Hunting for Legionnaire's bacteria.

Hunting for Legionnaire's bacteria

In July 1976 a little-known bacterium became infamous when it killed 34 people attending an American Legion convention in Philadephia. Since then, at least 700 nonfatal cases of Legionnaire's disease have been reported each year. The discovery of Legionella pneumophila in the plumbing system of hospitals and cooling towers in a number of cities has caused concern among officials who worry that the bacterium may be ubiquitous throughout city water supplies.

In this regard, a recent study of the Pittsburgh water system offers mostly good news. Stanley J. States at the Pittsburgh Department of Water and his colleagues report that they "were unable to detect [the bacterium] anywhere in the system, including a number of sites in the treatment plant, the reservoir and the main system.' The results, he says, are consistent with findings in several other cities. However, the researchers did isolate Legionella in very low numbers in the Allegheny River and in some hospital tapwater samples. They also pegged a few sites--such as the reservoir bottoms--where Legionella could easily multiply since the water was stagnant, nutrient-rich or inadequately chlorinated.

According to States, Legionella is less susceptible to chlorine than are the coliform bacteria that are usually used as a guage of water quality, but he notes that chlorine levels of well maintained water systems should discourage the bacteria from homesteading. The group also found that zinc and iron, which can be leached from plumbing pipes, and potassium in the water supply enhance the organism's growth.

Finally, States stresses that the presence of the bacterium is by itself not necessarily dangerous. In general, it has attacked only people whose immune systems have already been compromised in some way. More work is needed, he says, to understand all the factors that must conspire to make people ill.