Epidemiology and surveillance of pertussis among infants in Catalonia, Spain, during 1997-2001.

BACKGROUND

Despite high levels of vaccination coverage in Spain and Catalonia (98% in 2002), pertussis is a significant cause of morbidity among infants. The study aim was to estimate the incidence of hospitalizations for pertussis among infants from 1997 through 2001 in Catalonia.

METHODS

A retrospective review of records for patients <12 months of age with a diagnosis of pertussis (International Classification of Diseases, 9th revision, code 033) at discharge from 11 Catalonian hospitals was performed.

RESULTS

Three hundred forty-six patients were identified, 62 (1997), 28 (1998), 59 (1999), 150 (2000) and 47 (2001), of whom 284 (82%) were <4 months of age. The incidence of hospitalizations because of whooping cough from 1997 through 2001 in Catalonia was estimated at 118 cases per 100,000 inhabitants <12 months of age. Symptoms included paroxysmal cough (95%), cyanosis (67.9%), vomiting (36.7%) and apneic episodes (27.7%). Three infants (0.8%) died, all <2 months of age. Two hundred thirty-four patients (67.6%) were unvaccinated (222 patients were <3 months of age). Six patients (1.7%) were fully vaccinated (3 doses). Considering that only 220 patients <12 months of age were reported through the Catalonian Notification System in 1997-2001, at least 126 hospitalizations (36.4%) for pertussis were not reported to this system (mean difference per year, 32.6%; range, 8.4-56%).

CONCLUSIONS

In this study, hospitalizations exceeded the number of notifications by at least 32.6%; therefore, the real incidence is likely to be greatly underestimated. Pertussis incidence remains high among infants, most of whom are <4 months of age and have had no or 1 dose of vaccine.