Barrow-in-Furness: a large community legionellosis outbreak in the UK

Abstract

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.

Fig. 1.

Location of Forum 28 Arts and Leisure Centre, Barrow-in-Furness.

Fig. 2.

Contemporary photograph of alleyway outside Forum 28 into which droplets of contaminated water were emitted. Red circle indicates the vent from which the Legionella-contaminated aerosol came. (Copyright © Dr Nigel Calvert, NHS Dumfries & Galloway.)

Fig. 3.

Disease burden during the outbreak.

Fig. 4.

Method of diagnosis for legionellosis cases reporting most reliable method. * Two cases accepted as legionellosis with clear conversion to 32 from negative.

Fig. 5.

Attack rate by home location, aggregated to Census Area Statistics (CAS) ward, Barrow-in-Furness.

Fig. 6.

Final epidemiological curve and estimated infection period. Number of legionellosis cases by date of onset of illness where known (n = 165) and date of hospital admission (n = 132), July to August 2002.

Fig. 7.

Dates of case visits and daily mean temperature during likely period of emission of Legionella-contaminated aerosol, against average monthly temperature 2001–2004 (n = 28).

Fig. 8.

Incubation period for subgroup of cases (one visit only) (n = 28). Number of cases with incubation period <2 days to >7 days = 7 (25%). All confirmed Legionnaires' disease cases.

Fig. 9.

Interval between onset of symptoms and admission to hospital (n = 127).