Tuberculosis in contacts need not indicate disease transmission

Area of Science:

• Microbiology
• Epidemiology
• Genetics

Background:

• Traditional contact investigation is vital for controlling tuberculosis (TB).
• Genotyping methods like DNA restriction fragment length polymorphism (RFLP) offer insights into TB transmission patterns.
• Contact investigations may sometimes overestimate TB transmission compared to genotyping.

Purpose of the Study:

• To analyze Mycobacterium tuberculosis isolates from a cluster of TB cases in Norway using RFLP.
• To compare transmission patterns identified by traditional contact investigation with those determined by genotyping.
• To assess the accuracy of TB transmission estimations in outbreak scenarios.

Main Methods:

• DNA restriction fragment length polymorphism (RFLP) analysis was performed on Mycobacterium tuberculosis isolates.
• Fifteen immigrant patients diagnosed with TB between February and September 2003 were included.
• Patient social contacts and community affiliations were documented.

Main Results:

• Fourteen of 15 patients had positive Mycobacterium tuberculosis cultures.
• Six distinct genotypes were identified among the isolates.
• All 15 patients reported social contact, with 13 belonging to the same church community.
• Five patients did not acquire TB from the presumed source case.

Conclusions:

• Reactivation of TB can occur in contacts during an outbreak, potentially leading to overestimation by traditional methods.
• Combining contact tracing with Mycobacterium tuberculosis genotyping is essential for accurate TB transmission assessment.
• Incorrect treatment decisions may arise if drug susceptibility patterns are presumed based on overestimated transmission data.