Source of Infection in Household Transmission of Culture-Confirmed Pertussis in Brazil

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To the Editors:The World Health Organization estimates that pertussis causes 300,000 deaths a year worldwide. A better understanding of the role of adults and adolescents in the spread of the disease is one of the priorities for control.1In the State of Pernambuco, Brazil there has been complete (100%) vaccine coverage for 3 doses of pertussis vaccine in infants since 1998.2 In this study, we identified household members of children with confirmed pertussis presenting to a medical school hospital. We followed the definitions of the Centers for Diseases Control and Prevention to confirm pertussis cases and to classify them as primary (source of infection) or secondary cases.3Cases were tabulated by age of primary and secondary cases. The similarity of proportions by age was tested by χ2 test. P was considered significant when ≤0.05.During 2003, we identified pertussis cases in 57 households of patients referred to the Pediatric Infectious Disease Service at the Oswaldo Cruz Hospital in Recife, Brazil. Pertussis was confirmed in 158 of the 349 household members, of whom 65 were primary cases and 93 were secondary cases; 52 of all cases were confirmed by culture and 106 by epidemiologic link. Of the remaining, 169 did not have pertussis and 22 were excluded because of insufficient information to confirm or excluded pertussis. Seventy-five percent (28 of 37) of the cases younger than 6 months of age were secondary cases. The primary case was older than 11 and 6 months years for 79% (66 of 84) of all secondary cases and in 76% (19 of 25) if the secondary case was younger than 6 months of age.These findings were similar to those of Bisgard et al4 in United States. They found a family member or relatives as the suspect source of pertussis for 75% of the infants from zero to 3 months of age and 73% of the infants from 4 to 11 months of age. Children younger than 6 months of age are at highest risk of complications and death from pertussis.The findings that subjects older than 11 years and 6 months were the sources for the majority of secondary cases, including these younger than 1 year of age, indicate that actions to prevent pertussis should be targeted at the age group older than 11 years and 6 months.Préziosi and Halloran5 have observed that pertussis vaccination decreases the transmission of a vaccinated subject with pertussis. Given that a pertussis vaccine for adults is available, the potential impact (and cost and benefit) of vaccination of older children and adults on interrupting transmission should be considered.This study was supported bythe Pan-American Health Organization/World Health Organization.Paulo Neves Baptista, PhDPediatric Infectious Diseases ServiceSchool HospitalUniversity of PernambucoRecife, BrazilVera Magalhães, PhDTropical Medicine DepartmentFederal University of PernambucoRecife, BrazilLaura C.

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