An outbreak of hepatitis A among homeless drug users in Rotterdam, The Netherlands.

From the end of January to mid-June 2004 (weeks 5-24) a hepatitis A virus (HAV) outbreak occurred among a homeless and drug user community in Rotterdam, The Netherlands. To prevent further spread of the virus within this group and to the general population, the Municipal Health Service of Rotterdam organized a mass vaccination campaign during which 83% (1,515/1,800) of the homeless people were vaccinated. As part of a national HAV typing study, blood and/or fecal samples of 30 Rotterdam HAV IgM+ patients who fell ill during the period of 1 September 2003-1 December 2004 were tested. The tests included RT-PCR and sequencing at the VP3-VP1 and VP1-P2a regions of the HAV genome. It was found that 12 homeless people, one family member of a homeless person and two people without a known risk were infected with a unique subtype 3a strain. Four of the homeless patients became ill after vaccination and were probably infected at the time. This study shows that Dutch homeless people and drug users involved in HAV outbreaks should be offered HAV vaccine actively to prevent further spread of the infection. Furthermore, it was shown by molecular techniques that the unique subtype 3a strain was not found before the Rotterdam outbreak or afterwards, indicating that the mass vaccination campaign was successful.