Laboratory Cross-Contamination of Mycobacterium tuberculosis: A Systematic Review and Meta-analysis.

BACKGROUND: Microbiological cultures are the mainstay of the diagnosis of tuberculosis (TB). False-positive TB results lead to significant unnecessary therapeutic and economic burden and are frequently caused by laboratory cross-contamination. The aim of this meta-analysis was to quantify the prevalence of laboratory cross-contamination. METHODS: Through a systematic review of five electronic databases, we identified studies reporting rates of laboratory cross-contamination, confirmed by molecular techniques in TB cultures. We evaluated the quality of the identified studies using the National Institute of Health (NIH) Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies, and conducted a meta-analysis using standard methodology recommended by the Cochrane Collaboration. RESULTS: Based on 31 eligible studies evaluating 29,839 TB cultures, we found that 2% (95% confidence intervals [CI] 1-2%) of all positive TB cultures represent false-positive results secondary to laboratory cross-contamination. More importantly, we evaluated the rate of laboratory cross-contamination in cases where a single-positive TB culture was available in addition to at least one negative TB culture, and we found a rate of 15% (95% CI 6-33%). Moreover, 9.2% (91/990) of all patients with a preliminary diagnosis of TB had false-positive results and received unnecessary and potentially harmful treatments. CONCLUSIONS: Our results highlight a remarkably high prevalence of false-positive TB results as a result of laboratory cross-contamination, especially in single-positive TB cultures, leading to the administration of unnecessary, harmful treatments. The need for the adoption of strict technical standards for mycobacterial cultures cannot be overstated.

Mixed tuberculosis infections in Northwest of Iran.

Primary Mycobacterium tuberculosis (MTB) infection doesn't provide protection against secondary infection and patients can suffer from multiple strains of M. tuberculosis simultaneously. The aim of this study was to use molecular genotyping to identify cases of mixed infection in Northwest of Iran. One hundred and twenty-one positive culture isolates of M. tuberculosis were prepared from patients consecutively in Northwest of Iran from March 2017 to March 2018 and then microevolution and mix infection were assessed using the mycobacterial interspersed repetitive unit-variable number tandem repeat (MIRU-VNTR) method. MIRU-VNTR analysis revealed that nine samples (7.3%) had double alleles in at least one locus, as observed by five cases of microevolution, and four cases (3.3%) of mixed infection. According to this study, mixed infection in Northwest of Iran has significantly decreased compared to 13 years ago (7.1% decreased to 3.3%), and in order to eradicate tuberculosis it is necessary to identify all cases of mixed infection, at least in recurrent cases, in the future.

Why the COVID-19 Is Not Significantly Reduced in Iran?

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was transported from China to Iran via passengers. The virus is transmitted through droplets from coughing, sneezing, talking and contact with infected surfaces. Due to high transmissibility in places such as clinics, medical offices, buses and offices where there are large crowds, it spread rapidly in Iran and caused the mortality of a significant number of people, especially the elderly with underlying disease. Preventing travel and gatherings, as well as applying house quarantine in Apr 2020, reduced COVID-19 somewhat but then due to lack of attention to social distancing, reducing the use of masks by the people and inappropriate decisions by the national committee on combating coronavirus (NCCC), including reducing the working hours of public offices and shops, reducing the staff of government offices, monopoly on the distribution of essential materials and supplies, the presence of overcrowding in clinics of medical centers, hospitals, and private clinics caused the decline of the disease in the country to decrease. Measures can be taken to prevent the spread of the virus as much as possible, including: rapid detection of infected people, their isolation, contact tracing, quarantine of people over 65 and under 15, protection of the elderly, prevention of gatherings, forcing the use of protective equipment in possible gatherings, and electronicizing public services.