Pertussis outbreak in a poorly immunized community

BACKGROUND: The aim of this study was to describe the clinical, serological and epidemiological findings of a pertussis outbreak in an insufficiently vaccinated gipsy community. PATIENTS AND METHOD: Ten cases (catarrhal illness with cough of 2 weeks duration) were identified through an active search. In four of them, two paired serum samples were obtained and total IgG against Bordetella pertussis and IgG and IgA against pertussis toxin (PT) and filamentous hemagglutinin (FHA) were determined. The diagnostic criteria was seroconversion. A comparative analysis between cases and healthy children younger than 15 years (gipsy community) was carried out and we estimated, by means of a logistical regression analysis, the odds ratio (OR) of several factors. RESULTS: The highest attack rate (50%) was found in the 5 to 9 year-old group; 30% cases had not been vaccinated while 50% had been incorrectly vaccinated. No significant differences for age, gender or the vaccine status were detected. Three cases showed seroconversion for total IgG and two for IgG-PT and IgA-PT. Other possible pathogens were ruled out by serology. CONCLUSIONS: Despite the high vaccine coverage against pertussis in paediatric age in Spain, some susceptible population groups remain, mainly due to an incorrect vaccination. Our serological results firmly support the suspicion of B. pertussis as the etiologic agent of the outbreak.