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Mycobacteriallting A
NUMBER OF ENVIRONMENTAL MYCOBACTERIA ON THE RISE
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The number of environmental mycobacteria isolates from both HIV positive and negative patients is s
on the rise both absolutely and relative to Mycobacterium tuberculosis isolates, according to a report from
the United Kingdom. w
Researcher M.D. Yates and colleagues suggest this finding could have a profound impact on E
Mycobacterium reference laboratories. E
"(Our) study clearly shows that identification of environmental mycobacteria from patients, whether as L
pathogens, saprophytes or contaminants, adds greatly to the workload of the reference laboratory," Yates et
al. wrote ("Isolation of Environmental Mycobacteria From Clinical Specimens in South-England: 1973 -1993," International Journal of Tuberculosis and Lung Disease, February 1997;1(1):75-80).
The environmental mycobacteria (EM) colonize damaged airways as secondary saprophytes or L
contaminate the pharynx and lower urethra. Their isolation from clinical specimens, especially bronchial u
secretions and urine, does not necessarily imply that they are the cause of disease. s
These mycobacteria occur naturally in water, including piped water supplies, and may be present in
high numbers in biofilms lining pipes and taps. They are known to contaminate inadequately disinfected A
endoscopes and other equipment used in clinical examinations. This, and the collection of sputum or urine P
in containers rinsed in water containing such mycobacteria, has given rise to 'pseudo-epidemics' of R
tuberculosis. I
"The number of EM submitted to a Mycobacterium reference laboratory may reflect the prevalence of L
actual disease due to them, notably in communities affected by the HIV/AIDS pandemic," Yates et al.
wrote. "It may also reflect an increase in the number and nature of specimens submitted for culture for 2
mycobacteria brought about by a greater awareness of tuberculosis, the increased use of endoscopy for
diagnostic purposes, changes in technical methods in the referring laboratories and by environmental
factors affecting the nature, number and distribution of EM in the environment, including piped water 1
9
supplies.9
"The workload of a reference laboratory is considerably increased by the receipt of EM as they must be 7
reliably distinguished from members of M. tuberculosis complex and identified, usually to species level."
For this reason, Yates et al. tracked the number of cultures of EM submitted to a reference center for
tuberculosis bacteriology serving South-East England during the period between 1973 and 1993.
The cultures were grouped according to year of first isolation, number of isolates, and data supplied by
the client laboratories, including age and HIV status of the patients, and the anatomical sites from which
the mycobacteria were isolated.
A total of 9,379 EM from 6,668 patients were received. Single and multiple isolates were received,
respectively, from 4,681 and 1,192 patients not known to be HIV positive and from 477 and 318 who were
known to be HIV positive. The annual number of patients not known to be HIV positive with isolates of
probable clinical significance increased steadily from less than 40 in 1973 to over 100 per year since 1990.
Isolates of doubtful clinical significance also showed an increase over time. The annual numbers from
HIV positive patients increased steeply following the first such isolates in 1984.
The data indicate that the annual number of isolates of EM from both H1V positive and negative
patients is increasing both absolutely and relatively to isolates of M. tuberculosis.
"In order to make the best use of limited financial resources while at the same time providing the most
useful and efficient reference service, cost-effective analysis of new identification techniques is required,"
Yates et al. wrote.
"Also, dialogue between the laboratory and clinicians is needed in order to minimize unnecessary and
duplicated investigations. For this purpose, a regular survey of the nature of, and factors affecting the
occurrence of, human disease due to EM should be of value."
The corresponding author for this study is Malcolm Yates, Public Health Laboratory Service
Mycobacterium Reference Unit, Dulwich Public Health Laboratory, Dulwich Hospital, London, SE22
8QF, United Kingdom.

- by Salynn Boyles, Senior Editor