SEASONAL-VARIATIONS IN THE OCCURRENCE OF ENVIRONMENTAL MYCOBACTERIA IN POTABLE WATER

A fluctuation in the prevalence of environmental mycobacteria in relat ion to nutritional conditions in nature has been repeatedly described in the literature. A seasonal difference in the potable water supply s ystem has not yet been documented. Potable water samples from the supp ly systems of 16 identical localities were analyzed. Samples of runnin g water and tap swabs or tap scrapings were collected twice a year, in the spring and in the autumn. The samples were processed as stipulate d by the international standards. McNemar's test was used to analyze t he difference in the occurrence of environmental mycobacteria between the vernal and the autumnal samples. A significant change in the prese nce of environmental mycobacteria in the potable water supply system w as observed, the vernal samples yielding more positive results, This f inding supports other observations respecting surface water. We sugges t that this effect on the potable water supply system may be caused by the change in temperature. Contamination rates were similar, with no statistically significant differences between running water samples an d those from swabs or scrapings. No time trend in the perod 1984-1989 respecting the prevalence of mycobacteria was detected. Direct microsc opy showed massive colonization with environmental mycobacteria of the potable water supply system. The public health consequences of these findings should be further evaluated, as colonization of water pipes c an be associated with outbreaks of mycobacterial disease in immunocomp romised patients. There has also been an increase in the incidence of mycobacterioses in the North Moravian region in recent years.