Persistence of specific IgM and low avidity specific IgG1 following primary rubella

Difficulty in Serologic Screening for Subclinical Rubella during Pregnancy

In Japan, rubella antibodies are tested in all pregnant women to detect subclinical infections. This study aimed to assess the validity of measuring rubella antibodies for detecting subclinical rubella among pregnant women in Japan. This single-center retrospective study measured rubella hemagglutination inhibition (HI) titers and rubella-specific IgM antibody index (IgM) values. IgM values were measured by conducting enzyme immunoassay, and IgM-values >1.2 were considered positive. Of 14,965 included pregnant women, 186 (1.2%) were IgM-positive. Only one patient was clinically diagnosed with rubella (HI titer, 1:2,048; IgM value, 10) and developed fever and skin rash. She decided to terminate her pregnancy without undergoing repeated blood tests. Of the IgM-positive patients, 136 (73.1%) had rubella HI titers of < 1:256. The correlation coefficient between rubella HI and IgM titers was weakly positive (0.2527; P < 0.0001). This study showed that a single combination of rubella HI and rubella-specific IgM measurements alone could not detect subclinical rubella. Creating awareness among pregnant women by informing them that almost all rubella-specific IgM-positive individuals without symptoms are not acutely infected could decrease their anxiety and prevent unnecessary pregnancy termination.

Peanut diversity and specific activity are the dominant IgE characteristics for effector cell activation in children

Background

IgE mediates allergic reactions to peanut; however, peanut-specific IgE (sIgE) levels do not always equate to clinical peanut allergy. Qualitative differences between sIgE of peanut-sensitized but tolerant (PS) and peanut-allergic (PA) individuals may be important.

Objective

We sought to assess the influence of IgE characteristics on effector cell activation in peanut allergy.

Methods

A cohort of 100 children was studied. The levels of IgE to peanut and peanut components were measured. Specific activity (SA) was estimated as the ratio of allergen-sIgE to total IgE. Avidity was measured by ImmunoCAP with sodium thiocyanate. IgE diversity was calculated on the basis of ImmunoCAP-Immuno Solid-phase Allergen Chip assays for 112 allergens or for 6 peanut allergens. Whole-blood basophils and mast cell line Laboratory of Allergic Diseases 2 sensitized with patients’ plasma were stimulated with peanut or controls and assessed by flow cytometry.

Results

SA to peanut (P < .001), Ara h 1 (P = .004), Ara h 2 (P < .001), Ara h 3 (P = .02), and Ara h 6 (P < .001) and the avidity of peanut-sIgE (P < .001) were higher in PA than in PS individuals. Diversity for peanut allergens was greater in PA individuals (P < .001). All IgE characteristics were correlated with basophil and mast cell activation. Peanut SA (R = 0.447) and peanut diversity (R = 0.440) had the highest standardized β-coefficients in combined multivariable regression models (0.447 and 0.440, respectively).

Conclusions

IgE specificity, SA, avidity, and peanut diversity were greater in PA than in PS individuals. IgE peanut SA and peanut diversity had the greatest influence on effector cell activation and could be used clinically.

Seroprevalence of rubella virus antibodies among pregnant women in the Center and South-West regions of Cameroon

Rubella infection in early pregnancy can lead to miscarriages, fetal death, or birth of an infant with congenital rubella syndrome (CRS). In Cameroon, like in many developing countries, rubella surveillance is not well-established. The aim of this study was to determine the prevalence of rubella virus specific antibodies among pregnant Cameroonians. We conducted a cross-sectional study for rubella infection among pregnant women attending antenatal clinics in the Center and South-West regions of Cameroon. Demographic data and blood were collected and tested for rubella specific antibodies (IgG and IgM), and for the IgM positive cases, IgG avidity and real time PCR was done. From December 2015 to July 2017, 522 serum samples were collected and tested from pregnant women. The seroprevalence of rubella specific IgG was 94.4%, presumably due to immunity induced by wild-type rubella virus. The seroprevalence of rubella specific IgM was 5.0%, possibly indicating rubella infection. However, IgG avidity testing of the IgM positive cases detected high avidity IgGs, ranging from 52.37% to 87.70%, indicating past rubella infection. 5.6% (29/522) of the participants had negative results for IgG to rubella virus, indicating susceptibility to rubella infection. None of the participants had received a rubella containing vaccine (RCV), but 51% (266/522) of the pregnant women lived in a house with a child with records of at least one dose of RCV. Rubella virus RNA was not detected in the urine of any IgM positive case. Findings from this study show that rubella infection is significant in Cameroon. Some pregnant women are still susceptible to rubella infection. For a better management of rubella infection in pregnancy in Cameroon, consideration should be taken to investigate for IgG-avidity test in cases with positive rubella IgM result to distinguish between recent from past rubella infection.

Clinical usefulness of Western blotting and ELISA avidity for the diagnosis of human toxocariasis

The serodiagnosis of human toxocariasis is difficult. Specific IgGs detected routinely with ELISA based on Toxocara excretory-secretory (TES) antigens often persist for years at an elevated level, which does not allow either the differentiation between an active and persistent infection or monitoring of the effect of treatment. Additionally, false-positive results may occur in co-infections with other helminths due to cross-reactions. We evaluated the usefulness of an IgG avidity index (AI) and a Western blotting (WB) IgG in the diagnosis of patients suspected of Toxocara infection. We studied 138 subjects who were submitted to serological testing two or more times. Confirmation of an infection by WB was achieved in 73.2% of patients. A high AI was obtained in 89.1% of patients, and low AI and borderline AI were found in only 10.9%. Low and borderline values of AI remained at similar levels in subsequent studies over 2-3 years. The results showed the necessity of obligatory verification of all ELISA IgG positive and questionable results by WB. The index of IgG avidity may be helpful in excluding recent infection, but its usefulness in detecting an active phase of invasion requires further research.

Oral fluid testing during 10 years of rubella elimination, England and Wales

Surveillance of rubella in England and Wales has included immunoglobulin M testing of oral (crevicular) fluid from reported case-patients since 1994. The need for laboratory confirmation to monitor rubella elimination is emphasized by poor sensitivity (51%, 95% confidence interval 48.9%–54.0%) and specificity (55%, 95% confidence interval 53.7%–55.6%) of the clinical case definition. During 1999–2008, oral fluid from 11,709 (84%) of 13,952 reported case-patients was tested; 143 (1.0%) cases were confirmed and 11,566 (99%) were discarded (annual investigation and discard rate of clinically suspected rubella cases was 2,208/100,000 population). Incidence of confirmed rubella increased from 0.50 to 0.77/1 million population when oral fluid testing was included. Oral fluid tests confirmed that cases were more likely to be in older, unvaccinated men. Testing of oral fluid has improved ascertainment of confirmed rubella in children and men and provided additional information for assessing UK progress toward the World Health Organization elimination goal.

Evaluation of rubella virus immunoglobulin G (IgG) and IgM assays with the new Vidia instrument

For rubella virus immunoglobulin G (IgG) and IgM detection, Vidia assays were compared to Vidas, AxSYM, and Liaison assays with 419 serum samples. Only Vidia produced a sensitivity of 100% for IgG and IgM. Vidia specificities were 98.4% for IgG and 99.8% for IgM, versus Vidas specificities of 100 and 99.3%. Vidia IgG and IgM assays performed equally well.

Development of a rapid and convenient method for determination of rubella virus-specific immunoglobulin G avidity

We describe here a rapid and semiautomated method for the determination of rubella virus immunoglobulin G (IgG) avidity with the VIDAS instrument. A total of 153 serum samples from persons with naturally acquired rubella virus infections (n = 98), from vaccinated persons (n = 44), and from patients with autoantibodies (n = 11) were included in this study. The rubella virus-specific IgG avidity assay we developed for the VIDAS instrument was evaluated by comparison with an in-house method. Results obtained with the VIDAS instrument allow considering this method valuable to help confirm or exclude acute primary infection or recent vaccination.

Humoral immune response after primary rubella virus infection and after vaccination

We measured rubella virus immunoglobulin G (IgG) and IgM levels, as well as IgG avidity indexes, in serum samples taken before or after 6 months either after infection or after vaccination. The results obtained indicate that humoral immune responses are different after primary infection and after vaccination. This may have important consequences on the serological diagnosis of rubella virus infection.

Evaluation of commercial rubella immunoglobulin G avidity assays

We compared the performances of five commercial rubella virus immunoglobulin G (IgG) avidity assays. The Adaltis (kappa = 0.28) and Diesse (kappa = 0.33) assays showed poor correlation, the Behring assay (kappa = 0.68) showed good correlation, and the Euroimmun (kappa = 0.95) and Radim (kappa = 0.94) assays showed excellent correlation with a well-established in-house rubella virus IgG avidity assay. The Euroimmun and Radim assays were statistically significantly better than the other commercial assays (P < 0.01).

Humoral immune response to primary rubella virus infection

An assay capable of distinguishing between the immune response generated by recent exposure to rubella virus and the immune response existing as a result of past exposure or immunization is required for the diagnosis of primary rubella virus infection, especially in pregnant women. Avidity assays, which are based on the premise that chaotropic agents can be used to selectively dissociate the low-avidity antibodies generated early in the course of infection, have become routinely used in an effort to accomplish this. We have thoroughly investigated the immunological basis of an avidity assay using a viral lysate-based assay and an enzyme-linked immunosorbent assay (ELISA) based on a peptide analogue of the putative immunodominant region of the E1 glycoprotein (E1208-239). The relative affinities of the antibodies directed against E1208-239 were measured by surface plasmon resonance and were found to correlate well with the avidity index calculated from the ELISA results. We found that the immune response generated during primary rubella virus infection consists of an initial low-affinity peak of immunoglobulin M (IgM) reactivity followed by transient peaks of low-avidity IgG3 and IgA reactivity. The predominant response is an IgG1 response which increases in concentration and affinity progressively over the course of infection. Incubation with the chaotropic agent used in the avidity assay abolished the detection of the early low-affinity peaks of IgM, IgA, and IgG3 reactivity while leaving the high-affinity IgG1 response relatively unaffected. The present study supported the premise that avidity assays based on appropriate antigens can be useful to confirm primary rubella virus infection.

Assessment of IgM enzyme immunoassay and IgG avidity assay for distinguishing between primary and secondary immune response to rubella vaccine

The primary test for the laboratory confirmation of rubella is IgM serology. It is important to distinguish IgM reactivity caused by primary infection from that caused by reinfection or persistence, especially in pregnant women; as termination of pregnancy is considered when primary rubella is diagnosed during the first trimester. In this study, the performance of rubella IgM enzyme immunoassay (IgM-EIA) and rubella IgG avidity assay were compared using well-defined panels of sera from persons vaccinated against rubella and commercial rubella IgM and IgG enzyme immunoassay kits (Dade Behring, Marburg, Germany). The sensitivity and specificity of rubella IgM-EIA were found to be 77.4 and 97.9%, respectively, while the results for rubella IgG avidity assay were 100 and 100%. IgG avidity assay showed higher positive and negative predictive values than the IgM-EIA (100 and 100% compare to 96.9 and 82.9%). In conclusion, the rubella IgG avidity assay is more sensitive and specific than IgM-EIA for differential detection of primary rubella infection from rubella reinfection.

Evaluation of three immunoassays used for detection of anti-rubella virus immunoglobulin M antibodies

Three automated assays (Abbott AxSYM, Bayer ADVIA Centaur, and bioMerieux VIDAS) used for the detection of rubella virus-specific immunoglobulin M were evaluated. A total of 57 samples from individuals with evidence of infection with rubella virus were used to estimate sensitivity, and 220 samples from blood donors and individuals attending an antenatal clinic who had no evidence of recent infection were used to estimate specificity. Seroconversion panels comprising an additional 31 samples from four individuals were used to determine clinical sensitivity. Samples containing potentially cross-reacting substances were also tested. The sensitivities of the three assays ranged from 84.2 to 96.5%, and the specificities ranged from 96.8 to 99.9%. The Abbott AxSYM assay detected more reactive samples than the other two assays when a panel of 57 positive samples was tested. Bayer ADVIA Centaur detected more reactive samples in the seroconversion panels than the other two assays. All three assays evaluated reported a reactive result in 1 or more of the 48 samples containing potentially cross-reacting analytes. The assays demonstrated comparable performance in testing of a well-characterized panel of samples.

Evaluation of rubella IgM enzyme immunoassays

BACKGROUND

Rubella virus generally causes a mild fever, rash illness similar in clinical presentation to infections by other viruses including measles and parvovirus B19. Rubella infections in pregnant women in the first trimester carry a high risk of congenital rubella syndrome (CRS) which can result in severe congenital defects in the infants. The goal of rubella immunization programs is therefore to eliminate CRS. The primary test for the laboratory confirmation of rubella is IgM serology. It is therefore important to evaluate currently available commercial rubella IgM immunoassays to ensure high quality rubella diagnostic testing.

STUDY DESIGN

In this study, we compared the performance of seven commercial rubella IgM enzyme immunoassays (EIA) (Meddens, Denka Seiken, Behring, Wampole, Captia, Sigma and Abbott Axsym) using well-defined panels of sera from rubella and non-rubella/rash-illness cases.

RESULTS

The Meddens, Denka Seiken, Behring and Wampole rubella IgM EIAs all performed similarly for sensitivity (range of 74.1-76.8%) and specificity (range of 93.9-96.1%). Relative to the other assays, the Axsym had a higher sensitivity (78.9%) but lower specificity (86.5%). The Captia assay had the lowest overall sensitivity (66.4%), while the Sigma assay had a lower specificity (85.6%) in relation to the other assays.

CONCLUSIONS

In conclusion, the Meddens, Denka Seiken, Behring and Wampole rubella IgM EIAs are comparable in their overall performance with respect to sensitivity and specificity.

Bilateral deafness due to congenital CMV and not rubella reinfection

We report on an infant with bilateral deafness discovered at the age of 5 months caused by a retrospectively diagnosed primary maternal CMV infection after definitive exclusion of maternal rubella reinfection as a cause of fetal infection.

Immunoglobulin G avidity in the serodiagnosis of congenital rubella syndrome

The avidity of specific IgG was investigated in three infants with serologically verified congenital rubella infection. Two sera were taken from each infant: the first soon after birth and the second at the age of 23 to 31 months. Avidity of specific IgG was measured by a protein-denaturing enzyme immunoassay using urea as the elution factor, and avidity then determined by the end-point ratio (derived from antibody titration) and the avidity index methods. Rubella-specific IgM was present in the first sera of all patients, but not in the second sera. However, low avidity of specific IgG persisted in two children until age 23 to 31 months, as determined by the end-point ratio method. These data are in agreement with the findings of previous studies of avidity in congenital rubella, and show the usefulness of the protein-denaturing IgG-avidity assays employing the end-point ratio method for serological diagnosis of congenital rubella even after disappearance of specific IgM.

Maturation of rubella IgG avidity over time after acute rubella infection

BACKGROUND

As the incidence of rubella has diminished, the proportion of unspecific rubella IgM reactivity among all samples with rubella IgM reactivity has increased. It is important to distinguish IgM reactivity caused by primary infection from that caused by reinfection or persistence, especially in pregnant women, as termination of pregnancy should be considered when primary rubella is diagnosed during the first trimester.

OBJECTIVES

To elucidate the changes over time of the avidity of rubella IgG antibodies after acute rubella infection.

STUDY DESIGN

Serial samples, 84, were collected from 15 patients up to 4-5 months after acute rubella infection. Rubella specific IgG avidity was tested by the eluting principle adding 35 mM diethylamine to the washing buffer of a commercially available rubella IgG ELISA. As controls, 137 samples from women with remote rubella and 94 samples from patients with a rubelliform rash, were tested.

RESULTS

The avidity index increased steadily in all patients during the observation time. A low avidity index (< 40%) was seen up to 6 weeks after onset of rash. A high avidity index (> 60%) was not observed until 13 weeks after infection and only in four of the 15 patients during the observation time.

CONCLUSIONS

An increase of rubella IgG antibody avidity was seen during the whole observation time but was most pronounced during the first 3 months after onset of rash. Measurement of rubella IgG avidity is a good supplemental test for cases with rubella IgM reactivity to confirm or exclude a recent rubella infection.

Behaviour of IgG antibody avidity for the antigen and of IgA antibody in active cytomegalovirus, Epstein-Barr virus, herpes simplex virus and human herpes virus 6 infections. Adaptation of a commercial test

The clinical value of specific IgA and IgG antibody avidity to herpes simplex virus, cytomegalovirus, Epstein-Barr virus and human herpes virus 6 for the detection of active disease and primary infection, respectively, was evaluated. The IgG avidity test, with a break point of 55%, for the detection of primary infection, and of the IgA test for the detection of disease, were associated with a sensitivity of 97% and 64%, respectively; specificity of 100% and 82%; a positive predictive value of 100% and 76%; and a negative predictive value of 96% and 72%, respectively.

Improvement in establishing the period of rubella virus primary infection using a mild protein denaturant

A more precise determination of the date of primary rubella infection in pregnancy is obtained by application of the urea denaturation method. Two denaturation buffers containing 6 and 8 M urea were compared for the detection of rubella IgG avidity by enzyme immunoassay. The results demonstrate that IgG avidity detected by 6M urea increases more rapidly, from 16% on the third day to 51% on the 46th day after the rash, than that obtained by 8 M urea, from 13 to 36%. The specific rubella IgG avidity detected by 6 M urea denaturation buffer increased significantly in paired sera obtained at an interval of 15 days. The same samples did not show any significant increase of IgG avidity when an 8 M urea denaturation buffer was used. The use of a mild denaturant such as 6 M urea indicates the presumptive date of primary rubella infection in pregnancy within 2 months of sampling.

Relative functional affinity of specific anti-core IgG in different categories of hepatitis B virus infection

While resolution of hepatitis B virus (HBV) infection occurs in most cases, a carrier state can exist in which the HBV surface antigen (HBsAg) persists. Some carriers are also positive for the HBV "e" antigen (HBeAg), indicative of high viral replication. Others are HBV "e" antibody (anti-HBe)-positive carriers in whom there appears to be a fall in the level of viral replication with the appearance of antibodies against the "e" antigen. The former group of carrier is considered to be at a higher risk of transmitting HBV infection than the latter. In order that a carrier state may occur, some degree of tolerance to the infectious agent must exist. A study of the rate of increase of specific antibody avidity following infection provides a means of assessing the maturity of the immune response to an infectious agent. Since antibodies specific for the HBV core antigen (HBcAg) are produced in almost all cases of HBV infection and the HBeAg and HBcAg share a large number of amino acids and some B- and T-cell epitopes, the increase in the avidity of antibodies against the HBV core antigen (anti-HBc) in cases of acute, resolving HBV infection and in HBV carriers has, therefore, been studied. An increase in the avidity of specific antibody, similar to that seen in other viral infections, was observed following acute, resolving infection. However, low avidity antibody persisted longer in carriers who remained positive for HBeAg, whereas in cases where there were antibodies specific for HBeAg, the anti-HBc antibody was of high avidity. Analysis of sequential sera from carriers who seroconverted from HBeAg-positive to anti-HBe-positive showed that an increase in anti-core avidity could predate seroconversion from HBeAg-positive to anti-HBe-positive status. Thus, anti-HBc avidity studies may be of diagnostic and prognostic significance.

Prenatal diagnosis of rubella virus infection by direct detection and semiquantitation of viral RNA in clinical samples by reverse transcription-PCR

A reverse transcription-nested PCR (RT-nPCR) method for prenatal diagnosis of rubella virus (RV) infection was developed. In the first step of RT-nPCR a synthetic RNA molecule (pRRV) differing from the RV target sequence by having a 21-nucleotide insertion was used as the internal control of amplification for the detection of PCR inhibitors. In addition, comparison of pRRV and RV-specific PCR signals allowed for the semiquantitation of RV input target sequences (range, 10 to > and = 1,000 RV genomes). In parallel, a complete RT-nPCR assay was performed with the same samples in the absence of the internal control to confirm the results of the first step and to detect RV RNA-positive samples containing < 10 RV genomes. Subsequently, the RT-nPCR method was used to examine retrospectively clinical samples (direct RT-nPCR) from eight congenitally infected and eight uninfected fetuses for RV RNA. RT-nPCR was also used to detect RV RNA in cell cultures (culture-RT-nPCR) 96 h after inoculation with the same specimens. With amniotic fluid (AF) samples, direct RT-nPCR identified eight of eight cases of RV transmission (sensitivity, 100%), whereas culture-RT-nPCR and virus isolation detected only six of eight cases (sensitivity, 75%). However, when the culture-RT-nPCR results were positive, culture-RT-nPCR confirmed the direct RT-nPCR results 3 days to 3 weeks earlier than virus isolation. The specificity of direct RT-nPCR was 100%, with eight of eight uninfected fetuses being negative. Semiquantitation showed only small amounts (< and = 100 copies) of viral RNA in clinical samples. In conclusion, direct RT-nPCR with AF samples (i) shows 100% sensitivity and specificity for prenatal diagnosis of RV infection and (ii) is a rapid technique, giving results in 24 to 48 h after sampling.

Infectious diseases

Routine antenatal screening can detect some potentially serious infectious diseases or susceptibility to infection and allow intervention to prevent adverse outcomes. However, screening programmes can only be justified if appropriate criteria are met for the quality of laboratory tests and interventions. For many infections that are associated with adverse maternal or fetal effects, there are no suitable, cost-effective methods of screening or prevention. However, early diagnosis of infection in high-risk women or those with symptoms can allow preventive intervention. Acute febrile illness or other symptoms consistent with infection during pregnancy should be investigated more diligently than in a non-pregnant woman. Early diagnosis of an apparently trivial maternal infection may prevent serious fetal disease. When the diagnosis of maternal infection is made, appropriate action depends on the nature of infection and the stage of pregnancy at which it occurs. The results of serological test should be confirmed, preferably by a reference laboratory, by retesting the original specimen(s) and/or testing further specimens, as appropriate. Management decisions generally should be made in consultation with an infectious disease physician or clinical microbiologist with experience of infectious diseases in pregnancy.

Comparison of four enzyme immunoassays for detection of immunoglobulin M antibodies against rubella virus

We evaluated four tests for the detection of rubella virus-specific immunoglobulin M antibodies. Primarily, consecutive serum samples were tested by two different assays. Selected panels of sera from patients with proven or likely recent rubella and false-positive and true-negative results in the two primary assays were further tested with two recently developed, fully automated techniques. The four tests were comparable in overall accuracy, but their dynamic ranges may differ considerably. Ways to optimize the predictive values are discussed. We conclude that automated assays may be used without causing significant changes in diagnostic accuracy or distortions in notifications of the incidence of rubella compared with the use of established tools.

Class and subclass distribution of Hantavirus-specific serum antibodies at different times after the onset of nephropathia epidemica

Sera from Dutch and Belgium individuals who suffered from nephropathia epidemica (NE), a mild form of haemorrhagic fever with renal syndrome (HFRS), were tested for the distribution of classes and subclasses of Hantavirus (HV)-specific antibodies at different times after the onset of the disease, with class- and subclass-specific Ig capture enzyme-linked immunosorbent assays (ELISAs). In the acute, early convalescent, and convalescent phases, predominantly specific IgA, IgM, and IgG3 antibodies were detected. Specific IgG2 antibodies were only detected at low levels in the early convalescent and convalescent phases. In the late convalescent phase specific IgG1 and IgG3 antibodies were found, whereas in the late postconvalescent phase only specific IgG1 antibodies proved to be present. Specific IgG4 antibodies were not detected in any of the respective phases. These data show that the simultaneous determination of classes and subclasses of HV specific serum antibodies allows the estimation of the time elapsed after the onset of NE.

The diagnosis of toxoplasmosis using IgG avidity

Current methods to establish the duration of toxoplasma infection in pregnant women and for the diagnosis of toxoplasmosis in the neonate or HIV infected patient have significant limitations. We assessed the precision of a commercial ELISA for the detection of toxoplasma specific IgG and adapted the assay to measure avidity using an elution agent washing step. The sensitivity and specificity of the ELISA were 100 and 75% respectively and optimal measurement of avidity was achieved using 6 M urea as the elution agent. Toxoplasma lymphadenopathy of less than 3 months duration was associated with low avidity specific IgG but some discordant findings were recorded. Serial measurement of IgG avidity assisted the distinction between actively produced antibody in infants with congenital toxoplasmosis and passively acquired antibody of maternal origin in uninfected babies. There was no significant difference between avidity levels in HIV infected patients with or without cerebral toxoplasmosis.

Slow maturation of IgG1 avidity and persistence of specific IgM in congenital rubella: implications for diagnosis and immunopathology

Without appropriately timed specimens, serological confirmation of congenital rubella infection may be a problem. We have compared the persistence of specific IgM and low avidity specific IgG1 in 141 sera from 120 cases of serologically confirmed congenital rubella infection with the known time scales for postnatal primary rubella. The results demonstrate that the maturation of the immune response to the rubella virus is abnormally slow in congenital rubella cases both in terms of the isotype switch and especially the development of high avidity specific IgG1. Thus avidity studies may permit serological confirmation of congenital rubella for longer than is possible with tests currently in use. The pathological implications of prolonged low avidity antibody production are discussed.

Application of low-avidity immunoglobulin G studies to diagnosis of Epstein-Barr virus infectious mononucleosis

Single serum samples from 121 patients suffering from clinical infectious mononucleosis were tested by an indirect immunofluorescence assay for avidity of Epstein-Barr virus (EBV) capsid antigen immunoglobulin G (IgG), involving a wash step with phosphate-buffered saline-8 M urea. Ninety-four samples showed serological markers of recent EBV infection (presence of viral-capsid antigen-specific IgM [87 cases] and/or presence of IgG in the absence of EBV nuclear antigen antibodies [85 cases]). The remaining 27 cases had serological evidence of prior infection (presence of viral-capsid IgG and EBV nuclear antibodies and absence of IgM). In the avidity assay, 89 samples from patients with recent infection showed low-avidity IgG and 25 samples from patients with prior infection had high-avidity IgG. The avidity assay showed a sensitivity that was at least equal to those of classical serological procedures for diagnosing EBV infectious mononucleosis. Further studies are necessary, however, to establish the specificity of the assay and the duration of low-avidity antibodies.