Serological cross reactivity to CMV and EBV causes problems in the diagnosis of acute hepatitis E virus infection.

Hepatitis E virus (HEV) infection is an important public health concern as a major cause of enterically-transmitted hepatitis worldwide. The detectable window of viraemia is narrow, and HEV IgM and IgG rise simultaneously in acute infection. Furthermore, previous investigators have shown HEV IgM false positive reactions occur against EBV, CMV and potentially hepatitis A. A retrospective analysis of HEV serology testing was performed at a London tertiary referral hospital over a 3-year period. A thousand four hundred and twenty three serum samples were tested for HEV serology, with 33 samples HEV IgM positive and 28 HEV IgM equivocal. One hundred and eleven samples were HEV IgG positive but IgM negative suggesting past infection. No patients with HEV IgM positivity had false positive reactions against hepatitis A. A high degree of EBV and CMV cross reactivity was noted, with 33.3% and 24.2% of HEV IgM positive samples also testing positive for EBV and CMV IgM, respectively. HEV RNA was detected in four HEV IgM positive samples, indicating true positivity, although three demonstrated cross reactivity against EBV. Only 13.3% of samples with positive HEV IgM were HEV PCR positive, highlighting a low positive predictive value of serology testing. Overall a high level of HEV, EBV and CMV IgM cross reactivity was demonstrated, indicating that serology is unreliable in the diagnosis of acute viral hepatitis. It is concluded that that the diagnosis of viral hepatitis should be based on clinical features, raised transaminases, serology, and confirmatory PCR testing.

Comparison of automated chemiluminescence immunoassays with capture enzyme immunoassays for the detection of measles and mumps IgM antibodies in serum.

Outbreaks of measles and mumps occur regularly in the UK. Rapid diagnosis of acute infection is important for both infection control and epidemiological purposes. The objective of this study was to compare the performance of an automated platform (DiaSorin Liaison(®), Saluggia, Italy) with a manual capture enzyme immunoassay (EIA; Microimmune, Hounslow, UK) for the detection of measles and mumps IgM antibodies in serum from symptomatic individuals. Ninety sera tested previously for measles (n=50) and mumps (n=40) IgM using the manual EIA were tested retrospectively using the DiaSorin Liaison(®) and the results compared. Sensitivity, specificity, inter-assay variability and intra-assay variability of the Liaison(®) assays were calculated. Sensitivity and specificity of the Liaison(®) assay for measles IgM were 92% and 100% respectively, with inter-assay variation of 14.1% and intra-assay variation of 12.5%. The sensitivity and specificity of the mumps IgM Liaison(®) assay were 88% and 95% respectively, with an inter-assay and intra-assay variation of 13.9% and 5.3% respectively. Both the measles and mumps IgM Liaison(®) assays gave fewer equivocal results than the EIA. Neither Liaison(®) IgM assay showed any cross-reactivity with sera positive against other viruses, however the measles IgM EIA cross-reacted with parvovirus IgM. The automated Liaison(®) assays are more specific, cheaper and less labour-intensive compared to the manual EIA. The Liaison(®) assays benefit from reduced number of equivocal results compared to the EIA for both measles and mumps IgM. This allows clinical decisions to be made accurately and in a timely manner.