Background:
Early evaluations (1990-93) of the Malmö needle and syringe program found hepatitis B incidence to be 11.7 seroconversions/100 years at risk. Vaccination against HBV was introduced to all eligible participants in 1994. Coverage and efficacy have since been sufficient to prevent outbreaks. HBV incidence declined to 3.4/100 pyr in 1997-2005. No incident cases have been observed for the past decade – until this spring. Five incident, symptomatic cases have been identified so far between February and June 2025.
Methods:
All five cases were admitted to the ID wards. Contact tracing resulted in approximately 25 contacts, of whom the majority were NSP participants. A team consisting of NSP staff (nurses, assistant nurses, ID physicians and social workers) implemented an outreach routine, visiting four low threshold centers providing information, testing and vaccination.
Results:
So far, two more cases with ongoing HBV infection were found. One was an asymptomatic acute infection identified via contact tracing, while the other was a person with a chronic infection acquired in childhood. This patient has been identified as the source of transmission. Whole genome sequencing revealed identical viral strains for all cases. At the low threshold shelters, around 40 persons have been tested for HBV, hiv and HCV and those susceptible for HBV have been offered vaccination. None of the contacts participating in the NSP had an ongoing HCV infection, while 3 HCV cases were found via the outreach team.
Conclusion:
HBV outbreaks have been rare in this target population. However, despite access to NSP and HBV vaccination, an outbreak may occur through introduction of a highly viremic patient with chronic HBV infection. Through a warm alliance with the target population, the NSP outreach team could rapidly gain access to the persons at risk, identify the source and conduct contact tracing. Whole genome sequencing established viral clustering. |