Importance of the cutoff ratio for detecting antibodies against hepatitis A virus in oral fluids by enzyme immunoassay

From a recombinant key antigen to an accurate, affordable serological test: lessons learnt from COVID-19 for future pandemics

Serological tests detect antibodies generated by infection or vaccination, and are indispensable tools along different phases of a pandemic, from early monitoring of pathogen spread up to seroepidemiological studies supporting immunization policies. This work discusses the development of an accurate and affordable COVID-19 antibody test, from production of a recombinant protein antigen up to test validation and economic analysis. We first developed a cost-effective, scalable technology to produce SARS-COV-2 spike protein and then used this antigen to develop an enzyme-linked immunosorbent assay (ELISA). A receiver operator characteristic (ROC) analysis allowed optimizing the cut-off and confirmed the high accuracy of the test: 98.6% specificity and 95% sensitivity for 11+ days after symptoms onset. We further showed that dried blood spots collected by finger pricking on simple test strips could replace conventional plasma/serum samples. A cost estimate was performed and revealed a final retail price in the range of one US dollar, reflecting the low cost of the ELISA test platform and the elimination of the need for venous blood sampling and refrigerated sample handling in clinical laboratories. The presented workflow can be completed in 4 months from first antigen expression to final test validation. It can be applied to other pathogens and in future pandemics, facilitating reliable and affordable seroepidemiological surveillance also in remote areas and in low-income countries.

Oral fluid testing facilitates understanding of hepatitis A virus household transmission

The public health response to sporadic hepatitis A virus (HAV) infection, hepatitis A, can be complex especially when the index case is a child and no obvious source is identified. Identifying an infection source may avoid mass immunisation within schools when transmission is found to have occurred within the household. Screening of asymptomatic contacts via venepuncture can be challenging and unacceptable, as a result non-invasive methods may facilitate public health intervention. Enzyme-linked immunoassays were developed to detect HAV immunoglobulin M (IgM) and immunoglobulin G (IgG) in oral fluid (ORF). A validation panel of ORF samples from 30 confirmed acute HAV infections were all reactive for HAV IgM and IgG when tested. A panel of 40 ORF samples from persons known to have been uninfected were all unreactive. Two hundred and eighty household contacts of 72 index cases were screened by ORF to identify HAV transmission within the family and factors associated with household transmission. Almost half of households (35/72) revealed evidence of recent infection, which was significantly associated with the presence of children ⩽11 years of age (odds ratio 9.84, 95% confidence interval: 2.74-35.37). These HAV IgM and IgG immunoassays are easy to perform, rapid and sensitive and have been integrated into national guidance on the management of hepatitis A cases.

Utility of oral fluid samples for hepatitis B antibody detection in real life conditions

BACKGROUND

Hepatitis B virus (HBV) testing in oral fluid samples may provide advantages in diagnosis, screening or prevalence studies, especially among individuals with venous access difficulties. This study aims to optimize one commercially available assay for detecting total anti-HBc marker in oral fluid samples and to evaluate its utility under real life conditions in different settings for the purposes of prevalence and diagnostic studies.

METHODS

Oral fluid was collected using a Salivette device and some parameters were initially evaluated: type of elution buffer and sample volume. Thereafter, the utility of oral fluid samples for detection of anti-HBc was evaluated in real life conditions in which, 1296 individuals gave serum and oral fluid samples. All serum samples were submitted to commercial EIAs to detect total anti-HBc, according to the manufacturer's instructions and oral fluid samples according to previous optimization.

RESULTS

In optimization evaluation, PBS/BSA 0.5% and 100 μL of oral fluid (volume was two-fold increased compared to serum in EIA) were chosen as transport buffer and sample volume. In the field study, anti-HBc was detected in 211 out of 1296 serum samples giving overall oral fluid sensitivity of 52.6% and specificity of 96%. Concordance was higher in ambulatory setting (67.7) compared to general population (31.8). Mean ± standard deviation values of optical density/cutoff (OD/CO) in serum samples were higher in false-negative oral fluid samples than those seen in true positive samples. Sensitivity was higher in those presenting active infection compared to anti-HBc isolate and past infection. Sensitivity also increased in the ambulatory group when HCV individuals were excluded.

CONCLUSIONS

It was possible to optimize a commercial EIA for detecting anti-HBc in oral fluid samples and where the highest concordance was found in ambulatory settings and among individuals with active infection.

A Cross-Sectional Study of Viral Hepatitis Perception among Residents from Southeast and North Regions of Brazil

Few data are available regarding viral hepatitis perception among the general global population. The present study aims to estimate the perception of viral hepatitis in a cohort of individuals living in two geographical regions of Brazil: North (Manaus city (MA)) and Southeast (Rio de Janeiro city (RJ)). A cross-sectional, descriptive study was carried out among 287 subjects recruited in MA (134) and RJ (153). All individuals answered a questionnaire assessing socio-demographic characteristics and viral hepatitis awareness. Participants’ responses were scored and divided using interquartile values. Associations between socio-demographic characteristics and knowledge were also evaluated. Interquartile analysis scored 0–21 correct answers as “Very Weak”; 22–27 as “Weak”; 28–31 as “Intermediate”; and 32–47 as “Desirable”. Mean ± standard deviations (SD) of correct responses were weak in both MA (24.1 ± 7.0) and RJ (26.3 ± 7.3). Bivariate analysis showed an association between viral hepatitis awareness and both education level (p < 0.001) and family income (p < 0.01). Desirable scores were more common in female participants (61%), those aged between 21–30 years (40%), those with a secondary education (51.7%), those who received high income (31.6%), and those from RJ (70.0%). Health education campaigns in these cities are recommended to increase knowledge and reduce the transmission of these viruses.

Developing a Salivary Antibody Multiplex Immunoassay to Measure Human Exposure to Environmental Pathogens

The etiology and impacts of human exposure to environmental pathogens are of major concern worldwide and, thus, the ability to assess exposure and infections using cost effective, high-throughput approaches would be indispensable. This manuscript describes the development and analysis of a bead-based multiplex immunoassay capable of measuring the presence of antibodies in human saliva to multiple pathogens simultaneously. Saliva is particularly attractive in this application because it is noninvasive, cheaper and easier to collect than serum. Antigens from environmental pathogens were coupled to carboxylated microspheres (beads) and used to measure antibodies in very small volumes of human saliva samples using a bead-based, solution-phase assay. Beads were coupled with antigens from Campylobacter jejuni, Helicobacter pylori, Toxoplasma gondii, noroviruses (G I.1 and G II.4) and hepatitis A virus. To ensure that the antigens were sufficiently coupled to the beads, coupling was confirmed using species-specific, animal-derived primary capture antibodies, followed by incubation with biotinylated anti-species secondary detection antibodies and streptavidin-R-phycoerythrin reporter (SAPE). As a control to measure non-specific binding, one bead set was treated identically to the others except it was not coupled to any antigen. The antigen-coupled and control beads were then incubated with prospectively-collected human saliva samples, measured on a high throughput analyzer based on the principles of flow cytometry, and the presence of antibodies to each antigen was measured in Median Fluorescence Intensity units (MFI). This multiplex immunoassay has a number of advantages, including more data with less sample; reduced costs and labor; and the ability to customize the assay to many targets of interest. Results indicate that the salivary multiplex immunoassay may be capable of identifying previous exposures and infections, which can be especially useful in surveillance studies involving large human populations.

Longitudinal Study of Hepatitis A Infection by Saliva Sampling: The Kinetics of HAV Markers in Saliva Revealed the Application of Saliva Tests for Hepatitis A Study

Despite the increasing numbers of studies investigating hepatitis A diagnostic through saliva, the frequency and the pattern of hepatitis A virus (HAV) markers in this fluid still remains unknown. To address this issue, we carried on a longitudinal study to examine the kinetics of HAV markers in saliva, in comparison with serum samples. The present study followed-up ten patients with acute hepatitis A infection during 180 days post diagnosis (dpd). Total anti-HAV was detected in paired serum and saliva samples until the end of the follow-up, showing a peak titer at 90th. However, total anti-HAV level was higher in serum than in saliva samples. This HAV marker showed a probability of 100% to be detected in both serum and saliva during 180 dpd. The IgM anti-HAV could be detected in saliva up to 150 dpd, showing the highest frequency at 30th, when it was detected in all individuals. During the first month of HAV infection, this acute HAV marker showed a detection probability of 100% in paired samples. The detection of IgM anti-HAV in saliva was not dependent on its level in serum, HAV-RNA detection and/or viral load, since no association was found between IgM anti-HAV positivity in saliva and any of these parameter (p>0.05). Most of the patients (80%) were found to contain HAV-RNA in saliva, mainly at early acute phase (30th day). However, it was possible to demonstrate the HAV RNA presence in paired samples for more than 90 days, even after seroconversion. No significant relationship was observed between salivary HAV-RNA positivity and serum viral load, demonstrating that serum viral load is not predictive of HAV-RNA detection in saliva. Similar viral load was seen in paired samples (on average 104 copies/mL). These data demonstrate that the best diagnostic coverage can be achieved by salivary anti-HAV antibodies and HAV-RNA tests during 30-90 dpd. The long detection and high probability of specific-HAV antibodies positivity in saliva samples make the assessment of salivary antibodies a useful tool for diagnosis and epidemiological studies. The high frequency of HAV-RNA in saliva and the probability of detection of about 50%, during the first 30 dpd, demonstrate that saliva is also useful for molecular investigation of hepatitis A cases, mainly during the early course of infection. Therefore, the collection of saliva may provide a simple, cheap and non-invasive means of diagnosis, epidemiological surveys and monitoring of hepatitis A infection purposes.

Saliva specimen sampling: a noninvasive method for diagnosis and basic investigation of viral hepatitis A, B and C

Saliva is a biological fluid that is easy to collect and manipulate. Collection of saliva samples is less expensive, noninvasive and painless compared with blood collection. Due to these advantages, saliva has been investigated as an alternative fluid to serum for diagnostic and epidemiological purposes. The aim of this article was to the review research on salivary biomarkers of viral hepatitis A, B and C, highlighting their current use, collection devices, and potential applications for diagnosis and epidemiological studies. This paper also explores recent findings of saliva as a possible source of viral hepatitis transmission.

Importance of collection methods and stability of oral fluid samples for hepatitis B surface antigen detection

BACKGROUND

Oral fluid (OF) sample collection and stability for HBsAg detection are not fully established. This study aims to investigate the applicability of OF collectors and sample stability for Hepatitis B virus surface antigen detection.

METHODS

Paired serum and OF samples were obtained from 191 individuals, and Chembio (Chembio Diagnostic System, USA) and Salivette (Sarstedt, Germany) devices were used for OF collection. Two HBsAg enzyme immunoassays (EIAs) were used (HBsAg One kit, Radim, Rome, Italy and ETI-MAK-4, DiaSorin, Vercelli, Italy) to determine the most efficient method according OF collector. Sample volume, incubation time, and cutoff (CO) value were evaluated. The stability of OF samples was determined under different environmental conditions.

RESULTS

Chembio samples analyzed using DiaSorin EIA without modification of the manufacturer's instructions, demonstrated a sensitivity of 95.24% and a specificity of 100%. Salivette samples analyzed with Radim EIA with receiver operating characteristic (ROC) curve for calculating the CO showed a sensitivity of 78.26% and a specificity of 89.88%. HBsAg was detected in Chembio and Salivette samples under different environmental conditions, but the Chembio samples were the most stable.

CONCLUSIONS

Both collectors can be used for HBsAg detection in OF samples, but some modifications of commercial EIAs should be incorporated for Salivette device. OF samples were reliably stable and could be stored for up to 90 days at 2-8°C.

Dried blood spot samples: optimization of commercial EIAs for hepatitis C antibody detection and stability under different storage conditions

This study was undertaken to optimize and compare the efficiency of two commercial EIAs for anti-HCV detection (HCV Ab Radim, Pomezzia, Italy and ETI-AB-HCVK-4 DiaSorin, Vercelli, Italy), in dried blood spot (DBS) samples. The long-term stability of anti-HCV on DBS samples stored at three environmental conditions was also evaluated at: 2-8 °C, 20-25 °C, and -20 °C. Paired DBS and serum samples were obtained from individuals with or without anti-HCV. The type of elution buffer, sample and conjugate volume, sample incubation time and cut-off values were evaluated. For both EIAs, a larger sample volume was used, and the cut-off value determined by the manufacturer was employed for Radim EIA; however, ROC curve analysis was used for the DiaSorin EIA. The sensitivity and specificity of Radim EIA on DBS were 97.5% and 99.5%, respectively, and of DiaSorin EIA were 88.9% and 98.9%, respectively. Accurate results were obtained for a period of 117 days using DBS samples stored at all storage conditions, but storage at -20 °C resulted in the lowest variation among the absorbance values. Both EIAs demonstrated the same limit of detection (until dilution of 1:10(4) with estimated viral load of 3.1 × 10(-1) UI/ml), but the Radim EIA was associated with the best performance because a low coefficient of variation was observed in the repetition and reproducibility studies. In conclusion, commercial EIAs can be optimized for anti-HCV detection in DBS samples that are extremely stable at different conditions for more than 100 days.

Could oral fluid be used to evaluate anti-hepatitis A virus status in individuals living in difficult-to-access areas?

A strategy adopted by different countries to reduce the number of new cases of hepatitis A is the vaccination. However, the mosaic of the epidemiological profile in developing countries has hampered the establishment of a unified nationwide vaccination program. To determinate national vaccination policies, the results of epidemiological studies need to be carefully considered. For this monitoring, the use of oral fluid is very important due to the painless and non invasive collection characteristics. There are few studies investigating which oral fluid collection device is optimal to detect low antibody levels and its use in selecting individuals for vaccination. So, the present study aimed to evaluate different oral fluid collection devices to detect humoral immune response against hepatitis A virus and its application in epidemiological studies. Therefore, 90 matched serum and oral fluid samples were collected from volunteers with different immune status, under ideal conditions of collection (optimization panel); and 224 matched samples in difficult-to-access areas (epidemiological study). Serum was collected by venipuncture and the oral fluid was obtained using three commercial devices: Salivette(®), OraSure(®) and ChemBio(®). Serum and oral fluid were submitted to a commercial immunoblot to detect total anti-HAV antibodies. The optimization panel demonstrated that ChemBio(®) device had the best performance (100% agreement), followed by OraSure(®) (95.4%) and Salivette(®) (90.8%). The optimal collection device (ChemBio(®)), tested in a difficult-to-access area and evaluated under precarious conditions of collection, showed similar prevalence of total anti-HAV between serum and oral fluid, 80.8% and 79%, respectively. A follow-up was performed to evaluate the stability of oral fluid and it was observed that 210 days after the collection it was possible to detect anti-HAV antibodies. Oral fluid can be used to detect low levels of specific-antibody, being important to select age groups to be vaccinated. Therewith, the choice of proper collection device is essential to evaluate HAV antibodies in the epidemiological scenario.

An evaluation of different saliva collection methods for detection of antibodies against hepatitis C virus (anti-HCV)

BACKGROUND

Saliva samples can be used as an alternative fluid for against hepatitis C virus (anti-HCV) detection owing to the ease of collection and excellent acceptability. This study was conducted to optimize a commercial enzyme immunoassay (EIA) to detect anti-HCV in saliva samples.

METHODS

Ninety-six individuals donated paired serum and saliva samples that were obtained, using a commercial device (Salivette) and spitting into a sterile container. Initially, elution buffer for the Salivette samples, sample volume, incubation time and temperature, and two different anti-HCV EIAs were evaluated. Using the optimized assay, three methods for cut-off calculation were also evaluated.

RESULTS

A 20-fold increase in the sample volume for both collection methods was needed. Moreover, the Radim assay was the most appropriate assay for anti-HCV detection in saliva samples, and the quality parameters were increased when a ROC curve was used to determine the cut-off value. Using this optimized assay, the sensitivities, specificities, accuracies, positive and negative predictive values were above 90% for saliva obtained using both the Salivette and spitting methods. Using this assay, discordant false-negative results were obtained for only two Salivette samples and five spitting samples. The concordance kappa was 93% for the Salivette method and 86.1% for the spitting method, demonstrating excellent performance.

CONCLUSIONS

Saliva samples obtained for both methods can be employed for anti-HCV detection among HCV-infected or HCV-suspected cases, but several modifications must be performed on commercial EIAs to obtain good results. Moreover, samples obtained with commercial devices are more appropriate for anti-HCV detection in saliva samples.

Laboratory diagnosis of hepatitis A

The diagnostic gold standard for hepatitis A is the detection of anti-hepatitis A virus (HAV) IgM antibodies and the determination of total anti-HAV by enzyme immunoassay. However, detection of HAV RNA can be useful in the diagnosis of patients without specific antibodies for hepatitis A and for the monitoring of infection. Studies using real-time PCR have demonstrated that HAV RNA can be detected not only in feces, but also in serum and saliva samples earlier than detection of antibodies, and that viremia may be present for a much longer period than the convalescent phase of hepatitis A. Alternative samples have been proposed for diagnosis, epidemiological studies, investigation of outbreaks and selection of persons receptive to vaccination. Understanding the events of clinical course that take place during the hepatitis A infection may lead to more effective diagnosis.

Oral fluid and hepatitis A, B and C: a literature review

BACKGROUND AND AIMS

Viral hepatitis is a significant global health problem that, depending upon the virus, affects individuals of the developing and/or developed world. In recent years, there has been renewed interest in whether oral fluids can be considered as a source of viral hepatitis transmission and whether oral fluid, in particular, whole saliva, may be a useful source for viral detection as part of the diagnosis and monitoring of viral hepatitis. The aim of this article was to review current data concerning the possible carriage of the hepatitis A, B and C viruses within saliva and gingival crevicular fluid. Such knowledge will indicate if (i) oral fluid is a possible source of infection and (ii) whether oral fluid can be used for diagnosis and monitoring of viral hepatitis.

DATA AND SOURCES

A literature search was conducted using PubMed (Medline), EMBASE/Excerpta medica, the Cochrane database and Scopus. The results were limited to published material after 2000. Relevant material was evaluated and reviewed.

CONCLUSION

There is some evidence that hepatitis viruses A, B and C are present in oral fluids, particularly whole saliva and gingival crevicular fluid and may thus be possible sources of viral detection in clinical diagnosis and monitoring. However, the data are inconsistent and warrant the need for well-planned longitudinal studies to explore the precise frequency of oral carriage of such viruses and to determine the virological and host factors that may influence the oral presence of hepatitis A, B and C viruses.