[Large-scale outbreak investigation for tuberculosis in Zeist]

Recently a large-scale outbreak investigation was held among customers of a supermarket in the Dutch town of Zeist after an employee was diagnosed with smear-positive pulmonary tuberculosis. About 14,000 people had a tuberculin skin test and an additional 6,000 had a chest X-ray. About 400 positive skin tests and 8 cases of active tuberculosis have been reported so far. Investigation of contacts of infectious tuberculosis cases is an important tool in tuberculosis control in low-prevalence countries. It includes chest X-ray examination for active pulmonary tuberculosis after or instead of tuberculin skin testing, and identifying contacts with latent tuberculosis infection followed by preventive treatment. Investigation of household and other close contacts is highly effective. This may not be true for sporadic contacts who are likely to have a low risk of infection, such as in this investigation, where the prevalence of recent infections estimated from reported data is only 3%. The benefits of detecting these cases must be weighed against the costs of such large-scale operations and the probability of false-positive skin test results.