Optimized molecular resolution of cross-contamination alerts in clinical mycobacteriology laboratories.
BACKGROUND
The phenomenon of misdiagnosing tuberculosis (TB) by laboratory cross-contamination when culturing Mycobacterium tuberculosis (MTB) has been widely reported and it has an obvious clinical, therapeutic and social impact. The final confirmation of a cross-contamination event requires the molecular identification of the same MTB strain cultured from both the potential source of the contamination and from the false-positive candidate. The molecular tool usually applied in this context is IS6110-RFLP which takes a long time to provide an answer, usually longer than is acceptable for microbiologists and clinicians to make decisions. Our purpose in this study is to evaluate a novel PCR-based method, MIRU-VNTR as an alternative to assure a rapid and optimized analysis of cross-contamination alerts.


RESULTS
MIRU-VNTR was prospectively compared with IS6110-RFLP for clarifying 19 alerts of false positivity from other laboratories. MIRU-VNTR highly correlated with IS6110-RFLP, reduced the response time by 27 days and clarified six alerts unresolved by RFLP. Additionally, MIRU-VNTR revealed complex situations such as contamination events involving polyclonal isolates and a false-positive case due to the simultaneous cross-contamination from two independent sources.


CONCLUSIONS
Unlike standard RFLP-based genotyping, MIRU-VNTR i) could help reduce the impact of a false positive diagnosis of TB, ii) increased the number of events that could be solved and iii) revealed the complexity of some cross-contamination events that could not be dissected by IS6110-RFLP.
Martín
Ana
A
Servicio de Microbiología Clínica y Enfermedades Infecciosas, Hospital Gregorio Marañón, Universidad Complutense, Madrid, CIBER-Enfermedades Respiratorias CIBERES, Spain. amartsan@yahoo.es
Herranz
Marta
M
Lirola
Miguel Martínez
MM
Fernández
Rosa Fernández
RF
Bouza
Emilio
E
García de Viedma
Darío
D
D003951:Diagnostic Errors; D005189:False Positive Reactions; D006801:Humans; D020071:Interspersed Repetitive Sequences; D018598:Minisatellite Repeats; D009169:Mycobacterium tuberculosis / Q000235:genetics* / Q000302:isolation & purification; D016133:Polymerase Chain Reaction / Q000379:methods* / Q000592:standards; D012150:Polymorphism, Restriction Fragment Length; D011446:Prospective Studies; D013048:Specimen Handling / Q000379:methods / Q000592:standards*; D014376:Tuberculosis / Q000175:diagnosis* / Q000382:microbiology