Abstract
Background and aims
Hepatitis E virus is traditionally regarded as a virus of the developing world and is emerging as a leading cause of non-A/B/C hepatitis. We wished to investigate locally acquired transmission of hepatitis E in the West of Scotland and compare our use of traditional serology versus polymerase chain reaction since the introduction of polymerase chain reaction in 2007.
Methods
Clinical details provided on specimens of blood positive for hepatitis E virus by serology or polymerase chain reaction were collated and analysed.
Results
Since 2007, 30 samples were hepatitis E virus-positive by serology or polymerase chain reaction. Polymerase chain reaction positivity was generally associated with positive serology although four samples were polymerase chain reaction-negative and strongly positive by serology. Interestingly, one-quarter of cases were likely to represent endogenous transmission of the infection.
Conclusions
Polymerase chain reaction is valuable in reliably diagnosing hepatitis E virus. However, serology is valuable for diagnosing resolved infection. There may be a high level of undiagnosed locally acquired hepatitis E virus in Scotland.
Keywords
Introduction
Hepatitis E virus (HEV) is a small RNA virus and the sole member of the Hepeviridae. It is thought to be a leading cause of non-A/B/C hepatitis, but in developed countries, it has hitherto been considered an imported infection. An increasing number of cases are thought to be locally acquired (autochthonous) 1 and there is little published Scottish data on this topic. The advent of polymerase chain reaction (PCR) to diagnose HEV is prompting us to reconsider the value of serology alone. In this report, we describe data pertaining to cases of HEV in the West of Scotland following the introduction of PCR, elucidate the proportion of autochthonous and imported cases, and consider the merits of serology and PCR in clinical and epidemiological diagnosis.
Diagnosing HEV in the West of Scotland
Figure 1 illustrates the serological response to HEV. Guidelines from the Health Protection Agency (UK) classify a confirmed case of HEV as being PCR-positive with a compatible clinical history. Both IgM- and IgG-positivity are required in the context of a convincing clinical history and exclusion of other diagnoses before a PCR-negative case can be assumed to have been infected with HEV.
2
Natural history of HEV infection. The incubation period is around 40 days. Transaminases may peak up to six weeks post exposure, and this roughly coincides with symptoms of acute infection as well as IgM-positivity. The duration of IgM-positivity varies between patients and also depends on assays used, but it is very unusual to see strongly positive results after approximately 12 weeks. As one can see, a peak in both IgM and IgG simultaneously (unusually for most viruses) appears to correspond to a peak in symptoms. Specific IgG is produced early in infection and detectable up to 12 years later. Peak viraemia occurs during the incubation period and early acute disease and the mean window-period is 28 days (17–48 days); there is variable clearance of RNA from blood, but it may be detectable in stool for two weeks after clearance from blood.
In the West of Scotland, HEV testing is offered to clinicians on a case-by-case basis (e.g. non-A/B/C hepatitis or travel history). Figure 2 demonstrates our diagnostic algorithm. Plasma samples are initially screened by serology and samples showing reactivity are then tested by PCR. IgM reactives with positive PCR are reported as suggestive of recent infection. In practice, cases of PCR- and IgM-positivity with negative IgG are uncommon. IgG-positive results with equivocal/negative IgM are reported as evidence of previous exposure. PCR has proven useful for clarifying weak IgM reactivity in the presence or absence of IgG. This has shown that we almost always find both IgG and IgM in people who are symptomatic with HEV, thus weak IgMs are likely non-specific reactions. An additional role for PCR would be in immunosuppressed patients where serology is unhelpful.
HEV diagnostic algorithm. Samples that test positive for IgG or IgM are then screened by PCR which is a more sensitive and specific method for diagnosis.
Results
Since PCR was introduced in 2007, 30 specimens have been positive for HEV by a serologic parameter or PCR. There was a male predominance (22/30) and a broad spread of ages.
Place of transmission
Half of our patients had a travel history. We were unable to elucidate any information on two cases. The remaining cases had no travel history and were likely to represent autochthonous cases (Figure 3).
Place of transmission. More than 25% of cases did not have a history of travel or exposure to high-risk contacts and were likely to represent locally acquired infection.
PCR-positive results
Sixteen patients were PCR-positive; 15 of these were strongly IgG- and IgM-positive (Figure 4). One patient tested IgG-negative but strongly IgM-positive twice. Nine of 16 cases were from abroad (with travel to the Indian Subcontinent being a prominent feature), six cases had no travel history and on one case no information was available. One patient had a concurrent Salmonella typhi bacteraemia, and one patient had recent travel to the Canary Islands and developed acute hepatitis, a full liver screen including imaging was undertaken and HEV was the only positive result. It is difficult to say whether his HEV was transmitted abroad or locally acquired. Of the six PCR-positive cases that were likely to be locally acquired, five were males, all were aged over 50 and one patient was admitted to intensive treatment unit with multiple organ failure and had a background of alcohol and drug abuse. Follow-up samples followed a classical course becoming PCR and IgM-negative.
PCR-positive results. Most of these were positive for both IgM and IgG, and six of these were likely to be locally acquired.
PCR-negative/serology-positive results
Fourteen of 30 patients were PCR-negative and serology-positive. Confirmatory specimens were requested but for the majority these were never received. In six cases, IgM alone was weakly positive and in the absence of follow-up samples this was difficult to interpret.
Four results were very strongly positive for serology. One was a 60-year-old gentleman who was IgG-positive, whose liver function tests had been greatly deranged and had no other relevant history. Another patient was positive for both IgM and IgG, and this was unusual in that we appeared to have missed the window-period during which PCR may be positive in the blood and it would have been interesting to test his stool. These two cases are likely to represent resolved or resolving infection.
Discussion
HEV may contribute to over half of the cases of faecal-orally acquired acute viral hepatitis.2,3 Interestingly, there appears to be up to a 3 : 1 male-to-female bias in adults. 4 Infection is often subclinical and does not usually lead to a chronic hepatitis or a carrier state, although it has a 1% mortality. 5 Clinical infection manifests with typical signs and symptoms of hepatitis such as jaundice and fever. Studies show that certain individuals are at increased risk of infection, severe disease and fatality. Autochthonous HEV which is most commonly diagnosed in elderly Caucasian males with no apparent risk factors and mortality rates in developed countries appear to be higher than developing countries, ranging from 8 to 11%. 2 Infection in pregnancy carries a 20% mortality, and immunocompromised patients are more likely to develop chronic infection, cirrhosis and have prolonged viral shedding.6,7 The mortality in chronic liver disease may be as high as 70%. 6 In addition to faecal-oral transmission, seroprevalence studies also suggest that HEV may be a porcine zoonosis, and there have also been reports of transfusion-associated transmission.2,6,7
Our data suggest that PCR can be used to reliably diagnose acute and ongoing HEV infection. PCR is particularly helpful in patients with weak positive serology, provided samples are taken during the window-period when viral nucleic acid can be detected. Serology has a role in the diagnosis of resolved infection. Given the morbidity and mortality associated with HEV, more diagnostic microbiology and virology laboratories in developed countries may opt to include HEV PCR in their first-line hepatitis screens as more reports of its autochthonous transmission emerge.
Footnotes
Declaration of conflicting interests
None declared.
Funding
This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.