The risk of intrauterine transmission of cytomegalovirus (CMV) during pregnancy is much greater for women who contract primary CMV infection after conception than for women with evidence of infection (circulating CMV antibodies) before conception. Thus, laboratory tests that aid in the identification of recent primary CMV infection are important tools for managing the care of pregnant women suspected of having been exposed to CMV. CMV IgM detection is a sensitive marker of primary CMV infection, but its specificity is poor because CMV IgM is also produced during viral reactivation and persists following primary infection in some individuals. Studies conducted over the last 20 years convincingly demonstrate that measurement of CMV IgG avidity is both a sensitive and a specific method for identifying pregnant women with recent primary CMV infection and thus at increased risk for vertical CMV transmission. IgG avidity is defined as the strength with which IgG binds to antigenic epitopes expressed by a given protein; it matures gradually during the 6 months following primary infection. Low CMV IgG avidity is an accurate indicator of primary infection within the preceding 3 to 4 months, whereas high avidity excludes primary infection within the preceding 3 months. In this minireview, we summarize published data demonstrating the clinical utility of CMV IgG avidity results for estimating time since primary infection in pregnant women, describe commercially available CMV IgG avidity assays, and discuss some of the issues and controversies surrounding CMV IgG avidity testing during pregnancy. C ongenital cytomegalovirus (CMV) infection is the most common intrauterine infection, occurring in approximately 40,000 newborns each year in the United States (1-4). The clinical manifestations include sensorineural hearing loss, visual impairment, mental retardation, and cognitive defects; 4% of infected infants do not survive (1,2,5,6).Several studies have demonstrated a strong link between primary CMV infection of the mother and in utero CMV transmission. The risk of congenital infection is approximately 40% in babies born to mothers who acquire a primary (initial) CMV infection after conception; in contrast, the risk is only about 1% in infants born to mothers who have evidence of CMV infection (i.e., circulating CMV antibodies) before conception (1,3,(6)(7)(8)(9). The few cases of CMV transmission in seropositive mothers reflect nonprimary CMV infections, defined as either viral reactivation or infection with a different strain of CMV during pregnancy (2, 3, 5). Preexisting maternal antibodies thus appear to offer substantial protection against congenital infection, most likely due to the ability of antibodies to control viremia (2, 9, 10).The established link between primary CMV infection during pregnancy and congenital infection makes identification of primary CMV infection an important goal in maternal and neonatal health care. However, Ͼ95% of pregnant women with primary CMV infection are asymptomatic and thus cannot be ...

Focus Technologies developed an indirect immunoglobulin G (IgG) enzyme-linked immunosorbent assay(ELISA) and a mu-capture IgM ELISA for the detection of West Nile virus (WNV)-specific antibodies based on a WNV preM/E protein recombinant antigen. Normal and disease state serum panels were used to assess the performance characteristics of the two WNV ELISA kits. Totals of 807 and 1,423 sera were used to assess the IgG ELISA and IgM ELISA kits, respectively. The Focus Technologies IgG ELISA had a sensitivity of 97.6% and a specificity of 92.1% (excluding non-WNV flavivirus sera). The comparative method for WNV IgG may lack sensitivity in detecting IgG in early WNV infection, so the specificity of the Focus IgG ELISA may be higher than 92.1%. When sera from patients either infected with or vaccinated against other flaviviruses were tested on the WNV IgG assay, 35% of the sera reacted as positive for WNV IgG. Yellow fever and Japanese encephalitis vaccinees were less reactive in the IgG ELISA than St. Louis and dengue fever patients. The Focus Technologies IgM ELISA had a sensitivity and a specificity of 99.3% (excluding the non-WNV flavivirus sera). The overall cross-reactivity for the IgM ELISA to flavivirus sera was 12%, with 31% of St. Louis encephalitis patients found to be WNV IgM positive and no yellow fever vaccinees found to be WNV IgM positive. In a selected population of 706 sera, 15 false-positive WNV IgM sera were identified. The use of a background subtraction method for the IgM ELISA eliminated all 15 false-positive results, giving a specificity of 100% for the Focus IgM ELISA.Since the initial outbreak of West Nile virus (WNV) in New York in 1999, WNV has spread rapidly across the entire continental United States in only 4 years (3,7,13,(16)(17)(18). WNV serology, in particular the detection of WNV immunoglobulin M (IgM) in both serum and cerebrospinal fluid, has become the primary tool for diagnosing human WNV infection. The detection of WNV IgM in serum represents a probable WNV infection, whereas the detection WNV IgM in cerebrospinal fluid is considered diagnostic of central nervous system involvement by WNV (13,15,24). Due to very low viremia at the time of clinical onset, nucleic acid detection methods and WNV culture are not useful diagnostic tools (10, 13). Only 20% of WNV-infected individuals are symptomatic; the majority of symptomatic patients present with a self-limited viral syndrome of fever, headache, malaise, and rash. Fewer than 1% of infected individuals progress to serious clinical disease, typically manifesting as either meningitis or encephalitis (19,22).WNV is a member of the Flaviviridae family and is in the Japanese encephalitis serocomplex that includes Japanese encephalitis (JE) virus and St. Louis encephalitis (SLE) virus. Other closely related flaviviruses include yellow fever (YF) virus and dengue virus types 1 to 4. The flavivirus antibody response is predominantly generated against the highly immunogenic envelope protein that contains both flavivirus crossreactive epitop...

During the westward spread of West Nile Virus (WNV) across the United States, most cases in a given season occurred in geographic areas where the virus was newly introduced. However, infections continue to occur in states with large numbers of cases in prior seasons, albeit at lower levels (4). In these areas where WNV is now endemic, the diagnostic utility of WNV immunoglobulin M (IgM) detection has come into question; this concern is based mainly on the findings of Roehrig et al. (18), who showed that WNV IgM remained detectable in some WNV encephalitis patients for more than a year. Thus, for some patients from areas of endemicity, it may be difficult to determine whether a positive WNV IgM result reflects recent infection versus infection during the prior season.Published findings for antibody responses to other flaviviruses suggest that WNV IgA detection may be a useful tool for distinguishing recent from past WNV infection. Virus-specific IgA appears quickly after infection by dengue viruses then falls to undetectable levels within a few months (6, 9, 22). Likewise, vaccine-induced yellow fever virus IgA disappears by about 80 days after vaccination (12). Preliminary findings consistent with these trends have been presented for WNV infection; Lanciotti (10) detected WNV IgA only between 11 and 50 days postinfection in most WNV-infected patients. However, systematic studies of WNV IgA production and persistence are lacking.A unique opportunity for assessing WNV antibody development and persistence recently emerged from efforts to identify donations from WNV-infected blood donors and thus reduce the risk of transfusion-associated transmission of WNV (13). During the 2003 WNV season, blood collection agencies began measuring levels of WNV RNA in plasma by nucleic acid amplification test (NAT) screening, and viremic (i.e., WNV RNA-positive) donors were enrolled in follow-up studies designed to assess the length of the viremic period and document the antibody response to WNV (3). We report here findings on the emergence and persistence of the major classes (IgM, IgA, and IgG) of WNV antibodies during follow-up of blood donors who donated a confirmed WNV RNA-positive unit during the 2003 season. MATERIALS AND METHODSBlood donor specimens. WNV RNA-positive blood donors were identified by NAT screening of donations made between June and November 2003 as previously described (3). Plasma from donations confirmed as WNV RNA-positive (hereafter referred to as the index donations), as well as plasma or serum specimens collected during follow-up visits, were supplied by Blood Systems Research Institute and American Red Cross Blood Services. Informed consent was obtained from all donors at the local blood donation site; protocols for NAT screening and follow-up were approved by local institutional review boards and the U.S. Food and Drug Administration.WNV antibody assays. Plasma and serum specimens were tested for WNV IgM and WNV IgG by using U.S. Food and Drug Administration-cleared enzyme-linked immunosorbent assay (...

Dengue virus (DV) IgM/IgG ratio and IgG avidity value (AV) can reliably distinguish between primary and secondary DV infections using sera collected within 30 days of disease onset, but little is known about their efficacies using sera collected >30 days after onset. To investigate this issue, we analyzed specimens submitted to our reference laboratory for DV antibody testing. We first classified patients as having primary (n ‫؍‬ 55) or secondary (n ‫؍‬ 58) infections based on seroconversion patterns in a comparison of two sera collected <30 days apart. We then evaluated IgM/IgG ratios and IgG AVs of the second specimens by using receiver operating characteristic curve analysis. The IgM/IgG ratio that best discriminated primary from secondary infection was 1.32; 95% of 55 primary infections exhibited ratios of >1.32, whereas 93% of 58 secondary infections exhibited ratios of <1.32. The discriminatory AV was 0.39; 95% of 41 primary infections exhibited AVs of <0.39, whereas 95% of 38 secondary infections exhibited AVs of >0.39. We then evaluated the IgM/IgG ratios and AV for primary-infection patients whose second serum samples were collected >30 days after the first serum samples; only 56% of 27 sera exhibited ratios of >1.32, whereas 81% of 21 sera exhibited AVs of <0.39. Assuming that the first specimens were collected within a week after symptoms appeared, these findings indicate that IgG AV is superior to the IgM/IgG ratio for distinguishing primary from secondary DV infections when using samples collected more than 5 weeks after disease onset.Infection with dengue virus (DV) poses a major public health burden in tropical and subtropical areas worldwide; many cases are associated with significant morbidity, ranging from a nonspecific febrile illness to severe hemorrhagic fever (8,16,23). Primary infection with any of the four DV serotypes induces an immune response that protects against later infection by that serotype; however, later infection by another serotype, referred to as secondary DV infection, is a risk factor for dengue hemorrhagic fever (17,19,25). Discrimination of primary from secondary DV infections is also a valuable epidemiological tool, providing information useful in determining if specific DV serotypes have been recently introduced or reintroduced within a given geographic area (22).DV IgM and IgG seroconversion patterns accurately distinguish primary from secondary DV infections (2, 5); for many patients, however, only one sample is available for testing, and it exhibits a DV IgM ϩ IgG ϩ reactivity pattern indicating that seroconversion has already occurred. In this setting, a reliable approach for determining if this IgM ϩ IgG ϩ result represents primary or secondary DV infection would be advantageous. Several groups have shown that the DV IgM/IgG ratio for sera collected within 30 days of symptom onset can be used to accurately classify patients as having primary or secondary infection (5,6,11,13,22). The discriminatory ratios range from 1.2 to 2.0, depending on the laboratory's assays...