BACKGROUND: Legionnaires’ disease (LD) incidence has increased nationwide and in New York City (NYC); during 2002–2009, incidence increased 230% in NYC. We examined trends in LD incidence in NYC during 2007–2015, overall and stratified by demographic subgroup.
METHODS: Confirmed LD cases diagnosed during 2007–2015 were obtained from NYC Department of Health and Mental Hygiene (DOHMH) surveillance data. “Definite” hospital-associated cases and 133 cases associated with an outbreak in 2015 in the South Bronx were excluded. Annual incidence rates were calculated using yearly intercensal population estimates and age-adjusted to the US 2000 standard population. Joinpoint regression was used to assess trends in age-adjusted incidence rates overall and stratified by sex, borough, and census tract-based poverty level, defined as the percent of residents with incomes below the federal poverty level (FPL), per the American Community Survey 2006-2010, 2007-2011, 2009-2013, and 2010–2014, categorized as low poverty (<10% below FPL), medium (10–<20% below FPL), high (20–<30% below FPL), and very high poverty (≥30% below FPL). The average annual percent change (AAPC) was calculated to characterize trends, with a maximum of 2 allowable “joinpoints” or instances of statistically significant change in trend.
RESULTS: During 2007–2015, 1,824 LD cases were diagnosed in NYC. Age-adjusted LD incidence per 100,000 citywide increased significantly over the study period, from 2.1 to 3.4 (AAPC=4.9%, 95% confidence interval [CI]: 2.9%–7.0%). In stratified analyses, the AAPC in LD incidence among women was twice that among men: 7.2% for women (95% CI: 3.6%–11.1%), and 3.6% for men (95% CI: 1.0%–6.3%). The AAPC in LD incidence significantly increased by 4.0% in Brooklyn (95% CI: 1.5%–6.5%), 7.3% in Queens (95% CI: 4.6%–10.0%), and 14.5% in Staten Island (95% CI: 5.4%–24.4%). The AAPC in incidence also significantly increased in low, medium, and very high poverty areas by 6.3% (95% CI: 2.6%–10.2%), 7.4% (95% CI: 1.1%–14.0%), and 9.5% (95% CI: 7.4%–11.7%), respectively. No joinpoints (significant changes in trend) were identified for the overall and stratified analyses.
CONCLUSIONS: Significant increasing trends in LD incidence were observed during 2007–2015 in NYC, with the greatest relative increases in Staten Island, areas of very high poverty, and among women. Future analyses should examine how changes in testing, exposure sources, and access to care might have contributed to these trends.