Background and objective: The currently low endemic level of hepatitis A in Spain favors manifestation of the disease as outbreaks among specific risk groups. The aim of this study is to analyze the hepatitis A outbreaks investigated in Catalonia (Spain) during the period of 1999 to 2003.
Methods: The criteria for including an outbreak were defined and outbreaks were classified according to the type of transmission. The variables analyzed were space, time, socio-demographic parameters, setting, risk factors, and preventive measures adopted. The incidence rate and rate ratio were calculated according to age and sex.
Results: Among 74 outbreaks, 73 fulfilled the inclusion criteria. Most outbreaks involved person-to-person transmission (83.8%) and the rest had a common source of infection (14.9%). In total, 334 cases were included (cumulative incidence 1999-2003: 5.27 per 100,000 inhabitants), with an average age of 24.5 years. The settings yielding the most cases were family (143), community (97) and schools/preschools (87). The number of cases per outbreak ranged from 2 to 11, except one outbreak that occurred in 83 young homosexual men with high-risk sexual practices. The main factors related to the case index or to coprimary cases included belonging to age groups with low immunity (children and young adults) and travelling to or from endemic areas.
Conclusion: Hepatitis A outbreaks in Catalonia are still frequent. They mainly occur in the family environment, by person-to-person transmission and in the most vulnerable groups (preschool or school employees, travelers, and men who perform high-risk sexual practices with other men).