Conference abstract

The contamination rate in the liquid and solid culture using sputum sample at the national TB reference laboratory, 2016

Pan African Medical Journal - Conference Proceedings. 2017:3(65).25 Dec 2017.
doi: 10.11604/pamj-cp.2017.3.65.181

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Keywords: Tuberculosis, culture, contamination rate
Oral presentation

The contamination rate in the liquid and solid culture using sputum sample at the national TB reference laboratory, 2016

Nilsa Nascimento1,&, Khalide Azam1

1National Institute of Health, Maputo, Mozambique

&Corresponding author
Nilsa Nascimento, National Institute of Health, Maputo, Mozambique

Abstract

Introduction: culture is the gold-standard procedure for tuberculosis (TB) diagnostic and treatment monitoring because of its high sensitivity allowing the mycobacteria isolation for identification and tests of drug sensitivity. However, the culture is prone to contamination allowing growth of other microorganisms than TB, which causes delays and invalid results for patients. The objective of the study was to determine the contamination rate (CR) in the solid and liquid culture of the sputum samples received at the National TB Reference Laboratory (NTRL) in 2016.

Methods: a cross-sectional study was carried out using secondary database from the NTRL, 2016. Contamination rate was determined for liquid and solid culture and compared with smear microscopy results. The data were analyzed using the statistical package SPSS (Version 20) and 95% confidence intervals.

Results: during 2016, up to 7,464 samples were received at NTRL, of which 5,979 (80.1%) were pulmonary samples. Among pulmonary samples, 88.5% (5,293/5979) were sputum. The CR was 17.1% for liquid culture and 6.8% for solid culture. Of the 3,281 smear-negative samples, the culture positivity rate was 6.9% for solid and 11.1% liquid culture with CR of 10.8% and 30%, respectively. The culture positivity rate was 61.2% for solid and 62% for liquid culture with CR of 10.7% and 25%, respectively for the 797 smear-positive samples.

Conclusion: contamination reduced the proportion of interpretative results and decreased the diagnostic value of the culture affecting the recovery rates of mycobacteria, as well as, causing loss of culture positivity for smear-positive. Specific studies are needed to assess the cause of contamination at NTRL, considering an evaluation of pre-analytical and analytical phase.