Soroka Medical Center in Be'er Sheva has diagnosed seven residents of the Negev desert city of Dimona with Legionnaires' disease in the past two weeks.
Three of the patients are in serious condition and no direct contact between any of the seven has been determined.
Legionnaires' disease, an atypical pneumonia caused by any type of Legionella bacteria, is not transmittable between people and is often found in infected water sources such as deep puddles, water fountains, hot tubs and pools that are not chlorinated.
It is detected via a PCR test similar to the one administered for COVID-19 or through a test of a suspected patient's urine.
Symptoms include severe pneumonia, but even before that appears patients will suffer from diarrhea, fever and muscle aches. Legionnaires' disease is treatable with antibiotics.
"We have no doubt more cases will appear," said Dr. Lior Nesher, an epidemiologist at Soroka Medical Center in Be'er Sheva.
"This is a foreign infection in our region and when it appears it usually comes in outbreaks as people breathe in air contaminated by the bacteria," he said.
"It's been years since we've had such an outbreak. We've alerted the medical teams in Dimona and [Soroka] to be on the lookout for more cases and have urged health officials to expedite their investigation and find the source of the disease."
Dimona municipal officials said they have begun an extensive epidemiological investigation to find the source, which is expected to take several days.