Outbreaks of hepatitis A in England and Wales associated with two co-circulating hepatitis A virus strains

During 2002, an upsurge in frequency of hepatitis A outbreaks among injecting drug users was observed in England and Wales. As lack of risk factor information and the high mobility of the cases made linkage of outbreaks difficult, the relationship of nucleotide sequences in the VP1/2PA junction of the hepatitis A virus (HAV) genome amplified from serum of case-patients was investigated. A total of 204 HAV RNA positive sera obtained from a network of 23 laboratories were studied. Comparison of the sequences identified two principal strains: ES1 (n = 95) belonging to type IB, and ES2 (n = 72) to type IMA. Of the remaining samples, 15 were type IA, 11 were type IB and 11 were type IIIA. ES1 predominated in Doncaster and other towns in Trent and northern England, and ES2 in the Midlands and southern England; the difference in geographical distribution between these two strains was significant (P < 0.0001). In comparison to the sporadic cases, cases infected by either ES1 or ES2 tended to be younger, injecting drug users, people in contact with injecting drug users, or those with a history of incarceration in prisons or homelessness (P < 0.0001). Cases infected by ES1 tended to be younger than those by ES2 (P < 0.0001). The association of the outbreaks to two geographically restricted strains implicates two principal transmission pathways associated with injecting behavior. Identifying these routes may be conducive to preventing further outbreaks.