Legionnaires' disease is a severe pneumonia caused by Legionella, bacteria that live in water. Reported cases in the U.S. rose 4.5-fold from 2000 to 2015, and in Wisconsin confirmed cases climbed from 63 in 2010 to 330 in 2018. About 9% of U.S. cases are fatal, and in 2015 two-thirds of patients with confirmed cases hadn't traveled or been in a health care or assisted-living setting when they were likely exposed.
In January 2018, Wisconsin's Division of Public Health (DPH) was notified of a culture-confirmed case in a patient who had died in hospital.
The patient
A nonsmoker in their 70s, diagnosed in 2016 with late-onset combined immunodeficiency after two opportunistic infections, came to the emergency department with a rash and fever, thought to be a reaction to a 30-day course of levofloxacin for a leg infection.
Timeline of the case and investigation. CDC
| Day | |
|---|---|
| 0 | admitted; confusion reported by family, dry cough, shortness of breath. Rhinovirus and parainfluenza found; chest x-ray normal |
| 5 | cough brings up dark brown sputum; new right upper lobe opacity; septic shock, thought to be hospital-acquired pneumonia; moved to ICU |
| 6 | urine antigen test for L. pneumophila serogroup 1 — negative; bronchoalveolar lavage (BAL) fluid sent for Legionella culture |
| 10 | dies of cardiopulmonary arrest from septic shock |
| 16–17 | the Wisconsin State Laboratory of Hygiene (WSLH) grows L. pneumophila from the BAL fluid — not serogroup 1, later identified as serogroup 3, which the urine test can't detect |
Serogroup 3 rarely causes Legionnaires' disease; serogroup 1 causes most cases.
Searching for the source
The hospital. Because the infection might have been caught in hospital, its water management program — set up after a 1990s outbreak — kicked in. Nine possible exposure points (sink faucets, ice machines, a shower and a warm-water pool) were cultured on day 17, and again on day 40 by both the hospital and WSLH. All negative.
The home. On day 26, at the family's request, hospital staff sampled two showers in the patient's home — a single-family house from the early 1910s, in good condition, on municipal water. Both positive for L. pneumophila.
Cleaning up. From day 52, following a 2010 home guidance manual, a plumber drained, chlorinated and superheated the water heater to 148 °F (64.4 °C), flushed the fixtures over three days, and soaked the showerheads in vinegar to remove scale.
Still there. On day 62, DPH sampled eight fixtures. The bathroom faucet and two kitchen sprayers were still positive.
The match. By day 75, pulsed-field gel electrophoresis showed the home and patient isolates matched; on day 114, CDC's whole-genome typing identified both as L. pneumophila serogroup 3, sequence type 93, sharing 99.7% of alleles. The home was the most likely source.
The other resident, who wasn't immunocompromised, didn't get sick. DPH shared the guidance manual and discussed prevention — keeping the water heater at recommended settings and maintained, flushing fixtures after they sit unused (after a vacation, for example) — and urged them to see a doctor if they developed respiratory symptoms.
Lessons
- Home water can be a source. Legionella in household drinking water is widely documented, and people at higher risk — such as those with weakened immune systems — can be exposed at home. But prevention guidance covers mainly complex building water systems, and little is known about the burden of home-acquired disease or whether testing and cleaning homes is useful or feasible. This case shows how hard home remediation can be.
- Test the lungs, not just the urine. The urine antigen test finds only serogroup 1; other types need polymerase chain reaction (PCR) testing or culture of lower respiratory specimens such as sputum or BAL fluid — and sputum can be cultured even if it's low quality. Because prompt antibiotics affect survival, CDC recommends ordering both a urine antigen test and a lower respiratory culture for suspected Legionnaires' disease. Cultures also let investigators confirm the source.
Sources
Based on Schumacher A, Kocharian A, Koch A, Marx J, "Fatal Case of Legionnaires' Disease After Home Exposure to Legionella pneumophila Serogroup 3 — Wisconsin, 2018," MMWR volume 69, number 8, Centers for Disease Control and Prevention; a work of the United States government in the public domain.
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