This explainer breaks down what happens next.
Once a person is exposed to Legionella bacteria and infected, Legionnaires’ disease typically has an incubation period of two to 10 days prior to the onset of symptoms. That means outbreaks actually begin as much as 10 days before they’re reported.
When a person does begin experiencing symptoms, they’ll normally go to a doctor for treatment, at which point they'll be tested for Legionnaires' disease. If that patient tests positive, their doctor will begin their examination by asking if they'd traveled anywhere the previous two weeks. Once they have that information, the doctor reports the case to the state health department and National Notifiable Disease Surveillance System (NNDSS).
A program of the Centers for Disease Control and Prevention (CDC), the NNDSS monitors cases of more than 120 diseases, including measles, E coli. and Zika, as well as Legionnaires'. When one is reported, it’s added to a database. With up to 15% of Legionnaires' patients traveling in the days preceding the manifestation of symptoms, this serves as a centralized hub to link the possible sources of seemingly random cases. If the NNDSS receives multiple reports of Legionnaires’ disease in sporadic locations, but connected to a common area, it will notify the local health department that they might have an outbreak on their hands.
Once the health department is alerted of an outbreak, the investigation begins.
The goal of a Legionnaires’ disease investigation is to determine its source as expeditiously and accurately as possible. To do so, each victim must undergo a comprehensive interview, documenting their activities throughout the preceding two weeks. They’ll be asked about everything from where they work and what stores they’ve shopped at to even the buildings they’ve passed, in the hope of finding similarities.
Sometimes, the source of an outbreak is clear. Multiple patients might recall eating at a certain restaurant, or staying at the same hotel. In these cases, officials will test the water systems of those locations for Legionella bacteria. If any test positive, the investigation is largely over, and the contaminated systems are disinfected.
But it’s not always that simple.
In many cases, officials are only able to narrow the source down to a general area—a neighborhood, or sometimes, an entire city. Unfortunately, this is common for outbreaks that originate from water cooling towers, as mist contaminated with Legionella can be carried several blocks before being inhaled by a victim, thus infecting them.
In cases like these, such as the 2018 Washington Heights outbreak, officials will test all cooling towers in the affected area. In Washington Heights, that meant testing 20 towers to find which one, if any, was contaminated.
Once a source is identified, the goal turns toward mitigation.
This is rarely an easy process for building owners and managers. In most cases, the water system from which the outbreak originated has to be shut down for disinfection. Sometimes, the entire building is forced to close.
Beyond the associated expenses of properly disinfecting water systems—which can run hundreds of thousands of dollars—buildings found to be the source of an outbreak of Legionnaires' disease can also be fined as much as $10,000, depending on their location.
The good news is that outbreaks are preventable.
Since the majority of outbreaks are caused by failing to follow Legionella prevention and management processes regarding cooling towers, the key to keeping out of the headlines is remaining compliant with standards developed to prevent the growth of Legionella bacteria, such as ANSI/ASHRAE 188-2015.