Occupation, Socioeconomic Status Tied to Legionellosis Risk

Diana Swift

October 27, 2014

Where you live and where you work can increase your risk of getting Legionnaires' disease.

Andrea Farnham, MPH, a research scientist with the Immunization Surveillance Team at the New York City Department of Health and Mental Hygiene, and colleagues analyzed federal and New York City data to identify epidemiological risk factors in cases of the aerosolized waterborne, pneumonia-like bacterial infection from 2002 to 2011. In a study published online October 15 and in the November 2014 issue of Emerging Infectious Diseases, the authors report that new cases in New York City rose by 230% from 2002 to 2009, peaking in 2009 at 2.74 cases per 100,000 population.

Established host risk factors for legionellosis are older age, smoking, chronic obstructive pulmonary disease, diabetes, compromised immunity, transplant, and chemotherapy. On the environmental front, risk factors include travel, healthcare facility residency, and proximity or exposure to cooling towers, whirlpool spas, fountains, and produce misters.

In New York City, routine surveillance documented 1449 confirmed cases from January 1, 2002, to December 31, 2011, with an average yearly incidence of 1.75 cases per 100,000 population and the largest increases seen in persons aged 70 to 79 years. The incidence of community-acquired cases was higher in summer and early fall and higher for men. When race/ethnicity was known, black race appeared to elevate risk, and the chance of also having diabetes was higher for persons with legionellosis in every age category.

Almost 90% of cases had at least one medical risk factor, such as smoking and diabetes. Of the 1279 community-acquired cases, 1261 were residentially geolocated according to six census-tract poverty levels. After age-adjustment, rates followed a gradient, with incidence in the highest-poverty areas being 2.5 times higher than in the lowest-poverty areas (3.0 vs 1.2 average yearly cases per 100,000 population). A similar gradient emerged along racial-ethnic lines, with rates among black non-Hispanics remaining higher than for other ethnicities in every poverty category.

Certain occupations, such as those involving machinery or the outdoors, including transportation, construction, and manufacturing, were associated with community-acquired legionellosis. Topping the list was transportation, with a 2.36 crude relative risk (95% confidence interval, 1.82 - 3.06), followed by janitorial and protection, with crude relative risks of 1.86 (95% CI, 1.11 - 3.11) and 1.77 (95% CI, 1.15 - 2.71), respectively. Risk also rose with cleaning and janitorial work (relative risk, 1.54 [95% CI, 1.07 - 2.22] and 1.49 [95% CI, 1.03 - 2.16]), possibly because of exposure to plumbing systems and aerosolized water. Legionellosis-associated protection occupations such as police officer, crossing guard, or security guard had a less clear causal pathway but might entail higher exposure to aerosolized water.

Although US studies on occupational risk are lacking, the New York City results for transportation workers were consistent with findings from England, the Netherlands, and Japan.

The authors acknowledge several study limitations, including the general underdiagnosis of legionellosis, the lack of racial/ethic data for almost 20% of their cases, and the low, 30% proportion of cases who reported having worked in the last 2 weeks. They made several recommendations, however, to public heath authorities.

"More careful measurement of occupation risk factors during routine surveillance may help clarify the cause pathway between occupation and risk of disease," the authors write. Furthermore, economic disparities in disease rates should be of serious concern to policy makers. "If environmental issues in high-poverty neighborhoods contribute to the disparity, greater effort may be warranted, for example, on the upkeep of cooling towers and water systems in the buildings of these areas." Occupations involving plumbing or construction might be rendered less risky by protective equipment such as respirators under certain conditions.

They called for further research into the understudied socioeconomic and occupational factors that may increase exposure to legionella, with a view to guiding public health interventions and reducing risk.

The increase in New York City appears to parallel that seen nationally, the authors note. Data from the Centers for Disease Control and Prevention indicate that 8000 to 18,000 people in the United States are hospitalized for Legionnaires' disease annually and that 5% to 30% of cases are fatal. From 2000 to 2011, the national incidence increased by 249%, going from 0.39 cases per 100,000 population in 2000 to 1.36 cases in 2011. However, the number of cases is likely underreported.

The study was funded by a Public Health Emergency Preparedness grant award from the Centers for Disease Control and Prevention. The authors have disclosed no relevant financial relationships.

Emerg Infect Dis. Published online October 15, 2014. Full text

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