Legionellosis on the rise: A scoping review of sporadic, community-acquired incidence in the United States

Abstract

Over the past two decades, the incidence of legionellosis has been steadily increasing in the United States though there is noclear explanation for the main factors driving the increase. While legionellosis is the leading cause of waterborne outbreaks in the US, most cases are sporadic and acquired in community settings where the environmental source is never identified. This scoping review aimed to summarise the drivers of infections in the USA and determine the magnitude of impact each potential driver may have. A total of 1,738 titles were screened, and 18 articles were identified that met the inclusion criteria. Strong evidence was found for precipitation as a major driver, and both temperature and relative humidity were found to be moderate drivers of incidence. Increased testing and improved diagnostic methods were classified as moderate drivers, and the ageing U.S. population was a minor driver of increasing incidence. Racial and socioeconomic inequities and water and housing infrastructure were found to be potential factors explaining the increasing incidence though they were largely understudied in the context of non-outbreak cases. Understanding the complex relationships between environmental, infrastructure, and population factors driving legionellosis incidence is important to optimise mitigation strategies and public policy.

Severe Legionnaires’ disease

“…Many studies have found that increased precipitation, temperature, and relative humidity are positively associated with the occurrence of LD, particularly a sequence of elevated temperatures followed by a period of increased precipitation, high relative humidity, and low wind [ 28 , 29 ]. The intensification of extreme meteorological events due to climate change (for instance, high temperature variations and heavy rainfall), may create conditions for the development of Legionella and increase the incidence of LD [ 30 , 31 ].…”

Comparative study on 16s rRNA gene Sequences for clinical and environmental isolates of legionella pneumophila.

“…Legionellosis, a result of Legionella bacterium infection, involves both LD and the flu-like disease known as Pontiac Fever [5]. LD is an increasingly prevalent atypical pneumonia that is possibly acquired in the community, through travel, or nosocomial infection.…”