Study population and setting
We performed an observational study of all cases of hepatitis A residing in Barcelona reported to the surveillance system of the Public Health Agency of Barcelona (PHAB) between 1989 to 2010. Acute hepatitis A is a communicable disease that has been reported since 1986, physicians and laboratories in the city report cases to the PHAB. A case is defined by acute hepatitis symptoms combined with the presence of immunoglobulin M antibodies against hepatitis A virus (IgM anti-HAV). Since 1989 an electronic and confidential database of hepatitis A has been established.
Inclusion criteria: To avoid inclusion of age groups for which sexual activity is less likely to be related with disease acquisition only individuals aged between 20-44 were included for incidence rates calculation (these limits are based on the range of age of MSM involved in the outbreaks). For the same reason, cases with a known history of travel to an endemic area or contact with children were excluded.
Data collection is made routinely by the PHAB, for routing surveillance we use a standard questionnaire for hepatitis A of the Health Department of the Government of Catalonia. The questionnaire contains demographic data, information on the disease and risk exposures. However the information on sexual preferences not was included until 2002. For outbreak investigation we use the standard questionnaire and an annexed questionnaire designed for that purpose which also include: sexual condition, known contact with a case and sexual activity in the 6 weeks before symptom onset, HIV serological status, sexual work and bathhouse use. For the last outbreak, 2008, travel to industrialized countries during the six weeks preceding symptom onset was also collected.
The surveillance information is obtained by interview of the patient case or his/her doctor and also from clinical and laboratory records. Interviews are made by telephone by public health nurses from the PHAB.
We performed a description and comparison of the characteristics of all outbreaks detected by the surveillance system of the PHAB for the period of the analysis. For outbreak investigations, a case was defined as MSM, resident in Barcelona, presenting symptoms of acute hepatitis, and positive IgM anti-HAV. Cases that during the incubation period were in contact with an outbreak case were also considered as part of the outbreak, independently of whether they were MSM or not. All cases considered as part of an outbreak were included in the analysis. Also, molecular epidemiology was studied as part of the outbreak investigation.
Serum from outbreak cases were sent to the Enteric Virus Laboratory of the Microbiology Department of the University of Barcelona for genetic analysis. Previously published primers , -3285 (5'AGTCACACCTCTCCAGGAAAACTT3'; reverse primer) and +2949 (5'TATTTGTCTGTCACAGAACAATCAG3'; forward primer) were used for the fragment amplification of the VP1X2A region containing an internal sequence of 168 bp (positions 3024 to 3191) that has been extensively used for genotyping. Sequencing of RT-PCR products was performed and multiple sequence alignments were performed using the ClustalW program (European Bioinformatics Institute).
We calculated annual incidence rates of new cases of hepatitis A per 100000 inhabitants for males and females for the population aged between 20-44. Population data was based on the census published annually by the Statistics Department of the city . Spearman's correlation coefficient was calculated to evaluate trends of rates. To determine sexual preference, we used the ratio male-to-female (M:F) as a surrogate marker for MSM, defined as the incidence of hepatitis A for male divided by the incidence for female. The M:F ratio is an indirect measurement for MSM which has been used when no direct data on sexual identity is available .
Categorical variables were presented as percentages, and continuous variables were presented as mean with corresponding range. The chi-squared test was used to compare categorical variables and F-ANOVA test for continuous variables. Statistical significance was established assuming an alpha error of 0.05. Foxpro was used to record data and SPSS software for Windows (version 18.0; SPSS, Chicago, IL) was used for analysis.
Patient consent was not needed as hepatitis A is a communicable disease. All data were treated in a strictly confidential manner following the ethical principles of the Helsinki Declaration of 1964 revised by the World Medical Organization in Tokio, 2008 and the Organic Law 15/1999 of Data Protection in Spain.