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Open Access Research article

Legionnaires’ disease case-finding algorithm, attack rates, and risk factors during a residential outbreak among older adults: an environmental and cohort study

Benjamin J Silk12*, Jennifer L Foltz13, Kompan Ngamsnga5, Ellen Brown2, Mary Grace Muñoz5, Lee M Hampton12, Kara Jacobs-Slifka27, Natalia A Kozak2, J Michael Underwood14, John Krick56, Tatiana Travis2, Olivia Farrow5, Barry S Fields2, David Blythe6 and Lauri A Hicks2

Author Affiliations

1 Epidemic Intelligence Service, Office of Workforce and Career Development, U.S. Centers for Disease Control and Prevention, Atlanta, Georgia, USA

2 Respiratory Diseases Branch, Division of Bacterial Diseases, National Center for Immunization and Respiratory Diseases, U.S. Centers for Disease Control and Prevention, Atlanta, Georgia, USA

3 Division of Nutrition, Physical Activity, and Obesity, National Center for Chronic Disease Prevention and Health Promotion, U.S. Centers for Disease Control and Prevention, Atlanta, Georgia, USA

4 Division of Cancer Prevention and Control, National Center for Chronic Disease Prevention and Health Promotion, U.S. Centers for Disease Control and Prevention, Atlanta, Georgia, USA

5 Baltimore City Health Department, Baltimore, Maryland, USA

6 Maryland Department of Health and Mental Hygiene, Baltimore, Maryland, USA

7 College of Human Medicine, Michigan State University, East Lansing, Michigan, USA

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BMC Infectious Diseases 2013, 13:291  doi:10.1186/1471-2334-13-291

Published: 27 June 2013

Abstract

Background

During a Legionnaires’ disease (LD) outbreak, combined epidemiological and environmental investigations were conducted to identify prevention recommendations for facilities where elderly residents live independently but have an increased risk of legionellosis.

Methods

Survey responses (n = 143) were used to calculate attack rates and describe transmission routes by estimating relative risk (RR) and 95% confidence intervals (95% CI). Potable water collected from five apartments of LD patients and three randomly-selected apartments of residents without LD (n = 103 samples) was cultured for Legionella.

Results

Eight confirmed LD cases occurred among 171 residents (attack rate = 4.7%); two visitors also developed LD. One case was fatal. The average age of patients was 70 years (range: 62–77). LD risk was lower among residents who reported tub bathing instead of showering (RR = 0.13, 95% CI: 0.02–1.09, P = 0.03). Two respiratory cultures were characterized as L. pneumophila serogroup 1, monoclonal antibody type Knoxville (1,2,3), sequence type 222. An indistinguishable strain was detected in 31 (74%) of 42 potable water samples.

Conclusions

Managers of elderly-housing facilities and local public health officials should consider developing a Legionella prevention plan. When Legionella colonization of potable water is detected in these facilities, remediation is indicated to protect residents at higher risk. If LD occurs among residents, exposure reduction, heightened awareness, and clinical surveillance activities should be coordinated among stakeholders. For prompt diagnosis and effective treatment, clinicians should recognize the increased risk and atypical presentation of LD in older adults.

Keywords:
Legionella; Community-acquired pneumonia; Elderly