Clade 4 includes L. rowbothamii, a species that was recognized in 200153. The organism belongs to a group of species that were historically called legionella-like amoebal pathogens (LLAP) because of their obligate intracellular parasitism of protozoa and lack of growth in media that is used to isolate Legionella54. LLAPs have been isolated from various water supplies during investigations of LD55. However, while there is speculation and some data suggesting that LLAPs may be associated with human disease, they more often are found as a co-infection with other respiratory pathogens such as Streptococcus pneumoniae and respiratory syncytial virus555657. L. rowbothamii is the only LLAP in our dataset and, therefore, it is not surprising that it forms a unique clade.