Laboratory diagnosis of Lyme borreliosis at the Portuguese National Institute of Health (1990-2004)

Lyme borreliosis is considered to be an emerging infection in some regions of the world, including Portugal. The first Portuguese human case of Lyme borreliosis was identified in 1989. Since 1999, this disease is considered a notifiable disease (DDO) in Portugal, but only a few cases are reported each year, which does not allow consistent analysis of risk factors and the impact on public health. In this study the authors analyse the data available at the Centre for Vectors and Infectious Diseases Research (CEVDI) laboratory, at the Instituto Nacional de Saúde Dr. Ricardo Jorge (National Institute of Health, INSA) during the past 15 years (1990-2004) and evaluate them against the registry of national reported cases (1999-2004). Serological tests were the basis for laboratory diagnosis. Data on year of diagnosis, sex, age, geographical origin and clinical signs are available for 628 well documented Portuguese positive cases. The number of cases per year varied between 2 and 78, with the highest number of cases reported in 1997. Of the positive cases, 53.5% were female and the age group most affected was 35-44 years old. Neuroborreliosis was the most common clinical manifestation (37.3%). Human cases were detected in 17 of the 20 regions of Portugal, and the highest number of laboratory confirmed cases were from the Lisbon district. The comparison of the number of notified cases and the number of positive cases confirmed by our laboratory show that Lyme borreliosis is clearly an underreported disease. Due to the scattered distribution of the positive cases and the low prevalence of the tick species Ixodes ricinus, the most effective prevention measure for Lyme borreliosis in Portugal is education of the risk groups on how to prevent tick bites.