The Blood Service has recently published the results of our recently completed hepatitis E virus (HEV) RNA prevalence study. HEV is a known transfusion-transmissible agent. HEV infection has increased in prevalence in many developed nations and a high proportion of HEV infections in donors are asymptomatic and therefore the exclusion of unwell donors has only limited effectiveness in preventing transfusion-transmission (TT).
HEV can lead to chronic infection in immunosuppressed patients such as transplant recipients. Because of this, and the high prevalence in donors in Europe, countries such as the UK have implemented HEV blood donor screening to protect transfusion recipients. However, there is treatment for chronic infection that will result in cure in the vast majority of infected patients.
In Australia in 2014, we performed a study that estimated the risk of blood donations being positive for HEV was 1 in 14,799 donations. Although this was lower than a number of other countries, we concluded that an additional study with a larger sample size was needed to ensure our risk assessment was based on adequate evidence with reduced uncertainty.
During 2016 we collected and tested 74,131 whole blood samples for HEV and only one sample was confirmed to be positive. This is the lowest reported prevalence in blood donors world-wide and, taking into account transmission factors and symptoms, we estimated the risk of an adverse outcome in Australia is approximately 1 in 3.5 million components transfused.
The risk of TT-HEV in Australia is low. As a result of our low prevalence, the expectation that complications due to TT would be exceedingly rare and feedback from clinician and government stakeholders, the Blood Service has concluded that HEV blood donor screening is not currently warranted in Australia. The vast majority of confirmed HEV infections in Australia are acquired through overseas travel, especially to developing countries. Blood donors are generally ineligible to donate fresh components on return from these countries because of deferrals related to the risk of malaria.
Although rare in Australia, food-borne infection (especially through inadequately cooked pork products) can occur in developed (western) countries. The risk from food-borne infection is far greater than the risk of acquisition through blood transfusion, which remains a relatively uncommon route of transmission, even in high risk countries.
Because chronic infection in immunosuppressed patients may be asymptomatic, a high index of suspicion is needed to diagnose HEV infection. Only low to moderate increases of ALT levels may occur and liver tests may be normal. The Blood Service and clinical experts recommend having a low threshold for considering testing for HEV in immunosuppressed patients, especially in the presence of mildly elevated ALT levels. Anti-HEV IgM and IgG may be negative so HEV RNA screening is the test of choice. It is recommended that clinicians considering a diagnosis of HEV obtain further advice from microbiologists.
All reports of suspected TT-HEV should be reported to the Blood Service for further evaluation. The Blood Service will continue to monitor the risk of HEV in Australia and will review our assessment if required.