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. CONCLUSION. 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.

Impact of laboratory cross-contamination on molecular epidemiology studies of tuberculosis.

Laboratory cross-contamination by Mycobacterium tuberculosis is known to be responsible for the misdiagnosis of tuberculosis, but its impact on other contexts has not been analyzed. We present the findings of a molecular epidemiology analysis in which the recent transmission events identified by a genotyping reference center were overestimated as a result of unnoticed laboratory cross-contamination in the original diagnostic laboratories.

Iron overload, an immunosuppression marker in HIV-infected patients.

Purpose: Iron overload (IO) has been associated with increased cardiovascular risk (CVR) and metabolic syndrome (MS) in the general population; both elevated CVR and MS are frequent in HIV- patients. Our aim was to analyze the prevalence of IO in a cohort of asymptomatic patients with HIV infection, and related factors. Methods: Cross-sectional study of a cohort of HIV outpatients in regular follow-up. Demographic, epidemiological, clinical, analytical and therapeutic data were collected. Patients completed a questionnaire about CVR factors and 10-year CV disease risk estimation (Framingham score), underwent a physical exam, and a fasting blood analysis. IO was defined as a plasma ferritin level higher than 200 m/L in women and 300 m/L in men. Results: 571 patients (446 men, 125 women), with a mean age of 43.2 years, sexual transmission of HIV in 68.5%, median CD4 count 474 cell/μL (IQR: 308-666), and 36.3% Aids cases 86.2% were on antiretroviral therapy (ART), and 74.8% of them had undetectable HIV viral load 14.6% met MS criteria, and mean CVR at 10 years was 6.67%. IO was detected in 11% of cases. Patients with IO were more immunosuppressed (CD4 count 369 vs 483/μL, p<0.0001), presented a higher prevalence of detectable HIV viral load (17.6% vs 8.9%; p<0.005), and of Aids cases (14.9% vs 8.7%; p<0.023), and lower plasma levels of cholesterol, HDLc and LDLc (154 vs 183, 34 vs 43, 93 vs 110 mg/dL, respectively; p<0.0001. In the multivariate analysis, the only related factor was CD4 count <350 cell/μL (OR 2.86, 95% CI 1.6-4.9; p<0.0001). IO was not associated with CVR nor with MS. Conclusions: IO is not uncommon in HIV patients, and it is only related with immunosuppression defined as CD4 count <350 cell/ mL, and in contrast to general population, it is not related with increased CVR nor with MS.