LIVING THE LAB LIFE
A BLOG FOR ASCLS REGION V
As many of you who live or work in the Twin Cities are aware, we are facing an outbreak of Legionella pneumophilia, the causative agent for Legionnaire’s disease and Pontiac fever. The Minnesota Department of Health has identified twenty-three cases of Legionnaire’s disease (as of a September 30th press release) clustered in the Hopkins, MN area. Further investigation has revealed the source of the outbreak as cooling towers atop the Citrus Systems, Inc. plant in Hopkins. The water source has been chemically cleaned and officials have stated that there is no risk of infection by any of the plant’s products, as the bacteria never contaminated inside of the plant.
Legionella pneumophila first made headlines back in the late 1960s after causing an outbreak of a febrile disease in a number of people working at (ironically) the Pontiac, Michigan Public Health Department. Then in the 1970s, L. pneumophilia made news again after instigating an outbreak of severe pneumonia which sickened a number of American Legion members who attended a conference in Philadelphia. These two illnesses would subsequently be referred to as Pontiac Fever and Legionnaire’s disease. Pontiac fever is self-limiting and requires no formal treatment, whereas Legionnaire’s disease can be fatal and requires antibiotic treatment and supportive therapies to ensure patient survival.
The causative agent for Legionnaire’s disease is a gram-negative bacillus named Legionella pneumophilia. Laboratory diagnosis of this disease is challenging because these bacteria do not grow on routine culture media and stain poorly with conventional staining procedures. Culture media supplemented with iron salts and L-cysteine like Buffered Charcoal Yeast Extract (BCYE) agar are needed to grow this organism. Antigen tests are useful in identifying infections with L. pneumophila serogroup 1, but they will like miss infections with other serogroups. Serological testing is also available; however, patients can take as long as six months to seroconvert. Molecular-based techniques, such as PCR, are the ideal option for diagnosis, using sputum, bronchial washings, or any respiratory specimen for testing. These methods are as sensitive and specific as culture methods, but with a reduced turn-around time (it typically takes three to five days of incubations for L. pneumophila to grow in culture).
This pathogen is spread when individuals inhale aerosols carrying the bacteria. It does not spread through person-to-person contact. Most people who have been sickened with L. pneumophila are exposed to the organism through contaminated water sources which produce aerosols containing the bacteria (cooling towers, shower heads, saunas, etc.). The Minnesota Department of Health is currently testing many water sources in Hopkins to determine the root cause of this current outbreak, with the focus of the investigation falling on various cooling towers in the area. Of note, L. pneumophila can also cause nosocomial infections. Hospital-acquired cases comprise approximately 25% of all reported cases, with these patients being exposed through contaminated water sources in the hospital (yikes!)
It is very important that these patients be diagnosed and treated as quickly as possible when L. pneumophila infection is suspected. There is a mortality rate of between 15-20% associated with Legionnaire’s disease, with that rate creepy higher with any delays in treatment.
If you encounter a patient at your facility who is suspicious for an infection with L. pneumophila, please refer to guidance from the Minnesota Department of Health or Centers for Disease Control and Prevention to aid in diagnosis of the patient. We as laboratorians have the power to ensure that patient gets the right care at the right time, let us be sure to use it.
UPDATE: This article has been updated to include the source of the outbreak, cooling towers on the Citrus System, Inc. plant in Hopkins, as revealed by the Minnesota Department of Health in a news release from October 12, 2016.
ReferencesMahon, C. R., Lehman, D. C., & Manuselis, G. (2011). Textbook of Diagnostic Microbiology (4th ed.). Maryland Heights, Missouri: W.B. Saunders Company.
Minnesota Department of Health. (2016, September 30). Hopkins Legionnaire's Investigation. Retrieved from http://www.health.state.mn.us/news/pressrel/2016/legion093016.html
Minnesota Department of Health. (2016, October 12). Health officials identify source of Hopkins Legionnaires' disease outbreak. Retrieved from http://www.health.state.mn.us/news/pressrel/2016/legion101216.html
Murray, P. R., Rosenthal, K. S., & Pfaller, M. A. (2009). Medical Microbiology (6th ed.). Philadelphia: Mosby Elsevier.