Legionella pneumophila Risk from Cooling Tower Systems in China

Legionella pneumophila widely exists in natural and artificial water environments, which enables it to infect people. L. pneumophila infection causes Legionnaires' disease (LD), which is a significant but relatively uncommon respiratory infection. Approximately 90% of LD is caused by L. pneumophila serogroup 1 (Lp1). Meteorological conditions may affect the infectivity and virulence of Lp1, but the exact relationship between them is still unclear. In this study, we evaluated the virulence of Lp1 by screening of total 156 Lp1 strains isolated from cooling tower water in different regions of China by detecting their abilities to activate NF-κB signaling pathway in vitro. In addition, we screened the distribution of some selected virulence genes in these strains. The virulence, virulence gene distribution, and the meteorological factors were analyzed. We found that both the virulence and the distribution of virulence genes had a certain regional and meteorological correlation. Although the loss of several virulence genes showed significant effects on the virulence of Lp1 strains, the distribution of virulence genes had very limited effects on the virulence of Lp1. IMPORTANCE LD is likely to be underrecognized in many countries. Due to the widespread existence of L. pneumophila in natural and artificial water environments and to the lack of cross-protection against different strains, L. pneumophila is a potentially serious threat to human health. Therefore, effective monitoring of the virulence of L. pneumophila in the water environment is very important to prevent and control the prevalence of LD. Understanding the virulence of L. pneumophila can not only help us to predict the risk of possible outbreaks in advance but can also enable more targeted clinical treatment. This study highlights the importance of understanding the epidemiology and ecology of L. pneumophila isolated from public facilities in terms of public health and biology. Due to the potential for water sources to harbor and disseminate L. pneumophila and to the fact that geographical conditions influence the virulence of L. pneumophila, timely and accurate L. pneumophila virulence surveillance is urgently needed.