Comparison of three commercial assays for the quantification of HIV-1 RNA in plasma from individuals infected with different HIV-1 subtypes.

BACKGROUND: Commercial human immunodeficiency virus 1 (HIV-1) ribonucleic acid (RNA) quantification assays vary in their ability to quantify different subtypes of HIV-1, a problem in regions where multipte HIV-1 subtypes may be circulating. OBJECTIVES: To assess commercial HIV-1 RNA quantification assays on two plasma panels. Panel 1 consisted of HIV-1 seronegative plasma 'spiked' with a known amount of cultured virus of different subtypes, and Panel 2 comprised plasma collected from individuals infected with different HIV-1 subtypes. STUDY DESIGN: The comparison involved the Amplicor HIV-1 reverse transcriptase-polymerase chain reaction (RT-PCR), Quantiplex branched DNA, and NucliSens HIV-1 QT assays. Panel 1 consisted of 11 plasma 'spiked' with cultured viruses of HIV-1 subtypes A-F, and Panel 2 included 33 plasma samples from 16 patients infected with subtypes A, B, C, E and G. RESULTS: In Panel 1, the Quantiplex branched deoxyribonucleic acid (bDNA) assay quantified subtypes A-F efficiently, comparable to published results from two other laboratories. The Amplicor RT-PCR assay quantified subtypes B, C, and D but was relatively less efficient with subtypes E, F, and did not or poorly quantified subtype A. Testing of Panel 2 showed some inter-assay differences. In contrast to Panel 1, the Amplicor RT-PCR assay performed variably with subtype A when compared with the Quantiplex bDNA and NucliSens QT assays, and higher viral load levels were generated with subtype E using the Amplicor RT-PCR assay. Subtypes B and C showed some inter-patient differences but the Quantiplex bDNA generally gave a lower quantification than the Amplicor RT-PCR and NucliSens QT assays. CONCLUSIONS: These studies confirm that commercial HIV-1 load assays vary in their ability to quantify different HIV-1 subtypes. This may be more apparent with individual patient samples than with 'spiked' panels. This variability emphasizes that it is preferable for patient samples to be tested with the same assay, and care should be taken where infection with unusual subtypes is suspected.

Effect of implant number on transverse bending moments during simulated unilateral loading of mandibular fixed-detachable prostheses.

High bending moments acting on osseointegrated implants due to transverse forces are believed to be potential contributors to mechanical implant failure. Theoretically, the rigidity of a system comprised of five implants would seem to counter these moments more effectively than one with only three implants. To study this, we built an experimental model comprised of five Brånemark implants embedded in an acrylic mandibular edentulous arch and connected by a metal framework. This lower prosthesis was mounted with an opposing maxillary complete denture in nonbalanced lingualized occlusion on a semiadjustable articulator. Eccentric static bites were simulated by fixing the dentures at 1.5 mm left and right working side (WS) and balancing side (BS) positions, respectively, and loading the upper member of the articulator with 50 N. The distal right implant abutment was transformed into a loadcell by bonding four strain gauges at 90 degrees intervals across its surface. Three 10-second static load ramps were carried out for each of 4 experiments: (1) WS loadcell with five implants, (2) BS loadcell with five implants, (3) WS loadcell with three implants, and (4) BS loadcell with three implants. Transverse bending moments were found to be significantly higher on the WS for the three-implant prosthesis as compared to the five-implant design (1.469 Ncm for five implants vs 2.151 Ncm for three implants; p = 0.001, Student's t-test). This difference was insignificant on the BS (0.532 Ncm for five implants vs 0.521 Ncm for three implants; p = 0.34). These results suggest that a higher number of mandibular implants may decrease the bending moments affecting mandibular fixed-detachable prostheses during unilateral biting tasks.

Unlinked anonymous screening of antenatal patients for antibody to human immunodeficiency virus type 1 (HIV-1).

OBJECTIVES: To determine the prevalence of HIV-1 infection in the general community by using a target population (antenatal patients) as an indicator of infection, to monitor any change in the prevalence of HIV infection in this population and provide baseline information on heterosexual spread of HIV infection into this low prevalence population. PATIENTS AND DESIGN: Between January 1989 and January 1992, 4537 unlinked anonymous antenatal sera were tested in two study groups at Westmead Hospital. Repeatedly reactive sera were confirmed by western blot and other supplementary assays as appropriate. RESULTS: No significant change in the seroprevalence of HIV-1 infection was detected between the two study periods. Of the 2208 sera tested in 1989-1990, one (0.05%) was confirmed as positive and one (0.05%) gave a non-specific reaction by enzyme immunoassay (EIA). Of the 2329 sera tested in 1991-1992, there was one (0.04%) HIV-1 antibody positive serum, and two gave non-specific EIA reactions. These results were compared with three other sample populations tested at Westmead Hospital during the same period: linked antenatal patients, antenatal methadone clinic attendees and all women tested. CONCLUSIONS: Periodic anonymous testing of a sample antenatal population (combined with screening of high risk patients) is useful for monitoring the prevalence of HIV infection in these populations and estimating any future need for generalised screening.

Identification of infection of an Australian resident with the human immunodeficiency virus type 2 (HIV-2).

OBJECTIVE: To present the first confirmed case of human immunodeficiency virus infection type 2 (HIV-2) in an Australian resident. CLINICAL FEATURES: HIV-2 infection in a west African man resident in Sydney was diagnosed in 1992 at Westmead Hospital, Sydney, by serological testing. He was asymptomatic and the blood CD4 T-lymphocyte concentration was not significantly reduced. Infection was probably acquired before migration to Australia. The patient was initially tested for HIV-1 antibody as part of an application for permanent residency. He was in no obvious risk group or transmission category. His serum was repeatedly positive by Genetic Systems enzyme immunoassay (EIA) and borderline by Abbott EIA, was reactive to the HIV-2 peptide on a synthetic envelope peptide assay, and was strongly reactive to all HIV-2 specific viral protein bands on an HIV-2 western blot test. HIV-2 was isolated by co-cultivation of the patient's peripheral blood mononuclear cells and identified by hybridisation using HIV-2 specific oligonucleotide probes, with further confirmation by polymerase chain reaction. INTERVENTION AND OUTCOME: The patient was counselled regarding the clinical course and prognosis of HIV-2 infection, the possible indications for zidovudine therapy, modes of transmission of the virus and safer sex precautions. CONCLUSIONS: This is the first documented case of HIV-2 infection diagnosed in Australia and raises the possibility of other undetected cases. The cost effectiveness of general testing for HIV-2 needs to be assessed and formal epidemiological sentinel programs should be established to monitor specific Australian populations.

Isolation of dengue viruses by intracerebral inoculation of mosquito larvae.

The isolation of dengue viruses from clinical specimens has always posed a particularly difficult problem. The use of invertebrate cell cultures such as AP-61 and C6/36 has reduced the time required for definitive diagnosis to within a week. More recently, inoculation of adult mosquitoes has been used but it requires more than a week to reach a confirmed laboratory diagnosis. We describe a method using intracerebral inoculation of immobilized fourth instar of Toxorhynchites splendens larvae for the isolation of dengue viruses from clinical specimens which yields results within a few days following incubation at 32 degrees C.