A Mycobacterium tuberculosis cluster demonstrating the use of genotyping in urban tuberculosis control.

BACKGROUND: DNA fingerprinting of Mycobacterium tuberculosis isolates offers better opportunities to study links between tuberculosis (TB) cases and can highlight relevant issues in urban TB control in low-endemic countries. METHODS: A medium-sized molecular cluster of TB cases with identical DNA fingerprints was used for the development of a visual presentation of epidemiologic links between cases. RESULTS: Of 32 cases, 17 (53%) were linked to the index case, and 11 (34%) to a secondary case. The remaining four (13%) could not be linked and were classified as possibly caused by the index patient. Of the 21 cases related to the index case, TB developed within one year of the index diagnosis in 11 patients (52%), within one to two years in four patients (19%), and within two to five years in six patients (29%). CONCLUSION: Cluster analysis underscored several issues for TB control in an urban setting, such as the recognition of the outbreak, the importance of reinfections, the impact of delayed diagnosis, the contribution of pub-related transmissions and its value for decision-making to extend contact investigations. Visualising cases in a cluster diagram was particularly useful in finding transmission locations and the similarities and links between patients.

Impact of mobile radiographic screening on tuberculosis among drug users and homeless persons.

RATIONALE: In 2002, a mobile radiographic screening program was started in Rotterdam to respond to high rates of tuberculosis (TB) among illicit drug users and homeless persons. OBJECTIVES: We studied trends and characteristics of TB among these risk groups and assessed the impact of the screening program on transmission, using molecular typing. METHODS: Description of trends, and of demographic and disease-related characteristics of tuberculosis cases among these risk groups between 1993 and 2005. TB was considered to result from recent transmission if the mycobacterial DNA fingerprints of cases were identical to those of other cases in the risk groups in the previous 2 years. MEASUREMENTS AND MAIN RESULTS: During the study period, 206 individuals with TB among illicit drug users and homeless persons were notified, representing 11.4% of the total case load of 1,811 in Rotterdam. The annual number of tuberculosis cases declined from 24 at the start of the screening program to 11 cases in 2005. The screening program identified 28 cases (a prevalence rate of 327 per 100,000 radiographs), of which 12 were smear positive. In 1997-2002, more than 80% of the illicit drug users or homeless persons with TB were infected with one of the Mycobacterium tuberculosis strains prevalent among these risk groups. After nearly 4 years of systematic radiographic screening this proportion declined to 45% in 2005. CONCLUSIONS: DNA fingerprinting can be a useful tool to evaluate the impact of a TB screening program. We advocate that screening of illicit drug users and homeless persons should be continued to prevent a resurgence of TB.