Background: An outbreak of legionnaires disease occurred in Zaragoza (Spain) in an uncommon environment such as a private apartment building was studied.
Methods: The investigation began upon notification of 3 patients admitted with pneumonia, living in the same apartment building. The suggestion of a common source of infection led to an active search for cases and a micro-environmental study of the zone where the patients lived, as well as a follow up study of other cases with hospital acquired pneumonia throughout the city.
Results: Six cases were detected over 9 days with a rate of 1.54%. The evolution of all the cases was favorable. The causal agent was serologically identified as Legionella pneumophilia serogroup 1 which was also found in the shower of one of the patient's bath with further confirmation that the strain isolated belonged to the Pontiac subgroup.
Conclusions: The probable source of infection was the potable water. The stagnation, low temperature of the boiler and the under-chlorination of the water are factors which may have contributed to the appearance of this outbreak. The control of this type of outbreak must be based on a specific information system which treats this disease as requiring individualized declaration.