A legionellosis outbreak at an industrial site was investigated to identify and control the source. Cases were identified from disease notifications, workplace illness records, and from clinicians. Cases were interviewed for symptoms and risk factors and tested for legionellosis. Implicated environmental sources were sampled and tested for legionella. We identified six cases with Legionnaires’ disease and seven with Pontiac fever; all had been exposed to aerosols from the cooling towers on the site. Nine cases had evidence of infection with either Legionella pneumophila serogroup (sg) 1 or Legionella longbeachae sg1; these organisms were also isolated from the cooling towers. There was 100% DNA sequence homology between cooling tower and clinical isolates of L. pneumophila sg1 using sequence-based typing analysis; no clinical L. longbeachae isolates were available to compare with environmental isolates. Routine monitoring of the towers prior to the outbreak failed to detect any legionella. Data from this outbreak indicate that L. pneumophila sg1 transmission occurred from the cooling towers; in addition, L. longbeachae transmission was suggested but remains unproven. L. longbeachae detection in cooling towers has not been previously reported in association with legionellosis outbreaks. Waterborne transmission should not be discounted in investigations for the source of L. longbeachae infection.

An outbreak of Legionnaires' disease occurred in an inner city district in Calgary, Canada. This outbreak spanned a 3-week period in November–December 2012, and a total of eight cases were identified. Four of these cases were critically ill requiring intensive care admission but there was no associated mortality. All cases tested positive for Legionella pneumophila serogroup 1 (LP1) by urinary antigen testing. Five of the eight patients were culture positive for LP1 from respiratory specimens. These isolates were further identified as Knoxville monoclonal subtype and sequence subtype ST222. Whole-genome sequencing revealed that the isolates differed by no more than a single vertically acquired single nucleotide variant, supporting a single point-source outbreak. Hypothesis-based environmental investigation and sampling was conducted; however, a definitive source was not identified. Geomapping of case movements within the affected urban sector revealed a 1·0 km common area of potential exposure, which coincided with multiple active construction sites that used water spray to minimize transient dust. This community point-source Legionnaires' disease outbreak is unique due to its ST222 subtype and occurrence in a relatively dry and cold weather setting in Western Canada. This report suggests community outbreaks of Legionella should not be overlooked as a possibility during late autumn and winter months in the Northern Hemisphere.

Legionnaires' disease (LD) is caused by the inhalation of aerosols containing Legionella, a Gram-negative bacteria. Previous national- or regional-level studies have suggested an impact of climate on LD incidence. The objective of this study was to investigate the effect of temperature, rainfall, and atmospheric pressure on short-term variations in LD notification rate. EU/EEA Member States report their LD surveillance data to the European Centre for Disease Prevention and Control. Community-acquired LD cases reported by Denmark, Germany, Italy, and The Netherlands with onset date in 2007–2012 were aggregated by onset week and region of residence. Weather variables were extracted from the European Climate Assessment & Dataset project. We fitted Poisson regression models to estimate the association between meteorological variables and the weekly number of community-acquired LD cases. Temperature, rainfall and atmospheric pressure were all associated with LD risk with higher risk associated with simultaneous increase in temperature and rainfall. Temperatures >20 °C were not associated with a higher risk for LD. LD cases occurring during wintertime may be associated with sources less influenced by meteorological conditions.

In June 2014 Public Health England confirmed a case of Legionnaires' disease (LD) in a neonate following birth at home in a hired birthing pool incorporating a heater and a recirculation pump which had been filled in advance of labour. The case triggered a public health investigation and a microbiological survey of an additional ten heated birthing pools hired or recently hired to the general public across England. The birthing pool used by the parent of the confirmed case was identified as the source of the neonate's infection following detection of Legionella pneumophila ST48 in both patient and environmental samples. Legionella species were detected by quantitative polymerase chain reaction but not culture in a further three pools together with other opportunistic pathogens identified by culture and matrix-assisted laser desorption ionization–time of flight (MALDI–ToF) mass spectrometry. A Patient Safety Alert from NHS England and Public Health England was issued stating that heated birthing pools filled in advance of labour should not be used for home births. This recommendation remains in place. This investigation in conjunction with other recent reports has highlighted a lack of awareness regarding the microbiological safety of heated birthing pools and their potential to be a source of LD and other opportunistic infections. Furthermore, the investigation raised important considerations with regards to microbiological sampling and testing in such incidents. Public health authorities and clinicians should consider LD in the differential diagnosis of severe respiratory infection in neonates within 14 days of a water birth.

During August and September 2010 an unexpected high number of domestic cases of Legionnaires' disease (LD) were reported in The Netherlands. To examine this increase, patient characteristics and results of source finding and environmental sampling during the summer peak were compared to other domestic cases in 2008–2011. This analysis did not provide an explanation for the rise in cases. A similar increase in LD cases in 2006 was shown to be associated with warm and wet weather conditions, using an extended Poisson regression model with adjustment for long-term trends. This model was optimized with the new data from 2008 to 2011. The increase in 2010 was very accurately described by a model, which included temperature in the preceding 4 weeks, and precipitation in the preceding 2 weeks. These results confirm the strong association of LD incidence with weather conditions, but it remains unclear which environmental sources contributed to the 2010 summer increase.

We studied the timing of occurrence of 1676 sporadic, community-acquired cases of Legionnaires' disease in England and Wales between 1993 and 2008, in relation to temperature, relative humidity, rainfall, windspeed and ultraviolet light using a fixed-stratum case-crossover approach. The analysis was conducted using conditional logistic regression, with consideration of appropriate lag periods. There was evidence of an association between the risk of Legionnaires' disease and temperature with an apparently long time lag of 1–9 weeks [odds of disease at 95th vs. 75th centiles: 3·91, 95% confidence interval (CI) 2·06–7·40], and with rainfall at short time lags (of 2–10 days) (odds of disease at 75th vs. 50th centiles: 1·78, 95% CI 1·50–2·13). There was some evidence that the risk of disease in relation to high temperatures was greater at high relative humidities. A higher risk of Legionnaires' disease may be indicated by preceding periods of warmer wetter weather.

A community outbreak of legionellosis occurred in Barrow-in-Furness, Cumbria, during July and August 2002. A descriptive study and active case-finding were instigated and all known wet cooling systems and other potential sources were investigated. Genotypic and phenotypic analysis, and amplified fragment length polymorphism of clinical human and environmental isolates confirmed the air-conditioning unit of a council-owned arts and leisure centre to be the source of infection. Subsequent sequence-based typing confirmed this link. One hundred and seventy-nine cases, including seven deaths [case fatality rate (CFR) 3·9%] were attributed to the outbreak. Timely recognition and management of the incident very likely led to the low CFR compared to other outbreaks. The outbreak highlights the responsibility associated with managing an aerosol-producing system, with the potential to expose and infect a large proportion of the local population and the consequent legal ramifications and human cost.

The notification rate of Legionnaires' disease (LD) in France was 2·4/100 000 population in 2010, varying across regions with an increasing rate from west to east. Two sources [mandatory notifications (MN) and a survey of hospital laboratories] were used in a capture–recapture study to estimate the number of LD cases and the sensitivity of the MN system at national and regional levels in 2010. The number of missed cases was estimated using Chapman's method. The estimated sensitivity of MN was 88·5% (95% CI 88·0–89·0) and ranged from 70% to 100% by region. The estimated incidence was 2·7/100 000 population. Sensitivity of the MN system improved since the previous capture–recapture estimates (10% in 1995, 33% in 1998). This study confirmed that the observed west–east gradient is not related to regional notification disparities. Ecological studies should be conducted to better understand the observed spatial variations in LD incidence.

Between April and August 2005 Christchurch, New Zealand experienced an outbreak of Legionnaires' disease. There were 19 laboratory-confirmed case including three deaths. Legionella pneumophila serogroup 1 (Lpsg1) was identified as the causative agent for all cases. A case-control study indicated a geographical association between the cases but no specific common exposures. Rapid spatial epidemiological investigation confirmed the association and identified seven spatially significant case clusters. The clusters were all sourced in the same area and exhibited a clear anisotropic process (noticeable direction) revealing a plume effect consistent with aerosol dispersion from a prevailing southwesterly wind. Four out of five cases tested had indistinguishable allele profiles that also matched environmental isolates from a water cooling tower within the centre of the clusters. This tower was considered the most probable source for these clusters. The conclusion would suggest a maximum dispersal distance in this outbreak of 11·6 km. This work illustrated the value of geostatistical techniques for infectious disease epidemiology and for providing timely information during outbreak investigations.

This study investigated the relationships between Legionnaires' disease (LD) incidence and weather in Glasgow, UK, by using advanced statistical methods. Using daily meteorological data and 78 LD cases with known exact date of onset, we fitted a series of Poisson log-linear regression models with explanatory variables for air temperature, relative humidity, wind speed and year, and sine-cosine terms for within-year seasonal variation. Our initial model showed an association between LD incidence and 2-day lagged humidity (positive, P = 0·0236) and wind speed (negative, P = 0·033). However, after adjusting for year-by-year and seasonal variation in cases there were no significant associations with weather. We also used normal linear models to assess the importance of short-term, unseasonable weather values. The most significant association was between LD incidence and air temperature residual lagged by 1 day prior to onset (P = 0·0014). The contextual role of unseasonably high air temperatures is worthy of further investigation. Our methods and results have further advanced understanding of the role which weather plays in risk of LD infection.

Despite US sanitation advancements, millions of waterborne disease cases occur annually, although the precise burden of disease is not well quantified. Estimating the direct healthcare cost of specific infections would be useful in prioritizing waterborne disease prevention activities. Hospitalization and outpatient visit costs per case and total US hospitalization costs for ten waterborne diseases were calculated using large healthcare claims and hospital discharge databases. The five primarily waterborne diseases in this analysis (giardiasis, cryptosporidiosis, Legionnaires' disease, otitis externa, and non-tuberculous mycobacterial infection) were responsible for over 40 000 hospitalizations at a cost of $970 million per year, including at least $430 million in hospitalization costs for Medicaid and Medicare patients. An additional 50 000 hospitalizations for campylobacteriosis, salmonellosis, shigellosis, haemolytic uraemic syndrome, and toxoplasmosis cost $860 million annually ($390 million in payments for Medicaid and Medicare patients), a portion of which can be assumed to be due to waterborne transmission.

This study evaluated the spatio-temporal variation of Legionella spp. in New Zealand using notification and laboratory surveillance data from 1979 to 2009 and analysed the epidemiological trends. To achieve this we focused on changing incidence rates and occurrence of different species over this time. We also examined whether demographic characteristics such as ethnicity may be related to incidence. The annual incidence rate for laboratory-proven cases was 2·5/100 000 and 1·4/100 000 for notified cases. Incidence was highest in the European population and showed large geographical variations between 21 District Health Boards. An important finding of this study is that the predominant Legionella species causing disease in New Zealand differs from that found in other developed countries, with about 30–50% of cases due to L. longbeachae and a similar percentage due to L. pneumophila for any given year. The environmental risk exposure was identified in 420 (52%) cases, of which 58% were attributed to contact with compost; travel was much less significant as a risk factor (6·5%). This suggests that legionellosis has a distinctive epidemiological pattern in New Zealand.

Sporadic community-acquired legionellosis (SCAL) can be acquired through contaminated aerosols from residential potable water. Electricity-dependent hot-water tanks are widely used in the province of Quebec (Canada) and have been shown to be frequently contaminated with Legionella spp. We prospectively investigated the homes of culture-proven SCAL patients from Quebec in order to establish the proportion of patients whose domestic potable hot-water system was contaminated with the same Legionella isolate that caused their pneumonia. Water samples were collected in each patient's home. Environmental and clinical isolates were compared using pulsed-field gel electrophoresis. Thirty-six patients were enrolled into the study. Legionella was recovered in 12/36 (33%) homes. The residential and clinical isolates were found to be microbiologically related in 5/36 (14%) patients. Contaminated electricity-heated domestic hot-water systems contribute to the acquisition of SCAL. The proportion is similar to previous reports, but may be underestimated.

An outbreak of Legionnaires' disease affected 12 customers of a supermarket in a town in Catalonia, Spain, between August and November 2006. An epidemiological and environmental investigation was undertaken. Preliminary investigation showed that all patients had visited the same supermarket in this town where a mist machine was found in the fish section. Water samples were collected from the machine and from the supermarket's water distribution system when high-risk samples were excluded. Environmental samples from the mist machine and clinical samples from two patients tested positive for L. pneumophila serogroup 1 and had the same molecular pattern. The PFGE pattern detected in the clinical and mist-machine isolates had never previously been identified in Catalonia prior to the outbreak and has not been identified since. Four days after turning off the machine, new cases ceased appearing. Molecular study supports the hypothesis that the mist machine from the fish section of the supermarket was the source of infection. We believe it is essential to include exposure to mist machines in any legionellosis epidemiological survey.

In July 2008, office workers in Dublin complained of influenza-like illness preceding and interspersing two cases of notified Legionnaires' disease. Legionella pneumophila serogroup 1 was identified in both cooling towers supplying the office. A retrospective cohort study was undertaken to investigate possible Pontiac fever (PF). Forty-seven employees (23%) met the clinical case definition for PF but confirmatory testing was negative. Exposure to the smoking area situated beside the cooling towers was associated with an increased risk of PF (RR 2·4, 95% CI 1·5–3·8). The diagnosis of PF should be considered when many persons exposed to a possible reservoir of Legionella spp. present with flu-like symptoms. More sensitive microbiological tests would allow better confirmation and more comprehensive reporting of PF. Early detection is vital to prevent potentially severe illness and outbreaks of PF or Legionnaires' disease.

Legionnaires' disease (LD) is a major cause of severe community-acquired pneumonia but the source and mode of transmission are not always apparent, especially in sporadic cases. We hypothesized that LD can be acquired from the air-conditioning systems of motor cars. Swabs were taken from the evaporator compartments of the air-conditioning system of scrapped cars. Healthy subjects who were mainly employees of regional transportation companies were tested for antibody to Legionella pneumophila serogroups 1–6; they also completed a questionnaire. Legionella species were detected in 11/22 scrapped cars by the loop-mediated isothermal amplification method. The prevalence of microplate agglutination titres ⩾1:32 was significantly higher in subjects who sometimes used car air-conditioning systems. Although we did not prove a direct link between Legionella spp. in the car evaporator and LD, our findings point to a potential risk of car air-conditioning systems in LD, which needs further investigation.

This study examined the impact of meteorological conditions on sporadic, community-acquired cases of Legionnaires' disease in England and Wales (2003–2006), with reference to the 2006 increase in cases. A case-crossover methodology compared each case with self-controlled data using a conditional logistic regression analysis. Effect modification by quarter and year was explored. In total, 674 cases were entered into the dataset and two meteorological variables were selected for study based on preliminary analyses: relative humidity during a case's incubation period, and temperature during the 10–14 weeks preceding onset. For the quarter July–September there was strong evidence to suggest a year, humidity and temperature interaction (Wald χ2=30·59, 3 d.f., P<0·0001). These findings have implications for future case numbers and resource requirements.

It has been suggested that warm and humid weather is related to a high incidence of Legionnaires' disease (LD), but no data on this association existed in The Netherlands. The objective of this study was to investigate the short-term effects of the weather on LD in The Netherlands. National LD surveillance and meteorological data were obtained. We analysed the data using Poisson regression, adjusting for long-term trends, and using principal components analysis. The highest weekly incidence of LD occurred when the mean weekly temperature was +17·5°C. Mean weekly relative humidity, temperature and precipitation intensity were associated with LD incidence in the multivariable model. Warm, humid and showery summer weather was found to be associated with higher incidence of LD in The Netherlands. These results may be used to predict an increase in the number of cases of LD in The Netherlands during the summer.