In the tropics, the cold tap is warm enough for Legionella

Legionellosis is a bacterial disease caused by inhaling or aspirating
Legionella bacteria; Legionnaires' disease is the form that comes with
pneumonia. The bacteria become a health risk when they contaminate a
building's water system.

In November 2024, the US Virgin Islands Department of Health was notified
of two confirmed Legionnaires' disease cases among travellers who had stayed
at two different hotels on St. Croix. The investigation found **two more
cases** — four in total, in patients aged 53–73. **Two were hospitalised;
none died.**

The finding that overturns an assumption

Legionellosis outbreaks are commonly associated with warm water sources.
At these two hotels, the probable sources of exposure included **both cold
(unheated) and hot (heated) water**, from showerheads and sinks in guest
rooms.

The explanation is climate. **In tropical climates, cold water systems operate
at 77–113°F (25–45°C)** — which is precisely the range in which Legionella
grows. A "cold" water system in the Caribbean is, biologically, a warm one.

Any water management plan written for a temperate building and applied in the
tropics is therefore guarding the wrong half of the plumbing.

What was found where

L. pneumophila was isolated from shower samples at both hotels.

Two lessons

Report legionellosis in returned travellers. Both outbreaks were found
because cases in travellers were reported, which let the local health
department investigate where the exposure actually happened — hundreds or
thousands of miles from where the patient fell ill.

**Water management programmes and system disinfection matter for hotel
operators**, and in a tropical climate they have to cover the cold water
system as seriously as the hot one.

*Source: Gallalee S, Cranford HM, Drummond A, et al. Legionellosis Outbreaks
Associated with Two Hotels — U.S. Virgin Islands, October 2024–April 2025.
MMWR, Centers for Disease Control and Prevention.*