Characteristics That Promote Transmission ofStaphylococcus aureusin German Nursing Homes

Objective:

To determine factors that influence transmission ofStaphylococcus aureusin nursing homes in the Rhine-Neckar region of southern Germany.

Design:

Ecologie study.

Setting:

Forty-seven nursing homes in the region.

Participants:

Residents of the approached nursing homes who agreed to participate.

Methods:

Personal data and swabs of the nares were collected from participants. Swabs were examined for growth ofS. aureus.AllS. aureusisolates were typed using pulsed-field gel electrophoresis (PFGE). Transmission rates were calculated by dividing the number of transmissions (ie, cases in which two inhabitants shared the same PFGE type) by the number of S.aureuscarriers. Characteristics of the nursing homes were correlated with a home's transmission rate.

Results:

In each nursing home, 12% to 54% of the residents were colonized with S.aureus.The transmission rates for the 47 nursing homes ranged from 0% to 70%. A linear regression model revealed that a stay in the nursing home of longer than 6 months and accommodation in a room with 3 or more beds were positively associated with the transmission rate. Receipt of antibiotics during the 4 weeks preceding the study was negatively associated with transmission.

Conclusions:

Stays beyond 6 months and accommodation in rooms with multiple beds are important for the transmission of S.aureus.One way to reduce transmission would be to design facilities with single and double rooms. However, the social needs of the residents must be evaluated and respected.

An epidemiologic survey of methicillin-resistant Staphylococcus aureus by combined use of mec-HVR genotyping and toxin genotyping in a university hospital in Japan

OBJECTIVE

To evaluate the usefulness of an assay using two polymerase chain reaction-based genotyping methods in the practical surveillance of methicillin-resistant Staphylococcus aureus (MRSA).

METHODS

Nosocomial infection and colonization were surveyed monthly in a university hospital in Japan for 20 months. Genotyping with mec-HVR is based on the size of the mec-associated hypervariable region amplified by polymerase chain reaction. Toxin genotyping uses a multiplex polymerase chain reaction method to amplify eight staphylococcal toxin genes.

RESULTS

Eight hundred nine MRSA isolates were classified into 49 genotypes. We observed differing prevalences of genotypes for different hospital wards, and could rapidly demonstrate the similarity of genotype for outbreak isolates. The incidence of genotype D: SEC/TSST1 was significantly higher in isolates causing nosocomial infections (49.5%; 48 of 97) than in nasal isolates (31.4%; 54 of 172) (P = .004), suggesting that this genotype may represent the nosocomial strains.

CONCLUSION

The combined use of these two genotyping methods resulted in improved discriminatory ability and should be further investigated.

Molecular epidemiology of methicillin-resistant Staphylococcus aureus in a pediatric ward

BACKGROUND

Nosocomial infections caused by methicillin-resistant Staphylococcus aureus (MRSA) are one of the most serious problems in pediatric wards. Epidemiological analysis of strains isolated in the ward is essential for infection control. There have been few reports in which a molecular epidemiological study of MRSA was performed in pediatric wards.

METHODS

Fifty-six MRSA strains isolated in the pediatric ward of Asahikawa Medical College Hospital between 1995 and 1997 were studied. Fifty-two and four isolates were obtained from 27 patients and from two medical staff members, respectively. Forty-one isolates were regarded as colonizing strains and 15 were causes of infections. Genotypes of the isolates were investigated by pulsed-field gel electrophoresis (PFGE).

RESULTS

The PFGE patterns of 56 isolates were classified into nine types: type A, its subtypes, A1 and A2, and types B through to G. Seventeen isolates were type A, 32 were type A1, and one of each type of A2 and B through to G were identified. Fifty of 56 isolates, which were isolated from 24 of 29 cases, belonged to type A or its subtypes.

CONCLUSIONS

The predominant strain of MRSA isolates in the pediatric ward was a certain strain that may be originated from the one clone. Cross-infection control therefore is the major procedure in the prevention of MRSA dissemination in the ward.

The role of methicillin-resistant Staphylococcus aureus in orthopaedic implant surgery

The problems presented by methicillin-resistant Staphylococcus aureus (MRSA) must be accommodated in both prophylactic and treatment regimens for orthopaedic implant surgery. The rationale of pre-admission nasal swabbing in directing prophylaxis for orthopaedic patients is discussed. The potential advantage of nasal mupirocin for Staphylococcus aureus and MRSA carriers is described. Methicillin-resistant Staphylococcus epidermidis is commented upon as another hazard in orthopaedics. Criteria for choosing glycopeptides in the treatment of implant infections are discussed, and need to be defined in orthopaedic units. Treatment regimens are briefly described.

The epidemiology of antibiotic resistance in hospitals: paradoxes and prescriptions

A simple mathematical model of bacterial transmission within a hospital was used to study the effects of measures to control nosocomial transmission of bacteria and reduce antimicrobial resistance in nosocomial pathogens. The model predicts that: (i) Use of an antibiotic for which resistance is not yet present in a hospital will be positively associated at the individual level (odds ratio) with carriage of bacteria resistant to other antibiotics, but negatively associated at the population level (prevalence). Thus inferences from individual risk factors can yield misleading conclusions about the effect of antibiotic use on resistance to another antibiotic. (ii) Nonspecific interventions that reduce transmission of all bacteria within a hospital will disproportionately reduce the prevalence of colonization with resistant bacteria. (iii) Changes in the prevalence of resistance after a successful intervention will occur on a time scale of weeks to months, considerably faster than in community-acquired infections. Moreover, resistance can decline rapidly in a hospital even if it does not carry a fitness cost. The predictions of the model are compared with those of other models and published data. The implications for resistance control and study design are discussed, along with the limitations and assumptions of the model.