Chapter 14, Problem 3CCS

Clinical Case Study Legionella in the Produce Aisle

Legionnaires’ disease, or legionellosis, is a potentially fatal respiratory disease caused by the growth of a bacterium, Legionella pneumophila, in the lungs of patients. The bacterium enters humans via the respiratory portal in aerosols produced by cooling towers, air conditioners, whirlpool baths, showers, humidifiers, and respiratory therapy equipment. Several years ago, the Louisiana state health department received reports of 33 cases of Legionnaires’ disease in the town of Bogalusa. LA (population 16,000).

Epidemiologists tried to ascertain the source of Bogalusa’s outbreak of Legionnaires’ disease by interviewing the victims and their relatives to develop complete histories and to identify areas of commonality among the victims that nonvictims did not share. Victims included a range of ages, occupations, hobbies, religions, and types and locations of dwellings. Although no significant differences were identified among the lifestyles, ages, or smoking habits of victims and nonvictims, one curious fact was discovered: all the victims did their grocery shopping at the same store. However, healthy individuals also shopped at that store.

The air-conditioning system of the grocery store proved to be free of Legionella, but the vegetable misting machine did not. The strain of Legionella isolated from the misting machine was identical to the strain recovered from the victims’ lungs.

1. 1. Would this outbreak be classified as endemic, epidemic, or pandemic?
2. 2. Is this a descriptive, analytical, or experimental epidemiological study?
3. 3. Knowing the epidemiology and causative agent of Legionnaires’ disease, what questions would you ask of the victims or of their surviving relatives?
4. 4. What, as an epidemiologist, would you examine at the store?
5. 5. How did the victims become contaminated? Why didn’t everyone who bought vegetables at the store get legionellosis? What could the owners of the store do to limit or prevent future infections?