Estimation of methicillin-resistant Staphylococcus aureus transmission by considering colonization pressure at the time of hospital admission

Our objective was to evaluate the accuracy of a methicillin-resistant Staphylococcus aureus (MRSA) rate using the imported MRSA reservoir identified at the time of hospital admission. Two indicators were used: the number of imported MRSA patient-days/total number of patient-days [representing colonization pressure (CP) at the time of admission] and the incidence of hospital-acquired MRSA isolated from clinical samples expressed as density/100 patient-days for carriers identified at the time of admission [representing the incidence taking CP into account (ICP)]. The variations of these indicators were analysed and compared with two more common indicators: percentage of MRSA acquired in our hospital and the incidence of hospital-acquired MRSA isolated from clinical samples expressed as density/1000 patient-days within three four-month periods during 2002. Common indicators varied similarly, with marked decline during the third period; first-period CP was twice that of other periods (P<10(-6)) and the highest (>two-fold) ICP was seen in the summer (second) period (P<0.001) when the personnel/patient ratio was the lowest. Thus, comparison of different indicators within four-month periods underlines important differences between common and novel indicators. Despite several limitations, ICP should be helpful in the interpretation of MRSA surveillance data, particularly for estimating the extent of MRSA transmission.     

Impact of the reinforcement of a Methicillin-Resistant Staphylococcus aureus Control Programme: A 3-year evaluation by several indicators in a French University Hospital

Our objective was to evaluate the impact of the reinforcement of a methicillin-resistant Staphylococcus aureus (MRSA) control programme and to assess the impact of risk adjustment on the interpretation of data. A stepwise, retrospective analysis of 3-year prospectively collected data was performed in a 600-bed French teaching hospital in the Parisian area. A reinforcement of a pre-existing programme for limiting the spread of MRSA was implemented in 2002 and 2003 by increasing the frequency of the feedback of surveillance data, by using alcohol-based disinfectants, and by increasing patient screening. Different indicators were used to follow the change over time of MRSA transmission: the proportion of MRSA acquired in our hospital, the incidence of newly acquired MRSA/1,000 patient-days (PD) (incidence of newly acquired MRSA), the incidence of newly acquired MRSA isolated in at least one clinical specimen/1,000 PD (incidence of newly acquired clinical MRSA), and a risk-adjusted indicator, the incidence of newly acquired-MRSA isolated in at least one clinical specimen/1,000 PD of carriers identified at admission (incidence related to the risk of acquisition). The change over time of these indicators was studied with the chi-square test for trend. During the study, all indicators decreased significantly, with a mean drop of 0.07/1,000 PD for the incidence of newly acquired clinical MRSA, and a mean drop of 3.0/1,000 PD for the incidence related to the risk of acquisition. The proportion of MRSA acquired in our hospital decreased from 49.3% in 2002 to 24.1% in 2004. Concurrently, between 2002 and 2004, the number of patients screened on admission to hospital or at the time of intra-hospital transfer increased by 31% and the consumption of waterless alcohol-based hand disinfectants increased by 244%. The decreasing trend of all indicators emphasizes the effectiveness of the reinforcement of our MRSA control programme. From 2002 to 2004, the trend of the indicator related to the risk of acquisition over time is similar to those of other indicators. Further studies should be useful to assess if risk-adjustment is absolutely necessary when tracking rates within a single institution.     

Resistance to ceftazidime is associated with a S220Y substitution in the omega loop of the AmpC beta-lactamase of a Serratia marcescens clinical isolate

OBJECTIVES: The aim of this study was to characterize the ampC beta-lactamase gene of a clinical isolate of Serratia marcescens resistant to ceftazidime. METHODS: S. marcescens SMSA was isolated from an intra-abdominal wound of a patient previously treated with ceftazidime. A susceptible strain, SLS73, was used as a control. Susceptibility testing, PCR, DNA sequencing, molecular cloning, site-directed mutagenesis and determination of kinetic parameters were carried out to investigate the mechanism of resistance to ceftazidime. RESULTS: MICs of ceftazidime were 64 and 0.2 mg/L for SMSA and SLS73, respectively. Sequencing of the ampC gene of SMSA was carried out. When compared with the closest AmpC enzyme, the S. marcescens S3 beta-lactamase, the novel protein showed E57Q, Q129K and S220Y substitutions. The S220Y substitution is located in the omega loop. Introduced by mutagenesis in the ampC gene of SLS73, this substitution conferred the same level of resistance to ceftazidime. The catalytic efficiency (k(cat)/K(m)) of the mutated enzyme toward ceftazidime was increased by about 100-fold. CONCLUSIONS: We present another example of in vivo selection of broad-spectrum resistance by amino acid substitution in the omega loop of chromosomal AmpC beta-lactamase in S. marcescens.     

Influence of tracheal suctioning systems on health care workers' gloves and equipment contamination: a comparison of closed and open systems

The impact of tracheal suctioning with an open or a closed system on equipment and health care workers contamination with multidrug-resistant pathogens was compared. Only the closed system reduced hand and equipment contamination during tracheal suctioning. This equipment could be systematically used to reduce risk of cross contamination in the intensive care unit.     

Genotypic characterisation of endemic VanA Enterococcus faecium strains isolated in a paediatric hospital

A total of 36 vancomycin-resistant Enterococcus faecium isolates obtained from 30 patients during a 28-month period in a paediatric university hospital was analysed by pulsed-field gel electrophoresis (PFGE) combined with Southern hybridisation of a vanA-specific DNA probe. All the isolates hybridised with the vanA probe. Seventeen different PFGE patterns and 11 PFGE subtypes were identified among the 36 clinical isolates, and the size of probe-positive bands ranged from c. 30 to 300 kb. These data are consistent with an increase in the overall genomic diversity of vancomycin-resistant E. faecium isolates during the study period. Two periods were distinguished. The prevalence of a single clone in the initial period suggested transmission between patients in three wards. During the following period, multiple genotypes of vancomycin-resistant E. faecium were identified, indicative of multiple introductions or the dissemination of resistance genes by recombinant transposition.     

Brain abscess caused by Nocardia cyriacigeorgica in a patient with human immunodeficiency virus infection

Nocardia cyriacigeorgica is a recently characterized species within the genus of Nocardia. We report a brain abscess, following a primary pulmonary colonization, due to this species in a human immunodeficiency virus-infected patient. This case confirms that isolation of Nocardia in sputum is associated with a high risk of disseminated infection in immunocompromised patients.     

Use of the squirrel monkey Saimiri sciureus to optimize serological tests for diagnosis of Bunyavirus infection in humans

Several arthropod-borne viruses of the large Bunyaviridae virus family have been isolated in South America. There are few data about the incidence of these viruses in man, except for the Oropuche virus. Since haemagglutination inhibition tests are difficult to perform, only enzyme-linked immunosorbent assays (ELISAs) are used. Nevertheless, positive controls are necessary for ELISA, and infected humans are rare. Squirrel monkeys (Saimiri sciureus) were therefore infected experimentally to assess their value as positive controls in such assays. The kinetics of viraemia and of antibody responses after infection with eight Bunyaviruses present in the Amazonian forest were studied. No viraemia was seen in most cases, but, with every virus studied, immunoglobulin (Ig)M and IgG antibody responses were observed, beginning between days 5 and 14 after infection for IgM and days 14--18 after infection for IgG. This model thus provides reliable positive controls for ELISAs in humans. Their availability will allow determination of the seroprevalence of Bunyaviruses in the human population of French Guiana.     

Evaluation of a strategy of screening multiple anatomical sites for methicillin-resistant Staphylococcus aureus at admission to a teaching hospital.

We compared the sensitivity of screening with nasal culture alone with that of a multiple-site screening method for the identification of carriers of methicillin-resistant Staphylococcus aureus at hospital admission. If nasal cultures alone had been used during the 1-year study, 27.0% of carriers of methicillin-resistant S. aureus would have been missed, which corresponds to 560 theoretical isolation days. If rectal screening had not been used, 431 theoretical isolation days would have been missed, and, if axillary screening had not been used, 99 theoretical isolation days would have been missed.