Lessons from the history of Legionnaires’ disease; Part 2.

FACTORS WHICH BROUGHT THE 2003 HEREFORD LEGIONNAIRES’ DISEASE OUTBREAK UNDER CONTROL

In the autumn of 2003 28 cases of Legionnaires’ disease were reported in Hereford. Two of those diagnosed with the disease died. All cases had tested positive using the Legionella urinary antigen test for Legionella pneumophilia serogroup 1.

An Outbreak Control Team was set up to declare the outbreak, prevent further transmission and investigate the source.

30 premises were inspected of which 24 had aerosol-producing devices including cooling towers, fountains, supermarket display humidifiers and displays of whirlpool spas.

Legionella pneumophilia 1 was found at 3 installations within 2 sites. These consisted of 2 cooling towers and one domestic spa pool.

INVESTIGATION METHODOLOGY

Using the three pronged approach of an Epidemiological investigation, and Environmental investigation and an Environmental Risk Assessment the team were able to find the source of the outbreak.

The environmental investigations were focused on cooling towers and these 2 had been decontaminated but the biocidal dosing was found to be insufficient.  These cooling towers were also found to be used seasonally and had been started up in the autumn.

The epidemiological investigation pointed towards Hereford City Centre as the most probable source of the outbreak and the domestic spa pool was discounted.

A questionnaire was used to evaluate where those who had contracted the disease had travelled and the locations of cooling towers in and around Hereford was obtained from the local authority.

Almost all the cases lived or had travelled within 500m of the site of the cooling towers.

Postcode data for cooling towers and the residences of those with the disease were mapped using Geographical Information System (GIS)

28 people who lived, visited or passed within 500m of Hereford City Centre between 8Th October and 20th November 2003 had contracted Legionnaires’ disease. Results from epidemiological, environmental and microbiological investigations pointed to contaminated aerosols from cooling towers at a specific site being responsible. After the cleaning and closure of these cooling towers no further cases of Legionnaires’ disease were reported.

STATISTICS OF THOSE WHO CAUGHT LD IN THIS OUTBREAK

There were 28 cases with a median age of 59.5 years

21 were male

8 cases had underlying medical conditions; 2 diabetics, 3 asthmatics, 1 chronic airways disease, 2 immunosuppressed and 18 were smokers.

23 lived within the city

2 lived within Herefordshire and had visited the city centre

3 had visited Hereford from outside the area.

CONCLUSIONS

It can be a complex and time-consuming exercise to identify the source of an outbreak of Legionnaires’ disease. Usually the more cases of illness there are the more likely it is to be a cooling system that is the source.

Underlying illness can make an individual more susceptible to catching the disease.

Adequate start up and shut down procedures are required for cooling systems to ensure the risks are minimised.

The presence of bacteria, in this case in the domestic spa pool, does not automatically mean someone will catch the disease, whilst not reported in this case the bacteria could lead to the lesser illness of Pontiac Fever which is non-fatal.

The results of this investigation suggest that obtaining, typing and comparing environmental and clinical specimens is of critical importance in the public health investigation of Legionnaires’ disease outbreaks.

 

Collaton Consultancy Limited can help you before, during and after an event such as this. We offer consultancy and auditing services along with Expert Witness services if required. Contact us on general@collatonconsultancy.com or phone +44 (0)7958 124563

 

Reference; Respiratory Medicine (2007) 101, 1639–1644

 

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