Bordetella pertussis infection in household contacts of cases of pertussis in the southeast zone of the city of Cali,Colombia, 2006-2007

Introduction: Bordetella pertussis causes whooping cough or convulsive cough, a contagious and immune-preventable disease. It is one of the 10 leading causes of death among children younger than one year of age, when not completely immunized. It is considered reemerging in several countries, with high rates of complications and hospitalizations. Objective: to learn of the proportion of infection by B. pertussis among suspected cases of whooping cough and their household contacts among children from the southeast zone of Cali, a geographic area with great consultation demand due to this infection.Methodology: This is a cross-sectional descriptive study. Epidemiological data and nasopharyngeal samples were taken from 24 suspected cases and from their 109 household contacts. The samples were analyzed via real-time polymerase chain reaction (Q-PCR) and through culture. Results: The proportion of positivity among the cases via the Q-PCR technique was at 50% (12/24) and at 40% via the culture technique (8/20), with good agreement between both techniques (Kappa 0.61). Regarding the household contacts, 30.3% (33/109) (CI 95%: 21.8%-39.8%) tested positive. The sibling contacts (7/15) and the mothers (7/22) presented the greatest proportion of positivity. Regarding age, 60% were 4 years of age (3/5) and 50% were in the group comprised of individuals 45 to 64 years of age. No significant differences were found among the presence or absence of symptoms and the presence of B. pertussis infection, except for the presence of nasal secretions (runny nose) (27%) and coughing (36%) during the last month. Conclusions: The study confirms the high prevalence of asymptomatic infection by B. pertussis among household contacts of children with whooping cough symptomatology and its household transmission. In Cali, health authorities need to review the effectiveness of implemented control strategies and the use of a vaccination scheme that does not cover adolescent and adult populations as a focus of infection control.