Too cheap to meter

Cooling towers could be evolutionary hotspots for new respiratory diseases.

Many species of bacteria, including those that cause legionnaires' disease, are thought to have evolved in association with an amoebic host. Now it seems that the warm, wet conditions found in cooling towers at factories and oil refineries make them a perfect spot for amoebas and bacteria to thrive, increasing the chances of new strains of pathogenic bacteria emerging.

Sharon Berk of Tennessee Technological University in Cookeville and her colleagues have found that amoebas in cooling towers are about 16 times as likely to host bacteria as those in ponds and lakes. "It's a problem that we have suspected, but now this confirms it," says Jeffrey Cirillo, a microbiologist at Texas A&M University in College Station.

Genetic tests identified several previously unknown strains of bacteria, including some that were similar to Legionella pneumophila, the cause of legionnaires' disease. Berk suggests that they might have been missed in the past because many of the bacteria could not be cultured outside of amoebas.

The cause of up to 50 per cent of pneumonia cases is unknown, and Berk says cooling towers might be one source of these pathogens, creating aerosols that help them to spread more widely. Cirillo says cooling towers should now be monitored for emerging pathogens.