Modelling the force of infection for hepatitis A in an urban population-based survey: a comparison of transmission patterns in Brazilian macro-regions.
BACKGROUND
This study aimed to identify the transmission pattern of hepatitis A (HA) infection based on a primary dataset from the Brazilian National Hepatitis Survey in a pre-vaccination context. The national survey conducted in urban areas disclosed two epidemiological scenarios with low and intermediate HA endemicity.


METHODS
A catalytic model of HA transmission was built based on a national seroprevalence survey (2005 to 2009). The seroprevalence data from 7,062 individuals aged 5-69 years from all the Brazilian macro-regions were included. We built up three models: fully homogeneous mixing model, with constant contact pattern; the highly assortative model and the highly assortative model with the additional component accounting for contacts with infected food/water. Curves of prevalence, force of infection (FOI) and the number of new infections with 99% confidence intervals (CIs) were compared between the intermediate (North, Northeast, Midwest and Federal District) and low (South and Southeast) endemicity areas. A contour plot was also constructed.


RESULTS
The anti- HAV IgG seroprevalence was 68.8% (95% CI, 64.8%-72.5%) and 33.7% (95% CI, 32.4%-35.1%) for the intermediate and low endemicity areas, respectively, according to the field data analysis. The models showed that a higher force of infection was identified in the 10- to 19-year-old age cohort (∼9,000 infected individuals per year per 100,000 susceptible persons) in the intermediate endemicity area, whereas a higher force of infection occurred in the 15- to 29-year-old age cohort (∼6,000 infected individuals per year per 100,000 susceptible persons) for the other macro-regions.


CONCLUSIONS
Our findings support the shift of Brazil toward intermediate and low endemicity levels with the shift of the risk of infection to older age groups. These estimates of HA force of infection stratified by age and endemicity levels are useful information to characterize the pre-vaccination scenario in Brazil.
School of Medical Sciences, State University of Pernambuco, Recife, Pernambuco, Brazil; Department of Tropical Medicine, Federal University of Pernambuco, Recife, Pernambuco, Brazil.
Ricardo Arraes de Alencar
RA
Ximenes
Department of Tropical Medicine, Federal University of Pernambuco, Recife, Pernambuco, Brazil; Institute of Tropical Pathology and Public Health, Department of Community Health, Federal University of Goias, Goiania, Goias, Brazil.
Celina Maria Turchi
CM
Martelli
Department of Preventive Veterinary Medicine and Animal Health, School of Veterinary Medicine, University of Sao Paulo, Sao Paulo, Brazil.
Marcos
M
Amaku
Department of Infectious and Parasitic Diseases, School of Medicine, University of Sao Paulo, São Paulo, Brazil.
Ana Marli C
AM
Sartori
Department of Preventive Medicine, School of Medicine, Sao Paulo University, Sao Paulo, Brazil.
Patricia Coelho
PC
de Soárez
Department of Preventive Medicine, School of Medicine, Sao Paulo University, Sao Paulo, Brazil.
Hillegonda Maria Dutilh
HM
Novaes
School of Medical Sciences, State University of Pernambuco, Recife, Pernambuco, Brazil; Liver Institute of Pernambuco - IFP, Recife, Pernambuco, Brazil.
Leila Maria Moreira Beltrão
LM
Pereira
Virology Centre, Adolfo Lutz Institute, Sao Paulo, Brazil.
Regina Célia
RC
Moreira
Institute of Tropical Medicine, School of Medicine, Sao Paulo University, Sao Paulo, Brazil.
Gerusa Maria
GM
Figueiredo
Department of Pathology, School of Medicine, Sao Paulo University, Sao Paulo, Brazil.
Raymundo Soares
RS
de Azevedo
D000293:Adolescent; D000328:Adult; D000368:Aged; D001938:Brazil; D002648:Child; D002675:Child, Preschool; D005260:Female; D006506:Hepatitis A / Q000453:epidemiology* / Q000635:transmission*; D006801:Humans; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D012189:Retrospective Studies; D016036:Seroepidemiologic Studies