Scientists who determined the source of the woman's illness, which occurred in February 2011, said during the disease's incubation period the woman only left her home twice to visit her dentist.
When they tested the water in both places, they discovered the bacteria that causes Legionnaires' in the dentist's water line. Water lines carry water from the main water supply to certain devices used during patient care.
While the authors wrote the most common sources of infection are air conditioning systems, hot water systems, spas and fountains, a recent study found dental water lines to be another major source of contamination with Legionella bacteria. Legionella pneumophila is the bacterial strain that causes Legionnaires' disease.
"However, as far as we are aware, no case of Legionnaires' disease has been associated with this source of infection," added the authors, led by Maria Luisa Ricci of the Italian National Health Service.
While it was not clear what kind of water line standards were in place in Italy, in the U.S., the American Dental Association (ADA) said infection control standards are very stringent in order to prevent cases like the one in Italy from happening.
"Since the ADA convened a special task force in the mid-1990s focusing on infection prevention, there have been a number of recommendations made to treat the water and keep the number of bacteria down," said John Molinari, the ADA's spokesman on infection control, infectious diseases and allergic reactions.
The ADA recommends that dental water lines contain no more than 500 colony-forming units of bacteria per milliliter of water, the same limit recommended by the U.S. Centers for Disease Control and Prevention.
The ADA also recommends that dentists monitor water quality and maintain a water reservoir that is separate from the municipal water supply, as well as use filters that will keep microorganisms out of the water.
Legionella bacteria is one of the most common types of bacteria found in water.
"Legionella is found in old homes, shower heads and anywhere else there can be stagnant water," Molinari said.
Most dentists take the necessary precautions to protect their water lines from contamination, but Molinari said that the Italian case is an important reminder.
"This report sends the message that it can happen," he said.
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