A large outbreak of Legionnaires’ disease in the Bronx in 2015 prompted NYC to enact law and NYS to propose emergency regulations on the registration and maintenance of cooling towers. This paper describes the fundamental characteristics of point sourced vs. potable water sourced outbreaks and discusses the Bronx outbreak from those perspectives. Ultimately a case is made that these new regulations will not have a measurable impact on reducing the incidence of Legionellosis. Rather, more detailed and open‐minded investigations of future outbreaks, including investigation of potential potable water sources, are called for to inform appropriate regulations and disease prevention activities.
Legionnaires’ disease (LD) is a severe form of pneumonia which is contracted by inhaling or aspirating water droplets containing Legionella deeply into the lungs. For many years it was believed the disease could be transmitted only by large equipment which emits aerosols or by equipment designed to aerosolize. Thus spas, decorative fountains, grocery misters, spray humidifiers, cooling towers and other aerosol sources were the only water systems investigated when an outbreak occurred. In the early 1980s investigations of potable water systems in hospital outbreaks indicated that the potable water is also a vector in disease transmission, either via aspiration of Legionella from the mouth into the lungs1 or via inhalation of droplets emitted by sinks and showers. It now appears that many LD outbreaks were initially blamed on cooling towers due to a “detection bias” that has not been widely recognized, and that these outbreaks were actually caused by potable water issues. In more recent years it has been found that the primary source of hospital‐acquired Legionnaires’ disease is potable water2 .
In the United States there have been requirements to address Legionella in hospital potable water systems from the Joint Commission on the Accreditation of Healthcare Organizations (JCAHO), Allegheny County (Pittsburgh), Maryland, New York, and others; however, until recently there have been no similar mandates in the United States for cooling towers. Although not mandated, many industrial groups such as CTI, ASHRAE, and AWT have published best practice guides that describe methods for maintaining equipment to minimize the risk of Legionellosis.
More than fifty Legionella species have been identified, but not all have been linked to disease. Legionella pneumophila serogroup 1 is the most virulent strain causing the majority of infections. Virulence varies not only between strains and their subtypes but can also vary within a particular cell. There are two major phases to the life cycle; a non‐pathogenic vegetative phase and a virulent transmissive phase. The concepts of ‘infectious dose’ or of ‘relative Legionella concentrations’ discussed within this paper pertain only to the virulent, or infectious, form of the bacteria.
The vast majority of LD occurs as apparently isolated cases. Of cases reported to the CDC, 96% are classified as sporadic and are not typically investigated.4 A cluster of cases is classified as an outbreak when two or more people are exposed to Legionella and get sick in the same place at about the same time. Recognized outbreaks of LD are rare; but when they occur, they provide opportunities to understand the epidemiology of the illness and improve prevention strategies. This opportunity is wasted if the extensive data that is generated during an outbreak is not evaluated impartially.
The recent outbreak in the South Bronx has resulted in New York City enacting a local law5 on the registration and maintenance of cooling towers in the city. Also, the State of New York has proposed emergency regulations for the registration and maintenance of cooling towers state‐wide6 . As more facts have emerged, it appears that the hastily prepared emergency regulations have fallen victim to the “detection bias” referred to in the first paragraph above and that authorities have not only squandered an opportunity to expand our understanding of the disease but imposed regulations and cost on cooling tower owners that have little chance of reducing the incidence of disease.
This paper will describe the outbreak in the Bronx that instigated these regulations. While a specific cooling tower was identified as the source of the original outbreak, two subsequent outbreaks occurred. Potable water in the building where people lived was positively identified as the source for second outbreak. Two months after the third outbreak ended a cooling tower was identified as the source, even though all of the cooling towers in the area had been recently cleaned in accordance with the newly enacted NYC laws.
The Bronx outbreak and regulatory response has many similarities to a French outbreak in the winter of 2003‐2004. In Pas‐de‐Calais a large outbreak was attributed to a cooling tower and resulted in the promulgation of regulations for the registration and maintenance of cooling towers. The inconsequential result of those regulations on the reduction of the incidence of disease will also be described in this paper.
New York Legionella regulations: are they missing the boat?