We evaluated a two-step algorithm for detecting toxigenic Clostridium difficile: an enzyme immunoassay for glutamate dehydrogenase antigen (Ag-EIA) and then, for antigen-positive specimens, a concurrent cell culture cytotoxicity neutralization assay (CCNA). Antigen-negative results were >99% predictive of CCNA negativity. Because the Ag-EIA reduced cell culture workload by Ϸ75 to 80% and two-step testing was complete in <3 days, we decided that this algorithm would be effective. Over 6 months, our laboratories' expenses were US$143,000 less than if CCNA alone had been performed on all 5,887 specimens.Clostridium difficile-associated diarrhea is an important illness among patients who are extensively treated with antibacterial or other chemotherapeutic agents (4,7,19). While definitive evidence of toxigenic C. difficile comes from microbiologic testing, laboratories are challenged to provide accurate results rapidly and cost-effectively (23). Cell culture assays for cytotoxin (toxin B) are considered the gold standard but require up to 4 days for results, expensive cells and media, and labor-intensive expertise (4,17,19).Consequently, many laboratories use immunoassays for C. difficile toxins, or "common" glutamate dehydrogenase antigen (2,6,13,16,19,21,23,24). Toxin enzyme immunoassays (EIAs) are frequently used as stand-alone assays but clinical sensitivity may be suboptimal, particularly if only toxin A is detected (4,6,8,9,12,19). Current antigen EIAs (Ag-EIAs) accurately detect an essential and constitutively synthesized enzyme (23), thereby rapidly identifying C. difficile while overcoming the low sensitivity of toxin EIAs and suboptimal performance of older, latex-agglutination antigen assays. Because Ag-EIAs detect nontoxigenic as well as toxigenic C. difficile, however, they must be used in combination with a toxin-detecting assay to provide specific laboratory evidence of C. difficile-associated diarrhea (2,3,10,11,16,19,(21)(22)(23)(24).Both of our institutions' C. difficile-testing laboratories had adopted a stand-alone EIA approach for detecting toxins A and B, using C. DIFFICILE TOX A/B II (ToxAB-EIA; TechLab, Blacksburg, Va.; distributed by Wampole Laboratories, Princeton, N.J.). These laboratories are in acute-care hospitals: one in the 900-bed Johns Hopkins Hospital (JHH), which also serves the 190-bed acute-care Howard County General Hospital in Columbia, Md.; the other is at the 350-bed Johns Hopkins Bayview Medical Center (JHBMC) and serves the 220-bed Johns Hopkins Care Center, a colocated facility for subacute and long-term care. During late 2003, it became apparent that the sensitivity of the ToxAB-EIA was unacceptably low at JHH (see below for analogous JHBMC data from 2004). After determining that the performance of similar assays was inadequate (unpublished data; e.g., 71% sensitivity, 73% specificity, and 25% negative predictive value for Premier C. difficile Toxin AϩB [Meridian Diagnostics, Cincinnati, Ohio] versus cytotoxin testing for 63 specimens), we decided to develop an alternati...

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River plumes often feature turbulent processes in the frontal zone and interfacial region at base of the plume, which ultimately impact spreading and mixing rates with the ambient coastal ocean. The degree to which these processes govern overall plume mixing is yet to be quantified with microstructure observations. A field campaign was conducted in a river plume in the northeast Gulf of Mexico in December 2013, in order to assess mixing processes that could potentially impact transport and dispersion of surface material near coastal regions. Current velocity, density, and Turbulent Kinetic Energy Values, ε, were obtained using an Acoustic Doppler Current Profiler (ADCP), a Conductivity Temperature Depth (CTD) profiler, a Vertical Microstructure Profiler (VMP), and two Acoustic Doppler Velocimeters (ADVs). The frontal region contained ε values on the order of 10−5 m2 s−3, which were markedly larger than in the ambient water beneath (O 10−9 m2 s−3). An energetic wake of moderate ε values (O 10−6 m2 s−3) was observed trailing the frontal edge. The interfacial region of an interior section of the plume featured opposing horizontal velocities and a ε value on the order of 10−6 m2 s−3. A simplified mixing budget was used under significant assumptions to compare contributions from wind, tides, and frontal regions of the plume. The results from this order of magnitude analysis indicated that frontal processes (59%) dominated in overall mixing. This emphasizes the importance of adequate parameterization of river plume frontal processes in coastal predictive models.

Unprecedented quantities of heat are entering the Pacific sector of the Arctic Ocean through Bering Strait, particularly during summer months. Though some heat is lost to the atmosphere during autumn cooling, a significant fraction of the incoming warm, salty water subducts (dives beneath) below a cooler fresher layer of near-surface water, subsequently extending hundreds of kilometers into the Beaufort Gyre. Upward turbulent mixing of these sub-surface pockets of heat is likely accelerating sea ice melt in the region. This Pacific-origin water brings both heat and unique biogeochemical properties, contributing to a changing Arctic ecosystem. However, our ability to understand or forecast the role of this incoming water mass has been hampered by lack of understanding of the physical processes controlling subduction and evolution of this this warm water. Crucially, the processes seen here occur at small horizontal scales not resolved by regional forecast models or climate simulations; new parameterizations must be developed that accurately represent the physics. Here we present novel high resolution observations showing the detailed process of subduction and initial evolution of warm Pacific-origin water in the southern Beaufort Gyre.