The journal Eurosurveillance recently published a study investigating hepatitis A virus (HAV) sequences. Sequence-based typing has helped to detect clusters and identify outbreaks of hepatitis A in Sweden, the study found.
Scientists researched HAV sequences of 447 cases reported in the country from 2009–2018.
In the country of Sweden, hepatitis A is monitored by a national passive surveillance system, and is a notifiable disease. Since 2006, the Public Health Agency of Sweden (Folkhälsomyndigheten) has been carrying out sequence-based typing of clinic samples, as part of the country's microbiological surveillance program.
During the 10-year period of the study, 990 cases of hepatitis A were confirmed and reported to the surveillance system, with a range of 54–154 per year. Half of those in the study were male, and 513 were travel-associated. The median age of cases was 17, but ages ranged from less than 1 year old to 100 years old. Almost half of the people were in the youngest age groups of 0 to 4, and 5 to 14 year olds.
Outbreak strains were associated with certain foods, sexual transmission, and traveling to a HAV endemic country.
Starting in 2020, Folkhälsomyndigheten's goal was to type all notified hepatitis A cases in Sweden. Only 38 of 57 cases were typed last year, so this target was not reached.
In 2016, an assessment found that only about 50 percent of European countries do not do sequence-based typing. With sequence-based typing, a HAV strain of a contaminated food item can be linked to an outbreak strain, and identified as the source.
Researchers found that while comprehensive sampling and typing would allow a complete overview of HAV strains in a country, limited resources made it hard for selection of strains to be sequenced, especially in a medium-to-high incidence setting.
From 2012–2014, typing was necessary to determine the different strains of hepatitis A during multi-country outbreaks linked to frozen berries, even though epidemiological information was sufficient in two of the three outbreaks to trigger an outbreak signal.