Changes in microbial ecology and use of cloxacillin

Review of MRSA screening and antibiotics prophylaxis in orthopaedic trauma patients; The risk of surgical site infection with inadequate antibiotic prophylaxis in patients colonized with MRSA

AIMS

The primary aim of this study was to determine whether orthopaedic trauma patients receive appropriate antibiotic prophylaxis keeping in view the results of their MRSA screening. The secondary aim was to analyse the risk of developing MRSA surgical site infection with and without appropriate antibiotic prophylaxis in those colonized with MRSA.

PATIENTS AND METHODS

We reviewed 400 consecutive orthopaedic trauma patient episodes. Preoperative MRSA screening results, operative procedures, prophylactic antibiotics and postoperative course were explored. In addition to these consecutive patients, the hospital MRSA database over the previous 5 years identified 27 MRSA colonized acute trauma patients requiring surgery.

RESULTS

Of the 400 consecutive patient episodes, 395(98.7%) had MRSA screening performed on admission. However, in 236 (59.0%) cases, the results were not available before the surgery. Seven patient episodes (1.8%) had positive MRSA colonization. Analysis of 27 MRSA colonized patients revealed that 20(74%) patients did not have the screening results available before the surgery. Only 5(18.5%) received Teicoplanin and 22(81.4%) received cefuroxime for antibiotic prophylaxis before their surgery. Of those receiving cefuroxime, five (22.73%) patients developed postoperative MRSA surgical site infection (SSI) but none of those (0%) receiving Teicoplanin had MRSA SSI. The absolute risk reduction for SSI with Teicoplanin as antibiotic prophylaxis was 22.73% (CI=5.22%-40.24%) and NNT (Number Needed to Treat) was 5 (CI=2.5-19.2) CONCLUSION: Lack of available screening results before the surgery may lead to inadequate antibiotic prophylaxis increasing the risk of MRSA surgical site infection. Glycopeptide (e.g.Teicoplanin) prophylaxis should be considered when there is history of MRSA colonization or MRSA screening results are not available before the surgery.

Risk factors for, and the effect of MRSA colonization on the clinical outcomes of severely burnt patients

BACKGROUND

MRSA is an on-going problem for burn patients.

AIM

To analyze risk factors for, and the effect of MRSA colonization on burn patients' outcome.

METHODS

During 21 months burn patients' details and MRSA isolates were analyzed, and a case-control study performed.

RESULTS

Of 357 burn patients, 57 (16%) tested positive for MRSA. Compared to the MRSA negative group, MRSA positive patients had a higher median total burn surface area (15%[IQR 5-17%] vs. 5%[IQR 2-8%]; p<0.001), more admissions to ICU (54% vs. 26%; p<0.001), longer ICU length of stay (4.3 vs. 1.0 days; p<0.001), required more operations (1.6 vs. 0.8; p<0.001), and had longer total hospital length of stay (25.5 vs. 8.0 days; p<0.001). MRSA positivity was a significant independent predictor of increased length of stay (6.0 days, 95%CI 2.39-9.6 days; p=0.001) in a multivariable regression model correcting for patients TBSA and co-morbidities. Cardiac comorbidities (OR 5.14, 95%CI 1.76-15.62; p<0.001) and a longer exposure to the hospital environment (OR 1.05, 95%CI 1.02-1.09, p=0.005) increased the likelihood for MRSA positivity.

CONCLUSION

The negative impact of MRSA positivity on burn patients outcome indicates the need for improved screening procedures for early identification and further efforts toward MRSA infection control to prevent cross-infection as this may significantly impair patients' outcome.

Contribution de la pression de sélection antibiotique dans l’acquisition de Staphylococcus aureus résistant à la méticilline (SARM) dans un centre hospitalier universitaire

Methicillin-resistant Staphylococcus aureus (MRSA) is a major nosocomial pathogen, which causes severe morbidity and mortality in hospitals. Antibiotic pressure is recognised as an individual risk factor in the acquisition of MRSA, however, some authors suggest that antibiotic use must be considered as an ecological and collective problem on a unit or hospital scale. The objective of our study was to determine whether antibiotic pressure affects the acquisition of MRSA. The study was conducted during 1 year (from October 2000 to September 2001) at Besançon hospital. The analysis was based on the research of a correlation between incidence of MRSA acquisition, the colonisation pressure exerted by imported MRSA and use of antimicrobials ineffective against MRSA at the unit level. Univariate analysis showed that acquired MRSA cases were significantly correlated with the use of all antimicrobials, as well as with the use of each class of antimicrobial and with colonisation pressure. In multivariate analysis, the stratification of the units into consumer classes allowed us to eliminate the scale effect of each antimicrobial class and to characterise the impact of high antimicrobial use compared to weak antimicrobial. The highest risks of MRSA acquisition were observed for beta-lactams and quinolones. This study shows that "MRSA acquisition" is correlated to antibiotic use and highlights the need to improve antibiotic usage in the control of MRSA.

Relationship between spread of methicillin-resistant Staphylococcus aureus and antimicrobial use in a French university hospital

The objective of our study was to determine whether antibiotic pressure in the units of a teaching hospital affects the acquisition of methicillin-resistant Staphylococcus aureus (MRSA), independently of the other collective risk factors previously shown to be involved (MRSA colonization pressure, type of hospitalization unit, and care workload). The average incidence of acquisition of MRSA during the 1-year study period was 0.31 cases per 1000 days of hospitalization, and the use of ineffective antimicrobials reached 504.54 daily defined doses (DDDs) per 1000 days of hospitalization. Univariate analysis showed that acquisition of MRSA was significantly correlated with the use of all antimicrobials, as well as correlated with the use of each class of antimicrobial and with colonization pressure. Multivariate analysis with a Poisson regression model showed that the use of antimicrobials was associated with the incidence of acquisition of MRSA, independently of the other variables studied, but it did not allow us to determine the hierarchy of the different antimicrobial classes with respect to the effect.

The relationship between the volume of antimicrobial consumption in human communities and the frequency of resistance

The threat to human health posed by antibiotic resistance is of growing concern. Many commensal and pathogenic organisms have developed resistance to well established and newer antibiotics. The major selection pressure driving changes in the frequency of antibiotic resistance is the volume of drug use. However, establishing a quantitative relationship between the frequency of resistance and volume of drug use has proved difficult. Using population genetic methods and epidemiological observations, we report an analysis of the influence of the selective pressure imposed by the volume of drug use on temporal changes in resistance. Analytical expressions are derived to delineate key relationships between resistance and drug consumption. The analyses indicate that the time scale for emergence of resistance under a constant selective pressure is typically much shorter than the decay time after cessation or decline in the volume of drug use and that significant reductions in resistance require equally significant reductions in drug consumption. These results highlight the need for early intervention once resistance is detected.

Methicillin-resistant Staphylococcus aureus versus the burn patient

Methicillin-resistant Staphylococcus aureus (MRSA) has become a frequent cause of nosocomial infection, its increasing prevalence posing serious therapeutic and infection control problems within the hospital environment. MRSA is a major challenge to the burn patient, with potential to cause significant morbidity and mortality. Burn patients have been shown to become colonised and infected more readily than other patient groups. Extensive burn injuries are particularly susceptible to infection as a result of the disruption of the normal skin barrier and accompanying depression of immune responses. Extended hospitalisation and antibiotic therapy have been identified as additional risk factors for MRSA carriage and infection. Microbial surveillance, epidemiological studies and the introduction of strict infection control regimes can reduce the prevalence of MRSA but may be insufficient for eradication or prevention of outbreak situations. Recognition of the clinical importance of MRSA to the burn patient highlights the need to take appropriate measures to minimise transmission and infection in this vulnerable group of patients.

The transmission dynamics of antibiotic-resistant bacteria: the relationship between resistance in commensal organisms and antibiotic consumption

We propose a mathematical model of the transmission dynamics of colonization by commensal bacteria within a human community subject to varying levels of antibiotic use designed to control morbidity induced by pathogenic strains of the normally commensal organisms. Colonization is assumed not to induce morbidity in the majority of cases, and antibiotic use is assumed to be related to the arrival and growth of pathogenic strains that give rise to infections including clinical symptoms of disease. In the absence of antibiotic resistance, the model shows how the pattern of antibiotic prescription and use can eliminate the non-pathogenic commensal strains from the host community if the fraction of people taking antibiotics with a defined efficacy exceeds some critical level. The model is extended to take account of the evolution of antibiotic resistance in the commensal population. We assume resistance may be either plasmid-mediated or conferred by selection of low-level pre-existing mutants, and that resistant organisms may experience reduced reproductive fitness. Invasion of the host community by drug-resistant commensals is possible if certain antibiotic prescribing patterns pertain. We calculate these conditions in terms of the transmission parameter of the organism and the level of antibiotic prescription and use. The model is employed to address the issues of how best to use antibiotics in populations harbouring resistant organisms, and when resistant bacteria will out-compete sensitive strains.

Multidrug resistance among methicillin-resistant Staphylococcus aureus in Greece

A total of 472 strains of Staphylococcus aureus isolated in a university hospital in Thessaloniki, Greece during 1993-1994 were studied; 202 (42.8%) of them were characterized as methicillin-resistant (MRSA) and were mainly recovered from respiratory materials. The minimal inhibitory concentrations (MICs) of methicillin-susceptible (MSSA) and methicillin-resistant strains to 10 alternative antibiotics were also compared. All MRSA isolates were resistant to penicillin and most of them, in contrast to MSSA, exhibited resistance to gentamicin, tobramycin, tetracycline, erythromycin and ciprofloxacin with resistance rates ranging from 89.6% to 59.4%. Also, considerable proportions of MRSA were found resistant to co-trimoxazole (47.0%) and rifampicin (27.7%). All isolates were sensitive to vancomycin while susceptibility to chloramphenicol was of equal incidence among the examined populations. Overall, MRSA vs. MSSA exhibited a significantly (chi 2; P < 10-8) higher incidence of resistance to 8 out of the 10 antibiotics examined.

Staphylococcal infections in the Sofia Burn Centre, Bulgaria

This study analysed staphylococcal infections in the Sofia Burns Centre in order to estimate their frequency, features and role in burns. For an 8-year period (1987-94) the bacterial aetiology of wound infections and bacteraemia in burned patients was studied. The prevalence of staphylococci in both wound exudation (31.4 per cent) and in blood cultures (60.7 per cent) was established. During the last year of the study there was a significant increase in the incidence of methicillin-resistant Staphylococcus aureus (MRSA) from 19.4 per cent in 1993 to 28.0 per cent in 1994 (P < 0.001). This raised serious therapeutic problems. MRSA were found more frequently in the ICU than in the wards and in wounds and blood cultures compared with other species/strains. MRSA caused infections in 18.8 percent of patients. Over 70 per cent of the MRSA strains were resistant to gentamicin, erythromycin and tetracycline and about one-third to lincomycin, co-trimoxazole, chloramphenicol and ciprofloxacin. All the MRSA strains were sensitive to vancomycin and 71.1 per cent to rifampicin. These findings show the necessity of urgent measures for restriction of the further distribution of MRSA infections in our burns centre.