About 20% of confirmed Legionnaires' disease cases reported in 2015 by 20 states and New York City were definitely or possibly health care-associated, according to the CDC.
Using national surveillance data from 2015, CDC researchers characterized Legionnaires' disease cases from the 21 jurisdictions which reported exposure information for 90% or more of the year's Legionella infections. The bacteria can grow in facilities' complex water systems, and individuals typically acquire the disease by inhaling aerosolized water containing Legionella (e.g., through showerheads, respiratory equipment, and cooling towers).
The researchers determined whether cases of the severe pneumonia were health care-associated (either definite or possible, defined respectively as continuous or any exposure to a hospital or long-term care facility for the 10 days before symptom onset). Their report appeared online on June 6 in Morbidity and Mortality Weekly Report.
Of 2,809 confirmed Legionnaires' disease cases reported in 2015 by the jurisdictions, 553 (20%) were health care-associated (85 [3%] definite and 468 [17%] possible). Definite health care-associated cases occurred at 72 facilities (15 hospitals and 57 long-term care facilities), mostly in patients ages 60 years or older.
The case fatality rate was 25% for definite and 10% for possible health care-associated cases. Of the 85 definite cases, 68 (80%) were associated with long-term care facilities, 15 (18%) with hospitals, and two (2%) with both. One explanation for the greater number of definite cases in long-term care facilities compared to hospitals is that hospital stays are typically shorter than the 10-day period used to define a definite health care-associated case, the study authors noted.
Among possible health care-associated cases, 61 (13%) were potentially associated with long-term care facilities, 227 (49%) with hospitals, 123 (26%) with clinics, 13 (3%) with other settings (e.g., outpatient laboratories), and 44 (9%) with more than one setting.
The study authors noted limitations to their findings, such as how data from more jurisdictions and more years would improve the accuracy of their estimates. They added that case fatality rates may be either overestimated (due to deaths from other causes) or underestimated (due to lack of information on deaths that occurred after reporting).
Implementation and maintenance of water management programs and rapid case identification and investigation could reduce the number of health care-associated cases of Legionnaires' disease, which is clinically indistinguishable from other causes of pneumonia, the authors noted.
“Legionella should be considered as a cause of health care-associated pneumonia, especially for groups at increased risk, when other facility-related cases have been identified, or when changes in water parameters might lead to increased risk for Legionnaires' disease,” they wrote. At-risk groups include patients ages 50 years or older, current or former smokers, and those with chronic diseases or a weakened immune system.