Probabilistic Analysis of a French Legionellosis Outbreak Shows Potential Role of Wastewater Basin

Abstract

Based on the data from a French outbreak of legionellosis, a probabilistic approach was developed to analyze and assess the potential role of several suspected sources of contamination. Potential dates of exposure of all cases were determined using back-calculation, using two probability distribution functions to model incubation period. A probabilistic analysis and risk assessment were then used to determine the most probable sources of contamination for each wave of the outbreak. The risk assessment was based on parameters representing emission and dispersion of Legionella: level and duration of emission; aerosol dispersion capacity; and probability of potential exposure for each patient. Four types of facilities containing the Legionella epidemic strain were analyzed: cooling towers, aerated wastewater basins, high pressure water cleaners, and car wash stations. The results highlighted the potential role of an aerated wastewater basin in the outbreak in addition to cooling towers. The role of high-pressure water cleaners and car wash stations appeared to be non-significant. This study also reveals the lack of knowledge on facility parameters that can be useful for microbial risk assessments. This type of probabilistic analysis can be used to quantitatively assess the risk for various facilities in order to manage a legionellosis outbreak.

Estimating the Epidemic Size of Superspreading Coronavirus Outbreaks in Real Time: Quantitative Study

“…Back-calculation was first designed for short-term prediction of diseases with a long incubation period [ 26 ] and has also been applied to point-source outbreaks with limited onward transmission, such as Legionnaires disease [ 27 ]. We extended the method and focused on estimating the final size of symptomatic or laboratory-confirmed cases at the early stage of a coronavirus SSE, and asymptomatic cases were not considered in the estimation if they were not confirmed and reported.…”

Climate change and opportunistic pathogens (OPs) in the built environment

“…Exposure to OPs in the built environment is usually associated with premise plumbing (e.g., direct contact and inhalation of contaminated aerosols from taps, showerheads, flushed toilets) and cooling towers that release aerosols. Other environmental exposures can occur, such as inhalation of contaminated aerosols released from hot tubs, decorative water features, or wastewater treatment plants (Vermeulen et al, 2021;Wallet et al, 2022). While most legionellosis outbreaks are associated with cooling towers, the majority of cases are sporadic (Fisman et al, 2005;Passer et al, 2020).…”

“…Cooling towers used in evaporative cooling systems (e.g., air conditioning) are prone to colonization by Legionella bacteria and can produce aerosols that are dispersed from buildings over a wide area. They have been found to be a primary cause of legionellosis outbreaks (Crook et al, 2020;Prussin et al, 2017;Wallet et al, 2022). Warming and other environmental factors may favour colonization of cooling towers if not adequately maintained (O'Keeffe et al, 2020).…”

Occurrence of Legionella sp. bacteria in hot water systems in hospitals and nursing homes in the Świętokrzyskie Province of south-eastern Poland

“…bacilli enter water systems from natural sources and colonize artificial water reservoirs [11]. Potential sources of infection are installations and devices producing water aerosol, especially with a droplet size of < 5 µm [12]. Data from literature demonstrate that in more than 50% of cases of legionellosis the sources of infection were cooling towers and external elements of air conditioning systems.…”