Trakas K, Stosor V, Dietrich S, Mosher L, Warren J R
Department of Pathology, Northwestern University Medical School, Chicago, IL 60611, USA.
Arch Pathol Lab Med. 2000 Jun;124(6):902-3. doi: 10.5858/2000-124-0902-PTOSC.
Cross-contamination during sequential processing of sputum specimens from different patients causes false-positive growth of Mycobacterium tuberculosis in culture. We describe an unusual case of cross-contamination in a 36-year-old man with acquired immunodeficiency syndrome and possible persistent tuberculosis. Culture with 1 of 3 sputum specimens was positive for rifampin-susceptible M tuberculosis. Review of processing revealed that his single culture-positive sputum specimen had followed a sputum specimen from another patient with active pulmonary tuberculosis that was positive in culture for M tuberculosis resistant to rifampin. Molecular strain typing by restriction fragment length polymorphism demonstrated the 2 isolates to be an identical strain of M tuberculosis. Agar proportion susceptibility testing of the rifampin-resistant isolate revealed low numbers of resistant organisms in a range of 1.5% to 3.3%. It was concluded that rifampin-susceptible organisms that constituted approximately 98% of the resistant isolate contaminated sputum from the patient with possible persistent tuberculosis. His culture result was, therefore, considered false positive, not an indication of tuberculosis.
在对不同患者的痰液标本进行连续处理过程中的交叉污染会导致结核分枝杆菌在培养物中出现假阳性生长。我们描述了一例不同寻常的交叉污染病例，患者为一名36岁的获得性免疫缺陷综合征男性，可能患有持续性结核病。三份痰液标本中的一份培养结果显示对利福平敏感的结核分枝杆菌呈阳性。对处理过程的回顾发现，他那份培养结果呈阳性的痰液标本在处理顺序上排在另一名活动性肺结核患者的痰液标本之后，后者的痰液培养结果显示对利福平耐药的结核分枝杆菌呈阳性。通过限制性片段长度多态性进行的分子菌株分型表明，这两株分离菌是同一株结核分枝杆菌。对耐利福平分离菌进行的琼脂比例药敏试验显示，耐药菌数量较少，在1.5%至3.3%之间。得出的结论是，构成耐利福平分离菌约98%的对利福平敏感的菌株污染了可能患有持续性结核病患者的痰液。因此，他的培养结果被认为是假阳性，并非结核病的指征。
