Abstract
Between 2000 and 2017, a total of 236 Legionella species isolates from Arizona were submitted to the CDC for reference testing. Most of these isolates were recovered from bronchoalveolar lavage specimens. Although the incidence of legionellosis in Arizona is less than the overall U.S. incidence, Arizona submits the largest number of isolates to the CDC for testing compared to those from other states. In addition to a higher proportion of culture confirmation of legionellosis cases in Arizona than in other states, all Legionellapneumophila isolates are forwarded to the CDC for confirmatory testing. Compared to that from other states, a higher proportion of isolates from Arizona were identified as belonging to L. pneumophila serogroups 6 (28.2%) and 8 (8.9%). Genome sequencing was conducted on 113 L. pneumophila clinical isolates not known to be associated with outbreaks in order to understand the genomic diversity of strains causing legionellosis in Arizona. Whole-genome multilocus sequence typing (wgMLST) revealed 17 clusters of isolates sharing at least 99% identical allele content. Only two of these clusters contained isolates from more than one individual with exposure at the same facility. Additionally, wgMLST analysis revealed a group of 31 isolates predominantly belonging to serogroup 6 and containing isolates from three separate clusters. Single nucleotide polymorphism (SNP) and pangenome analysis were used to further resolve genome sequences belonging to a subset of isolates. This study demonstrates that culture of clinical specimens for Legionella spp. reveals a highly diverse population of strains causing legionellosis in Arizona which could be underappreciated using other diagnostic approaches.IMPORTANCE Culture of clinical specimens from patients with Legionnaires' disease is rarely performed, restricting our understanding of the diversity and ecology of Legionella Culture of Legionella from patient specimens in Arizona revealed a greater proportion of non-serogroup 1 Legionellapneumophila isolates than in other U.S. isolates examined. Disease caused by such isolates may go undetected using other diagnostic methods. Moreover, genome sequence analysis revealed that these isolates were genetically diverse, and understanding these populations may help in future environmental source attribution studies.
Highlights
Between 2000 and 2017, a total of 236 Legionella species isolates from Arizona were submitted to the coordinate this project. Jeffery Mercante (CDC) for reference testing
The incidence of legionellosis in Arizona is lower than the overall U.S incidence and nearly 4-fold less than that reported for the states with the highest incidence of the disease [4]
Compared to that for isolate submissions to CDC from other states, the proportion of Legionella pneumophila serogroup 1 (Lp1) isolates from Arizona is smaller while the proportion of other serogroups is larger
Summary
Between 2000 and 2017, a total of 236 Legionella species isolates from Arizona were submitted to the CDC for reference testing. In addition to a higher proportion of culture confirmation of legionellosis cases in Arizona than in other states, all Legionella pneumophila isolates are forwarded to the CDC for confirmatory testing. This study demonstrates that culture of clinical specimens for Legionella spp. reveals a highly diverse population of strains causing legionellosis in Arizona which could be underappreciated using other diagnostic approaches. Culture of Legionella from patient specimens in Arizona revealed a greater proportion of non-serogroup 1 Legionella pneumophila isolates than in other U.S isolates examined. Disease caused by such isolates may go undetected using other diagnostic methods. While the surveillance definition of a possible or definite health care-associated LD case in some public health jurisdictions involves any exposure to a health care facility during the incubation period, the definition in Arizona (since 2016) requires the patient to have an overnight stay in a health care facility
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