Seasonal variations in the occurrence of environmental mycobacteria in potable water.

A fluctuation in the prevalence of environmental mycobacteria in relation to nutritional conditions in nature has been repeatedly described in the literature. A seasonal difference in the potable water supply system has not yet been documented. Potable water samples from the supply systems of 16 identical localities were analyzed. Samples of running water and tap swabs or tap scrapings were collected twice a year, in the spring and in the autumn. The samples were processed as stipulated by the international standards. McNemar's test was used to analyze the difference in the occurrence of environmental mycobacteria between the vernal and the autumnal samples. A significant change in the presence of environmental mycobacteria in the potable water supply system was observed, the vernal samples yielding more positive results. This finding supports other observations respecting surface water. We suggest 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 and those from swabs or scrapings. No time trend in the period 1984-1989 respecting the prevalence of mycobacteria was detected. Direct microscopy 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 can be associated with outbreaks of mycobacterial disease in immunocompromised patients. There has also been an increase in the incidence of mycobacterioses in the North Moravian region in recent years.