What suggests a possible waterborne outbreak in a nursing home?

A single case of Legionnaires' disease can indicate a possible waterborne outbreak, especially in a nursing home setting. Legionnaires' disease is caused by the Legionella bacteria, which commonly thrive in water systems, particularly in large buildings such as nursing homes. When there is an isolated case of this disease, it raises concerns about the specific water source used in the facility, which may be contaminated.

On the other hand, the other options imply broader patterns or issues that are less indicative of a waterborne source. For instance, multiple cases of the flu typically suggest viral transmission from person to person rather than through water. High rates of gastrointestinal illness might associate with foodborne pathogens or poor hygiene practices rather than a water-related source. Similarly, increased reports of respiratory infections could have various causes, including airborne pathogens or environmental factors, but do not specifically pinpoint water contamination as the source. Thus, the presence of a singular case of Legionnaires' disease stands out as a strong indicator of potential water quality problems that need further investigation in a nursing home.