Diagnosis of Clostridium difficile-associated disease: examination of multiple algorithms using toxin EIA, glutamate dehydrogenase EIA and loop-mediated isothermal amplification.

The laboratory diagnosis of Clostridium difficile infection (CDI) needs to be accurate and timely to ensure optimal patient management, infection control and reliable surveillance. Three methods are evaluated using 810 consecutive stool samples against toxigenic culture: CDT TOX A/B Premier enzyme immunoassay (EIA) kit (Meridian Bioscience, Europe), Premier EIA for C. difficile glutamate dehydrogenase (GDH) (Meridian Bioscience, Europe) and the Illumigene kit (Meridian Bioscience, Europe), both individually and within combined testing algorithms. The study revealed that the CDT TOX A/B Premier EIA gave rise to false-positive and false-negative results and demonstrated poor sensitivity (56.47%), compared to Premier EIA for C. difficile GDH (97.65%), suggesting this GDH EIA can be a useful negative screening method. Results for the Illumigene assay alone showed sensitivity, specificity, negative predictive value (NPV) and positive predictive value (PPV) of 91.57%, 98.07%, 99.03% and 84.44%, respectively. A two-stage algorithm using Premier EIA for C. difficile GDH/Illumigene assay yielded superior results compared with other testing algorithms (91.57%, 98.07%, 99.03% and 84.44%, respectively), mirroring the Illumigene performance. However, Illumigene is approximately half the cost of current polymerase chain reaction (PCR) methods, has a rapid turnaround time and requires no specialised skill base, making it an attractive alternative to assays such as the Xpert C. difficile assay (Cepheid, Sunnyvale, CA). A three-stage algorithm offered no improvement and would hamper workflow.

Effectiveness of introducing blood culture collection packs to reduce contamination rates.

Contaminated blood cultures result in a significant waste of healthcare resources and can lead to inappropriate antibiotic therapy. Practitioners have taken measures to reduce contamination rates. These include thorough skin disinfection, effective hand decontamination, introduction of a standardised approach to collection, and the introduction of blood culture collection packs (BCCP). This study aims to assess the impact of introducing BCCP and staff training on the rate of contamination. The study demonstrated that contamination rates are greatest in high patient throughput units where practitioners are under most pressure. The introduction of blood culture packs and staff training has reduced contamination rate significantly from 43% to 25% of the total number of positives, equating to an overall reduction of 42%. Thus, there is a demonstrable benefit in the purchase of commercially produced blood culture packs and the investment in staff training.

The interaction of cationic liposomes with the skin-associated bacterium Staphylococcus epidermidis: effects of ionic strength and temperature.

Cationic liposomes have been prepared from dipalmitoylphosphatidylcholine (DPPC), cholesterol (Chol) and stearylamine (SA). These phospholipid vesicles were exposed to adsorbed biofilms of the skin-associated bacteria Staphylococcus epidermidis, to which they showed a strong affinity. The interaction (as assessed by the apparent monolayer coverage of the biofilms by liposomes) was described in terms of a Langmuir adsorption isotherm which enabled determination of the maximum theoretical coverage of the bacterial surface and association/dissociation constants. The interaction was shown to be dependent on the ionic strength of the surrounding medium; on increasing the ionic strength the biofilm-vesicle dissociation constant decreased. This suggested that the adsorption was mediated by electrostatic effects. The adsorption of the vesicles was examined at various temperatures, enabling determination of thermodynamic parameters for the interaction. The adsorbed state of the liposomes was energetically favoured and the interaction was enthalpy driven. The Gibbs energies of adsorption were in a range from -15 to -19 kJ mol-1 and the enthalpies of adsorption from -26 to -22 kJ mol-1. Studies using cell populations of different hydrophobicity showed that the hydrophobic character of the bacterial cells also had an effect on the adsorption of the vesicles to the biofilm.

Effect of pH changes in cerebrospinal fluid specimens on bacterial survival and antigen test results.

AIMS: To determine the effect of pH changes occurring in cerebrospinal fluid (CSF) after sampling on the viability of meningitis causing bacteria, and on the performance of agglutination assays used for the rapid detection of bacterial antigens. METHODS: The pH of CSF collected via lumbar puncture was measured by various methods, and the effects of the following different incubation conditions on subsequent changes were determined: air at 4 degrees C; air at room temperature (22 degrees C); air at 37 degrees C; and air with 5% CO2 at 37 degrees C. The growth/survival in pooled CSF of 15 bacterial isolates collected from 74 patients with meningitis was assessed in these incubation conditions over 24 hours. The effects of pH changes in the CSF on the sensitivity of two latex agglutination and one co-agglutination kits for detecting Haemophilus influenzae, Neisseria meningitidis groups B and C, and Streptococcus pneumoniae were determined. RESULTS: The measured pH of CSF was highly affected by the method used and particularly the time delay between patient sampling and assay. Measured pH values at the time of sampling (mean 7.5) increased rapidly within 60 seconds by about one unit. CSF pH continued to increase during incubation in all tested conditions (up to approximately pH 10), with the exception of in air with 5% CO2 at 37 degrees C where pH changes were reversible and near physiological values were attained. Bacterial survival for all species tested was poorest in CSF incubated in air at 37 degrees C and best following exposure to air with 5% CO2 at 37 degrees C. Agglutination in rapid antigen detection kits with CSF incubated in air as opposed to air with 5% CO2 generally took longer to occur and in some instances was less prominent. In one case a false negative result was obtained with CSF seeded with N meningitidis group B incubated in the former but not the latter conditions. CONCLUSIONS: CSF pH increases after patient sampling are minimised and/or mostly reversed by incubation in an atmosphere containing 5% CO2. CSF samples should ideally be placed in such an atmosphere as soon as possible after collection, and left there until laboratory processing occurs, to reduce the detrimental effects of pH stress on bacterial survival. pH increases may also reduce the likelihood of obtaining a positive result in rapid antigen detection assays.

Financial burden of hospital-acquired Clostridium difficile infection.

Clostridium difficile infection has become endemic in many hospitals and yet few data on the associated costs of such cases are available. We prospectively followed 50 consecutive cases of C. difficile infection and 92 control patients, who were admitted to the same geriatric wards within 72 h of the cases. Cases and controls had similar age, sex and major diagnosis distributions. Cases stayed significantly longer (mean 21.3 days, median 20.5 days; P < 0.001) in hospital than controls, including an average 14 days in a side room. Diarrhoea developed in cases on average 10.8 days after admission, which, when compared with a mean duration of stay for controls of 25.2 days, implies that C. difficile infection caused an increased duration of stay, as opposed to infection occurring because of longer residence. There was a significantly higher death rate in cases compared with controls (P < 0.01). Antibiotic treatment of C. difficile infection cost an average of Pounds 47 per case. The average number of laboratory investigations per day was similar for cases and controls, but the increased length of stay meant an extra cost for tests of approximately Pounds 210 per case. Assuming hotel costs of Pounds 150 (Pounds 200) per day stay (in a side room), 94% of the additional costs associated with C. difficile infection were due to increased duration of stay (Pounds 3850). The total identifiable increased cost of C. difficile infection was, therefore, in excess of Pounds 4000 per case. Such high costs can be used to justify expenditure on personnel and/or other control measures to reduce the incidence of this hospital-acquired infection.

Stomatococcus mucilaginosus lower respiratory tract infection in a patient with AIDS.

We describe a case of recurrent Stomatococcus mucilaginosus lower respiratory tract infection in a patient with AIDS. Apart from S. mucilaginosus no other pathogens were found to account for infection. There was a rapid response to rifampicin, the organism being resistant to penicillin, co-trimoxazole and ciprofloxacin. Infections caused by this organism are increasingly described, but there are few reports of lower respiratory tract infection.