosed based on standard criteria. Data on MRSA nasal carriage, exit-site and tunnel infections and peritonitis were prospectively collected. A total number of 167 patients with 225.9 patient dialysis years were studied with a mean follow-up duration of 16.2 +/- 9.5 months. There were 28 patients with MRSA nasal carriage. The carrier state was unrelated to age, sex and presence of diabetes mellitus. MRSA nasal carriage was associated with a significant increase in the rate of peritonitis (P < 0.01) and exit-site infections (P < 0.01), the number of catheter losses, and CAPD patient dropout (P < 0.001). A total of 30 patients had MRSA infections. In this group, 15 patients had 24 episodes of peritonitis; 20 had 22 episodes of exit-site infections; and 1 had tunnel infection. Fourteen patients had a combination and/or multiple episodes of infections. Treatment of MRSA infections with intraperitoneal vancomycin was unsuccessful in 12 patients (40.0%) resulting in catheter loss. Nine patients (30.0%) dropped out of CAPD after treatment failure for MRSA peritonitis. The patient dropout rate per infection for MRSA infections was comparable to Pseudomonas and fungal infections, but was significantly higher than MSSA infections (P < 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)

Phage susceptibility, enterotoxigenicity and antibiograms of Staphylococcus aureus strains isolated from human wounds and diarrhoea

The phage types, enterotoxigenicity and antibiograms of Staphylococcus aureus strains isolated from human diarrhoea and skin wounds in Nigeria were determined. Of 194 strains tested, 140 (72.2%) were typable using a combination of phages in the International Phage Set (IPS) for human strains of S. aureus and the bovine phage set. IPS phages lysed 118 (60.8%) strains while 96 (49.5%) were susceptible to bovine phages. S. aureus strains from adult diarrhoea were significantly (P less than or equal to 0.01; x2) more sensitive to bovine phages (52.8%) than to IPS human phages (16.7%). Strains isolated from wounds were however significantly (P less than or equal to 0.001; x2) more susceptible to IPS human phages (72.9%) than to bovine phages (41.5%). Phage group III strains were predominant amongst diarrhoeal isolates while wound strains were most susceptible to group II phages. Phage 119, a bovine phage, lysed all 19 strains of diarrhoeal origin sensitive to group M phages but all wound strains were resistant. Overall, 132 (68.0%) strains were enterotoxigenic producing staphylococcal enterotoxins A (SEA), B (SEB), C (SEC) or a combination of these. A majority of diarrhoeal strains elaborated SEC while SEB production was predominant amongst wound strains. Of the eight antimicrobial agents used, S. aureus strains were most resistant to penicillin (71.6%) and least to sulfamethoxazole/trimethoprim (1.0%). Occurrence of resistance to one or more antibiotics was higher amongst wound strains (97.5%) than amongst strains isolated from diarrhoea (52.6%). It was concluded that bovine phage 119 may be a useful epidemiologic marker for S. aureus strains of bovine origin associated with human diarrhoea in Nigeria. It is however difficult to ascribe any aetiological significance to these strains because other enteropathogens not assayed for may have been present.

Methicillin-resistant Staphylococcus aureus colonization in a long-term-care facility

OBJECTIVE

To study the prevalence and risk factors for colonization with MRSA at a long-term-care facility.

DESIGN

Cross-sectional surveillance culture survey.

SETTING

A 233-bed university-affiliated long-term-care facility.

MEASUREMENTS

Surveillance cultures for MRSA were performed on patients of two adjacent nursing units and on new admissions to the entire facility over a 4-month period.

RESULTS

On the chronic medical unit, where patients known to be colonized had been cohorted, 20 of 38 (52.6%) were colonized vs 3 of 67 (4.5%) on the skilled/intermediate unit (P less than 0.001), suggesting that little intra-facility spread of MRSA occurs. Twenty-four of 55 (43.6%) chronic medical admissions were colonized vs 6 of 63 (9.5%) admitted to the other units (P less than 0.001). Thirteen of 30 (43.3%) admissions were not previously known to be colonized. By univariate analysis, colonized admissions were younger and more often male; had more listed diagnoses, including pressure sores, a previous positive MRSA culture, and urinary incontinence; were more often fed by feeding tube; and had longer durations of hospital stay prior to admission. Logistic regression analysis showed that the most powerful independent predictors of colonization at admission were: a prior positive culture for MRSA (OR 8.8, 95% CI 2.4, 32.4), male sex (OR 8.2, 95% CI 2.3, 29.7), urinary incontinence (OR 3.8, 95% CI 1.4, 10.4), and presence of pressure sores (OR 2.9, 95% CI 0.9, 9.2).

CONCLUSIONS

Unrecognized colonization of nursing home residents with MRSA is common, and nursing homes are unwittingly repositories for patients colonized with MRSA following acute hospitalization. Gloving and careful attention to handwashing may limit spread of MRSA within nursing homes, and identification of colonized patients may be facilitated by targeted surveillance cultures of the most debilitated patients at admission.

Lack of care giver hand contamination with endemic bacterial pathogens in a nursing home

Prevalences of Clostridium difficile and multiply resistant Staphylococcus aureus (MRSA) were determined in nursing staff and residents of a 233-bed long-term care facility. Twenty of 38 (52.6%) patients in the long-term care ward and three of 69 (4.3%) in the skilled-nursing ward were colonized with MRSA; 16 of 48 (33%) patients in the long-term care ward and seven of 52 (13%) in the nursing home ward were colonized with C. difficile. None of the 79 staff members whose hands were cultured had chronic C. difficile hand carriage and MRSA was present on only three of 79 (3.9%). Over a 6-month period, 128,000 pairs of gloves were worn. Since C. difficile and MRSA are rarely present on washed hands of care providers, appropriate handwashing and gloving should make a significant contribution to reducing the spread of these agents in long-term care facilities.

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.

Increasing Prevalence of Methicillin-Resistant Staphylococcus aureus in the United States

In the period 1975 to 1981, methicillin-resistant Staphylococcus aureus (MRSA) emerged as an important nosocomial pathogen in tertiary care centers in the United States. To determine if the prevalence of this organism has continued to increase, a questionnaire was sent to hospital epidemiologists in 360 acute care hospitals. A total of 256 (71%) of the 360 individuals responded. Overall, 97% (246/256) of responding hospitals reported having patients with MRSA in the period 1987 through 1989. Respondents in 217 hospitals provided estimates of the number of cases seen in 1987, 1988 and 1989. The percentage of respondents reporting one or more patients with MRSA increased from 88% in 1987 to 96.3% in 1989 (p = .0008). The percent of respondents reporting large numbers (≥50) of cases per year increased from 18% in 1987 to 32% in 1989 (p = .0006). Increasing frequency of large outbreaks was observed in community, community-teaching, federal, municipal and university hospitals.

A probe for the detection of methicillin-resistant Staphylococcus aureus

An approximately 300 base pair DNA fragment for use as a probe was isolated from methicillin-resistant Staphylococcus aureus DNA partially digested with Sau3AI. This probe hybridized with 25 methicillin-resistant clinical isolates of Staphylococcus aureus belonging to 18 different phage types, but not with 41 clinical isolates susceptible to methicillin.

Methicillin-resistant Staphylococcus aureus outbreak at a Veterans' Affairs Medical Center: importance of carriage of the organism by hospital personnel

The reported prevalence of nasal carriage of methicillin-resistant Staphylococcus aureus (MRSA) by hospital personnel averages 2.5%. From August 1985 to September 1987, 155 patients at our Veterans' Affairs Medical Center (VAMC) were colonized or infected with MRSA. In December 1986, only two (2.1%) of 94 healthcare workers were identified as nasal carriers. Prompted by a sharp increase in the number of patients with MRSA in early 1987, contact tracing identified 450 employees, of whom 36 (8%) were nasal carriers. Thirty-five percent of surgical residents (7 of 20) were nasal carriers. Prior to being identified as a nasal carrier, one surgical resident was associated with the inter-hospital spread of the VAMC MRSA strain to the burn unit of the affiliated university hospital. Three family members of two employee carriers were also found to harbor the epidemic strain. All 36 carriers were decolonized with various antimicrobial combinations. Vigorous infection control measures were effective in controlling the epidemic. The frequency of MRSA carriage by hospital personnel at our medical center during the epidemic proved higher than previously appreciated. Thus, healthcare workers may comprise a sizable MRSA reservoir. During an MRSA epidemic, infection control should attempt to identify and decolonize this hospital reservoir, as these individuals can disseminate MRSA both within the hospital as well as into the community.

Importation of methicillin-resistant Staphylococcus aureus from Baghdad to Dublin and subsequent nosocomial spread

We report the spread of a methicillin- and gentamicin-resistant Staphylococcus aureus strain (MGRSA) from the Middle East and its subsequent dissemination within two hospitals in Dublin. The index case, a 30-year-old male with serious blast injuries was transferred from a Baghdad hospital to a Dublin hospital in May 1985. He was heavily infected with two MGRSA strains, one of which spread and was responsible for numerous episodes of nosocomial infection. This strain was very similar to MGRSA isolates recovered in a Baghdad hospital during 1984. This imported strain has now spread to two hospitals in our group causing sepsis. This report emphasizes the difficulty of detecting an imported strain in an endemic area, but above all points to the potential for spread when there is considerable movement of patients and personnel.

A laboratory-confirmed outbreak of rifampicin-methicillin resistant Staphylococcus aureus (RMRSA) in a newborn nursery

The routine laboratory monitoring of methicillin-resistant strains of Staphylococcus aureus (MRSA) at a large teaching hospital led to the detection of a new, multiply-resistant strain of MRSA, which was resistant not only to penicillin, oxacillin, methicillin, cephamandole, erythromycin, tetracycline, kanamycin and gentamicin but also to rifampicin and sulphamethoxazole-trimethoprim. The rifampicin-methicillin resistant strain of S. aureus (RMRSA) was first detected in blood cultures of babies from the newborn nursery. A bacteriological investigation of the nursery revealed the source to be a paediatric medical officer who was colonised with the resistant strain, and who at the time was receiving rifampicin for pulmonary tuberculosis. The rifampicin resistance was presumably acquired during rifampicin therapy. The outbreak in the nursery was brought to an abrupt end by treatment of the colonised medical officer with mupirocin, applied nasally twice a day for a week, and by the introduction of standard infection-control measures. Reference laboratory assistance was needed to confirm the initial assumption that the outbreak was caused by a single strain.

Methicillin-resistant Staphylococcus aureus: a ten-year survey in a Dublin hospital

We undertook a retrospective, longitudinal survey to monitor the changing incidence, phage types and patterns of antibiotic resistance of methicillin-resistant Staphylococcus aureus (MRSA) in St Laurence's Hospital (SLH), Dublin over the last 10 years. Following a peak in 1979, the incidence of MRSA has gradually decreased to around 17% of S. aureus isolates in 1986, almost identical to its incidence 10 years before. However, the spectrum of antibiotic resistance among these organisms remains broad and this seems to be at least partially related to antibiotic usage. Many strains could not be phage typed and others were typable only by the additional phage 90. This has severely limited the usefulness of phage typing in the tracing of sources of outbreaks. Thus, there is a need for a more specific method of typing as well as a rational antibiotic policy, to successfully monitor and curtail the hospital spread of MRSA.

Efficacy of mupirocin in methicillin-resistant Staphylococcus aureus burn wound infection

Methicillin-resistant Staphylococcus aureus strains (MRSA) have become increasingly prevalent as nosocomial pathogens, especially in burn wounds. MRSA constituted 38% of all S. aureus isolates in our 25-bed burns unit despite the utilization of a combination of 1% silver sulfadiazine and 0.2% chlorhexidine as topical therapy. Mupirocin, a new antibiotic, has proved in vitro and in vivo to be highly effective in the treatment of MRSA infections. A prospective clinical trial with mupirocin ointment in MRSA burn wound infection was untertaken. Forty-five children with 59 discrete burn wounds and from whom MRSA were isolated were treated with 2% mupirocin ointment under occlusive dressings, applied twice daily for 5 days. The average burned area treated was 8% (range, 2 to 20%) of the total body surface area. The burn wounds were assessed clinically and bacteriologically daily. Mupirocin eliminated MRSA in all 59 wounds treated, with the maximum therapeutic response seen within 4 days. In three wounds, gram-negative organisms persisted after 5 days of topical therapy. Treatment was well tolerated by all children. We recommend that mupirocin in its present polyethylene glycol base should be used only on a selective basis, when current prophylactic topical therapy has failed to control MRSA infection in burns of less than 20% of the total body surface area, and that it should be applied only for a limited period of 5 days. The safety and the efficacy of mupirocin in burns exceeding 20% of the total body surface area need to be established.

Staff carriage of epidemic methicillin-resistant Staphylococcus aureus

Twenty-six nurses were repeatedly screened for carriage of epidemic methicillin-resistant Staphylococcus aureus (EMRSA) immediately before and after duty periods in which they solely attended six patients widely colonized with two EMRSA strains distinguishable by plasmid analysis. EMRSA carriage was detected in 13 nurses. Three EMRSA carriage patterns emerged: transient carriage in 12 nurses, when the EMRSA was isolated from noses or fingers of nurses after duty but was gone before their next day's duty; short-term nasal carriage, seen on occasion in 4 of these 12 nurses, when EMRSA carriage was detected on two consecutive screens; and persistent nasal carriage, seen in 1 nurse only, when the EMRSA was seen on more than two consecutive occasions. All but one of these incidents of carriage could be explained by close patient, rather than environmental, exposure and occurred despite an intensive control programme. Transient or short-term carriage in nurses probably resulted in transfer of the EMRSA between patients. Staff decontamination should be considered following a period of cohort nursing of EMRSA patients, especially if staff members are shortly to nurse unaffected patients. Our findings may explain some of the difficulties in controlling EMRSA.

Complex typing of methicillin-resistant Staphylococcus aureus (MRSA)

To discriminate between methicillin-resistant Staphylococcus aureus from 5 nosocomial outbreaks and from sporadic nosocomial infections, the efficacy of a complex typing scheme by phage typing, biochemical typing, resistance phenotype, plasmid profiles, plasmid patterns and attribution of resistance determinants to the chromosome was studied. In addition to the International Basic Set and experimental phages 88-93, 10 experimental phages from the Public Health Laboratory Service, Colindale, London, were used for phage-typing. The 10 experimental phages from PHLS in particular, in combination with plasmid profiles and plasmid patterns, were of special discriminative value.

The changing pattern of severe neonatal staphylococcal infection: a 10-year study

Forty-two cases of severe staphylococcal infection occurring over a 10-year period in the neonatal unit at Queen Mary Hospital are described. There was a 4.5-fold increase in incidence in the latter half of the study period, when methicillin-resistant Staphylococcus aureus (MRSA) emerged. The isolated MRSA were also resistant to gentamicin, but sensitive to vancomycin, fusidic acid, co-trimoxazole and amikacin. Comparison between MRSA and methicillin-sensitive cases showed that the former was associated with a longer hospital stay after diagnosis. Overall mortality was 9.5%. Two cases with meningitis died. MRSA is at least as virulent as its methicillin-sensitive counterparts. The treatment implications of severe neonatal staphylococcal infection are discussed.

Methicillin-resistant Staphylococcus aureus: associated morbidity and effectiveness of control measures

The strain of methicillin-resistant Staphylococcus aureus (MRSA) prevalent in south-east England produced in one acute hospital in a year 40 infections (bacteraemia, pneumonia and surgical wound, skin and urinary tract infections) with three attributable deaths. Rigorous measures succeeded in controlling the outbreak despite its extent, but our results suggest that less stringent measures could fail to control outbreaks of this scale. Several subsequent localized outbreaks within the hospital, probably caused by separate re-introductions of MRSA from other hospitals, were controlled by re-instigation of control measures on individual wards. The overall success of the intervention was shown by the decline in the incidence of MRSA infections from 27 in the 6 months beforehand to 2 in the most recent 6 months, and by the decline in the prevalence of colonization among patients 10 or more days in hospital from 52% immediately before the intervention to 3% 7 months after it. The incidence of attributable morbidity and death without control measures warrants a concerted effort to tackle the epidemic in all affected hospitals in Britain.

A descriptive survey of uncontrolled methicillin-resistant Staphylococcus aureus in a twin site general hospital

Over a five year period beginning in 1981, during which control measures were applied intermittently, the incidence of methicillin-resistant Staphylococcus aureus (MRSA) isolates increased steadily within a twin site general hospital. A retrospective chart review of 154 patients identified in 1984-1985 showed that the MRSA 'definitely' contributed to three deaths (2%) and 'probably' contributed to a further 15 (10%). The prolonged median duration of hospital admission (22 days) before first isolation of MRSA, together with the clustering of cases in time on certain wards, suggested that most, if not all, affected patients acquired the MRSA in hospital. As the virulence of MRSA in our outbreak appeared the same as that reported from teaching hospitals, MRSA control measures need to be comprehensively applied in general hospitals.

Methicillin resistant Staphylococcus aureus; the role of antisepsis in the control of an outbreak

Between February 1983 and September 1985, an outbreak of methicillin-resistant Staphylococcus aureus involving 151 patients and staff occurred in a district general hospital. At its peak, 43 cases occurred in 3 months. Sixty-two patients suffered morbidity and two died. Conventional isolation techniques and once-daily whole body washing of affected patients with triclosan successfully controlled the outbreak.