Investigation of a Cluster of Legionella Infections of Unknown Origin in a Brooklyn Community

ISSUE: Legionnairesʹ disease is a rare form of pneumonia resulting in about 9,000 deaths in the U.S. annually. Early symptoms include fever, headache, dry cough, chills, and muscle aches. Other manifestations may include diarrhea, mental confusion, and kidney failure. Potable water systems are a common source of this infection. Cooling towers have been implicated as a disseminator of Legionella, which occurs most often in autumn months. No recent outbreaks of Legionnairesʹ disease had been reported from either the surrounding community or Brookdale University Medical Center (BUMC). Between August and October 2002, eight cases of Legionella were reported to the Department of Infection Control by the BUMC laboratory. All cases were in turn reported to the New York City (NYC) New York State (NYS) departments of health. PROJECT: To determine if a cluster of Legionella cases were nosocomial or a seasonal community-acquired outbreak and to pinpoint the source of the cluster. RESULTS: Cases were diagnosed by Legionella pneumophila serogroup urine antigen testing. A line listing was compiled of all cases reported from laboratory reports and information systems including date of admission, previous admission history, chest X-ray results, and specimen results. The cases were reported to the NYC and NYS departments of health and the investigation was conducted in conjunction with epidemiologists and public health investigators. Medical records were reviewed for all cases. Patient zip codes and addresses were acquired to rule out a common source exposure. Record reviews and interviews did not indicate common workplaces, housing areas, or social gathering sites for the patients (i.e., areas where contaminated water sources could be found). LESSON LEARNED: Healthcare facilities should be vigilant for clusters of patients with Legionella symptoms, educate their staff about the disease, perform prompt reporting, and enhance communication between the hospital lab, infection control, and the local health department. An investigation to rule out a nosocomial outbreak should include the compilation of specific information that differentiates between nosocomial and community-acquired infection.