Difference in incidence and transmission mode of methicillin-resistant Staphylococcus aureus among surgery, orthopedics, and pediatrics wards: a prospective study at a university hospital

Early experience with linezolid for infections in orthopaedics

In infections following orthopaedic surgery, isolated staphylococci are reported to be methicillin resistant (MRSA) in up to 50% of cases. Linezolid, the first in a new class of antibiotics, has excellent efficacy against gram positive organisms that are resistant to other therapies and is 100% orally bioavailable. We report early results of its use for the treatment of resistant infections in orthopaedic practice. Infections were characterised according to the UK Nosocomial Infections National Surveillance Service classification of surgical infections as superficial, deep or organ/space. Osteomyelitis, joint sepsis and deep infection involving orthopaedic implants were included into the final category. Outcome was recorded as clinical, microbiological and blood parameter cure or fail. Over the 12-month study period, 54 patients received linezolid therapy, 41% of these had significant co-morbidity that might affect their ability to fight infection. Sixty-seven percent of infections were in association with implanted metal work. The majority of patients were treated with vancomycin for a short period before linezolid was used as oral 'switch' therapy for longer-term administration, allowing early discharge in all cases. MRSA was isolated in 87% of the patients treated. The mean length of linezolid therapy was 39 days (2-151). Clinical success was achieved in 90% of patients overall. Though there were no life-threatening complications, adverse event rates were significantly higher than those recorded in the literature, with 19% of patients needing to cease therapy. Linezolid offers an alternative to traditional treatments for resistant infections and can facilitate early discharge. Patients need to be monitored closely, particularly where long-term therapy is planned.

Prevalence of methicillin-resistant Staphyloccocus aureus and associated risk factors on admission to a specialist care eye hospital

BACKGROUND

Staphylococcus aureus is known to be a frequent pathogen in hospital settings, with its well-known and resistant forms to the anti-staphylococcal penicillins. Reports on community carriage outside hospital settings have been feared to be on the increase due to the frequency of reported cases on admission to hospitals. We undertook this study to determine the prevalence of, and to establish predictors for, nasal carriage of methicillin-resistant S. aureus (MRSA) at the time of admission to a specialist care eye hospital.

MATERIALS AND METHODS

A prospective survey was conducted at King Khaled Eye Specialist Hospital (KKESH), Riyadh, during three differing weeks randomly selected from the year 1999. The first 100 patients admitted during those three weeks were selected according to inclusion criteria. The hospital is a 220-bed tertiary ophthalmic care facility, with an average 7,500 admissions per year. Nasal bacterial swabs were taken within 48 hours of admission and tested for all strains of S. aureus and sensitivity to methicillin. Detailed interviews were conducted about medical history and habitual environment.

RESULTS

Of 306 nasal cultures tested, none was isolated for MRSA and 102 (33%) were sensitive to methicillin (MSSA). We found 0% nasal carriage rate for MRSA. Respondents had difficulty with questions related to antibiotic administration. No identifiable medical or environmental risk factors could be found.

CONCLUSION

Nasal swabs of patients admitted to KKESH did not reveal MRSA colonization, indicating that MRSA may not be prevalent in the community at present.

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.