Rising Incidence of Legionnaires' Disease and Associated Epidemiologic Patterns, United States, 1992-2018

Abstract

Reported Legionnaires' disease (LD) cases began increasing in the United States in 2003 after relatively stable numbers for >10 years; reasons for the rise are unclear. We compared epidemiologic patterns associated with cases reported to the Centers for Disease Control and Prevention before and during the rise. The age-standardized average incidence was 0.48 cases/100,000 population during 1992-2002 compared with 2.71 cases/100,000 in 2018. Reported LD incidence increased in nearly every demographic, but increases tended to be larger in demographic groups with higher incidence. During both periods, the largest number of cases occurred among White persons, but the highest incidence was in Black or African American persons. Incidence and increases in incidence were generally largest in the East North Central, Middle Atlantic, and New England divisions. Seasonality was more pronounced during 2003-2018, especially in the Northeast and Midwest. Rising incidence was most notably associated with increasing racial disparities, geographic focus, and seasonality.

Keywords: Legionella; Legionnaires’ disease; United States; bacteria; epidemiology; legionellosis; pneumonia; respiratory infections; surveillance.

Figure 1

US Census Bureau regions and divisions. Regions: Northeast: Connecticut, Maine, Massachusetts, New Hampshire, New Jersey, New York City, New York State, Pennsylvania, Rhode Island, Vermont; Midwest: Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, South Dakota, Wisconsin; South: Alabama, Arkansas, Delaware, District of Columbia, Florida, Georgia, Kentucky, Louisiana, Maryland, Mississippi, North Carolina, Oklahoma, South Carolina, Tennessee, Texas, Virginia, West Virginia; West: Alaska, Arizona, California, Colorado, Hawaii, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, Washington, Wyoming. Divisions: New England: Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, Vermont; Middle Atlantic: New Jersey, New York City, New York State, Pennsylvania; East North Central: Illinois, Indiana, Michigan, Ohio, Wisconsin; West North Central: Iowa, Kansas, Minnesota, Missouri, Nebraska, North Dakota, South Dakota; South Atlantic: Delaware, District of Columbia, Florida, Georgia, Maryland, North Carolina, South Carolina, Virginia, West Virginia; East South Central: Alabama, Kentucky, Mississippi, Tennessee; West South Central: Arkansas, Louisiana, Oklahoma, Texas; Mountain: Arizona, Colorado, Idaho, Montana, Nevada, New Mexico, Utah, Wyoming; Pacific: Alaska, California, Hawaii, Oregon, Washington.

Figure 2

Reported cases of Legionnaires’ disease by month and incidence (cases/100,000 population) by year, United States,1992–2018. Monthly cases reported to the Centers for Disease Control and Prevention through the National Notifiable Diseases Surveillance System and the crude and age-standardized annual incidence for 1992–2018 are shown.

Figure 3

Average annual number of cases of Legionnaires’ disease and average incidence (cases/100,000 population), by age group, United States, 1992–2018. A) Reported average number of annual cases and average incidence by age group for 1992–2002. B) Reported average number of annual cases and average incidence by age group for 2003–2018.

Figure 4

Trends in median and mean age of Legionnaires’ disease patients by year, United States, 1992–2018.

Figure 5

Average annual number of cases of Legionnaires’ disease and age-standardized average incidence (cases/100,000 population) by race, United States, 1992–2018. A) Reported average number of annual cases and age-standardized average incidence by race for 1992–2002. B) Reported average number of annual cases and age-standardized average incidence by race for 2003–2018.

Figure 6

Age-standardized average incidence (cases/100,000 population) of Legionnaires’ disease by jurisdiction, United States, 1992–2018. A) Age-standardized average incidence by jurisdiction, 1992–2002. Legionnaires’ disease was not reportable in Connecticut during 1992–1996 or in Oregon or West Virginia during 1992–2002. B) Age-standardized average incidence by jurisdiction, 2003–2018.

Figure 7

Seasonality of Legionnaires’ disease cases by Census Bureau region, United States, 1992–2018. A) Seasonality of cases by US Census Bureau region, 1992–2002. The monthly percentage of each region’s cases is shown. If no seasonality existed, approximately the same number of cases would be expected to occur each month (i.e., 1/12 [8.3%] of annual cases would occur each month). B) Seasonality of cases by US Census Bureau region, 2003–2018. The monthly percentage of each region’s cases is shown. If no seasonality existed, approximately the same number of cases would be expected to occur each month (i.e., 1/12 [8.3%] of annual cases would occur each month).

Figure 8

International crude incidence (cases/100,000 population) trends of Legionnaires’ disease, United States (National Notifiable Diseases Surveillance System), Europe (39), Ontario, Canada (40,41), and Australia (42), 1991–2018.