Introduction: Transmission of Mycobacterium tuberculosis (MT) in most cases requires extended exposure.
Objectives: To document that MT transmission may occur even after very short exposure.
Material and methods: All first-time culture-confirmed tuberculosis (TB) cases in Denmark have since 1992 been subjected to genotyping, using the IS6110-Restriction Fragment Length Polymorphism (RFLP) technique. A young nurse with no risk factors developed pulmonary TB: the DNA pattern of her MT strain was compared to The Danish TB Subtyping Database, comprising >6000 DNA patterns from TB patients nationwide.
Results: Only one single MT DNA pattern matched the DNA profile of the isolate from the nurse. The pattern originated from a patient shortly admitted to the department where she worked at the time. MT transmission had occurred in spite of very short exposure.
Conclusion: By adding modern molecular epidemiological methods to traditional epidemiological surveys, a more detailed picture of MT-transmission pathways can be obtained, showing that MT transmission can occur even after extremely short exposure. This stresses the necessity for adequate respiratory protection among hospital staff taking care of patients with pulmonary symptoms suspected for TB.