Legionellosis - Prevention

Prevention

A recent research study provided evidence that Legionella pneumophila, the causative agent of Legionnaires' disease, can travel airborne at least 6 km from its source. In 2000, ASHRAE issued guidelines to maintain water systems and to decrease the chances of Legionnaires’ disease transmission. The guidelines were not valued because legionella multiply in such temperatures. On the other hand, a lot of states had regulations that limited temperatures in health care facilities in order to reduce scalding injuries. It was previously believed that transmission of the bacterium was restricted to much shorter distances. A team of French scientists reviewed the details of an epidemic of Legionnaires' disease that took place in Pas-de-Calais in northern France in 2003–2004. There were 86 confirmed cases during the outbreak, of whom 18 died. The source of infection was identified as a cooling tower in a petrochemical plant, and an analysis of those affected in the outbreak revealed that some infected people lived as far as 6–7 km from the plant.

A study of Legionnaires' disease cases in May 2005 in Sarpsborg, Norway concluded that: "The high velocity, large drift, and high humidity in the air scrubber may have contributed to the wide spread of Legionella species, probably for >10 km. "...

In 2010 a study by the UK Health Protection Agency reported that 20% of cases may be caused by infected windscreen washer systems filled with pure water. The finding came after researchers spotted that professional drivers are five times more likely to contract the disease. No cases of infected systems were found whenever a suitable washer fluid was used.

Temperature affects the survival of Legionella as follows:

• 70 to 80 °C (158 to 176 °F): Disinfection range
• At 66 °C (151 °F): Legionellae die within 2 minutes
• At 60 °C (140 °F): They die within 32 minutes
• At 55 °C (131 °F): They die within 5 to 6 hours
• Above 50 °C (122 °F): They can survive but do not multiply
• 35 to 46 °C (95 to 115 °F): Ideal growth range
• 20 to 50 °C (68 to 122 °F): Growth range
• Below 20 °C (68 °F): They can survive but are dormant

Removing slime, which can carry legionellae when airborne, may be an effective control process.