False-positive tuberculous meningitis due to laboratory contamination: importance of a holistic clinical evaluation

Incidence of tuberculosis in Nebraska is 1.9/100,000 people. Tuberculous meningitis is rare and comprises 1% of extrapulmonary tuberculosis. An elderly Caucasian man presented with fever, headache, altered mentation and a history of tick bite. Cerebrospinal fluid (CSF) analysis showed negative cultures and the patient was treated empirically for tickborne illness. Forty-five days later, CSF nucleic acid amplification test (NAAT) was positive for tuberculosis. On readmission, repeat neurological examination and CSF analysis were benign and the patient was not offered antituberculous treatment. Genotype investigation of the culture and NAAT specimen by the Center for Disease Control confirmed laboratory contamination. The literature reports an incidence of 2-4% for false-positive tuberculosis cultures. Contaminated devices, clerical errors and laboratory errors have been implicated. Laboratory contamination results in smear-negative culture-positive cases. Epidemiological investigation with genotype testing is confirmatory. Detailed clinical assessment with good clinical and laboratory communication and frequent laboratory surveillance is advocated to mitigate these cases.