A prevalence screen of MRSA nasal colonisation amongst UK doctors in a non-clinical environment.

Screening for methicillin-resistant Staphylococcus aureus (MRSA) carriage in healthcare workers (HCWs) is both contentious and confounded by a lack of knowledge of background prevalence rates. This study examines prevalence of nasal MRSA carriage amongst a spectrum of medical professionals in a non-clinical environment. Medical conference attendees volunteered for screening for nasal MRSA carriage, and anonymised demographic data and attitudes towards screening were recorded. Two hundred sixty volunteers participated. One hundred seventy-three participants (67%) were from the British Medical Association's Annual Representatives Meeting, and 87 participants (33%) were attending the Association of Surgeons in Training conference. Six (2%) participants were positive for MRSA nasal carriage (BMA = 1%, ASIT = 5%; p = 0.099). Participants from a surgical specialty (4.8%) were more likely to be MRSA positive (p = 0.039). All positive samples came from male participants (p = 0.182). However, there was no significant association with gender, seniority or country of employment and MRSA status. Routine screening for MRSA was supported by 63% of participants in HCWs; 36% had previously undergone such screening. MRSA nasal carriage rates within this cross-sectional study are lower than studies reporting carriage rates in HCWs within the clinical environment. Further research is required to examine the relationship between MRSA nasal colonisation status of a HCW and subsequent MRSA infection in patients.

Dose considerations for alcohol-based hand rubs.

BACKGROUND: Manufacturers' recommended dosages for alcohol-based hand rubs are typically determined by measuring product efficacy using a model protocol such as EN 1500; however, anecdotal reports and informal observation suggests that in many cases users self-titrate to much lower doses in real-world application. AIM: To examine the interdependence of alcohol-based hand-rub volume on in-vivo efficacy using the EN 1500 standard test method, on drying time on users' hands, and on their perceptions of acceptability. METHODS: Three formulations were studied using EN 1500 and a modification of this method. The modification used volumes ranging from 0.5 to 3.0 mL and 30 s application. Drying times were recorded and user acceptability was established using a three-point scale (too long, OK, or too short). Dying times were analysed in relation to hand surface area. FINDINGS: The drying time for all three products increased as a function of volume. The drying time displayed a positive association with volume and a negative association with hand surface area. The optimum volume for user acceptability was between 1.5 and 2 mL, yielding a drying time of between 20 and 30 s. CONCLUSION: Whereas EN 1500 is appropriate for establishing the efficacy of a hygienic hand-rub formulation compared to a benchmark, it does not reflect actual in-use conditions or the likely clinical effectiveness of the product. In particular, it fails to address the need to optimize the volume of application and user acceptability of the product.

An outbreak of Serratia marcescens on the neonatal unit: a tale of two clones.

Serratia spp. are an important cause of hospital-acquired infections and outbreaks in high-risk settings. Twenty-one patients were infected or colonized over a nine-month period during 2001-2002 on a neonatal unit. Twenty-two isolates collected were examined for antibiotic susceptibility, beta-lactamase production and genotype. Random-amplified polymorphic DNA polymerase chain reaction and pulsed-field gel electrophoresis revealed that two clones were present. The first clone caused invasive clinical infection in four babies, and was subsequently replaced by a non-invasive clone that affected 14 babies. Phenotypically, the two strains also differed in their prodigiosin production; the first strain was non-pigmented whereas the second strain displayed pink-red pigmentation. Clinical features suggested a difference in their pathogenicity. No environmental source was found. The outbreak terminated following enhanced compliance with infection control measures and a change of antibiotic policy. Although S. marcescens continued to be isolated occasionally for another five months of follow-up, these were sporadic isolates with distinct molecular typing patterns.

Development of a sporicidal test method for Clostridium difficile.

BACKGROUND: Disinfectants with claimed activity against Clostridium difficile must be evaluated to ensure efficacy against the spores that comprise an environmental source of patient infection. Unfortunately there is, at present, no generally accepted method for evaluating these disinfectants. In the absence of such a method, laboratories have to adapt protocols that were not designed for products used in medical environments and consequently may use inappropriate test organisms, exposure times, and pass criteria. AIM: To develop and evaluate a method for testing the activity of disinfectants against C. difficile spores using exposure times and pass criteria which are relevant to clinical application. METHODS: A Joint Working Party of the Healthcare Infection Society (HIS) and the Advisory Committee on Antimicrobial Resistance and Healthcare Associated Infections (ARHAI) of the Department of Health in England was assembled. The Working Party adapted a previously described enzyme-based method for spore purification (the Clospore method) using an exposure time of 5 min and a 5 log10 kill as a pass criterion. FINDINGS: Evaluation of the method by three laboratories demonstrated that the method is simple to follow and that the results are repeatable and reproducible. CONCLUSION: The method described by the Working Party produces a clean suspension with a high titre of spores. It is recommended that, for a disinfectant used in the environment, the product should demonstrate a 5 log10 reduction in 5 min under clean or dirty conditions to fulfil the requirements of the test.

Use of Sentinel blood culture system for analysis of specimens from potentially infected prosthetic joints.

The Sentinel blood culture system was used for the analysis of 657 specimens from infected prosthetic joints and blood cultures (83 from prosthetic joints and 574 from standard blood cultures). The positivity rate was similar for specimens from prosthetic joints and blood cultures (18% compared with 14%). However, there was an unacceptable rate of false positive results with specimens from prosthetic joints (58% compared with 8%). This high false positivity rate was due to (i) prolonged incubation and (ii) the lack of blood in these specimens. It is therefore recommended that the Sentinel system should only be used for the initial seven days of incubation of specimens taken from prosthetic joints. Further incubation should take place in a standard incubator and a terminal subculture performed after 21 days.

Potential of exocellular carbohydrate antigens of Staphylococcus epidermidis in the serodiagnosis of orthopaedic prosthetic infection.

The potential of exocellular carbohydrate antigens of Staphylococcus epidermidis as markers of infection in bone was investigated by immunoblotting and enzyme-linked immunosorbent assay (ELISA). Exocellular antigens were prepared by gel filtration chromatography of concentrated brain heart infusion culture supernates. The antigenic material appeared as diffuse bands between 24 and 32 kDa on the immunoblots and was not susceptible to digestion with trypsin, indicating that the response in the patients was to non-protein (polysaccharide or teichoic acid, or both) exocellular material. Significant differences were detected between the immunoblot antigen profiles for serum IgG from patients with S. epidermidis bone infection and those with an uninfected prosthetic joint. Thirteen of 16 patients with S. epidermidis prosthetic joint infection showed an elevated serum IgG level by ELISA compared with controls with uninfected joints. However, the antigen was not specific for S. epidermidis bone infection; high levels of IgG were also detected in patients with other serious staphylococcal and streptococcal infections. The ELISA test may be valuable in distinguishing between staphylococcal infection of joints and aseptic loosening by excluding cases of infection.

Choosing disinfectants.

Disinfectant choice is an important part of the role of the infection control team. Its importance has increased due to concern over transmission of blood-borne viruses and the need to identify alternatives to gluteraldehyde. Factors to be taken into account when choosing disinfectants include compliance with COSHH regulations, user acceptability, instrument compatibility and antimicrobial activity. Compounds vary in their suitability for different uses and an agent's properties must be fully evaluated before adopting it for a particular purpose. This review outlines the main properties that need to be established and covers the major characteristics of main classes of disinfectants.

Triclosan resistance in methicillin-resistant Staphylococcus aureus (MRSA).

Two triclosan selected mutants showed four-fold and 16-fold increases in their minimum inhibitory concentrations (MICs) of triclosan (1 mg/L and 4 mg/L) compared with their parent strains. Four clinical isolates of MRSA were detected with the same triclosan susceptibility as the mutants. One mutant had a predicted change in the gene product on FabI (Thr 147-->His), whilst only one clinical isolate had predicted FabI amino-acid changes (Ala 198-->Gly, and Leu 208-->Phe). The lack of fabI mutations in one mutant and three of the clinical isolates showing reduced triclosan susceptibility suggest that genetic loci other than fabI may be involved in triclosan resistance.

Heat and chemical resistance of enterococci.

Recent reports have highlighted the tolerance of vancomycin-resistant strains of enterococci to heat. This study examined the tolerance of vancomycin-resistant and sensitive strains of enterococci and an NCTC type strain to 65, 71 and 80 degrees C, and also to low concentrations of a chlorine-releasing agent, alcohol and glutaraldehyde. Variation in the tolerance to chemicals was observed but there was no correlation between vancomycin resistance and tolerance to chemical disinfectants. The NCTC type strain was killed within the time/temperature parameters set by the Department of Health for thermal washer/disinfectors, i.e. 65 degrees C for 10 min, 71 degrees C for 3 min and 80 degrees C for 1 min. However, the clinical strains showed varying resistance to heat, irrespective of their vancomycin susceptibility. One strain survived 80 degrees C for 3 min. These results showed that clinical isolates can be resistant to commonly used disinfection processes, although the practical significance of these results is debatable.

How useful are microbial filters in respiratory apparatus?

Following an outbreak of hepatitis C in surgical patients in Australia, it has been suggested that transmission can take place as a result of contaminated anaesthetic circuits. It has therefore been recommended that filters should be placed between patients and breathing systems with a new filter being used for each patient. Although nosocomial pneumonia is a major manifestation of hospital-acquired infection, it is unclear whether contamination of ventilator circuits is implicated in the aetiology of this condition. Some data suggest that bacteria cannot survive well in anaesthetic circuits and several studies have failed to demonstrate significant contamination of circuits in clinical situation. Several outbreaks of pneumonia related to contaminated anaesthetic equipment have been described, but many of these were controlled by appropriate decontamination of the respiratory equipment. Although ventilator filters are used by the majority of intensive care units and filters do have the ability to filter bacteria and viruses, there are few data suggesting that the use of filters reduce the rate of pulmonary infections in long-term ventilated patients. Furthermore, to change filters between operations would have significant financial implications, and there is no conclusive evidence that they would reduce cross infection. Until more data are available on the role of filters in both long-term ventilated patients and operations, standard hygienic measures such as appropriate disinfection protocols are still the most effective way of reducing ventilator-associated infections.

An unusual source for an outbreak of methicillin-resistant Staphylococcus aureus on an intensive therapy unit.

During a four-month period, six patients on an intensive therapy unit became colonized or infected with methicillin-resistant Staphylococcus aureus (MRSA). Four of these patients were colonized by the Epidemic MRSA strain 15 (EMRSA 15). The outbreak was characterized by the fact that all four of these patients were nursed in the same bed on the unit before acquisition of the organism. Investigation of the outbreak led the authors to believe that the source of the MRSA may have been the exhaust ducting of the adjacent isolation room ventilation system which allowed the organisms to enter the unit via a partially open window positioned above that particular bed. The cycle was broken once the ventilation system was repaired and the window above the bed was properly sealed.

Infection risk and potential contamination of urine specimens associated with sample port design of catheter leg bags.

The ease of disinfection of the sample ports of three types of urine drainage leg bags with different sampling port systems was assessed using a bladder bag model. The ports were contaminated with Escherichia coli, 'disinfected' using a standard method, then sampled at time intervals up to one week after contamination. It was discovered that leg bags which employ a needle-based sampling system (the 'sample safe port system') were easier to disinfect than those which did not, and that organisms are retained in large enough numbers to lead to misdiagnosis of a urinary tract infection or to pose a retrograde infection risk.

Mycobactericidal activity of selected disinfectants using a quantitative suspension test.

In this study, a quantitative suspension test carried out under both clean and dirty conditions was used to assess the activity of various instrument and environmental disinfectants against the type strain NCTC 946 and an endoscope washer disinfector isolate of Mycobacterium chelonae, Mycobacterium fortuitum NCTC 10,394, Mycobacterium tuberculosis H37 Rv NCTC 7416 and a clinical isolate of Mycobacterium avium-intracellulare (MAI). The disinfectants tested were; a chlorine releasing agent, sodium dichloroisocyanurate (NaDCC) at 1000 ppm and 10,000 ppm av Cl; chlorine dioxide at 1100 ppm av ClO2 (Tristel, MediChem International Limited); 70% industrial methylated spirits (IMS); 2% alkaline glutaraldehyde (Asep, Galan); 10% succinedialdehyde and formaldehyde mixture (Gigasept, Schulke & Mayr); 0.35% peracetic acid (NuCidex, Johnson & Johnson); and a peroxygen compound at 1% and 3% (Virkon, Antec International). Results showed that the clinical isolate of MAI was much more resistant than M. tuberculosis to all the disinfectants, while the type strains of M. chelonae and M. fortuitum were far more sensitive. The washer disinfector isolate of M. chelonae was extremely resistant to 2% alkaline activated glutaraldehyde and appeared to be slightly more resistant than the type strain to Nu-Cidex, Gigasept, Virkon and the lower concentration of NaDCC. This study has shown peracetic acid (Nu-Cidex), chlorine dioxide (Tristel), alcohol (IMS) and high concentrations of a chlorine releasing agent (NaDCC) are rapidly mycobactericidal. Glutaraldehyde, although effective, is a slow mycobactericide. Gigasept and Virkon are poor mycobactericidal agents and are not therefore recommended for instruments or spillage if mycobacteria are likely to be present.

Mycobacterium terrae: a potential surrogate for Mycobacterium tuberculosis in a standard disinfectant test.

The susceptibility of Mycobacterium tuberculosis and Mycobacterium avium-intracellulare to the disinfections used for spillage and heat sensitive instruments has received much attention in recent years. The use of clinical isolates of M. tuberculosis and M. avium-intracellulare as test organisms is considered unsuitable for standard tests due to their hazardous nature (category 3 pathogens and slow growth rates). This has led to much debate in standards committees on the selection and use of a possible surrogate which would be safer and more practical to use and yet mimic the susceptibility of clinical isolates. This study compared the susceptibility of one possible surrogate Mycobacterium terrae NCTC 10856, with that of clinical isolates of M. tuberculosis H37 Rv and M. avium-intracellulare using a quantitative suspension test. The instrument and environmental disinfectants tested were a chlorine-releasing agent, sodium dichloroisocyanyurate (NaDCC) at 1000 ppm and 10,000 ppm av. Cl, chlorine dioxide at 1100 ppm av. ClO2 (Tristel, HayMan MediChem), 0.35% peracetic acid (NuCidex, Johnson & Johnson), 70% industrial methylated spirit (IMS), 2% alkaline glutaraldehyde (Asep, Galen), 10% succine dialdehyde and formaldehyde mixture (Gigasept, Schulke and Mayr). Results showed that the clinical isolate of M. avium-intracellulare was the most resistant of the three test organisms. M. terrae, which is not a category 3 pathogen, was slightly more resistant than M. tuberculosis and this would appear to be a suitable surrogate for establishing tuberculocidal activity. However, with an increase in the clinical significance of M. avium-intracellulare, particularly in human immunodeficiency virus (HIV) and immunocompromised patients, a more resistant surrogate is required. In the absence of such a surrogate, testing with M. avium-intracellulare in a clinical laboratory equipped for handling category 3 pathogens is still advised to establish mycobactericidal activity.

The antibacterial activity and stability of acetic acid.

Acetic acid has been shown to have good antibacterial activity against micro-organisms such as Pseudomonas aeruginosa. This study examined the activity against a range of bacterial pathogens and also assessed any reduction in antibacterial activity due to evaporation or inactivation by organic material in dressings. Acetic acid was active at dilutions as low as 0.166% and the activity was not reduced by evaporation nor by inactivation by cotton swabs. Burn injuries are a major problem in countries with limited resources. Acetic acid is an ideal candidate for use in patients who are treated in those parts of the world.

Sporicides for Clostridium difficile: the devil is in the detail.

A taskforce has now been formed with representatives from the Department of Health's Advisory Committee on Antimicrobial Resistance and Healthcare Associated Infection (ARHAI), the Hospital Infection Society (HIS), the Department of Health (England) and the Health Protection Agency. The aims of the ARHAI/HIS Taskforce on Sporicidal Disinfectants are: to develop an accepted standard for laboratory testing of disinfectants which claim to have activity against C. difficile spores; to develop a network of laboratories with capability to perform in vitro assays of sporicidal activity of disinfectants; and to explore the creation of a national quality assessment scheme for laboratories which perform in vitro assays of sporicidal activity of disinfectants.