BACKGROUND: Minnesota Department of Health (MDH) staff follow up and interview all Legionnaires’ disease cases promptly; approximately 60 cases are reported annually.
METHODS: On 12/5/15, a 65 year-old male with no underlying health conditions developed respiratory symptoms and was hospitalized on 12/8; urine antigen test performed 12/10 was positive for Legionella pneumophilia serogroup 1 (Case 1). Case reported 12/9 and next-of-kin proxy interviewed 12/10. No common exposures to previously reported cases noted. On 12/9, a 24 year-old male (Case 2) with smoking (1 ½ packs/day) as the only underlying health condition was hospitalized after 12/5 onset; urine antigen test 12/10 was positive for L. pneumophila serogroup 1. Case reported 12/14; following transfer to another hospital a next-of-kin proxy was located and interviewed 12/17. Case 2 reported to work at Restaurant A, located in the same city of residence as Case 1. We immediately launched an investigation.
RESULTS: Case 1’s proxy re-interviewed 12/16 and reported Case 1 being present at Restaurant A on 11/27, 11/28, and 12/5. On further proxy interview on 12/17, we learned Case 2 worked as Restaurant A dishwasher approximately 6 days/week, including on 11/27 and 11/28. MDH epidemiologists, including a Registered Sanitarian, visited Restaurant A on 12/17. The dishwashing area, with standard NSF-certified dishwasher and sprayer rinse-arm, was noted to be in a very small enclosed corner with a ventilation hood not turned on while dishwasher in use. When hood was on there appeared to be little airflow. Case 1 occasionally sat at a table <10 feet from the kitchen swinging door. Multiple issues with plumbing in the basement feeding the kitchen area were noted with many long dead-end pipes and loops. A city plumbing inspector and mechanical inspector were requested to inspect the building. On 12/18 and 12/21 they did, and noted many plumbing code violations, work done without permits, and dead-end pipes and unnecessary piping resulting in stagnant water.
CONCLUSIONS: Two Legionnaires’ disease cases with onsets on the same day were linked to a common exposure source. Deficient plumbing and a confined dishwashing area was the likely direct source of the employee; drifting of aerosolized Legionella from the dishwashing area to the restaurant area was likely source of the patron. The dishwashing area was closed and major plumbing reconstruction was initiated as soon as possible. Timely interviewing and iterative re-interviewing of cases with continuous comparison to previously reported cases is best practice to identify clusters.