Pertussis in infants. Who infects them?

Objective: The re-emergence of pertussis has a bipolar age distribution: infants younger than 6 months, and adolescents and adults. The aim of this study was to determine the source of infection in infants hospitalized with pertussis, and describe the epidemiological, clinical and microbiological characteristics. Material and methods: Observational, prospective design. Infants aged < 12 months hospitalized for pertussis in the paediatric area of the Hospital Universitari Vall d'Hebron, Barcelona (Spain) between 2005 and 2008 and their household contacts were included. Pertussis was confirmed by RT-PCR assay for Bordetella pertussis and B. parapertussis, and by culture in agar-charcoal of nasopharyngeal aspirate. An immunofluorescence test was also performed to determine coinfection with respiratory syncytial virus, influenza A and B, parainfluenza virus, and adenovirus. The following variables were recorded: age, sex, seasonal distribution, vaccination status, clinical manifestations, evolution, microbiological data and type of contacts. Results: Fifty-two infants were included. Forty-nine were aged < 6 months and 3 were aged 6-11 months. Thirty infants (57.7%) had not received any vaccine dose as they were aged < 2 months and only 3.8% had received three doses. The majority of cases (67.3%) occurred in spring and summer. Eight patients required paediatric ICU admission. The case fatality rate was 1.9%. RT-PCR was positive in 96.1% of cases and nasopharyngeal aspirate culture in 56%. Viral coinfection was detected in 26% of patients. Cough, cyanosis and vomiting were the most frequent manifestations at admission; 21% of infants suffered apnoea. Primary cases among household contacts were detected in 80.4% (41 patients) and pertussis was confirmed by microbiological study in 14 (27.5%). Thirty five (85.4%) primary cases were in adults (44% in parents, 17% in aunts and uncles and 15% in grandparents). Conclusions: Pertussis can be a serious disease in infants, especially in those under 4 months of age. RT-PCR is a highly sensitive microbiological test. Of the 51 cases studied, 87.8% were infected in the household and 85.4% of transmitters were adults. Universal vaccination of adolescents and adults must be recommended, particularly those in contact with infants (cocoon strategy). © 2012 Elsevier España, S.L. Todos los derechos reservados.