European Society of Mycobacteriology - Instituto Nacional de Saúde ...

PP-93
CONTRIBUTION OF LABORATORY FACTORS TO HIGH MGIT
CULTURE CONTAMINATION RATE IN ZAMBIA
de Haas, Petra 1 , Moyoyeta, Monde 2 , Samutela, Mulemba 2 , Mwanza, Winnie
2
, Musunsa, Alan 3 , Mbulo, Grace 2 , Muvwimi, Mweemba 3 , Ayles, Helen 1
1. Zambart project, Lusaka, Zambia and LSHTM, London
2. Zambart project, Lusaka, Zambia
3. National reference laboratory, Lusaka, Zambia
Background:
An evaluation study of the MGIT liquid culture system in Zambia found a high contamination rate. It was suggested that factors
such as delayed sample processing due to long distances, inadequate storage of samples once submitted, poor laboratory
infrastructure and inexperienced staff may have contributed to the high contamination. The objective of this study was
to investigate the contribution of laboratory factors to the higher than expected rate of MGIT contamination.
Method:
As part of the National drug resistance survey, 917 sputum specimens were collected from smear-positive TB patients
and transported to the TB Reference Laboratory in Lusaka. After decontamination using NALC-NAOH (1,5% final concentration)
MGIT and LJ cultures were inoculated. In addition 584 of the decontaminated samples were inoculated onto
blood agar plates (BA). When the MGIT culture showed growth Ziehl Nielsen staining was performed. If micro-organisms
other then acid fast bacilli were seen, a BA was inoculated and subsequent colonies identified using biochemical tools.
Results
Time between sample submission and processing varied from 1-50 days with a median of 9 days. Increased contamination
in MGIT was found when the time between sample submission and processing was extended; 18.6% for 1-7 days,
27.4% for 8-14 days and 37.5% for more than 15 days. The overall contamination rate was 27.6% (95% CI 24.0-31.4). Of
584 decontaminated sputum 197 (33.7%) showed growth on BA. Out of the 197 samples showing growth 86 (43.6%)
were also contaminated in MGIT whereas for samples that showed no growth on BA, 70 (18%) out of 387 were contaminated.
Contaminated organism from the sputum and from the contaminated MGIT culture were identified for 35
out of the 86. Identical species were identified in only sixteen (45.7%) of these 35 samples, whereas in 19 (54.3%) cases
a different contaminanting species was found in the MGIT culture compared to the decontaminated sample.
Conclusion
High contamination on MGIT is a problem in our setting. Delayed processing of samples increases the chance of samples
being contaminated. The contamination of samples that did not show any growth on BA from decontaminated sputum
as well as different species isolated from the contaminated MGIT compared to the decontaminated sputum suggest that
a major part of the contamination may be due to laboratory factors.
Oral Communication
European Society of Mycobacteriology | 30 th Annual Congress | July 2009 | Porto - Portugal
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