Category Archives: Legionella

Research – Heterotrophic Plate Count Can Predict the Presence of Legionella spp. in Cooling Towers



Legionella pneumophila (Lp) colonizes aquatic environments and is a potential pathogen to humans, causing outbreaks of Legionnaire’s disease. It is mainly associated with contaminated cooling towers (CTs). Several regulations, including Spanish legislation (Sl), have introduced the analysis of heterotrophic plate count (HPC) bacteria and Legionella spp. (Lsp) in management plans to prevent and control Legionella outbreaks from CTs. The 2003 Sl for CTs (RD 865/2003) considered that concentrations of HPC bacteria ≤10,000 cfu/mL and of Lsp ≤100 cfu/L are safe; therefore, no action is required, whereas management actions should be implemented above these standards. We have investigated to what extent the proposed standard for HPC bacteria is useful to predict the presence of Lsp in cooling waters. For this, we analyzed Lsp and HPC concentrations, water temperature, and the levels of chlorine in 1376 water samples from 17 CTs. The results showed that in the 1138 water samples negative for Legionella spp. (LN), the HPC geometric mean was significantly lower (83 cfu/mL, p < 0.05) than in the positive Lsp. samples (135 cfu/mL). Of the 238 (17.3%) LP samples, 88.4% (210/238) were associated with values of HPC ≤10,000 cfu/mL and most of them showed HPC concentrations ≤100 (53.7%). In addition, a relatively low percentage of LP (28/238, 11.6%) samples were associated with HPC bacteria concentrations >10,000 cfu/mL, indicating that this standard does not predict the colonization risk for Legionella in the CTs studied. The present study has demonstrated that a threshold concentration ≤100 cfu/mL of HPC bacteria could better predict the higher concentration of Legionella in CTs, which will aid in preventing possible outbreaks.

Research – Exploring the Link Between Legionnaires’ Disease and Pneumonia

CDC legionella

Most of us have heard of Legionnaires’ disease and we are all likely to be aware of pneumonia too, but did you know there is a link between the two?

There are many illnesses and conditions that can affect the lungs. Legionnaires’ disease presents as a serious type of pneumonia. This is an inflammation of the lungs. Below, we’ll go into more detail about the link between Legionnaires’ disease and pneumonia. Both can be fatal, particularly among those who are more susceptible to this type of infection than others.

A version of this story exploring the link between Legionnaires’ disease and pneumonia appeared in Legionella Control International’s newsletter. To get it in your inbox, sign up for free at the link above

Research – Legionella pneumophila Risk from Air–Water Cooling Units Regarding Pipe Material and Type of Water


Legionella A


Legionellosis is a respiratory disease related to environmental health. There have been manifold studies of pipe materials, risk installations and legionellosis without considering the type of transferred water. The objective of this study was to determine the potential development of the causative agent Legionella pneumophila regarding air–water cooling units, legislative compliance, pipe material and type of water. Forty-four hotel units in Andalusia (Spain) were analysed with respect to compliance with Spanish health legislation for the prevention of legionellosis. The chi-square test was used to explain the relationship between material–water and legislative compliance, and a biplot of the first two factors was generated. Multiple correspondence analysis (MCA) was performed on the type of equipment, legislative compliance, pipe material and type of water, and graphs of cases were constructed by adding confidence ellipses by categories of the variables. Pipe material–type of water (p value = 0.29; p < 0.05) and legislative compliance were not associated (p value = 0.15; p < 0.05). Iron, stainless steel, and recycled and well water contributed the most to the biplot. MCA showed a global pattern in which lead, iron and polyethylene were well represented. Confidence ellipses around categories indicated significant differences among categories. Compliance with Spanish health legislation regarding the prevention and control of legionellosis linked to pipe material and type of water was not observed.

USA – FDA investigates cases of Legionnaires disease on cruise ships

Food Safety News

FDA Warning Letters

American Cruise Lines
Guilford, CT

American Cruise Lines is on notice from the Food and Drug Administration (FDA) after an inspection of their American Star and American Heritage vessels. According to the warning letter, the FDA continues to have concerns with the potential exposure of passengers and crew members to Legionella onboard American Cruise Lines’ vessels.

In Jan. 24, 2023, warning letter, the FDA described an April 30 through June 17, 2022, an inspection of American Cruise Lines’ American Star and American Heritage vessels.

The warning letter includes information about failed water tests for a sink in the galley and hand-washing sinks for wait staff. The FDA also found that disinfection was ineffective.

American Star
Presence of Legionella Onboard the Vessel

On April 30, 2022, FDA investigators collected 10 biofilm swabs and 14 bulk one-liter potable water samples from various locations on the vessel. The Maryland Department of Health laboratory recovered Legionella from:

Biofilm Swabs with 60 percent of samples positive:

American Heritage

Presence of Legionella Onboard the Vessel

On June 15, 2022, FDA investigators collected 24 biofilm swabs and 29 bulk one-liter potable water samples from various locations on their vessels. The Maryland Department of Health laboratory recovered Legionella from:

Biofilm Swabs with 8 percent of samples positive:

USA – Legionnaire’s Disease Outbreak Linked to American Cruise Lines

Daily Hornet

The U.S. Food and Drug Administration (FDA) sent a warning letter to American Cruise Lines after 3 passengers got Legionnaire’s disease and the company failed to adequately treat the ships’ drinking water.

The first confirmed case of Legionnaire’s disease was reported in April 2021, with two more cases reported in September and October 2021.

Between April and August 2022, FDA inspectors tested the drinking water on the American Star and American Heritage and found ongoing evidence of Legionella bacteria.

Shockingly, 93% of water samples on the American Star tested positive for Legionella bacteria in April 2022, including samples taken from showerheads in the rooms for passengers and crew.

In June 2022, multiple samples of drinking water from showerheads and faucets on the American Heritage also tested positive for Legionella, according to the FDA.

Despite problems with Legionella contamination and illnesses, the FDA said that American Cruise Lines failed to take adequate stops to treat the ships’ water supply.

Research – Impact of Pipe Material and Temperature on Drinking Water Microbiome and Prevalence of Legionella, Mycobacterium, and Pseudomonas Species



In drinking water distribution systems (DWDSs), pipe material and water temperature are some of the critical factors affecting the microbial flora of water. Six model DWDSs consisting of three pipe materials (galvanized steel, copper, and PEX) were constructed. The temperature in three systems was maintained at 22 °C and the other 3 at 32 °C to study microbial and elemental contaminants in a 6-week survey using 16S rRNA next-generation sequencing (NGS) and inductively coupled plasma-optical emission spectrometry (ICP-OES). Pipe material and temperature were preferentially linked with the composition of trace elements and the microbiome of the DWDSs, respectively. Proteobacteria was the most dominant phylum across all water samples ranging from 60.9% to 91.1%. Species richness (alpha diversity) ranking was PEX < steel ≤ copper system and elevated temperature resulted in decreased alpha diversity. Legionellaceae were omni-prevalent, while Mycobacteriaceae were more prevalent at 32 °C (100% vs. 58.6%) and Pseudomonadaceae at 22 °C (53.3% vs. 62.9%). Heterogeneity between communities was disproportionately driven by the pipe material and water temperature. The elevated temperature resulted in well-defined microbial clusters (high pseudo-F index) in all systems, with the highest impact in PEX (10.928) followed by copper (9.696) and steel (5.448). Legionellaceae and Mycobacteriaceae are preferentially prevalent in warmer waters. The results suggest that the water temperature has a higher magnitude of impact on the microbiome than the pipe material.

Research Breakthrough in fighting Legionnaires’ disease


A new study of domestic and hospital drinking water systems found Legionella in 41% of samples – with Flinders University researchers making a key connection between the pathogen’s co-existence with a ‘host’ microorganism in all samples tested.

The study found Legionella bacteria “infect the amoeba host and then once inside these hosts are protected from disinfection strategies,” says Flinders University Associate Professor of Environmental Health Harriet Whiley, a co-author of the new journal article in Water Research.

Researchers tested for Legionella and its likely amoebae hosts in 140 samples of water or biofilm (the slime found on showerheads and end of faucets) to understand how the potentially dangerous bacterium colonises and proliferates in both domestic and hospital plumbing and poses a threat to human health.

Research – Concept about the Virulence Factor of Legionella



Pathogenic species of Legionella can infect human alveolar macrophages through Legionella-containing aerosols to cause a disease called Legionellosis, which has two forms: a flu-like Pontiac fever and severe pneumonia named Legionnaires’ disease (LD). Legionella is an opportunistic pathogen that frequently presents in aquatic environments as a biofilm or protozoa parasite. Long-term interaction and extensive co-evolution with various genera of amoebae render Legionellae pathogenic to infect humans and also generate virulence differentiation and heterogeneity. Conventionally, the proteins involved in initiating replication processes and human macrophage infections have been regarded as virulence factors and linked to pathogenicity. However, because some of the virulence factors are associated with the infection of protozoa and macrophages, it would be more accurate to classify them as survival factors rather than virulence factors. Given that the molecular basis of virulence variations among non-pathogenic, pathogenic, and highly pathogenic Legionella has not yet been elaborated from the perspective of virulence factors, a comprehensive explanation of how Legionella infects its natural hosts, protozoans, and accidental hosts, humans is essential to show a novel concept regarding the virulence factor of Legionella. In this review, we overviewed the pathogenic development of Legionella from protozoa, the function of conventional virulence factors in the infections of protozoa and macrophages, the host’s innate immune system, and factors involved in regulating the host immune response, before discussing a probably new definition for the virulence factors of Legionella.

Research – The European Scientific Conference on Applied Infectious Disease Epidemiology (ESCAIDE)



Page 71 – An Easter Surprise: Salmonella Typhimurium outbreak linked to chocolate products in the United Kingdom, 2022; a case control study

Page 72  – International outbreak of Salmonella Typhimurium linked to a chocolate factory in 2022: Belgian findings

Page 73 – Whole Genome Sequencing identified a prolonged Salmonella Poona nursery outbreak (2016-2021) in North West England, UK

Page 74 – Climate Warming and increasing Vibrio vulnificus infections in North America

Page 106 – Timely and reliable outbreak investigation using a non-probabilistic online panel as a source of controls – two parallel case-control studies investigating a Salmonella Braenderup outbreak in Germany

Page 107 – An outbreak of Escherichia coli-associated haemolytic uremic syndrome linked to consumption of an unexpected food vehicle, France 2022

Page 108 – Outbreak investigation of cholera in a peri-urban village of Panchkula district, Haryana, India, 2021

Page 109 – Cholera Outbreak Investigation, Ballo Adda Mohalla, Lucknow District, Uttar Pradesh 2021

Page 110 – Norovirus GII.3[P12] outbreak associated with the drinking-water supply in a rural area in Galicia, Spain, 2021

Page 111 – Impact of COVID-19 restrictions on the epidemiology of Cryptosporidium spp. in England and Wales

Page 149 – Monophasic Salmonella Typhimurium outbreak linked to chocolate products, Ireland, 2022

Page 151 – Successful containment of a Listeria monocytogenes outbreak caused by shredded vegetables, Hesse/Germany, 2021-2022

Page 152 – Outbreak of monophasic Salmonella Typhimurium linked to fresh small tomatoes, Sweden, 2021

Page 194 – Cholera Outbreak Investigation, Kamarhati-Municipality, North-24-Parganas District, West Bengal, India 2021

Page 195 – Botulism outbreak and response in Dangara District Tajikistan, October 2020

Page 196 – Outbreak of suspected Clostridium perfringens associated with consumption of roast beef in a restaurant, January 2022 South West England

Page 198 – Doughnuts for weight loss? A norovirus outbreak in the Australian Capital Territory, November 2021

Page 212 – Outbreak of Legionnaires’ disease linked to unregistered cooling towers, West Midlands, England, July-September 2020



Research – Energy conservation can cause growth of Legionella in hot water systems


CDC legionella

Due to the current energy crisis, the authorities have various proposals for, and requirements for, saving on energy. Among other things, you can lower the temperature in hot water systems, and you can use less hot water by e.g. taking shorter baths, washing your hands in cold water and installing water-limiting measures, e.g. energy-saving showers.

However, both parts can contribute to increased growth of Legionella pneumophila in the water systems with a risk of infection and disease. It is therefore important that Danes think carefully before saving on energy.

Hot water systems can cause severe pneumonia

Most of our hot water systems contain Legionella pneumophila . The bacterium can cause a serious pneumonia called Legionnaires’ disease. Infection occurs by inhaling atomized water that is contaminated with the bacteria, e.g. while showering.

“The disease particularly affects elderly and debilitated people and causes up to 300 hospitalizations per year, but the bacterium is presumably the cause of far more mild cases of the disease, also in younger people. Since the bacteria are common in our hot water systems, it is important to limit their growth. This happens at home primarily by ensuring that cold water is no more than 20 °C and that hot water is at least 50 °C, as the bacteria cannot grow at these temperatures and begin to die at 50 °C,” says Søren Anker Uldum , who is head of department at the Statens Serum Institut.

Rinse through with very hot water

It is therefore important to continue to maintain at least 50 °C throughout the hot water system. The temperature must be reached at all tapping points after no more than 30 seconds. rinse and in the return water (before hot water tank or heat exchanger). In most cases, this can be achieved by heating the hot water to 55 °C in the hot water tank.

With reduced consumption of hot water, the water has longer residence times in the pipes and can have temperatures in the bacteria’s growth area for a longer period of time, so there must be a certain consumption of hot water.

Taps, such as faucets and showers that are rarely used, should be flushed with hot water at a minimum of 50 °C for a few minutes at least once a week.

When showering (which may well be short), it is also a good idea that at least once a week you first set the mixer to the maximum temperature and let the water run (to the drain) until it is as hot as it can be before setting it to bath water temperature (approx. 36 °C).

This advice applies especially if there are vulnerable people in the household or institution, such as the elderly or people with chronic illness or a weakened immune system.