Assessment of immunometric parameters in malaria: role of enzyme immunoassay

Human blood samples collected from local malaria clinics, hospitals, and by cross-sectional surveys in malaria endemic areas were tested by enzyme immunoassay for circulating malarial antigen, antimalarial antibody, and antigen-specific circulating immune complexes. The assays were done in serum and finger-prick blood absorbed on filter paper. The results obtained from the present study suggest their roles as effective immunometric indicators.     

Evaluation of a commercial enzyme immunoassay for HIV screening in urine

A cross-sectional study was conducted to evaluate the utility of a commercial enzyme immunoassay (EIA) as a screening test for detecting HIV-1 antibody in urine in a population at risk for HIV infection in Catalonia, Spain. Paired urine and serum samples were collected consecutively from 99 patients who attended two drug-dependency treatment centres and 151 patients who attended a sexually transmitted diseases (STD) clinic in Barcelona. Antibodies against HIV in urine samples were detected using the Calypte HIV-1 Urine EIA (Calypte Biomedical Corporation, Berkeley, CA, USA) and confirmed by urine-based Western blot (WB) analysis. Sera were analysed using Bioelisa HIV-1+2 EIA (Biokit Laboratories, Barcelona, Spain), and the results were verified using serum-based WB analysis. Results of both urine and serum testing were available for 246 of 250 participants. For 52 individuals the results of both urine and serum testing were positive and for five the results were discordant (2 with urine-negative/serum-positive results and 3 with urine-positive/serum-negative results). The respective sensitivity and specificity values obtained for the urine EIA were 100% and 96.2% for intravenous drug users (IDUs) and 80% and 99.3% for persons attending the STD clinic. According to the 1997 UNAIDS/WHO strategy I recommendations, these values are acceptable for surveillance purposes, particularly in populations with a high prevalence of HIV infection.     

HIV抗体酶联免疫诊断试剂检测不同基因型抗体的研究

目的 分析不同HIV抗体酶联免疫诊断试剂对检测HIV不同基因型抗体的情况。方法 对不同地区的20份HIV抗体阳性样品中HIV核酸进行扩增，对PCR产物进行测序并进行基因型别分析。用不同试剂对系列稀释的不同基因型样品进行检测。结果 20份样品均为HIV RNA阳性，其中9份样品为HIV B亚型，9份样品为：HIV C或BC重组，2份为HIVAE重组。不同试剂对HIV不同基因型抗体的检测灵敏度无明显差异。结论 我国主要的商业化HIV抗体诊断试剂产品检测不同基因型抗体的能力无明显差异。     

Identifying recent HIV infections using the avidity index and an automated enzyme immunoassay

We evaluated a procedure for identifying recent HIV infections, using sequential serum samples from 47 HIV-positive persons for whom the seroconversion date could be accurately estimated. Each serum sample was divided into two aliquots: one diluted with phosphate-buffered saline and the other diluted with 1 M guanidine. We assayed the aliquots with the automated AxSYM HIV1/2gO test (Abbott Diagnostics Division), without modifying the manufacturer's protocol. We then calculated the avidity index (AI): the ratio of the sample/cutoff value for the guanidine aliquot to that of the phosphate-buffered saline aliquot. We analyzed 216 serum samples: 34 samples were collected within 6 months of seroconversion (recent seroconversions), and 182 were collected after 6 months. The mean AIs, by time from seroconversion, were 0.68 +/- 0.16 (within 6 months) and 0.98 +/- 0.10 (after 6 months) (P < 0.0001). AI of <0.90 correctly identified 88.2% of recent infections but misclassified as recent infections 13.2% of serum samples collected afterward. The probability of an infection being classified as recent and having AI of > or = 0.90 would be 0.7% in a population with 5% recent infections. AI can identify with a certain degree of accuracy recent HIV infections, and being a quantitative index, it provides different levels of sensitivity and specificity, depending on the selected cutoff value. The standard assay procedure is not modified. This test is simple and inexpensive and could be used for surveillance, decision-making in treatment, and prevention.     

Economic comparison of enzyme immunoassay and virus isolation procedures for surveillance of arboviruses in mosquito populations.

Cost-effectiveness analysis of an enzyme immunoassay (EIA) for the surveillance of arboviruses was conducted. The EIA was compared with conventional virus isolation and serologic identification procedures (virus isolation procedures; VIP). Under most circumstances, EIA was more cost-effective than VIP. Costs for processing mosquito pools by VIP increased with the number of viruses included in the surveillance program and with the prevalence rate of each virus. In contrast to VIP, the prevalence rate did not affect costs for processing pools by EIA. In general, EIA was the most cost-effective procedure, followed by cell culture and mouse bioassays. In a 5-year cost-effectiveness analysis of a model surveillance program in which EIA and cell culture bioassays were used, the EIA again proved to be the most cost-effective assay procedure under most circumstances.     

HIV surveillance: a global perspective

This article provides an overview of recommendations for HIV surveillance. Results of surveillance are used in practice to inform program decisions, judge the effectiveness of the national response, lobby for effective programs, and to provide accurate measures of trends and the absolute state of the epidemic. Recommended surveillance activities differ for different epidemic situations-epidemics that are concentrated in defined groups with high-risk behavior, and epidemics that are well established among heterosexuals in the population at large. Surveillance systems in countries with different levels of the epidemic face major challenges, most of which revolve around identifying and obtaining information from representative samples of the at-risk populations. A brief examination of surveillance systems in Botswana and Vietnam illustrate how these challenges are being met in practice. While there is room for improvement, HIV surveillance systems in many developing countries are relatively robust, and are growing stronger all the time. In most countries, however, insufficient use is made of the information generated by these systems in terms of strengthening HIV prevention and care programs.     

HIV/AIDS surveillance in Denmark: the challenges ahead

In Denmark, AIDS has been a mandatory reportable disease since 1983, and confirmed HIV infection has been the same since August 1990. The annual AIDS incidence increased initially and peaked in 1993 (4.6 per 100,000 inhabitants), then decreased to 1.2 per 100,000 inhabitants in 1998 and further to 0.9 in 2000. Most AIDS cases occur among men who have sex with men (MSM), representing 92% in 1980-1985 and 31% in 2000. Recently, AIDS incidence and mortality has decreased due to the new antiretroviral drugs. In 1995, 43 per million inhabitants died of AIDS, compared with 5 per million in 1998. HIV reporting in Denmark is anonymous. The annual number of new identified cases has been fairly stable at approximately 5.7 per 100,000 inhabitants. Immigrants represent 24% of identified HIV-infected persons and represent nearly 50% of all heterosexually acquired cases. Estimates show that HIV prevalence as of 2000 is 0.1% of the total population, distributed at 0.03% among heterosexuals and 4.8% among MSM. Estimated annual HIV incidence is around 5.6 per 100,000 inhabitants; three times higher among men than women, and as high as 220 per 100,000 among MSM. The spread of HIV is limited in Denmark but the prevalence is increasing due to the effect of antiretroviral therapy. This is a challenge to the existing HIV/AIDS surveillance and prevention strategy.     

Homogeneous enzyme immunoassay of acetaminophen in serum

A new commercially available homogeneous enzyme immunoassay, using the glucose-6-phosphate dehydrogenase (G6PDH) catalyzed conversion of NAD to NADH, has been evaluated and applied to the determination of acetaminophen in serum. Replicate analysis of serum control samples over the range of 10-200 micrograms/mL demonstrated a within-assay coefficient of variation of less than or equal to 4.6% and a between-assay coefficient of variation of less than or equal to 5.8%. Regression analysis of two separate groups of 98 and 47 serum samples by this technic, using different reagent lots, and a HPLC reference method gave equations of y = 0.981x - 0.941 (r = 0.984) and y = 1.06x - 2.21 (r = 0.994), respectively. No interference due to hemolysis or turbidity was noted. Evaluation of samples containing 35 commonly prescribed or over the counter medications demonstrated no significant cross-reactivity. Prepared reagents were stable over a period of at least 2 months when stored at 4 degrees C. Correlations between two reagent lots were excellent (r = 0.998). A single sample can be analyzed expeditiously. The result may help evaluate a potential acetaminophen poisoning. Another way to assess this toxicity, calculation of the elimination half-life, has limitations that depend on the precision of the analysis.     

Discriminant analysis of data in enzyme immunoassay

A critical step in the development of both qualitative and quantitative enzyme immunoassays is establishing the positive/negative discrimination, or cut-off, value. Data derived from an indirect immunofluorescence assay, hemagglutination inhibition, and enzyme immunoassay to detect IgG antibodies to measles virus were applied to a discriminant analysis program to determine the positive/negative cut-off value. Application of the discriminant analysis demonstrated a greater utilization of the sensitivity of the enzyme immunoassay than the most commonly used methods. This method also illustrates the importance of examining both antibody positive and negative sera, rather than negative sera alone, in determining the cut-off value. In addition, probability of membership in the antibody positive or negative group is included in the determination. This increases the information base for risk assessment and clinical evaluation.     

Toxocariasis: serological diagnosis by enzyme immunoassay.

An enzyme-immunoassay was developed to measure the concentration of serum antibody specific for the secretory antigens released by migrating toxocaral larvae. This technique was evaluated by testing sera from healthy UK adults, and from patients with and without toxocariasis. In 922 healthy adults, 2.6% were found to have elevated specific antibody levels. Elevated values were observed twice as frequently in males as in females but showed no significant regression with age between 20 and 65 years. Of 62 patients with non-toxocaral helminthic infections, all had antitoxocaral antibody levels within the range of values observed in healthy controls and had a mean level which was not significantly elevated. All of 13 patients with clinical toxocariasis had enzyme-linked immunosorbent assay (ELISA) antibody levels above the 100th percentiles of both the healthy population and the helminth-infected group and had a significantly high mean value (p less than 0.001) more than 12 times that of the healthy or infected controls. The high degree of sensitivity and specificity of the toxocariasis enzyme-immunoassay indicates that this new test should be useful in reference immunodiagnostic applications and in large-scale seroepidemiological surveys.     

Performance characteristics of a new less sensitive HIV-1 enzyme immunoassay for use in estimating HIV seroincidence

Less sensitive (LS) HIV-1 enzyme immunoassays (EIAs) have significantly improved the quantity and quality of HIV surveillance data. The first LS-HIV-1 EIA, the Abbott 3A11-LS, provided reliable incidence data, but the assay required specialized equipment, and the lack of available reagents made testing difficult. This study evaluated the use of an alternate assay, a modified version of the Vironostika HIV-1 EIA (Vironostika-LS), to be used for LS testing. The Vironostika-LS has similar performance characteristics to the Abbott 3A11-LS with additional advantages. This 96-well formatted assay is commonly found in public health laboratories for routine HIV-1 testing and can be used with both serum and dried blood spot specimens. The estimated mean time from seroconversion (defined using a standardized optical density cutoff of 1.0) with the Vironostika-LS was 170 days (95% CI, 145-200 days). When the Vironostika-LS was applied to a matched serum set previously tested with the Abbott 3A11-LS, the Vironostika-LS accurately identified 97% of specimens with recent or long-standing HIV infection. The paper also reports Vironostika-LS quality control guidelines and the results from 3 rounds of proficiency testing.     

Evaluation of infection by Helicobacter pylori in HIV positive patients trough enzyme immunoassay and specific amplification of DNA

The objective of this work was to assess the effectiveness of detection of specific antibodies anti-Helicobacter pylori (H. pylori) by ELISA and amplification of specific DNA by polimerase chain reaction (PCR) as diagnostic methods of infection of H. pylori in HIV positive patients. Twenty two patients with HIV infection were studied, with ages between 26 to 35 years, 17 masculine, 55% with gastrointestinal symptoms, controlled in the Unit of Immunology, CHET. Inclusion approaches: older than 18 years, with confirmed diagnosis of HIV infection (ELISA and WB), lymphocyte subpopulation and good general conditions. Consent in writing was obtained. Exclusion approaches: previous diagnosis of H. pylori infection or treatment with antibiotics in the three previous months to their inclusion. The quantification of IgG anti H. pylori was carried out by Enzyme Immunoassay methods (ELISA). Biopsy of gastric mucosa was obtained by superior endoscopic study. The amplification of DNA for H. pylori was performed by PCR (Wizard SV Genomik and PCR Ready-Promega). In the statistical analysis was used the test of Fisher, with a level of significance of 5% (0.05). In 15 patients of the total group, antibodies anti H. pylori were confirmed, without statistical association with the presence or not of digestives symptoms, neither with the number of lymphocytes CD4 + in peripheral blood. Also 15 patients were positives by PCR for H. pylori DNA, 73.3% of them presented levels of CD4+ above 200 cells. There was not statistical association between the positivity of this method and levels of lymphocytes CD4+. In 12 of the 15 patients with positive results by PCR, antibodies anti H. pylori were evidenced, and among the 7 patients with negative serology to H. pylori, PCR was positive in three of them. In conclusion, serology is an effective method for the diagnose of H. pylori infection in VIH+ patients, but its negativity doesn't discard the infection for this bacillus.     

Histoplasmosis-associated cross-reactivity in the BioRad Platelia Aspergillus enzyme immunoassay

We observed false-positive results in the Platelia Aspergillus enzyme-linked immunoassay (EIA) for specimens from patients with histoplasmosis and mice with experimental infection. Platelia Aspergillus EIA-positive specimens were negative in the second-generation Histoplasma antigen EIA. Care must be taken to exclude histoplasmosis for patients with positive Platelia Aspergillus EIA results.     

HIV/AIDS surveillance in Germany

In Germany, since 1982, information on AIDS cases has been collected at the AIDS Center of the Robert Koch Institute. Since 1987, all laboratories performing HIV confirmatory testing have been required to report positive results anonymously. AIDS incidence peaked at about 2000 cases per year in 1993 and began to decline in 1995 following the widespread use of highly effective antiretroviral treatment. Current data indicate that the AIDS incidence has stabilized at a level of 750 cases per year since 1998. The number of newly diagnosed HIV infections has remained fairly stable at approximately 2000 to 2500 per year since 1993. Unlinked anonymous testing of dried blood spots from newborns is carried out in two federal states. The average prevalence of HIV seropositivity from 1993 to 1997 among women bearing children was 0.57 per 1000 in Berlin and 0.14 per 1000 in Lower Saxony.