Despite the recent onset of the SARS epidemic, genetic signatures are emerging that partition the worldwide SARS viral isolates into groups on the basis of contact source history and geography. These signatures can be used to trace sources of infection. In addition, a common variant associated with a non-conservative aminoacid change in the S1 region of the spike protein, suggests that immunological pressures might be starting to influence the evolution of the SARS virus in human populations.

Infection with hepatitis B virus (HBV) remains a difficult worldwide challenge to public health. The World Health Organization estimates that more than one-third of the world's population has been infected with HBV (25). Epidemiological trends suggest there are currently 400 million HBV chronic carriers worldwide, with over 1 million deaths annually due to HBV-associated liver disease (13,23). HBV is the leading cause of cirrhosis and hepatocellular carcinoma globally (25; Centers for Disease Control and Prevention hepatitis fact sheet [www.cdc.gov/hepatitis]). The development and utilization of molecular diagnostic assays for the detection and quantification of HBV genomes have provided insight into the natural history of HBV and the pathogenesis of HBV infection as well as facilitated the monitoring of viral response to treatment (15,17). In addition, a quantitative evaluation of HBV DNA concentrations can provide valuable information on the levels of viral replication and may be useful as a prognostic indicator of liver disease (4, 21). A number of commercial assays are currently available for the quantification of HBV DNA in patient serum or EDTA-plasma, including hybridization-, signal-, and target-amplification-based technologies (5,11,(16)(17)(18)22). Selection of the optimal assay is dependent on the intrinsic performance characteristics of the methodology as well as the necessity to make appropriate clinical decisions in the context of HBV-associated disease (4, 15, 21).The VERSANT HBV 3.0 Assay (referred to herein as VER-SANT 3.0) is a third-generation branched-DNA (bDNA) assay for the direct quantification of HBV DNA in human serum and plasma. After HBV genomic DNA is released from the virions, the viral DNA is captured by a set of specific, synthetic oligonucleotide capture probes fixed in a microtiter well. A set of target probes (or label extender probes) then hybridizes to both the captured viral DNA and unique preamplifier probes. The capture probes and the target probes bind to conserved DNA regions throughout the entire HBV genome. The amplifier probes subsequently hybridize to the preamplifier probes, forming a bDNA complex. Multiple copies of an alkaline phosphatase-labeled probe are then hybridized to this immobilized complex. Detection is achieved by incubating the alkaline phosphatase-bound complex with a chemiluminescent substrate. The intensity of light emission is directly related to the amount of HBV DNA present in each sample, and results are recorded as relative light units by the luminometer. A standard curve is defined by light emission from quantitative standards containing known concentrations of recombinant DNA. Concentrations of HBV DNA in specimens are determined from this standard curve. This third-generation sandwich nucleic acid hybridization procedure differs from earlier bDNA assays by using the unique preamplifier probes to increase the number of labeled probes that can bind to the target, thereby

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SummaryOne hundred and seventy-eight samples from 168 individuals were tested for Mycobacterium tuberculosis complex (Mtc) using Amplicor PCR, IS6110-PCR (in-house), acid fast (AF)-staining and culture. Thirty-one samples were positive by culture, but 37 samples were later resolved to be truly positive for Mtc. Of these, Amplicor detected 32 (86.5%), IS6110-PCR detected 31 (83.6%), and AF-staining 21 (56.8%). None of the 141 Mtc-negative samples was positive by these tests, thus giving 100% specificity. Although the IS6110-PCR was more sensitive than Amplicor in detecting spiked Mtc DNA, it was not more sensitive than the latter in detecting Mtc in clinical samples. Reasons likely to account for the PCR false negativity were (i) sample inoculum size, (ii) nonuniform samples due to clumping effect of Mtc and (iii) the absence of target gene sequences for IS6110-PCR. Culture negativity, on the other hand, was likely to be associated with nonviable Mtc. Amplicor PCR is promising for direct detection of Mtc. The IS6110-PCR, however, may not be as suitable because of possible existence of IS6110-deleted Mtc strain in Singapore.

We describe a patient with severe acute respiratory syndrome (SARS) whose clinical symptoms were masked by Escherichia coli bacteremia. SARS developed in a cluster of healthcare workers who had contact with this patient. SARS was diagnosed when a chest infiltrate developed and when the patient’s brother was hospitalized with acute respiratory failure. We highlight problems in atypical cases and offer infection control suggestions.