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.

Orthopaedic implant infections.

Recent advances have defined risk factors for orthopaedic implant infections that suggest modifications in the clinical care of certain patients. For diagnosis, new work shows the importance of obtaining multiple specimens for culture, and the enlarging spectrum of causative organisms. The potential for the polymerase chain reaction is demonstrated. In treatment, the value of rifampicin is shown in controlled and open trials.

International epidemiological and microbiological study of outbreak of Salmonella agona infection from a ready to eat savoury snack--I: England and Wales and the United States.

OBJECTIVES: To identify the source of an international outbreak of food poisoning due to Salmonella agona phage type 15 and to measure how long the underlying cause persisted. DESIGN: Case-control study of 16 primary household cases and 32 controls of similar age and dietary habit. Packets of the implicated foodstuff manufactured on a range of days were examined for salmonella. All isolates of the epidemic phage type were further characterised by pulsed field gel electrophoresis. RESULTS: 27 cases were identified, of which 26 were in children. The case-control study showed a strong association between infection with S agona phage type 15 and consumption of a peanut flavoured ready to eat kosher savoury snack imported from Israel. S agona phage type 15 was isolated from samples of this snack. The combined food sampling results from the United Kingdom, Canada, the United States, and Israel showed that contaminated snacks were manufactured on at least seven separate dates during a four month period between October 1994 and February 1995. Voluntary recalls of the product successfully interrupted transmission. CONCLUSIONS: Rapid international exchanges of information led to the identification of the source of a major outbreak of S agona in Israel and of associated cases in North America. The outbreak showed the value of the Salm-Net surveillance system and its links outside Europe, both for increasing case ascertainment and for improving the information on the duration of the fault at the manufacturing plant.

Environmental contamination by organisms causing urinary tract infection.

We have examined the bedsheets, floor and bedside chairs of 33 patients with urinary tract infections for organisms causing urinary infection. In ten patients the causative organism was recovered from the undersheet, and in two of these it was also recovered from the floor and bedside chair. Escherichia coli, Enterobacter cloacae, Klebsiella pneumoniae and Enterococcus faecalis were recovered from sheets, while Group B beta-haemolytic streptococci and Candida tropicalis were also found on floors and chairs.

Endemic cross-infection in an acute medical ward.

Urine samples from patients on an acute medical ward were examined each week over a three-month period in order to detect endemic cross colonization or infection. The bed positions for each patient in the ward were recorded continuously and the patients cared for by each different nurse team noted. We found an outbreak of urinary colonization/infection with a strain of Klebsiella K8 in nine patients. Two groups of two patients probably suffered cross colonization/infection with different strains of Escherichia coli. These episodes were not detected by our routine laboratory ward liaison surveillance, but by the weekly samples and molecular typing methods applied to these relatively common strains. This survey demonstrates that cross colonization/infection may occur more widely than is normally detected. The implications of these findings to surveillance audit programmes are discussed.

Contamination of surgeons' glove fingertips during surgical operations.

The external surfaces of surgeons' gloves were examined for contamination by bacteria during the course of surgical operations. Of 31 operations studied the surgeons' glove surfaces yielded bacteria at the end of the operation in 16 cases. Bacterial contamination increased during the course of the operation. The surgeons' fingertip skin and nail beds were cultured after surgical hand scrub and drying, but before donning gloves; bacteria were recovered from these sites in 10 of 21 and 13 of 21 cases, respectively.

Antimicrobial prophylaxis in surgery: microbiological factors.

Various aspects of prophylaxis in surgery are discussed. The timing of antibiotic doses is analysed in relation to the Burke laboratory model and the lag-phase of bacterial growth. Areas where further data is required: the effect of locally applied antibiotics, protection against sources of organisms and new approaches to prophylaxis are discussed. The ecological effects of antibiotics are described in relation to prophylaxis.

Correlation of bacteriological flora of the urethra, glans and perineum with organisms causing urinary tract infection in the spinal injured male patient.

Positive urine cultures are common and often asymptomatic in the male spinal injured patient performing self clean intermittent catheterisation. It is possible that the positive urine cultures result from contamination from the colonised urethra at the time of catheterisation. This contamination could result in true infection of the bladder urine or yield false positive results, explaining the frequently seen asymptomatic cases. In a prospective study positive urine cultures were found on 58 occasions (74%) in 10 asymptomatic patients studied. In 19% of screenings, with positive urine cultures, an identical organism was cultured from the catheter specimen of urine, the perineum and the urethra. The flora of the anterior urethra is strongly correlated to that of the perineum (37.1%), as well as that of the bladder (52.6%). In 4 patients a correlation also existed between the urethra and fingers, and the perineum and fingers. This was associated with an increased incidence of positive urine culture in these patients. Suprapubic aspirates of urine before and after catheterisation cultured the same organisms. However, quantitative culture revealed colony counts that approached a 10-fold increase following catheterisation in one patient. This suggests that catheterisation is at least partially responsible for ascending infection in this group of patients. Catheter specimens were found to be a good representation of the bladder urine, with an 87.5% correlation.

Recovery of coliforms from the hands of nurses and patients: activities leading to contamination.

Coliform type organisms were recovered from the hands of nurses and patients in an Orthopaedic Hospital. Coliforms were frequently recovered from nurses' hands after touching patients' washing materials and clothing as well as after bed making, sluice room activities and handling clean or dirty linen and curtains. The recovery rates were higher in wards for spinally injured patients than in the surgical wards. Coliforms were recovered with similar frequencies, to those from nurses, from the hands of patients in both types of wards.

Infection in orthopaedic implants.

The infection rate in hip prostheses should be less than 1.0% but in other joints is higher probably because of proximity to the skin surface and less experience in joint design. The organisms causing hip implant infection are Staphylococcus aureus 35%, S. epidermidis 15%, coliforms 25%, and anaerobes and others 25%; in other joints there may be a higher incidence of staphylococci. Clinical diagnosis is difficult since symptoms, X-rays and scans do not distinguish infection from loosening, but the erythrocyte sedimentation rate (ESR) moderately rises in infection. Treatment of deep infection by antibiotics alone is unlikely to succeed, but suppression of infection in patients unsuited to operation is possible. Surgeons should be encouraged to aspirate from the affected joint to obtain a bacteriological diagnosis; in the absence of this procedure broad spectrum antibiotics with good activity against S. aureus and S. epidermidis are required. Antibiotics must penetrate the membrane which forms in many patients at the implant or cement/bone interface but there is no evidence as to which antibiotics do so best. For prophylaxis there are three areas of uncertainty: (1) does antibiotic-impregnated cement provide additional effect to systemic antibiotics, since antibiotics can be found in the wound fluid after operation and gentamicin remains at the interface for many months?; (2) what proportion of late infections are haematogenous and do they demand prophylaxis for dental and surgical procedures?; (3) should greater protection from spread of staphylococci for the patient's skin and carrier sites be considered?