Stability of total and rubella-specific IgG in oral fluid samples: the effect of time and temperature

Clinical Assessment of SARS-CoV-2 Antibodies in Oral Fluids Following Infection and Vaccination

BACKGROUND

SARS-CoV-2 variants continue to circulate globally, even within highly vaccinated populations. The first-generation SARS-CoV-2 vaccines elicit neutralizing immunoglobin G (IgG) antibodies that prevent severe COVID-19 but induce only weak antibody responses in mucosal tissues. There is increasing recognition that secretory immunoglobin A (SIgA) antibodies in the upper respiratory tract and oral cavity are critical in interrupting virus shedding, transmission, and progression of disease. To fully understand the immune-related factors that influence SARS-CoV-2 dynamics at the population level, it will be necessary to monitor virus-specific IgG and SIgA in systemic and mucosal compartments.

CONTENT

Oral fluids and saliva, with appropriate standardized collection methods, constitute a readily accessible biospecimen type from which both systemic and mucosal antibodies can be measured. Serum-derived IgG and immunoglobin A (IgA) are found in gingival crevicular fluids and saliva as the result of transudation, while SIgA, which is produced in response to mucosal infection and vaccination, is actively transported across salivary gland epithelia and present in saliva and passive drool. In this mini-review, we summarize the need for the implementation of standards, highly qualified reagents, and best practices to ensure that clinical science is both rigorous and comparable across laboratories and institutions. We discuss the need for a better understanding of sample stability, collection methods, and other factors that affect measurement outcomes and interlaboratory variability.

SUMMARY

The establishment of best practices and clinical laboratory standards for the assessment of SARS-CoV-2 serum and mucosal antibodies in oral fluids is integral to understanding immune-related factors that influence COVID-19 transmission and persistence within populations.

Saliva biomarkers in oral disease

Saliva is a versatile biofluid that contains a wide variety of biomarkers reflecting both physiologic and pathophysiologic states. Saliva collection is noninvasive and highly applicable for tests requiring serial sampling. Furthermore, advances in test accuracy, sensitivity and precision for saliva has improved diagnostic performance as well as the identification of novel markers especially in oral disease processes. These include dental caries, periodontitis, oral squamous cell carcinoma (OSCC) and Sjögren's syndrome (SS). Numerous growth factors, enzymes, interleukins and cytokines have been identified and are the subject of much research investigation. This review highlights current procedures for successful determination of saliva biomarkers including preanalytical factors associated with sampling, storage and pretreatment as well as subsequent analysis. Moreover, it provides an overview of the diagnostic applications of these salivary biomarkers in common oral diseases.

SARS Antibody Testing in Children: Development of Oral Fluid Assays for IgG Measurements

Seroepidemiological studies to monitor antibody kinetics are important for assessing the extent and spread of SARS-CoV-2 in a population. Noninvasive sampling methods are advantageous for reducing the need for venipuncture, which may be a barrier to investigations, particularly in pediatric populations. Oral fluids are obtained by gingiva-crevicular sampling from children and adults and are very well accepted. Enzyme immunoassays (EIAs) based on these samples have acceptable sensitivity and specificity compared to conventional serum-based antibody EIAs and are suitable for population-based surveillance. We describe the development and evaluation of SARS-CoV-2 IgG EIAs using SARS-CoV-2 viral nucleoprotein (NP) and spike (S) proteins in IgG isotype capture format and an indirect receptor-binding-domain (RBD) IgG EIA, intended for use in children as a primary endpoint. All three assays were assessed using a panel of 1,999 paired serum and oral fluids from children and adults participating in school SARS-CoV-2 surveillance studies during and after the first and second pandemic wave in the United Kingdom. The anti-NP IgG capture assay was the best candidate, with an overall sensitivity of 75% (95% confidence interval [CI]: 71 to 79%) and specificity of 99% (95% CI: 78 to 99%) compared with paired serum antibodies. Sensitivity observed in children (80%, 95% CI: 71 to 88%) was higher than that in adults (67%, CI: 60% to 74%). Oral fluid assays (OF) using spike protein and RBD antigens were also 99% specific and achieved reasonable but lower sensitivity in the target population (78%, 95% CI [68% to 86%] and 53%, 95% CI [43% to 64%], respectively). IMPORTANCE We report on the first large-scale assessment of the suitability of oral fluids for detection of SARS-CoV-2 antibody obtained from healthy children attending school. The sample type (gingiva-crevicular fluid, which is a transudate of blood but is not saliva) can be self collected. Although detection of antibodies in oral fluids is less sensitive than that in blood, our study suggests an optimal format for operational use. The laboratory methods we have developed can reliably measure antibodies in children, who are able to take their own samples. Our findings are of immediate practical relevance for use in large-scale seroprevalence studies designed to measure exposure to infection, as they typically require venipuncture. Overall, our data indicate that OF assays based on the detection of SARS-CoV-2 antibodies are a tool suitable for population-based seroepidemiology studies in children and highly acceptable in children and adults, as venipuncture is no longer necessary.

Stabilization of Salivary Biomarkers

The use of saliva as a diagnostic biofluid has been increasing in recent years, thanks to the identification and validation of new biomarkers and improvements in test accuracy, sensitivity, and precision that enable the development of new noninvasive and cost-effective devices. However, the lack of standardized methods for sample collection, treatment, and storage contribute to the overall variability and lack of reproducibility across analytical evaluations. Furthermore, the instability of salivary biomarkers after sample collection hinders their translation into commercially available technologies for noninvasive monitoring of saliva in home settings. The present review aims to highlight the status of research on the challenges of collecting and using diagnostic salivary samples, emphasizing the methodologies used to preserve relevant proteins, hormones, genomic, and transcriptomic biomarkers during sample handling and analysis.

A Multiplex Noninvasive Salivary Antibody Assay for SARS-CoV-2 Infection and Its Application in a Population-Based Survey by Mail

Noninvasive salivary antibody immunoassays can enable low-cost epidemiological surveillance of infections. This study involved developing and validating a multiplex suspension immunoassay on the Luminex platform to measure immunoglobulin G (IgG) responses to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleocapsid and spike (S) proteins, and the spike protein’s S1 and S2 subunits and receptor binding domain. Multiple versions of these recombinant proteins acquired from commercial and noncommercial sources were evaluated. Assay development and validation utilized saliva and serum samples from coronavirus disease 2019 (COVID-19) cases procured from commercial sources and negative controls from a prepandemic survey. Saliva was also collected in a demonstration survey by mail involving adult individuals in the United States who were diagnosed with SARS-CoV-2 infection 15 to 80 days prior to sample collection. The survey had an 83% valid sample return rate (192 samples from 38 states). Most COVID-19 cases (93%) reported mildly symptomatic or asymptomatic infections. The final salivary assay based on the best-performing spike and nucleocapsid proteins had a sensitivity of 87.1% (95% bootstrap confidence interval, 82.1 to 91.7%) and specificity of 98.5% (95.0 to 100%) using 227 and 285 saliva samples, respectively. The same assay had 95.9% (92.8 to 98.9%) sensitivity and 100% (98.4 to 100%) specificity in serum (174 and 285 serum samples, respectively). Salivary and serum antibody responses to spike and nucleocapsid proteins were strongly correlated in 22 paired samples (r = 0.88 and r = 0.80, respectively). Antibody responses peaked at approximately 50 days postonset; greater illness severity was associated with stronger responses. This study demonstrated that a salivary antibody assay can be used in large-scale population surveys by mail to better characterize public health impacts of COVID-19.

IMPORTANCE Given the enormous impacts of the COVID-19 pandemic, developing tools for population surveillance of infection is of paramount importance. This article describes the development of a multiplex immunoassay on a Luminex platform to measure salivary immunoglobulin G responses to the spike protein, its two subunits and receptor binding domain, and the nucleocapsid protein of SARS-CoV-2. The assay validation utilized serum and saliva samples from prepandemic controls and recent COVID-19 cases. A survey by mail targeting recent COVID-19 cases across the United States also demonstrated the utility of safe, at-home self-collection of saliva. By incorporating multiple SARS-CoV-2 proteins, this assay may differentiate responses to natural SARS-CoV-2 infections from responses to most vaccines. Application of this noninvasive immunoassay in COVID-19 surveillance can help provide estimates of cumulative incidence rates of symptomatic and asymptomatic infections in various communities and subpopulations, temporal patterns of antibody responses, and risk factors for infection.

Adjustments for oral fluid quality and collection methods improve prediction of circulating tetanus antitoxin: Approaches for correcting antibody concentrations detected in a non-invasive specimen

OBJECTIVES

To examine whether anti-tetanus toxoid (anti-TT) immunoglobulin G (IgG) levels measured in oral fluid and adjusted for collection difficulties and specimen quality are associated with total IgG and anti-TTIgG in oral fluid and assess if statistical adjustment for them improves prediction of anti-TT IgG in serum.

METHODS

267 children, ages 12 to 15 months, enrolled in the M-SIMU randomized controlled trial participated in this nested cross-sectional analysis. Venous blood and oral fluid (OF) specimens were collected, and OF collection difficulties such as crying or gagging were recorded. OF volume was documented and total IgG was measured in OF specimens and anti-TT IgG was measured in OF and serum by enzyme immunoassay (EIA). Collection difficulties, volume and sociodemographic characteristics were assessed in relation to total IgG and anti-TT IgG in OF via multivariate regression. These models were extended to evaluate the association between anti-TT IgG in OF and in serum. A prediction model was developed to adjust anti-TT IgG in OF estimates as proxy for serum.

RESULTS

Blood in the specimen, sores in the mouth and crying were positively associated with total IgG concentration while high oral fluid volume and sucking on the swab were inversely associated. None were significant predictors of anti-TT IgG in OF after adjusting for total IgG (geometric mean [GM] ratio: 1.99; 95% confidence interval: 1.78-2.24) and vaccination history (GM ratio: 2.44; 95% CI: 1.98-3.01). When predicting anti-TT IgG levels in serum with OF, total IgG modified the effect of anti-TT IgG in OF.

CONCLUSIONS

Anti-TT IgG in OF is a good proxy for levels in serum, after controlling for total IgG in the specimen and other variables. Post hoc adjustments for OF volume and total IgG concentration are an important consideration when conducting serosurveys with oral fluid.

Diagnostic sensitivity and specificity of host-derived salivary biomarkers in periodontal disease amongst adults: Systematic review

OBJECTIVE

To systematically assess the diagnostic value of host-derived salivary biomarkers based on their reported sensitivity and specificity in relation to clinical parameters of periodontal disease diagnosis in adults.

MATERIALS AND METHODS

Comprehensive search of PubMed, Nature, Cochrane and OVID (Embase, MEDLINE [R] and PsycINFO) was conducted up to 1 August 2018, using key terms relevant to the research questions and Cochrane methodology, supplemented by a grey literature search. The revised Quality Assessment of Diagnostic Accuracy Studies (QUADAS- 2) tool was used to assess the methodological quality of all included studies.

RESULTS

Seven studies were included in the review. Macrophage inflammatory protein-1αlpha (MIP-1α), interleukin-1beta (IL-1β), interleukin-6 (IL-6) and matrix metalloproteinase-8 (MMP-8) were identified as diagnostically acceptable biomarkers for periodontal disease. Overall, the combination of IL-6 and MMP-8 showed best diagnostic performance. Also, a combination of the four key biomarkers (IL-1β, IL-6, MMP-8 and MIP-1α) showed promising results for distinction between gingivitis and periodontitis, as well as for periodontitis compared with gingival health. Results are interpreted with caution due to limitations in the number of studies included and their quality.

CONCLUSION

Certain salivary biomarkers can potentially be useful in combination and singularly for the diagnosis of periodontal disease. However, further methodically robust research is required to validate these biomarkers.

Noninvasive Detection of Antibodies to Human T-Cell Lymphotropic Virus Types 1 and 2 by Use of Oral Fluid

Human T-lymphotropic viruses type 1 and 2 (HTLV-1/2) are prevalent in endemic clusters globally, and HTLV-1 infects at least 5 to 10 million individuals. Infection can lead to inflammation in the spinal cord, resulting in HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), or adult T cell leukemia/lymphoma (ATL). Obtaining venous blood for serological screening, typically performed using enzyme immunoassays (EIAs), is invasive, sometimes socially unacceptable, and has restricted large-scale seroprevalence studies. Collecting oral fluid (OF) is a noninvasive alternative to venesection. In this study, an IgG antibody capture EIA was developed and validated to detect anti-HTLV-1/2 IgG in OF. OF and plasma specimens were obtained from seropositive HTLV-1/2-infected patients attending the National Centre for Human Retrovirology (n = 131) and from HTLV-1/2-uninfected individuals (n = 64). The assay showed good reproducibility and high diagnostic sensitivity (100%) and specificity (100%) using both OF and plasma. The Murex HTLV I+II commercial assay was evaluated and did not detect anti-HTLV-1/2 IgG in 14% (5/36) of OF specimens from seropositive donors. The reactivities of OF and plasma in the IgG capture correlated strongly (r = 0.9290) and were not significantly affected by delayed extraction when held between 3°C and 45°C for up to 7 days to simulate field testing. The use of OF serological screening for HTLV-1/2 infection could facilitate large-scale seroprevalence studies, enabling active surveillance of infection on a population level.

The effects of collection and storage conditions in the field on salivary testosterone, cortisol, and sIgA values

AIM

To determine if field-typical storage and collection conditions are related to salivary testosterone (T), cortisol (cort) and secretory immunoglobulin A (sIgA) as measured using commercially available kits.

SUBJECTS AND METHODS

This study assessed whether storage time (∼6 months to 1.5 years) at -35 °C impacted levels of the measured biomarkers (n = 10,247 samples). For a sub-set of T samples (n = 2954), we also evaluated the impact of collection conditions, such as time spent at room temperature in participants' homes (0-39 hours) and time spent in coolers (0.3-10 hours) in transit.

RESULTS

T was unrelated to storage and collection variables and there was no evidence of reduced sample fidelity at longer storage times. Cort samples stored at -35 °C for longer had significantly lower values, but the effect was small (β = -0.003 nmol/L/day, SE <0.001, p = 0.005). sIgA trended higher with longer storage at -35 °C (β = 0.84 µg/mL/day, SE = 0.45, p = 0.063). Collection and storage time variables did not improve the fit of any of the models except the one that evaluated cortisol.

CONCLUSIONS

Salivary T was unaffected by extended storage at -35 °C and only a weak relationship was found between storage time and salivary cort or sIgA. Findings underscore the robustness of these biomarkers under field-typical freezer storage conditions.

Role of Salivary Biomarkers in Oral Cancer Detection

Oral cancers are the sixth most frequent cancer with a high mortality rate. Oral squamous cell carcinoma accounts for more than 90% of all oral cancers. Standard methods used to detect oral cancers remain comprehensive clinical examination, expensive biochemical investigations, and invasive biopsy. The identification of biomarkers from biological fluids (blood, urine, saliva) has the potential of early diagnosis. The use of saliva for early cancer detection in the search for new clinical markers is a promising approach because of its noninvasive sampling and easy collection methods. Human whole-mouth saliva contains proteins, peptides, electrolytes, organic, and inorganic salts secreted by salivary glands and complimentary contributions from gingival crevicular fluids and mucosal transudates. This diagnostic modality in the field of molecular biology has led to the discovery and potential of salivary biomarkers for the detection of oral cancers. Biomarkers are the molecular signatures and indicators of normal biological, pathological process, and pharmacological response to treatment hence may provide useful information for detection, diagnosis, and prognosis of the disease. Saliva's direct contact with oral cancer lesions makes it more specific and potentially sensitive screening tool, whereas more than 100 salivary biomarkers (DNA, RNA, mRNA, protein markers) have already been identified, including cytokines (IL-8, IL-1b, TNF-α), defensin-1, P53, Cyfra 21-1, tissue polypeptide-specific antigen, dual specificity phosphatase, spermidine/spermineN1-acetyltransferase , profilin, cofilin-1, transferrin, and many more. However, further research is still required for the reliability and validation of salivary biomarkers for clinical applications. This chapter provides the latest up-to-date list of known and emerging potential salivary biomarkers for early diagnosis of oral premalignant and cancerous lesions and monitoring of disease activity.

Effect of chemical clarification of oral fluids on the detection of porcine reproductive and respiratory syndrome virus IgG

Routine collection and testing of oral fluid (OF) samples facilitates porcine reproductive and respiratory syndrome virus (PRRSV) surveillance in commercial swine herds in a cost-effective, welfare-friendly fashion. However, OFs often contain environmental contaminants that may affect liquid handling and test performance. Traditional processing methods (e.g., filtration or centrifugation) are not compatible with high-throughput testing because of the burden of additional processing costs and time. OF "clarification" using chemical flocculants is an alternative approach not widely explored. Therefore, we evaluated the effect of chitosan-based clarification treatment on a commercial PRRSV OF ELISA. Serum and individual OFs were collected from vaccinated pigs ( n = 17) at -7 to 42 d post-vaccination and subdivided into 4 aliquots. Each aliquot was clarified (treatment A, B, C), with the 4th aliquot serving as untreated control. All samples were tested by PRRSV OF ELISA immediately after treatment and then were held at 4°C to be re-tested at 2, 4, 6, and 14 d post-treatment. Quantitative and qualitative treatment effects were evaluated. A Kruskal-Wallis test found no significant difference in ELISA S/P responses among treatments by days post-treatment. No difference was detected in the proportion of positive PRRSV antibody samples among treatments (Cochran Q, p > 0.05). Treatment of swine OFs using chitosan-based formulations did not affect the performance of a commercial PRRSV OF ELISA. Chitosan (or other flocculants) could improve OF characteristics and could be adapted for use in the field or in high-throughput laboratories.

Ebola exposure, illness experience, and Ebola antibody prevalence in international responders to the West African Ebola epidemic 2014-2016: A cross-sectional study

BACKGROUND

Healthcare and other front-line workers are at particular risk of infection with Ebola virus (EBOV). Despite the large-scale deployment of international responders, few cases of Ebola virus disease have been diagnosed in this group. Since asymptomatic or pauci-symptomatic infection has been described, it is plausible that infections have occurred in healthcare workers but have escaped being diagnosed. We aimed to assess the prevalence of asymptomatic or pauci-symptomatic infection, and of exposure events, among returned responders to the West African Ebola epidemic 2014-2016.

METHODS AND FINDINGS

We used snowball sampling to identify responders who had returned to the UK or Ireland, and used an online consent and questionnaire to determine their exposure to EBOV and their experience of illness. Oral fluid collection devices were sent and returned by post, and samples were tested using an EBOV IgG capture assay that detects IgG to Ebola glycoprotein. Blood was collected from returnees with reactive samples for further testing. Unexposed UK controls were also recruited. In all, 300 individuals consented, of whom 268 (89.3%) returned an oral fluid sample (OFS). The majority had worked in Sierra Leone in clinical, laboratory, research, and other roles. Fifty-three UK controls consented and provided samples using the same method. Of the returnees, 47 (17.5%) reported that they had had a possible EBOV exposure. Based on their free-text descriptions, using a published risk assessment method, we classified 43 (16%) as having had incidents with risk of Ebola transmission, including five intermediate-risk and one high-risk exposure. Of the returnees, 57 (21%) reported a febrile or diarrhoeal illness in West Africa or within 1 mo of return, of whom 40 (70%) were not tested at the time for EBOV infection. Of the 268 OFSs, 266 were unreactive. Two returnees, who did not experience an illness in West Africa or on return, had OFSs that were reactive on the EBOV IgG capture assay, with similar results on plasma. One individual had no further positive test results; the other had a positive result on a double-antigen bridging assay but not on a competitive assay or on an indirect EBOV IgG ELISA. All 53 controls had non-reactive OFSs. While the participants were not a random sample of returnees, the number participating was high.

CONCLUSIONS

This is the first study, to our knowledge, of the prevalence of EBOV infection in international responders. More than 99% had clear negative results. Sera from two individuals had discordant results on the different assays; both were negative on the competitive assay, suggesting that prior infection was unlikely. The finding that a significant proportion experienced "near miss" exposure events, and that most of those who experienced symptoms did not get tested for EBOV at the time, suggests a need to review and standardise protocols for the management of possible exposure to EBOV, and for the management of illness, across organisations that deploy staff to outbreaks.

Assessing the Archaeoparasitological Potential of Quids As a Source Material for Immunodiagnostic Analyses

In the present study, quids from La Cueva de los Muertos Chiquitos (CMC) were subjected to ELISA tests for 2 protozoan parasites, Toxoplasma gondii (n=45) and Trypanosoma cruzi (n=43). The people who occupied CMC, the Loma San Gabriel, lived throughout much of present-day Durango and Zacatecas in Mexico. The known pathoecology of these people puts them into at-risk categories for the transmission of T. gondii and T. cruzi. Human antibodies created in response to these 2 parasites can be detected in modern saliva using ELISA kits intended for use with human serum. For these reasons, quids were reconstituted and subjected to ELISA testing. All test wells yielded negative results. These results could be a factor of improper methods because there is no precedence for this work in the existing literature. The results could equally be a simple matter of parasite absence among those people who occupied CMC. A final consideration is the taphonomy of human antibodies and whether or not ELISA is a sufficient method for recovering antibodies from archaeological contexts. An additional ELISA test targeting secretory IgA (sIgA) was conducted to further examine the failure to detect parasite-induced antibodies from quids. Herein, the methods used for quid preparation and ELISA procedures are described so that they can be further developed by future researchers. The results are discussed in light of the potential future of quid analysis.

Modelling anti-pertussis toxin IgG antibody decay following primary and preschool vaccination with an acellular pertussis vaccine in UK subjects using a modified oral fluid assay

Recent vaccination with pertussis vaccine can confound serological and oral fluid (OF) assays targeting anti-pertussis toxin (anti-PT) IgG antibodies as a marker of recent infection. This study sought to establish the minimum potentially confounding time period based on experimental data to assist interpretation from such samples submitted from UK subjects for pertussis diagnosis. Anti-PT IgG antibody response and decay were measured post-vaccination using a modified OF IgG antibody-capture ELISA (GACELISA). Data were obtained from 72 infants after the third acellular pertussis vaccine dose in the primary schedule (4 months of age) and from 119 children after the single dose at preschool age (3 years 4 months to 5 years 8 months of age). Specimens were taken at approximately 1 month intervals for 9 months post-primary immunization (third dose) and 13 months post-preschool booster (PSB). The modified GACELISA demonstrated a sensitivity of 52/56 (92.9 %: 95 % CI 82.7–98.0) and a specificity of 120/128 (93.8 %: 95 % CI 88.0–97.3) and showed good agreement with the National Reference Laboratory standard anti-PT IgG serum ELISA (rank correlation = 0.80) and the original OF assay (rank correlation = 0.79). Modelling of the decline in antibody titres showed a reduction of 54 % and 34 % for each doubling of time after day 14 for the post-third primary dose and post-PSB subjects, respectively. These data suggest that the minimum confounding time period is approximately 300 days for samples obtained post-primary immunization and at least 3 years for samples submitted from UK children following immunization with the PSB. These data will greatly assist the interpretation of single high diagnostic anti-PT IgG titres by allowing an estimate of the positive predictive value, when the number of days post-immunization and prevalence are known or assumed.

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.

Sample collection and handling considerations for peptidomic studies in whole saliva; implications for biomarker discovery

BACKGROUND

Proteomic studies in saliva have demonstrated its potential as a diagnostic biofluid, however the salivary peptidome is less studied. Here we study the effects of several sample collection and handling factors on salivary peptide abundance levels.

METHODS

Salivary peptides were isolated using an ultrafiltration device and analyzed by tandem mass spectrometry. A panel of 41 peptides common after various treatments were quantified and normalized. We evaluated the effects of freezing rate of the samples, nutritional status of the donors (fed vs. fasted), and room-temperature sample degradation on peptide abundance levels. Repeatability of our sample processing method and our instrumental analysis method were investigated.

RESULTS

Increased sample freezing rate produced higher levels of peptides. Donor nutritional status had no influence on the levels of measured peptides. No significant difference was detected in donors' saliva following 5, 10 and 15 min of room-temperature degradation. Sample processing and instrumental variability were relatively small, with median CVs of 9.6 and 6.6.

CONCLUSIONS

Peptide abundance levels in saliva are rather forgiving towards variations in sample handling and donor nutritional status. Differences in freezing methods may affect peptide abundance, so consistency in freezing samples is preferred. Our results are valuable for standardizing sample collection and handling methods for peptidomic-based biomarker studies in saliva.

Hepatitis A and travel amongst Nova Scotia postsecondary students: evidence for a targeted vs. universal immunization strategy

BACKGROUND

Canadian guidelines recommend hepatitis A virus (HAV) vaccination for high-risk persons, such as travelers to HAV-endemic areas. The US CDC advocates universal immunization.

OBJECTIVES

To explore whether a universal strategy for HAV immunization rather than the Canadian targeted approach for travelers is justified by measuring compliance of postsecondary students with Canadian guidelines.

METHODS

A cross-sectional study using an electronic survey method elicited HAV risk factors, immunization history, disease status, and factors affecting immunization status from postsecondary students. Seropositivity was determined by measuring HAV antibodies in saliva from a convenience sample of survey participants within each study group. Statistical analysis used Fisher's exact test and logistic regression.

RESULTS

We received 2279 completed surveys (10.6% response) and 235 saliva samples (58.7% response). A total of 1380 (60.6%) participants had traveled to HAV-endemic regions and 1851 (81.2%) were planning to do so within the next 5 years. Less than half who traveled to HAV-endemic areas reported a history of HAV vaccination (48.0%). HAV seropositivity rates were higher amongst those who traveled to (63.6%) or were planning to travel to (55.0%) HAV-endemic areas than those who had never traveled or had no plans to travel to such areas (17.4%). Only 8.9% of unvaccinated students were seropositive (5.3% of Canadian-born students). Amongst unvaccinated, seropositive students, there was a nonsignificant trend for higher seropositivity in those who had previously traveled to HAV-endemic areas (14.7%) than those who had not traveled abroad (4.4%), suggesting an exposure to HAV during travel. Nearly all (96.5%) unvaccinated students, who were willing to be vaccinated based on current knowledge or if their doctor recommended it, indicated a willingness to receive vaccine if it were provided free of charge.

CONCLUSIONS

Current Canadian guidelines for HAV vaccination are not being followed within the postsecondary student population. Given high rates of travel to HAV-endemic areas in this population, a universal approach to HAV vaccination may be warranted.

Recent diarrhea is associated with elevated salivary IgG responses to Cryptosporidium in residents of an eastern Massachusetts community

BACKGROUND

Serological data suggest that Cryptosporidium infections are common but underreported. The invasiveness of blood sampling limits the application of serology in epidemiological surveillance. We pilot-tested a non-invasive salivary anti-Cryptosporidium antibody assay in a community survey involving children and adults.

MATERIALS AND METHODS

Families with children were recruited in a Massachusetts community in July; symptoms data were collected at 3 monthly follow-up mail surveys. One saliva sample per person (n = 349) was collected via mail, with the last survey in October. Samples were analyzed for IgG and IgA responses to a recombinant C. hominis gp15 sporozoite protein using a time-resolved fluorometric immunoassay. Log-transformed assay results were regressed on age using penalized B-splines to account for the strong age-dependence of antibody reactions. Positive responses were defined as fluorescence values above the upper 99% prediction limit.

RESULTS

Forty-seven (13.5%) individuals had diarrhea without concurrent respiratory symptoms during the 3-month-long follow-up; eight of them had these symptoms during the month prior to saliva sampling. Two individuals had positive IgG responses: an adult who had diarrhea during the prior month and a child who had episodes of diarrhea during each survey month (Fisher's exact test for an association between diarrhea and IgG response: p = 0.0005 for symptoms during the prior month and p = 0.02 for symptoms during the entire follow-up period). The child also had a positive IgA response, along with two asymptomatic individuals (an association between diarrhea and IgA was not significant).

CONCLUSION

These results suggest that the salivary IgG specific to Cryptosporidium antigens warrants further evaluation as a potential indicator of recent infections.

Feasibility of collecting oral fluid samples in the home setting to determine seroprevalence of infections in a large-scale cohort of preschool-aged children

Oral fluid is a non-invasive biological sample, which can be returned by post, making it suitable for large-scale epidemiological studies in children. We report our experience of oral fluid collection from 14 373 preschool-aged children in the UK Millennium Cohort Study. Samples were collected by mothers in the home setting following the guidance of trained interviewers, and posted to the laboratory. Samples were received from 11 698 children (81.4%). Children whose mothers were of Black Caribbean ethnicity and who lived in non-English-speaking households were less likely to provide a sample, and those with a maternal history of asthma more likely to provide a sample [adjusted risk ratio (95% CI) 0.85 (0.73-0.98), 0.87 (0.77-0.98) and 1.03 (1.00-1.05) respectively]. Collection of oral fluid samples is feasible and acceptable in large-scale child cohort studies. Formal interpreter support may be required to increase participation rates in surveys that collect biological samples from ethnic minorities.

Sample Stability and Protein Composition of Saliva: Implications for Its Use as a Diagnostic Fluid

Saliva is an easy accessible plasma ultra-filtrate. Therefore, saliva can be an attractive alternative to blood for measurement of diagnostic protein markers. Our aim was to determine stability and protein composition of saliva. Protein stability at room temperature was examined by incubating fresh whole saliva with and without inhibitors of proteases and bacterial metabolism followed by Surface Enhanced Laser Desorption/Ionization (SELDI) analyses. Protein composition was determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) fractionation of saliva proteins followed by digestion of excised bands and identification by liquid chromatography tandem mass spectrometry (LC-MS/MS). Results show that rapid protein degradation occurs within 30 minutes after sample collection. Degradation starts already during collection. Protease inhibitors partly prevented degradation while inhibition of bacterial metabolism did not affect degradation. Three stable degradation products of 2937 Da, 3370 Da and 4132 Da were discovered which can be used as markers to monitor sample quality. Saliva proteome analyses revealed 218 proteins of which 84 can also be found in blood plasma. Based on a comparison with seven other proteomics studies on whole saliva we identified 83 new saliva proteins. We conclude that saliva is a promising diagnostic fluid when precautions are taken towards protein breakdown.

Saliva specimen: a new laboratory tool for diagnostic and basic investigation

The assay of saliva is an increasing area of research with implications for basic and clinical purposes. Although this biological fluid is easy to manipulate and collect, careful attention must be directed to limit variation in specimen integrity. Recently, the use of saliva has provided a substantial addition to the diagnostic armamentarium as an investigative tool for disease processes and disorders. In addition to its oral indications, the analysis of saliva provides important information about the functioning of various organs within the body. In this respect, endocrine research certainly occupies a central role. The present review considers the laboratory aspects of salivary assays with respect to the different analytes including ions, drugs and various non-protein/protein compounds such as hormones and immunoglobulins. This review also examines the consequences of preanalytical variation with respect to collection strategy and subsequent storage conditions. It is likely that the use of saliva in assays will continue to expand thus providing a new instrument of investigation for physiologic as well as pathophysiologic states.

Participant-collected, mail-delivered oral fluid specimens can replace traditional serosurveys: a demonstration-of-feasibility survey of hepatitis A virus-specific antibodies in adults

BACKGROUND

Although population-based serosurveys offer an optimal measure of cumulative infection rates, they are seldom performed due to high cost and complex logistics. Use of participant self-collected oral fluid as a diagnostic specimen and mail for specimen delivery has the potential of generating reliable, population-representative data at limited cost.

METHODS

A survey of oral fluid HAV-specific immunoglobulin G (an indicator of past HAV infection) was undertaken in a provincially representative sample of 20-39 year olds as a pilot study. A provincial administrative database served as the sampling frame. Potential participants were invited by mail to collect oral fluid and complete a questionnaire at home and return both by mail. Additional telephone prompting was directed at slow responders. Oral fluid was tested using a validated ELISA.

RESULTS

From among 2,448 potential participants, contact by mail or telephone was made with 1,009 eligible subjects; 59% (585) participated. Materials withstood mailing and the quality of self-collected specimens was excellent. A positive test result was found in 22.1% overall and in 15.7% of self-reported non-vaccinated subjects. Among Canadian-born, non-vaccinated individuals, the positive test rate increased progressively from 1.2% (95% CI: 0-6.3) in 20-24 year olds to 16.4% (95% CI: 9.5-23.3) in 35-39 year olds. Antibody prevalence was higher among Canadian-born non-immunized 20-29 year olds who reported travel to developing countries (33.3%, 95% CI: 11.6-55.1) than in non-travellers (2.5%, 95% CI: 0.7-6.2).

CONCLUSIONS

Mail-based population surveys of infection markers in oral fluid are feasible provided an appropriate sampling frame is used. This survey revealed a high anti-HAV antibody prevalence in young Canadian adults, increasing with age and travel to developing countries.

Application of a noninvasive oral fluid test for detection of treponemal IgG in a predominantly HIV-infected population

The performance of a time-resolved fluorescence immunoassay (TRFIA) for detection of treponemal IgG from oral fluid specimens has been assessed in a predominantly HIV-infected population. Serological investigation is the method of choice for confirming clinical suspicion of syphilis; however, in the primary stage of disease, direct detection of treponemes in lesion fluid or Treponema pallidum DNA is recommended because of the reduced sensitivity of serological tests. There may be occasions when blood for serological investigation is difficult to obtain due to individual patient preference or logistical necessity to improve participation in screening initiatives, particularly in outreach situations. Collection of oral fluid for detection of treponemal antibody may prove an attractive alternative and, with this in mind, an oral fluid assay for detection of treponemal IgG was developed. Time-resolved fluorescence was used to detect treponemal IgG extracted from commercially available oral fluid collection devices. Paired serum and saliva samples were obtained from 210 individuals, 101 of whom were diagnosed with syphilis on the grounds of medical examination confirmed by serological testing. Oral fluid specimens from 14 subjects were rejected because they contained insufficient control antibody or were inhibitory. The population tested was predominantly men who have sex with men, many of whom were HIV infected. The overall sensitivity and specificity of the oral fluid assay was 95.8 and 86.1%, respectively, based on the 5th percentile of the positive results, and 93.7 and 91.1%, respectively, based on a cutoff derived by mixture model analysis. For individuals with primary syphilis, the optimum sensitivity of the oral fluid assay was 87.5%, whereas in those with disease classified as secondary syphilis and early latent syphilis, the sensitivity of the oral fluid assay was 100 and 94.7%, respectively. The oral fluid assay is a useful alternative to serological testing in certain situations, and further development of this technology to enable detection of treponemal IgM should increase its sensitivity for detecting cases of primary syphilis.

Performance of a Western immunoblot assay to detect specific anti-Toxoplasma gondii IgG antibodies in human saliva

Toxoplasma gondii represents the most prominent infectious parasitic organism found in humans. While normally asymptomatic in healthy individuals, toxoplasmosis can cause abortion in patients during pregnancy, or can be fatal in immunosupressed individuals such as persons suffering from acquired immunodeficiency syndrom (AIDS). Toxoplasma gondii infection in humans is routinely assesssed by serological means. Here, we show that detection of anti-T. gondii IgG is also possible using a non-invasive methodology employing saliva. Sera and saliva of 201 healthy volunteers were investigated for the presence of anti-T. gondii-IgG antibodies by immunoblotting. The sera of 59 (29.4%) individuals showed IgG antibodies against T. gondii by ELISA, Vidas, and immunoblotting; 58 (98.3%) of these were also positive for anti-T. gondii IgG in the saliva immunoblot, with diagnostic relevant bands of Mr of 32-35 kDa and 40-45 kDa. The saliva immunoblot test exhibits a specificity of 100% and a sensitivity of 98.5%. Thus, saliva could be used as an alternative, non-invasive means for the detection of specific anti-T. gondii IgG in humans.

Validation of a modified commercial assay for the detection of rubella-specific IgG in oral fluid for use in population studies

Matching serum and oral fluid (saliva) samples were collected from 369 subjects in Tunisia in 2002, from a city in the north and a rural district in the south. Rubella-specific IgG was detected in sera by commercial ELISA (Dade Behring) and in matching oral fluids by two methods, a previously described IgG-capture ELISA (GACELISA) [J. Clin. Microbiol. 37 (1999) 391] and the Dade Behring ELISA with the assay protocol modified for use with oral fluids. Total IgG concentration of oral fluids was also measured. Rubella-specific IgG was detected in 289 (78.3%) sera overall. Differences in the age distribution of the study population in the north and south led to a higher prevalence being found in the north (86.2%) than in the south (71.8%). This difference was reflected in the oral fluid rubella-specific IgG results. With GACELISA, rubella-specific IgG was detected in 79.4% of oral fluids from the north and 69.7% from the south and with the modified Dade Behring assay, in 81.4% of oral fluids from the north and in 64.9% from the south. The sensitivity and specificity of GACELISA in comparison to results from the matching sera were 92.4 and 93.2%, respectively. The sensitivity and specificity of the modified Dade Behring ELISA were 89.8 and 92.0%, respectively. Total IgG concentration in oral fluid showed a weak correlation (r=0.19) with the modified Dade Behring results and with samples where total IgG was >7.5 mg/l, the sensitivity and specificity were 94.4 and 90.0%, respectively. Twenty-nine oral fluids, which gave false negative rubella-specific IgG results with the modified Dade Behring ELISA, had a lower mean total IgG concentration than 256 oral fluids which gave concordant positive results (7.0mg/l versus 15.8 mg/l, P<0.001). The study validated the modified Dade Behring ELISA, providing an alternative to the GACELISA for assessing levels of rubella immunity for population studies using oral fluid samples.