Measurement of antibody avidity for hepatitis C virus distinguishes primary antibody responses from passively acquired antibody

A new IgG antibody avidity test for hepatitis C virus (HCV) has been developed and was validated using sera from 12 renal dialysis patients infected with HCV. In primary HCV infection low avidity antibody (mean avidity index 24%) was detected within 50 days of seroconversion whereas in long-term infection (at least 300 days after seroconversion), the mean avidity index was high (88%); in five patients, the avidity index was shown to increase rapidly as time elapsed after primary infection, whereas immunosuppressive therapy was found to delay maturation of the immune reponse in two further patients. The assay was then employed to confirm that a spurious outbreak of primary HCV infection in eight bone marrow transplant patients was explicable by passive acquisition of high avidity anti-HCV after intravenous immunoglobulin therapy. It is concluded that this avidity test will have an important role in the investigation of HCV infection in patients. © 1994 Wiley-Liss, Inc.     

Anti-HCV IgG avidity index in acute hepatitis C.

BACKGROUND: The diagnosis of acute hepatitis C (AHC) is based on seroconversion to positive anti-HCV, which is usually not clinically possible. OBJECTIVE: To determine if avidity of anti-HCV IgG can be used for the diagnosis of AHC infection. STUDY DESIGN: We enrolled 40 consecutive patients with AHC, 16 drug addicts (IVDA) with exacerbation of chronic hepatitis C (IVDA e-CHC group), 21 non-IVDA with exacerbation of chronic hepatitis C (IVDA-free e-CHC group) and 40 with chronic hepatitis C (CHC group). HCV avidity index (HCV-AI) was determined by ELISA on sera pre-diluted 1:10 with 1M guanidine. RESULTS: On admission, HCV-AI values were significantly lower in the AHC group (mean+/-S.D.: 0.50+/-0.30) than in IVDA-free e-CHC group (0.97+/-0.08, p<0.0001), IVDA e-CHC group (0.90+/-0.29, p<0.0001) or CHC group (1.06+/-0.20, p<0.0001). An HCV-AI lower than 0.7 obtained within the 8th day of illness distinguished patients with AHC infection from the IVDA-free e-CHC cases. An increase in HCV-AI was observed in 24 (72.7%) of 33 in AHC group, in none of 13 in IVDA-free e-CHC group and in 3 (27.3%) of 11 in IVDA e-CHC group. CONCLUSION: HCV-AI is useful in identifying AHC infection in patients observed within the 8th day from the onset of symptoms.     

Use of an Anti-Hepatitis C Virus (HCV) IgG Avidity Assay To Identify Recent HCV Infection

There is no reliable and simple diagnostic marker available to diagnose recent hepatitis C virus (HCV) infection. It has been shown that the avidity of specific IgG antibody is low in primary viral infection and increases with time. We report the development of an anti-HCV avidity assay derived from a commercially available test. A panel of 117 sera was first examined for IgG avidity. It was composed of samples from patients with recent (group 1, n = 14), chronic (group 2, n = 70), and resolved (group 3, n = 33) HCV infections. Avidity index (AI) values observed in recently infected patients were significantly lower (12.0% ± 9.2% [mean ± standard deviation]) than those found in chronic carriers (83.1% ± 15.2%). Using a threshold of 43.0%, this assay distinguished between groups 1 and 2 with very high sensitivity (98%) and specificity (100%). For group 3, a broader distribution of the AI values was observed (54.8% ± 27.3%), suggesting that this index would not be useful in HCV RNA-negative patients. Blind validation of the test was carried out with a panel of 36 serum samples from 17 HCV seroconverters. The assay described here is a useful tool to distinguish recent from chronic infection in HCV-viremic patients.Hepatitis C virus (HCV) can be acquired or transmitted via any blood-borne route. Intravenous drug use has become the main transmission mechanism of HCV in Western countries (5). Patients with acute HCV infection are generally asymptomatic. Those who are symptomatic may exhibit jaundice but more often complain of fatigue, nausea, abdominal pain, or flulike symptoms. An average of 30% of patients with acute hepatitis C experience spontaneous viral clearance during the first 3 months after the clinical onset of the disease (15). Chronic disease should be considered if viremia persists for more than 6 months. Chronic hepatitis C is also generally clinically silent for a sustained period of time. This results in fortuitous diagnosis at a late stage of disease in most cases.There is no reliable and simple diagnostic marker currently available to diagnose recent hepatitis C virus infection. Increases in serum aminotransferase may be indicative of a recent infection but are also seen in exacerbation phases of chronic hepatitis C. They may also arise due to other acute disorders, such as alcohol-induced hepatitis. Specific IgM responses to HCV do not serve as useful markers in the diagnosis of recent hepatitis C, because IgM may be present at similar levels in both recent and chronic disease (14, 20). HCV seroconversion remains the only useful marker of recent HCV infection.An accurate estimate of HCV incidence would be useful to target interventions to high-risk populations but is a major challenge for epidemiologists. The avidity of an antibody may be an early and reliable marker of recent viral infection. Avidity increases progressively with time after exposure to an immunogen due to rapid mutations in the DNA coding for the variable part of the antibody (8, 19). Antibodies of low avidity are usually indicative of recent infection. Avidity assays have been developed for many viral infections (rubella virus, cytomegalovirus, varicella-zoster virus, and HIV-1) (2, 6, 7, 10, 16). Commercial immunoassays for anti-HCV antibody detection have been adapted to test for avidity. They have confirmed that anti-HCV avidity increases with time after primary infection (3, 11, 17). However, the limited evaluation of such assays in small populations has hampered their development for use in clinical practice. More recently, the development of an “in-house” anti-HCV IgG avidity assay, using a combination of target antigens, has been validated with seroconversion panels and samples from chronically infected individuals (12).Here, we report the development of an anti-HCV avidity assay, derived from a commercially available third-generation enzyme-linked immunosorbent assay (ELISA). The test was evaluated using a panel of established recent and chronic HCV infections. The usefulness and the clinical significance of the anti-HCV avidity index (AI) are also discussed.     

IgM- and IgG-class antibodies to the hepatitis C virus]

The test system widely used currently for the determination of anti-HCV permits the detection of anti-HCV IgG alone. The data recently published by T. G. Wreghitt et al. confirm the probability of the presence of anti-HCV of both IgG and IgM classes in sera from hepatitis C patients. Anti-HCV IgM was detected by Ortho test with some modifications using an anti-M conjugate in the last stage of the experiment. Anti-HCV IgG were detected by regular Ortho test. A total of 46 patients with different forms of HCV infection and a control group were examined. According to the preliminary data, 18 patients were positive in the routine anti-HCV Ortho test. Among 18 anti-HCV-positive patients, nine had chronic HCV infection and the other 9 acute HCV infection. The distribution of IgM and IgG anti-HCV in the acute patients was as follows: 4 patients (44.5%) had approximately equal titres of IgG and IgM, 3 (33.5%) had predominantly IgG, 2 (22.2%) mainly IgM. A similar pattern was observed in the group with chronic HCV infection. Thus, 5 subjects (55.6%) showed approximately equal ratio of IgM and IgG anti-HCV, 2 (22.2%) had mostly IgM and the rest 2 mainly IgG. No anti-HCV in the control group was found. The control group consisted of 18 patients with chronic liver diseases without markers of HBV or HDV infection, 3 with HAV infection, 2 with HBV infection and 5 healthy subjects. The specificity of anti-HCV IgM test was confirmed by Chiron Western blot analysis using the same modification.(ABSTRACT TRUNCATED AT 250 WORDS)     

Quantitative antibody analysis: use for the diagnosis of hepatitis C virus chronic infection

Hepatitis C virus (HCV) infection has been estimated in 600,000 subjects in France, with about 80 % of chronic infection. In the latter, anti-HCV antibodies and viral RNA are found together in patients blood. Today, only the use of polymerase chain reaction (PCR) technology allows the diagnosis of HCV chronic infection, confirmed by a positive PCR. However, PCR is a laborious and cost effective method. The aim of this study was to distinguish HCV chronic infection to past-infection or false reactivity only using the serology testing. Therefore, we looked for a correlation between the results of PCR, using the HCV Cobas Amplicor 2.0 assay, and the level of anti-HCV antibodies, assessed by the AxSYM HCV v.3.0 and expressed in signal/cutoff (s/co) ratio. We found using a panel of 200 sera issued from 181 patients, a significant variation of s/co ratios between PCR positive and negative patients (respectively, 87.76 +/- 27.18 vs 10.13 +/- 13.68 s/co, p < 0.0001), only in non treated or previously treated patients, non HIV coinfected, non renal transplanted or haemodialysis patients. An anti-HCV cutoff value at 34 s/co allows a predictive PCR results with 100 % sensitivity and 93.3 % specificity. Thus, for patients having a s/co equal or over 34, a positive PCR was found in 98.1 % of cases, allowing the diagnosis of HCV chronic infection (positive predictive value). Conversely, in patients with less than 34, HCV chronic infection can be excluded in 100 % of cases (negative predictive value). In conclusion, in most cases, the use of anti-HCV quantitative analysis in the AxSYM HCV v.3.0 assay could avoid PCR testing and facilitate the diagnosis of HCV chronic infection.     

Intrafamilial transmission of hepatitis C virus in Japan.

To clarify the intrafamilial transmission of hepatitis C virus (HCV), the prevalence of antibody to HCV (anti-HCV) in 107 index patients with type C chronic liver disease was studied and compared with the prevalence of anti-HCV antibody in their 296 family members. Of the 85 index patients who were positive for anti-HCV, 15 (8%) of 196 of their family members were also HCV antibody positive, whereas of the 22 index patients who were anti-HCV antibody negative, none of the family members of the 100 evaluated was positive for anti-HCV antibody, a statistically significant difference between groups (P less than 0.02). No specific relative (spouse, child, parent, and sibling) was linked to HCV positivity in the index cases making it difficult to identify the route of infection that is believed to occur via the parenteral route in the home or community.     

Validation of an in-house assay for cytomegalovirus immunoglobulin G (CMV IgG) avidity and relationship of avidity to CMV IgM levels

Measurement of cytomegalovirus (CMV)-specific immunoglobulin G (IgG) avidity has proven to be a powerful tool for distinguishing primary from nonprimary CMV infection. An in-house enzyme-linked immunosorbent assay (ELISA) for measuring CMV IgG avidity was validated using 84 sera from pregnant women who had recently seroconverted following primary CMV infection and 74 sera from individuals with past CMV infection (IgG-positive and IgM-negative profile). Of the 84 sera from pregnant women, 73 sera were collected within 120 days of the last IgG-negative sample, and 72 of these 73 sera (99%) exhibited an avidity index (AI) of <50%. In contrast, 71 of 74 (96%) sera from individuals with past CMV infection exhibited CMV AI values of > 60%. Thus, low avidity in the in-house ELISA was defined as an AI of < or = 50%, whereas high avidity was defined as an AI of > or = 60%. In additional studies, the relationship between CMV IgG avidity and CMV IgM levels was examined using 64 CMV IgG-positive sera (time since seroconversion unknown) exhibiting equivocal or positive results in a CMV IgM capture ELISA (Diamedix). Of these 64 sera, 29 exhibited IgM index values of > or = 3.0, and 27 of these 29 (93%) exhibited low IgG avidity. A similar trend was observed when a subset of these 64 sera (n = 48) was tested in another CMV IgM capture ELISA (Trinity); of 18 sera with IgM index values of > or = 3.0, 17 (94%) exhibited low IgG avidity. These findings demonstrate the validity of an in-house ELISA for CMV IgG avidity and further show that strong reactivity of CMV IgG-positive sera in either of two CMV IgM capture assays is a reliable indicator of low CMV IgG avidity, and thus, recent CMV infection.     

Distinguishing acute from chronic and resolved hepatitis C virus (HCV) infections by measurement of anti-HCV immunoglobulin G avidity index

An assay to measure avidity index (AI) was developed to diagnose incident hepatitis C virus (HCV) infections. The assay demonstrated an AI value statistically significantly lower in primary HCV infections than in chronic infections. When the assay was applied to past resolved infections, the difference in AI values was not as significant as the difference between incident and chronic infections. Lower AI values obtained in past resolved infections may be directly related to lower levels of immunoglobulin G anti-HCV in past resolved infections than in either new infections or chronic infections.     

Prevalence of antibodies and RNA genome of hepatitis E virus in a cohort of French immunocompromised

BackgroundRecently, cases of chronic hepatitis E have been identified in immunocompromised patients.ObjectivesTo evaluate the prevalence of anti-HEV IgG antibodies and the persistence of HEV-RNA in sera of immunocompromised patients with regular follow-up at Saint-Louis Hospital in Paris, France.Study design307 samples collected from 261 HIV-infected patients and 46 kidney transplant (KT)-patients were retrospectively tested for the presence of the following hepatitis E virus (HEV) infection markers: anti-HEV IgM antibodies, anti-HEV IgG antibodies, anti-HEV IgG avidity index, and HEV-RNA.ResultsAnti-HEV IgG positive serology was found in 4 HIV-infected patients (1.5%) and 3 KT-patients (6.5%), leading to an overall seroprevalence of 2.3%. HEV-RNA detection was not observed among 55 HIV-patients at higher risk of chronic HEV (<200 CD4 cells/mm³, elevated alanine aminotransferase (ALT) levels, and/or positive anti-HEV antibodies) and among 44 KT-patients. None of the seven patients had anti-HEV IgM antibodies, thereby excluding any acute infection. The IgG avidity index confirmed past HEV infection among tested patients.ConclusionsThe low seroprevalence observed in the Paris region does not warrant a systematic evaluation of HEV infection in immunocompromised patients. However, HEV infection must be examined as a possibility if unexplained increases in ALT should occur and after more common viral hepatitis infections are excluded.     

Serum immunoglobulin G antibodies to the GOR autoepitope are present in patients with occult hepatitis C virus (HCV) infection despite lack of HCV-specific antibodies

Antibody responses to the GOR autoepitope are frequently detected among anti-hepatitis C virus (anti-HCV)-positive patients with chronic hepatitis. Sera from 110 anti-HCV-negative patients with occult HCV infection, as diagnosed by detection of HCV RNA in hepatic tissue, were investigated for GOR antibody reactivity. A positive test for anti-GOR immunoglobulin G (IgG) was found for 22 (20%) of them. The frequency and titers of anti-GOR IgG were significantly lower than those in chronic hepatitis C patients (70/110, 63.6%; P < 0.001). Anti-GOR IgG was not detected in any of the 120 patients with HCV-unrelated liver disease. The anti-GOR IgG assay showed specificity and sensitivity values of 100% and 20%, respectively, among the sera from patients with occult HCV infection; the positive and negative predictive values were 100% and 44.3%, respectively. None of the clinical, laboratory, or histological characteristics of the patients with occult HCV infection were different according to GOR antibody status, except that the percentage of HCV RNA-positive hepatocytes was significantly greater (P = 0.042) in patients with occult HCV infection who tested positive for anti-GOR IgG. In conclusion, serum anti-GOR IgG is present in patients with occult HCV infection, despite a lack of detectable HCV-specific antibodies as determined by commercial tests. Testing for anti-GOR IgG in patients in whom HCV RNA is not detected in their sera may help with the identification of a subset of patients with occult HCV infection without the need to perform a liver biopsy.     

Antibody to hepatitis C virus in cryptogenic chronic liver disease.

The prevalence of antibody to hepatitis C virus (HCV) was studied in 207 patients with chronic liver disease of unknown etiology, in relation to clinical, epidemiological and histological features. Serum antibody to C-100 epitope of HCV was detected by ELISA in 82.6% of patients, with a significant difference compared with a group of patients with primary biliary cirrhosis (10%). The presence of anti-HCV antibody in serum did not correlate with age, sex, histological diagnosis, and activity and duration of the disease, nor with serum anti-HBc, used as a marker of exposure to hepatitis B virus infection. These results strongly support the view that most cases that were previously defined as cryptogenic forms of chronic liver disease are in fact related to HCV infection. There was a correlation between serum anti-HCV antibody and history of risk for parenteral exposure or of acute hepatitis. This correlation was particularly evident for transmission by parenteral route, suggesting that HCV infection may be transmitted often by this route (36.8% among anti-HCV antibody-positive patients and 11.1% among anti-HCV-negative patients). Liver disease in patients without risk factors for parenteral transmission and with lower prevalence of anti-HCV antibody may be caused by other as yet unidentified non-A, non-B (non-C) agents or may be of nonviral origin.     

Multicenter evaluation of a rapid and convenient method for determination of cytomegalovirus immunoglobulin G avidity

An easy, rapid, and reproducible test to distinguish residual cytomegalovirus (CMV) immunoglobulin M (IgM) antibodies from antibodies produced in primary infection could be useful, especially for pregnant women. The CMV avidity of IgG antibodies with the VIDAS automated enzyme-linked fluorescent assay and 6 M urea was evaluated in a multicenter study to differentiate between primary CMV infections and past infections or reactivations. A total of 416 serum specimens were tested: 159 specimens were from follow-up of primary infections, and 257 were from past infections. All of the specimens from primary infections collected within 4 months (17 weeks) after the onset of the infection had an avidity index lower than 0.8. An avidity index higher than 0.8 excludes a recent primary infection of less than 4 months. However, an avidity index higher than 0.8 cannot confirm all past infections, since 48 specimens (18%) from past infections had an avidity index lower than 0.8 (between 0.5 and 0.8). The exclusion capacity could be improved (96.9%) by using a cutoff of 0.7, but this index would decrease the specificity of the technique, since the avidity index was found to be between 0.7 and 0.8 in two patients with recent primary infection. All specimens from primary infections obtained more than 4 months after the onset of infection had an avidity index more than 0.2. In this study, an avidity index less than 0.2 confirms the presence of a recent primary infection of less than 4 months. The VIDAS CMV IgG avidity test is a rapid, reproducible test with very good performance.     

Gamma glutamyltranspeptidase activity and viral hepatitis in dialysis population

BACKGROUND: Numerous investigations have reported that viral hepatitis is associated with significant hepatocellular damage, as expressed by raised aminotransferases in serum, in dialysis population. However, scarce information exists on the activity of gamma glutamyltranspeptidase (GGTP) in dialysis patients with infection by hepatotropic viruses. OBJECTIVES: We measured serum GGTP values in a large cohort (n=757) of patients receiving long-term dialysis; healthy controls were also included. The relationship between GGTP values and a series of demographic, clinical, and biochemical parameters was analyzed. METHODS: Serum GGTP levels were tested by spectrophotometry. A subset (n=333) of dialysis patients was tested by molecular technology (branched-chain DNA (bDNA) assay) to evaluate the relationship between serum GGTP and HCV viremia. A subgroup (n=78) of dialysis patients was analyzed by an ultrasound scan of gallbladder and biliary tract to assess the presence of gallstone disease. Multivariate analyses were made using regression models; serum GGTP values were included as a dependent variable. The usefulness of serum GGTP levels in detecting HBsAg and anti-HCV positivity was evaluated using receiver operating characteristics (ROC) curve analysis. RESULTS: Univariate analysis showed that serum GGTP levels were significantly higher in HBsAg positive and/or anti-HCV positive patients than in HBsAg negative/anti-HCV negative patients on dialysis; 85.1+/-184.1 versus 25.86+/-23.9 IU/l (P=0.0001). The frequency of raised GGTP levels was 22.2% (41/184) among dialysis patients with chronic viral hepatitis. Multivariate analysis showed a significant and independent association between serum GGTP values and positive HBsAg (P=0.005) and anti-HCV antibody (P=0.0001) status. Mean GGTP values were significantly higher in study patients than controls, 32.32+/-60.02 versus 23.5+/-16.92 IU/L (P=0.01); however, no significant difference with regard to GGTP between study and healthy cohorts persisted after correction for age, gender, race, and viral markers. No relationship between gallstone disease and serum GGTP was found (NS). An independent and significant association (P=0.0291) between raised GGTP levels and detectable HCV RNA in serum was noted among patients tested by biology molecular techniques. ROC technology demonstrated that GGTP was equally useful for detecting HBV (P=0.0004) and HCV (P=0.0005) among dialysis patients. CONCLUSIONS: We found an independent and significant association between serum GGTP values and HBsAg and/or anti-HCV antibody in dialysis population. Twenty-two percent of dialysis patients with chronic viral hepatitis had elevated GGTP. No difference in GGTP between HBsAg- negative/anti-HCV- negative dialysis patients and healthy individuals was found. Routine testing for serum GGTP levels to assess liver disease induced by hepatotropic viruses or other agents in dialysis population is suggested.     

Variability of IgM response in hepatitis C virus infection

The IgM and IgG antibody response to various hepatitis C virus (HCV) antigens was studied in 8 patients who acquired posttransfusion HCV infection. IgM anti-HCV was detectable in only 4 of these patients, coincident with (1 patient) or later than (3 patients) the IgG anti-HCV response. Seven patients had initially decreasing IgG anti-HCV titres, indicating passive transfer of antibodies from donor to recipient. All 8 patients showed active IgG seroconversion, as demonstrated by increasing IgG anti-HCV titres, on average, 75 days after infection. Five years after infection, all patients were still reactive for IgG anti-HCV antibodies and 7 were positive for HCV RNA by the polymerase chain reaction (PCR). Two of these PCR positive patients were also reactive for IgM anti-HCV. It is concluded that the serology of HCV infection does not follow the classical pattern of IgM response preceding detection of IgG. The IgM response may be absent, late, or persistent after HCV infection. The serological diagnosis of recent HCV infection should be based on the polymerase chain reaction or rising IgG titres in at least 2 sequential patient blood samples. © 1993 Wiley-Liss, Inc.     

HCV replication in mononuclear cells stimulates anti-HCV-secreting B cells and reflects nonresponsiveness to interferon-α

Recently, it was demonstrated in chronic hepatitis C that the release of IgG and IgM anti-HCV antibodies by mononuclear cells (PBMCs) correlated with inflammatory activity, HCV persistence in serum, and negative outcome from antiviral therapy. Thus, persistent antigenic stimulation of the antibody-secreting B cells has been suggested. In this study, PBMCs were derived from 13 patients with chronic hepatitis C. Nucleic acids were extracted by the guanidine-thiocy-anate-method, and plus- and minus-stranded HCV-RNAs were determined using primers from the 5′-untranslated region of HCV. Simultaneously, unstimulated PBMCs were cultured for 8 days and anti-HCV antibodies were detected in the supernatants by EIA and RIBA. Seven patients (53.8%) had both plus- and minus-stranded HCV-RNA in PBMCs, while anti-HCV antibodies were secreted in vitro. One of 2 patients with plus- but not minus-stranded HCV- RNA in PBMCs was anti-HCV positive in vitro, whereas 4 patients without HCV-infected PBMCs were anti-HCV negative in vitro. Eight patients received antiviral therapy with interferon-α2b. Four nonresponders and 1 partial responder had plus- and minus-stranded HCV- RNA in PBMCs and anti-HCV secretion in vitro. On the other hand, 2 complete responders and another partial responder showed neither HCV infection of PBMCs nor anti-HCV secretion in vitro. In conclusion, infection of PBMCs by HCV is observed frequently in patients with chronic hepatitis C, and may be related to the high rate of nonresponders to antiviral treatment. The close correlation of anti-HCV secretion in vitro and viral replication suggests that the humoral response to HCV is triggered by viral antigens that are expressed on infected mononuclear cells. © 1995 Wiley-Liss, Inc.     

Hepatitis C virus (HCV) infection in childhood

We studied the prevalence of hepatitis C virus (HCV) infection in childhood by determining HCV antibody (Ortho Diagnostic Systems, USA). Among patients with post-transfusion non-A, non-B hepatitis, anti-HCV was positive in 8 (72.7%) out of 11 patients. On the other hand, only 1 (25.0%) out of 4 patients of the children with acute non-A, non-B hepatitis, and only 1 (20.0%) out of 5 with chronic non-A, non-B hepatitis patients were positive for anti-HCV. Among the infants with non-A, non-B hepatitis, anti-HCV was positive in 3 (7.5%) out of 40 infants. To demonstrate mother-to-infant transmission of HCV, we examined 7 infants born to 4 anti-HCV positive mothers for their GPT values and anti-HCV. Liver dysfunction occurred in all the infants but one. And 1 infant was positive for anti-HCV. This infant with positive anti-HCV and liver dysfunction was considered to be a case of mother-to-infant transmission of HCV. And in the infants with liver dysfunction and negative anti-HCV, it was suggested that liver dysfunction occurred in association with HCV infection.     

National prevalence estimates for cytomegalovirus IgM and IgG avidity and association between high IgM antibody titer and low IgG avidity

Primary cytomegalovirus (CMV) infection of the mother during pregnancy presents risk of CMV infection of the fetus with resulting permanent disability. CMV IgM antibody is generated following primary CMV infection but also can appear during nonprimary CMV infection and is thus of limited diagnostic use by itself. In contrast, the presence of low CMV IgG avidity has been shown to be a unique and reliable serologic indicator of primary CMV infection. We measured CMV IgG and IgM antibody levels and IgG avidity in sera from a population sample of 6,067 U.S. women aged 12 to 49 years from NHANES (National Health and Nutrition Examination Survey). The CMV IgG prevalence was 58% overall and increased strongly with age. The CMV IgM prevalence was 3.0% overall and remained relatively flat across age groups. The prevalence of low IgG avidity was 2.0% overall, decreased sharply with age, and was seen mainly among IgM-positive sera. Fourteen to 18% of the CMV IgM-positive sera were low IgG avidity, presumably representing primary CMV infection. High CMV IgM antibody titer was a strong predictor of low IgG avidity. The ability to reliably identify primary CMV infection during pregnancy is important for management of the pregnancy, including possible treatment options for the fetus. Both IgM and IgG avidity measurements provide useful clinical information for evaluating primary CMV infection, although commercial tests for CMV IgG avidity are not yet widely available in the United States.     

Clinical evaluation of the Roche Elecsys® CMV IgG Avidity assay

Congenital cytomegalovirus (CMV) infection has potentially severe consequences in newborns. The testing of pregnant women for CMV-specific antibodies may be useful for the identification of women at risk of transmitting the infection to the fetus. The determination of CMV IgG avidity helps to establish the timing of infection as IgG avidity matures during the course of infection. This study examines the performance of the Elecsys® CMV IgG Avidity assay using preselected samples from patients at different phases of CMV infection. The Elecsys® CMV IgG Avidity assay was tested at three sites using sequential samples from patients with recent primary CMV infection, as well as single samples from patients with recent primary or past CMV infection. The Elecsys® assay discriminated well between early (low avidity) and late (high avidity) phases of infection in sequential serum samples. Overall, 98.8 % of low-avidity samples corresponded to infection onset <180 days before sampling and 77.8 % of all high-avidity results corresponded to infection onset >90 days before sampling. The assay’s sensitivity was 90–97 %, with specificity ranging from 89 to 100 %, depending on the consideration of gray-zone avidity values. Single samples from recent primary or past infection showed similar distributions of avidity results. The Elecsys® CMV IgG Avidity assay results are in agreement with preselected samples from patients with primary or past CMV infection, showing that the test is an adequate predictor of the phase of infection.