Successful Investigation of a False-Positive Tuberculosis Culture Result

Abstract

INTRODUCTION: To prove a positive tuberculosis culture report to be erroneous is extremely difficult in a TB ward setting. A successful investigation case is presented. CASE PRESENTATION: A 71-years-old bronchiectasis patient on treatment with isoniazid, rifampicin and ethambutol for suspected Mycobacterium scrofulaceum lung infection for 2 months was admitted because of severe intolerance with gastrointestinal upset and blurring of vision. In view of the significant treatment side effects, the mycobacteria being nontuberculous and the absence of respiratory symptoms nor x-ray deterioration, it was decided to stop treatment and observe. However, about 6 weeks later, a report was received with a sputum saved from this patient during that admission showing presence of Mycobacterium tuberculosis on culture. All other sputum culture of this patient before or after this were negative for tuberculosis. The case was investigated for possible wrong labeling or contamination of specimens in the laboratory but with no avail. A new light shedded on the investigation when the report on the drug susceptiility test result showed resistance to rifampicin only. As rifamipicin mono-resistance was very rare, it was decided to change the direction of investigation to search for any other patients in the ward around that time with sputum culture showing such susceptibility pattern. Another patient in the same ward around that time was identified. Rpo-B gene mutation analysis was requested for the specimens from these two patients and they showed exactly the same gene mutation pattern. The evidence was speaking for the positive sputum culture being a mislabeled sputum specimen from another patient. This laboratory report of positive sputum culture was disregarded and the patient was spared of the anti-TB treatment. Further confirmatory analysis by Restriction Fragment Length Polymorphism method done subsequently confirmed identical DNA fingerprints of the two cultures. . DISCUSSION: With clinical vigilance and by means of molecular biology techniques, a false-positive sputum tuberculosis culture could be successfully identified to be from another patient and the victum of this erroneous result could be spared of the prolonged and significant sufferings from the unnecessary treatment side effects. CONCLUSIONS: Molecular biology technique could be useful in the investigation of erroneous laboratory results.