A pseudo outbreak of tuberculosis.

Three cases of suspected tuberculosis were diagnosed over a ten day period at an oncology unit. Case finding was carried out and six further cases were diagnosed. However, doubts were raised about these diagnoses and a review of the outbreak investigation was carried out. Investigation of laboratory procedures found that the 'outbreak' was likely to be due to a contaminated phenol red solution. This incident highlights the importance of a critical evaluation of outbreak investigations, and the need for close collaboration between clinicians, epidemiologists and laboratory staff.